Lab Ventilation Design Manage

Transcription

SEFA
Laboratory Ventilation
Design Guide
Exposure Control Technologies, Inc.
231-C East Johnson St.
Cary, NC 27513
919-319-4290
ExposureControlTechnologies.com
Table of Contents
1
Purpose and Introduction............................................................................1
2
Energy and Sustainability ............................................................................1
3
The Laboratory Design Process ....................................................................2
4
Laboratory Demand for Ventilation .............................................................2
4.1
Types of Hazardous Procedures ............................................................................................... 2
4.2
Risk Assessment ....................................................................................................................... 3
4.2.1
Quantity of Materials Used and Generation Rates ................................................................ 3
4.2.2
Effluent Characteristics......................................................................................................... 4
4.2.3
Control Banding ................................................................................................................... 5
4.3
Lab Air Quality and Conditioning .............................................................................................. 6
4.4
Occupancy and System Utilization ............................................................................................ 6
5
Exposure Control Device Selection ..............................................................6
5.1
Description of Exposure Control Device .................................................................................... 6
5.2
ECD Risk Matrix ........................................................................................................................ 6
5.3
Types of ECDs (need to harmonize descriptions with current RP from SEFA) ............................ 6
5.3.1
Laboratory Fume Hoods ....................................................................................................... 9
5.3.2
Constant Air Volume (CAV), Conventional Fume Hood ....................................................... 10
5.3.3
CAV, Bench-Type, Bypass Fume Hood ................................................................................. 10
5.3.4
Auxiliary Air Bypass Fume Hood ......................................................................................... 11
5.3.5
CAV – High Performance Fume Hoods (HP Fume Hoods) .................................................... 13
5.3.6
Variable Air Volume (VAV) Fume Hood Systems ................................................................. 13
5.3.7
Distillation Laboratory Fume Hoods .................................................................................... 14
5.3.8
Floor Mounted Laboratory Fume Hoods ............................................................................. 15
5.3.9
Perchloric Acid Laboratory Fume Hoods ............................................................................. 16
5.3.10
Radioisotope Fume Hoods .............................................................................................. 16
5.3.11
Pass Through Hood ......................................................................................................... 17
5.3.12
California Hood .............................................................................................................. 17
5.3.13
Teaching Lab Hood ......................................................................................................... 17
5.3.14
Ductless Fume Hood ....................................................................................................... 17
5.3.15
6
Laminar Flow Fume Hood ............................................................................................... 17
Exposure Control Device Operation........................................................... 19
6.1
Laboratory Hood Operation ................................................................................................... 19
6.1.1
Escape of Contaminants ..................................................................................................... 19
6.1.2
Sash Opening Configurations .............................................................................................. 20
6.1.3
Airfoil Sills .......................................................................................................................... 22
6.1.4
Baffle Design and Configuration ......................................................................................... 22
6.1.5
Fume Hood Specifications .................................................................................................. 24
6.1.6
Distillation Laboratory Fume Hood Specifications ............................................................... 36
6.1.7
Walk-in Fume Hood Specifications...................................................................................... 36
6.1.8
Perchloric Acid Fume Hood Specifications .......................................................................... 36
6.1.9
Radioisotope Fume Hood Specifications ............................................................................. 37
6.1.10
Ductless Fume Hood Specifications................................................................................. 37
6.1.11
Laminar Flow Fume Hood Specifications ......................................................................... 37
6.2
6.2.1
6.3
6.3.1
6.4
6.4.1
6.5
6.5.1
6.6
6.6.1
6.7
6.7.1
6.8
Ventilated Balance Enclosures (VBE) ...................................................................................... 37
Ventilated Balance Enclosure Specifications ....................................................................... 38
Canopy Exhaust Hoods ........................................................................................................... 38
Canopy Exhaust Hood Specifications .................................................................................. 39
Flexible Spot Exhausts (FSE) ................................................................................................... 39
Flexible Spot Exhaust Specifications ................................................................................... 40
Slot Hoods.............................................................................................................................. 40
Slot Hood Specifications ..................................................................................................... 41
Downdraft Necropsy Tables ................................................................................................... 41
Downdraft Necropsy Table Specifications ........................................................................... 42
Glove Boxes ........................................................................................................................... 42
Glove Box Specifications ..................................................................................................... 42
Biological Safety Cabinets....................................................................................................... 43
6.8.1
Class I Biological Safety Cabinet .......................................................................................... 44
6.8.2
Class II, Type A Biological Safety Cabinet ............................................................................ 45
6.8.3
Class II, Type A2 Biological Safety Cabinet........................................................................... 47
6.8.4
Class II, Type B1 Biological Safety Cabinet ........................................................................... 48
6.8.5
Class II, Type B2 (Total Exhaust) Biological Safety Cabinet ................................................... 49
6.8.6
Class III Biological Safety Cabinet ........................................................................................ 50
6.9
Ventilated Enclosure .............................................................................................................. 50
6.9.1
6.10
Ventilated Enclosure Specifications .................................................................................... 51
Canopy Hoods ........................................................................................................................ 51
6.10.1
6.11
Gas Cabinets .......................................................................................................................... 51
6.11.1
6.12
Flammable Liquid Storage Cabinet Specifications ........................................................... 52
Special Purpose Hoods ........................................................................................................... 52
6.13.1
7
Gas Cabinet Specifications .............................................................................................. 51
Flammable Liquid Storage Cabinets ........................................................................................ 52
6.12.1
6.13
Canopy Hood Specifications............................................................................................ 51
Special Purpose Hood Specifications ............................................................................... 52
Types of Laboratories ................................................................................ 52
7.1
Categorization and Risk Control Bands ................................................................................... 53
7.2
Bio-Safety Levels .................................................................................................................... 53
7.2.1
BSL 1 .................................................................................................................................. 53
7.2.2
BSL 2 .................................................................................................................................. 53
7.2.3
BSL 3 and Higher Labs......................................................................................................... 53
7.3
Teaching Laboratories ............................................................................................................ 53
7.4
Necropsy Laboratories ........................................................................................................... 53
7.5
Radiation Laboratories ........................................................................................................... 53
7.6
Gross Anatomy Laboratories .................................................................................................. 53
8
Laboratory Design and Layout Specifications ............................................ 53
8.1
Laboratory Systems and Operating Modes ............................................................................. 54
8.2
Hood Location ........................................................................................................................ 55
8.2.1
Air Distribution Effectiveness ............................................................................................. 56
8.2.2
Doors and Traffic Aisles ...................................................................................................... 57
8.2.3
Location and Type of Supply Diffusers ................................................................................ 57
8.2.4
Type of Air Supply Diffusers ................................................................................................ 60
8.3
Ventilation Effectiveness (Air Change Rates in Laboratories) .................................................. 62
8.4
Specification of Airflow Rates for Laboratories ....................................................................... 63
8.5
Calculating Air Change per Hour Rate (ACH) ........................................................................... 64
8.6
Laboratory Pressurization ...................................................................................................... 64
8.6.1
8.7
Lab Offset Volume .............................................................................................................. 65
Airflow Controls ..................................................................................................................... 66
8.7.1
CAV .................................................................................................................................... 66
8.7.2
VAV .................................................................................................................................... 66
8.7.3
Demand Control Ventilation (DCV) ..................................................................................... 66
8.7.4
Occupancy Based Control Schemes .................................................................................... 67
8.7.5
Purge Modes ...................................................................................................................... 67
8.8
9
Laboratory Temperature Control............................................................................................ 67
Lab Ventilation .......................................................................................... 67
9.1
Laboratory Exhaust Ventilation .............................................................................................. 67
9.1.1
Materials of Construction ................................................................................................... 68
9.1.2
Manifolds and Duct Design ................................................................................................. 73
9.1.3
Dampers ............................................................................................................................ 74
9.1.4
Duct Pressures ................................................................................................................... 74
9.1.5
Duct Velocities ................................................................................................................... 74
9.1.6
Exhaust Fans ...................................................................................................................... 75
9.1.7
Exhaust Stack ..................................................................................................................... 77
9.1.8
General Exhaust ................................................................................................................. 77
9.1.9
Fire Dampers ...................................................................................................................... 77
9.2
Air Supply Systems ................................................................................................................. 77
9.2.1
100% OA vs. Recirculated (can you recirculated GEX and when) ......................................... 78
9.2.2
Outside Air Intakes ............................................................................................................. 78
9.2.3
Airflow Measurement ........................................................................................................ 78
9.2.4
Humidity Control ................................................................................................................ 78
9.2.5
Supply Air Temperature...................................................................................................... 78
9.2.6
Fire Dampers ...................................................................................................................... 78
9.2.7
Noise .................................................................................................................................. 78
9.2.8
Insulation ........................................................................................................................... 78
9.2.9
Filtration ............................................................................................................................ 78
9.3
Energy Recovery .................................................................................................................... 79
9.4
Smoke and Fire Control .......................................................................................................... 79
9.5
Noise ..................................................................................................................................... 79
9.5.1
Criteria ............................................................................................................................... 79
9.5.2
Equipment ......................................................................................................................... 80
9.5.3
Ventilation System Layout .................................................................................................. 82
9.5.4
Layout of Laboratory .......................................................................................................... 83
9.5.5
External Noise .................................................................................................................... 84
9.5.6
Vibration ............................................................................................................................ 85
9.5.7
Other Considerations ......................................................................................................... 85
9.6
Insulation ............................................................................................................................... 86
9.7
Filtration ................................................................................................................................ 86
9.8
Energy Recovery .................................................................................................................... 87
10
Laboratory Ventilation Construction, Renovation and Commissioning ...... 87
10.1
Lab Designer's Checklist ......................................................................................................... 87
10.2
TAB Plan................................................................................................................................. 87
10.3
Commissioning Plan (building and lab) ................................................................................... 87
10.4
ECD Commissioning................................................................................................................ 87
10.5
Laboratory Environment Tests (LETs) ..................................................................................... 87
10.6
System Mode Operating Tests (SOMTs) .................................................................................. 87
11
Laboratory Ventilation Management Program .......................................... 87
11.1
LVMP and the Design Process ................................................................................................ 88
11.2
Routine Testing ...................................................................................................................... 88
11.3
Management of Change ......................................................................................................... 88
11.4
BAS Trends and Reports ......................................................................................................... 88
12
References ................................................................................................ 89
SEFA Laboratory Ventilation Design Guide
1
Purpose and Introduction
The primary objective in laboratory design should be to provide a safe environment for laboratory
personnel to conduct their work. Secondary objectives include providing maximum flexibility for
research, efficiently operating systems and sustainability.
The Laboratory Ventilation Design Guide (Guide) was prepared to aid the design community with
planning and design issues related to laboratory and critical environment ventilation. The Guide is a
resource document for use by design professionals, management and staff during planning, design
and construction of new and renovated laboratory facilities.
The requirements in the Guide illustrate some of the basic health and safety ventilation design
features required for new and remodeled laboratories. These health and safety guidelines are to be
incorporated, as appropriate, in facility-specific construction documents by the architects and
engineers to ensure that health and safety protection is engineered into the design of any new or
renovated facility.
While many of the requirements for health and safety ventilation design and engineering are
incorporated in the Guide, it is impossible to cover all possible concerns and not all regulatory issues
or design situations are contained herein. The architects, engineers, designers and planners should
in all cases, consult with Environmental Health and Safety personnel for guidance on questions
regarding health, safety and the environment.
Safety is the inviolable constraint. No matter how well designed a laboratory is, improper usage of
its facilities will always overcome the engineered safety features.
2
Energy and Sustainability
Due to high ventilation needs of laboratories, the associated energy use required to operate labs far
exceeds the energy required to operate typical office buildings. Depletion of energy resources and
resultant increase in energy costs advocates efficient energy use should be a prominent criteria in
laboratory design. Even the most energy efficient laboratory design may increase energy use over
time due to:
 changes in laboratory use and equipment
 changes in laboratory physical configuration
 HVAC equipment and controls performance degradation.
It is important to design sustainability in laboratories. Items influencing sustainability include:
 life of HVAC components
 preventative maintenance
 physical location and ease of access to components and controls
1



3
BAS monitoring of performance trends
technical capability of facility maintenance personnel
management of change
The Laboratory Design Process
[content to be added]
Determine process
Select ECDs
Design Lab
Design Systems
4
Comment [GG1]: potential content ideas
Laboratory Demand for Ventilation
Researchers are potentially exposed to a wide variety of hazards. The hazards must be
characterized and evaluated to determine the demand for ventilation, ensure appropriate exposure
control devices (laboratory hoods) and establish appropriate operating specifications and
performance criteria. The demand for ventilation is defined by the airflow required to ensure a safe
and comfortable lab environment at varying levels of occupancy. The Ventilation Demand Risk
Assessment includes evaluation of:
1. Hazards
 The types of hazards and procedures
 Hazard generation characteristics (i.e. gases, vapors, mists, dusts, etc.)
 Quantity of materials used or generated during lab procedures
2. Safety Requirements
 Hood Types
 Hood Exhaust Requirements
 Laboratory Pressurization (Transfer Air)
 Laboratory Airflow for dilution (ACH)
3. Comfort Requirements
 Conditioning Loads
 Temperature
 Humidity
4. Occupancy
 Operating Hours
 Time Spent In Laboratory
 Time Spent in Office
4.1
Types of Hazardous Procedures
The quantity, toxicity and characteristics of airborne hazardous materials generated during
laboratory procedures determines the level of ventilation control required to provide adequate
2
protection. Research safety staff should work with Principal Investigators (PIs) to characterize
hazardous procedures, estimate the volume of hazardous material used and determine potential
generation rates. The following categories can be helpful for characterizing hazardous procedures:
4.2

Storage: Emissions may occur from improperly sealed containers during storage. The rate
and quantity of generation may be small, but not negligible. Complaints of odors indicate
escape of small concentrations from inadequately sealed containers.

Closed Process: Materials are contained within an experimental apparatus, which may
include beakers, flasks, tubing, equipment, etc. The volume of material that could be
released during a catastrophic incident such as accidental over pressurization, damage to
the system, or leaks should be estimated. Closed processes are often found in chemical
dispensing and transferring procedures.

Normal Process: A normal process typically involves procedures that result in low volume
generation and where little energy is added to the process. Generation of materials is
typically through diffusion, evaporation, etc. Some procedures in a normal process involve
liquid transfers (pouring) and small quantity weighing. Pipetting is an example of a normal
process.

Complex Process: A complex process generally involves procedures that apply significant
energy and produce a larger volume of airborne contaminants. Such processes might
involve volatile reactions, stirring and mixing, heating and boiling, bulk material transfers
and weighing. The application of energy complicates the determination of contaminant
generation rates.

Leaks to Catastrophic Failure: Release of material from a physical defect (pinhole in weld,
worn gaskets, etc.) up to sudden and total release of entire contents (rupture, activation of
emergency release valve).
Risk Assessment
4.2.1
Quantity of Materials Used and Generation Rates
There are no standardized categories for the quantities of materials used or generated during
laboratory procedures. Research conducted by Exposure Control Technologies, Inc. (ECT, Inc.)
indicates the following common contaminant generation rates typically resulting from lab activities
or scenarios:
Table 1 Sample of Laboratory -Scale Generation Rates
Source
Category
Generation Rate
Fugitive emissions and leaky
seals on containment vessels
Storage and Closed Process*
<0.1 lpm
Evaporation and Spills
Normal Process
0.1 - 1 lpm
3
Boiling/mixing/stirring
Complex Process
1 - 14 lpm
Leaking or Failed
Compressed Gas Cylinders
Leaks to Catastrophic Failure*
<0.1 lpm to >1400 lpm
Note: * - Worst case release from catastrophic failure should be estimated.
Table 2 Quantity of Material Used or Generated During Hazardous Processes
4.2.2
Description/Quantity
Volume
Mass
Generation Rate
Minute
< 1 mL
< 1 mg
< 0.01 lpm
Small
< 10 mL
<1g
< 0.1 lpm
Moderate
<lL
< 10 g
< 1 lpm
Large
< 10 L
< 100 g
≥ 1 lpm
Extra Large
≥ 10 L
≥ 100 g
≥ 10 lpm
Effluent Characteristics
The design of the laboratory ventilation system is dependent on the quantity, generation rate and
characteristics of the contaminant (sometimes called effluent). In particular, determining effluent
characteristics is necessary to specify capture and transport velocities, select appropriate materials
of construction and establish the exhaust stack discharge criteria. The following categories can be
used to help characterize the hazardous effluent.

Gas – A substance that exists in the gaseous state and lacks inherent volume and shape at
normal atmospheric conditions. Examples: oxygen or helium.

Vapor - A substance in the gaseous state, exerting a partial pressure that can be condensed
into the liquid form. Examples: formaldehyde, xylene and acetone.

Fume - Condensed solid particles produced by physicochemical reactions such as
combustion, sublimation, or distillation. Examples: fumes from spectroscopy samples and
laser surgical procedures.

Mist - Airborne liquid droplets associated with the disruption of a liquid. Examples include
sonication, spraying, mixing, and violent chemical reactions.

Particulate - Solid particles (Silica gel, Aluminum oxide) or nanoparticle products that are
temporarily suspended in a volume of air. Deposition of suspended particulates is
dependent on particle size and turbulence.
4
To properly design ventilation systems, prevent staff exposure and deposition of materials within
the hood and duct system, effluent characteristics must be known. These topics are reviewed in
later sections of this chapter. In addition, selection of stack discharge criteria and exhaust filtration
requirements depend on the characteristics of the substance being controlled. For example, a HEPA
filter is commonly used on hoods and is extremely efficient at removing particles greater than 0.3
micrometers in diameter, but it is ineffective for removing most gases and vapors.
4.2.3
Control Banding
Renovating laboratory buildings to reduce energy consumption or upgrade the capabilities of the
mechanical systems requires understanding the functional requirements of the building occupants
and risks associated with the research activities. Work in research laboratories can vary and often
involves a diverse range of hazardous materials and procedures. Evaluating and minimizing risk by
ensuring proper protection of people, property and the environment can be a challenging task that
requires specialized skills, experience and expertise evaluating laboratories, hazards and exposure
control systems.
The control banding process involves meeting with stakeholders to define specific facility objectives,
interviews with principal investigators, surveys of the laboratories, inspection of the laboratory
hoods, review of the ventilation systems, evaluation of hazards and analysis of key metrics.
Information collected from the laboratories and exposure control devices is compiled, analyzed,
weighted and assigned to different control bands developed specifically to achieve the desired
objectives. The bands are developed to distinguish low risk from high risk for the purposes of
assigning air change rates (Air Changes Per Hour – ACH) and other relevant ventilation parameters
and specifications. Error! Reference source not found. below illustrates the control banding process
for laboratories.
5
Start
Survey Lab
1.
Identify
ECDs
Evaluate
Hazardous
Processes in ECDs
2.
3.
ECD Risk
Assessment
Physical
or Other
Hazard
Haz. Op.
Analysis
Airborne
Health
Hazard
Determine
Theoretical
ACH
Apply Chem
Generation
Emission Model
Implement
Safety Measures
Remove or Hibernate
ECD
NO
YES
YES
Is ECD
Appropriate
NO
Is ECD
Necessary
7.
4.
Install or
Utilize
Appropriate
ECD
Evaluate
Hazardous
Processes outside
ECD
Assign ECD Risk
and Airflow
Specifications
Implement
Safety Measures
8.
Evaluate Room
Air Change
Effectiveness
6.
Lab Ventilation
Risk Assessment
9.
NO
5.
Or
Haz. Op.
Analysis
Increase ACH to
Next High
Category
Physical
or Other
Hazard
Stop
Improve Room
Air Change
Effectiveness
Assign Lab Risk
and Airflow
Specifications
Preliminary
ACH
Acceptable
YES
Accept
Preliminary
ACH as Final
10.
Figure 1 Lab Ventilation Risk Assessment Process
4.3
Lab Air Quality and Conditioning
4.4
Occupancy and System Utilization
5
5.1
Exposure Control Device Selection
Description of Exposure Control Device
5.2
ECD Risk Matrix
5.3
Types of ECDs (need to harmonize descriptions with current RP from SEFA)
6
ECDs must be constructed, manufactured, installed, and used according to specific requirements.
Mechanical Engineers, Principal Investigators, Laboratory Directors, Research Safety Officers, and
other experts, should be responsible for selecting devices and sizes that are appropriate for the
intended use. ECDs are often the primary means of protecting personnel and should be considered
an integral part of the overall building HVAC system. They should be part of the Test, Adjustment
and Balance (TAB) and Commissioning of mechanical systems prior to building acceptance, lab
occupancy and hood use. Any design process that involves selection and installation of ECDs should
consider:

Any user-specific needs from the Laboratory Demand Ventilation Assessment

The type of ECD needed to perform a specific operation

Specific containment and ECD size requirements

Satisfactory performance testing of potential ECD/control-system configurations
There are many different types of ECDs. Figure 2 shows different ECDs and potential applications.
7
Bench-Top Bypass Hood
High Performance Fume Hood
VAV Fume Hood
Hazard: Chemical
Toxicity: Low to IDLH
Generation Rate: Small to Large
Effluent Gases, Vapors, Mists, Fumes, etc.
Distillation Hood
Laboratory Fume Hoods
Floor Mounted Hood
Hazard: Radioisotopes, Chemical
Effluent Generation Rate: Small to Moderate
Effluent Type: Gases, Vapors, Mists, Fumes, etc.
Radiation Hood
Perchloric Acid Hood
Auxiliary Air Hood
Class I
Ventilated Balance Enclosure
Class II Type A1
Class II Type A2
Biological Safety
Cabinets
Class II Type A2 Ducted
Class II Type B1
Hazard: Chemical, Perchloric Acid
Hazard: Chemical
Toxicity: Low to High
Effluent Generation Rate: Small to Large
Hazard: Chemical, Biological, Radionuclides
Toxicity: Low to High
Effluent Type: Gases, Vapors, Particulates
Hazard: Biological
Toxicity: Low to Moderate
Effluent Generation Rate: Small
Effluent Type: Particulates
Hazard: Chemical, Biological
Class II Type B2
GloveBox
Class III Glove Box
Effluent Generation Rate: None
Other Lab Hoods
Canopy Hood
Slot Hood
Snorkel
Hazard: Chemical
Toxicity: Negligible to Low
Effluent Type: Gases, Vapors, Particulates, Heat
Downdraft Table
Ventilated Enclosure
Ventilated Cylinder Cabinet
Figure 2 Diagram of Different ECD Types and Potential Applications
8
5.3.1
Laboratory Fume Hoods
Laboratory fume hoods are available in many different types, sizes and configurations to
accommodate laboratory procedures and processes. Unlike biological safety cabinets that have well
defined classes and types to identify different models, fume hoods are not categorized. They are
often identified by describing the size and key components of the design. For example, a common
fume hood is a 6-ft, bench-top, bypass fume hood. This fume hood can easily be confused with a 6ft, bench-top, radiation hood that differs only by the design and construction of the internal liner.
Furthermore, hoods can be further described by the type and configuration of the moveable sash
leading to a description such as a 6-ft, bench-top, vertical sash, bypass fume hood. The distinction
between fume hood types and sizes is cumbersome, but critical to ensure the hood is appropriate
for the intended procedures. Figure 3 shows the common components that comprise a fume hood
and could be used to differentiate hood types.
Figure 3 Typical Laboratory Fume Hood Components (from ASHRAE 110)
Hood size is generally the nominal size, determined by the width of the hood including the width of
the opening plus the width of the exterior enclosing panels. The size is not a measure of the sash
opening width. This oversight during design has caused many errors in flow specifications and
subsequent problems during TAB of the systems.
Other critical dimensions include the width, depth and height of the interior chamber. The hood
must be large enough to accommodate apparatus and equipment used in the hood during
hazardous procedures. Typical specifications for the depth and interior height of a bench-top fume
hood are a minimum of 24 inches and 48 inches, respectively; OSHA Lab Standard 1910.1450 has
requirements for a specific size of laboratory fume hood. According to the standard, fume hood
openings must provide at least 2.5 linear feet of space per person for every two people working with
hazardous chemicals in the laboratory. The interior dimensions together with the opening size and
9
design of the hood components are used to determine the flow specifications and resulting ability to
provide containment performance.
5.3.2
Constant Air Volume (CAV), Conventional Fume Hood
Conventional fume hoods were intended to operate at a constant exhaust volume. They have all
the components of a typical fume hood with the exception of sufficient bypass area to maintain a
constant hood static pressure and prevent excessive face velocities when closing the sash. As such,
conventional fume hoods are not recommended as flows can vary depending on the sash
configuration and resulting hood static pressure. Figure 4 shows the airflow entering the hood
through the opening when the sash is open and through the bypass opening when the sash is
closed.
Bypass
Bypass
Bypass
Vortex Region
Sash Full Open
Reduced Sash Open
Sash Closed
Figure 4 Diagram Showing Airflow Patterns When the Sash is Opened and Closed
5.3.3
CAV, Bench-Type, Bypass Fume Hood
A bench-top bypass fume hood is a generic type of chemical hood that has a bypass opening above
the sash through which room air can enter the hood chamber when the sash is lowered. Bench-top
bypass hoods can be used for a variety of chemical procedures and are appropriate for generation of
small to large quantities of low to highly toxic materials. Bypass fume hoods can have vertical,
horizontal or combination sash types and open or restricted bypass areas. Refer to Figure 5 for a
photo of a CAV, Horizontal Sash, Bench-top, Bypass Fume Hood.
10
Bypass Grilles
Figure 5 Hood Depicting Bypass Openings at the Top
The bypass is sized to meet the following conditions:
5.3.4

The total airflow volume is essentially the same at all sash positions. The hood static
pressure should not vary more than 5-10% when opening or closing the sash.

The bypass must provide a barrier between the hood work space and the room when the
sash is lowered. The bypass opening is dependent only on sash operation.

The bypass areas shall be sufficient to prevent velocities exceeding three times the design
average face velocity at sash heights less than 10% open (Vbypass ≤ 3 x Vfavg).
Auxiliary Air Bypass Fume Hood
An auxiliary air hood is a bypass hood equipped with an air supply plenum mounted over the sash
opening. The auxiliary air supply is designed to provide either conditioned, or in some cases
unconditioned, air gathered from outside the building and directed to the plane of the hood sash.
The objective is to reduce the volume of conditioned laboratory make up air necessary for the hood
to operate by providing this alternate source of make-up air. In concept, the design provides energy
savings by supplying minimally conditioned or unconditioned outside air to the hood for exhaust
rather than all of the exhaust being expensive conditioned air from the laboratory. In addition, an
auxiliary air hood would function in a laboratory that had a shortage of air supply.
However, auxiliary fume hoods come with a variety of deficiencies including:

Supplying unconditioned auxiliary air may affect room temperature stability and the
variations in air temperature may cause unwanted reactions to sensitive processes
undertaken in the hood
11

The balance between the auxiliary air flow and the exhaust flow is critical to ensure that
auxiliary air is properly captured by the hood. Adjusting the flow to achieve the desired
volumes can be complicated

Excessive auxiliary air discharge velocities can jeopardize hood containment due to
excessive cross drafts produced by the auxiliary air supply discharge
Current recommendations discourage the use of auxiliary air-type hoods in new construction. Their
use may be justified under special circumstances, when renovations to the existing ventilation
system are inadequate and where expansion of system ventilation capacity may be mechanically
unfeasible or too costly. Auxiliary air must not be supplied behind the sash as this arrangement can
pressurize the work chamber and cause escape from the hood. Figure 6 shows the auxiliary air
entering above the sash when the sash is lowered and through the sash opening when the sash is
raised.
Figure 6 Auxiliary Air Supply System and Resulting Airflow Patterns at Different Sash
Configurations
Manufacturers of auxiliary air hoods specify that the auxiliary air volume should be as much as 70%
of the required exhaust air volume. ECT, Inc. has found that the resultant auxiliary air velocity is too
high for capture and the downward flow shears past the opening and can cause hood escape. ECT,
Inc. data suggests auxiliary air velocities should not exceed 1.5 to 2 times the average face velocity
(Vaux air ≤ 1.5~2.0 x Vfavg). The auxiliary air velocity is measured 6 inches below the outlet of the
plenum.
Due to the impact of auxiliary air at the opening, the auxiliary air must be turned off or redirected
during measurement of fume hood face velocities.
12
5.3.5
CAV – High Performance Fume Hoods (HP Fume Hoods)
A high performance (HP) fume hood is a bypass fume hood operated at face velocities 30% to 40%
less than traditional fume hoods. A traditional, bench-top, bypass fume hood generally requires an
average face velocity of approximately 100 fpm at the full open sash opening to provide
containment. High performance fume hoods incorporate enhanced aerodynamic design features,
particularly the airfoil sill, sash handle, side posts and baffles, that enable equivalent containment at
reduced face velocities (as low as 60 fpm). By providing equivalent performance, a HP hood can be
used for the same hazards and procedures appropriate for a traditional fume hood. The primary
benefit of a HP fume hood is the reduction in total exhaust flow at the design opening and potential
for reduced energy use. However, HP hoods may be more expensive than traditional hoods and the
savings from reduced flow would need to justify the additional expense. Despite the aerodynamic
modifications, HP hoods are still affected by cross drafts and other external factors the same as
traditional fume hoods. In addition, all HP fume hoods do not perform the same and validation
testing is recommended to evaluate performance prior to purchase.
5.3.6
Variable Air Volume (VAV) Fume Hood Systems
A VAV fume hood is the same design as a CAV, bypass fume hood but the bypass area is restricted to
accommodate reduced flow when the sash is closed. Therefore, the key differences between a CAV
bypass fume hood and a VAV bypass fume hood is the size of the bypass and the application of VAV
controls to modulate flow. There are multiple types of VAV control strategies applied to VAV fume
hoods. The simplest VAV control type is two state control that limits flow modulation to only two
flows (low and high or occupied and unoccupied). A full VAV control system modulates flow in
response to sash position and attempts to maintain a constant face velocity when operating
between the minimum and maximum flow set points. VAV controls can be based on sash position,
velocity, or occupancy.
The type of VAV system dictates the fume hood operating specifications and the applicable test
methods. When determining the type of VAV control and required operating specifications, all hood
operating modes need to be considered including:

sash open

sash closed

hood in use but unoccupied (materials being generated in the hood with no one standing at
the opening or sash closed)

hood in use and occupied (materials being generated in the hood and a person is standing in
front of the hood with the sash open
13
Depending on the type of controls, flow can be reduced through a VAV fume hood when the sash is
lowered or the hood or lab is unoccupied. However, the VAV controls become more complex when
accommodating multiple modes of operation, increasing the potential for problems that can affect
energy savings and, more importantly, hood containment. Special techniques and methods are
necessary to evaluate and maintain operation of VAV controls and ensure safe and efficient
operation.
Use of VAV fume hoods are not appropriate for all applications, such as processes involving
generation of acid mists or vapors greater than 1 liter per minute (> 1 lpm). When the sash is closed
or the hood is unoccupied (or not equipped with an occupancy sensor), the resultant exhaust air
volume may not be adequate to maintain sufficient dilution and resist condensation/accumulation
of hazardous materials within the hood and exhaust ducts. To address this, a minimum sash height
should be specified or the hood should be operated as CAV during the procedure.
5.3.7
Distillation Laboratory Fume Hoods
A distillation fume hood (Figure 7) is designed for use with tall apparatus and procedures that
involve small to medium quantities of low to high toxicity materials. A distillation hood has the
same components as a bench top hood with the exception that the design provides a greater
interior height for use of a larger apparatus. The distillation hood work surface should be between
12 and 18 inches above the floor.
Figure 7 Diagram of a Distillation Hood
14
Distillation hoods can have vertical rising sashes or horizontal sliding panels. Generally more than
one sash panel is used on a vertical rising sash. The vertical sash design generally enables a rather
large opening and care must be taken in determining the maximum allowable sash opening and
required exhaust flow.
5.3.8
Floor Mounted Laboratory Fume Hoods
A floor mounted hood (Figure 8) is used for large apparatus and storage of containers that pose
some hazard but will not fit into an approved storage cabinet. A floor mounted hood is suitable for
the same type of work conducted in bench-top hoods and distillation hoods and typically equipped
with horizontal sliding sashes, although some models may be equipped with multiple vertical sliding
sashes.
Floor mounted hoods can also be termed “walk-in” hoods. However, the name "walk-in hood"
implies that the hood can be entered and the name is a misnomer as the same safety precautions
should be applied to this hood as those required for a bench-top hood. The hood must never be
entered during generation of hazardous materials.
Floor mounted hoods are particularly susceptible to variations in face velocity across the opening
and room air disturbances due to the large opening area afforded by the hood design. For this
reason it is prudent not to use a floor mounted hood for work with highly toxic materials.
Figure 8 Photo of a Floor-Mounted Hood Equipped With Horizontal Sash Panels
15
5.3.9
Perchloric Acid Laboratory Fume Hoods
Perchloric Acid Laboratory Fume Hoods should be clearly labeled “For Use with Perchloric Acid”.
The hood should be constructed from materials that are non-reactive, acid-resistant, and relatively
impervious. Type 316 stainless steel with welded joints should be specified. Corners should be
rounded to facilitate cleaning. Work surfaces should be watertight, with an integral trough at the
rear of the hooded area, for collection of wash-down water.
A wash-down system (Figure 9) must be provided that has spray nozzles to adequately wash the
entire assembly including the stack, blower, all ductwork, and the interior of the hood, with an easily
accessible strainer to filter out particulates. The wash-down system should be activated
immediately after the hood has been used and the hood must be washed down following the use of
perchlorates. Waste stream must be disposed of in accordance with hazardous waste policies.
Figure 9 Diagram of Perchloric Acid Fume Hood with Duct Wash System
The ductwork should be constructed of stainless steel with smooth-welded seams. All welded
ductwork should be installed with a minimal amount of horizontal runs and no sharp turns.
Ductwork also must not be shared with any other hood or joined (manifold) with other nonperchloric acid exhaust systems. Perchloric acid is highly reactive to organic materials; materials
used in the construction of the fume hood, including gaskets, caulking, etc., must be compatible
with this hazard.
5.3.10 Radioisotope Fume Hoods
Radioisotope fume hoods should meet all requirements for constant volume bypass-type or VAV
fume hoods. The primary exception is the interior liner material should be stainless steel with coved
16
corners to facilitate cleaning. Refer to the Radiation Chapter for more information about use of
radioactive materials and system requirements.
5.3.11 Pass Through Hood
5.3.12 California Hood
5.3.13 Teaching Lab Hood
5.3.14 Ductless Fume Hood
5.3.15 Laminar Flow Fume Hood
17
Table 3 Recommended Criteria and Specifications for ECDs
Functional and
Performance Tests
CAV
Fume
Hood
CAV HP
Fume
Hood
VAV
Fume
Hood
Biosafety
Cabinet
VBE
FSE
Canopy
Slot Hood
VE
Down
draft
table
Filtered
Ductless
Hood
Inspection
Pass
Pass
Pass
Pass
Pass
Pass
Pass
Pass
Pass
Pass
Pass
Flow
Design
Design
Design
(1)
Design
Design
Design
Design
Design
Design
Design
Design
Hood Static Pressure
Inches W.G.
<0.5
<0.5
<0.5
<1.0
<1.0 (2)
Design
Design
Design
Design
Design
N/A
Capture or Face Velocity
(FV)
100 fpm
60 fpm
100 fpm
75 – 100
fpm
60-100
fpm
Design
100 fpm
Design
100 fpm
100 fpm
(3)
100 fpm
Cross Draft Velocity
<50% of
FV
<50% of
FV
<50% of
FV
<50% of FV
<50% of FV
<50% of
FV
<50% of
FV
<50% of
FV
N/A
<50% of
FV
<50% of FV
VAV Response
N/A
N/A
< 5 sec.
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
VAV Stability
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
No
Escape
< 0.1
ppm (4)
No
Escape
< 0.1
ppm (4)
No Escape
& Split
No Escape
Good
Capture
Good
Capture
Good
Capture
No
Escape
Good
Capture
No Escape
Alternative Tracer Gas
Design
Filter Leak Tests
None
detectable
< 0.1 ppm
(4)
< 0.1 ppm
(5)
None
detectable
Smoke Test
ASHRAE 110 Tracer Gas
Auxiliary Air
< 20%
COV
No
Escape
< 0.1
ppm (4)
< 0.1 ppm
(4)
< 0.1
ppm (6)
None
detectable
< 1.5 x
Vavg.
The flow at the design opening and the minimum flow shall be defined in advance. The minimum flow should be capable of providing 375 ACH.
The hood static pressure is measured downstream of the filter if equipped.
Down draft velocity measured 6 inches above table in downward direction.
Criterion for “as installed” tests.
VBEs can be tested with a particulate challenge. The criteria should be appropriate to the procedure
Downdraft tables should be challenged with an evaporative challenge such as IPA in a spill tray located on the work surface.
18
6
Exposure Control Device Operation
6.1
Laboratory Hood Operation
Airflow drawn through the opening of a fume hood creates an air barrier at the plane of the sash to
minimize escape of contaminants generated inside the hood chamber. A fume hood cannot be
counted on to provide 100% containment due to the sash opening or lack of complete physical
isolation. Only a glove box approaches 100% containment and should be considered whenever
working with materials that are immediately dangerous to life and health (IDLH). The effectiveness
of the air barrier is a function of the speed, direction, distribution and turbulence of the air entering
the hood through the plane of the sash opening. The plane of the sash opening is defined as the
imaginary vertical plane formed at the exterior surface of the outermost glass panel. Hazardous
materials generated within the hood should not escape outside the plane of the sash. The
aerodynamics of the hood entries and the baffles at the back of the hood help control the direction
and distribution of flow through the opening and the capture efficiency of the hood. See Figure 10
for a diagram of the hood showing the airflow through the plane of the sash and the location of the
imaginary air barrier formed at the sash plane.
Figure 10 Diagram Showing Side View of Fume Hood and Airflow Patterns
6.1.1
Escape of Contaminants
The direction, speed, turbulence and distribution of airflow through the opening are the primary
factors associated with hood containment. The direction of airflow into the hood through the sash
opening is generally perpendicular to the plane of the sash. The speed of the air measured at the
sash plane is referred to as the face velocity. The average face velocity is the average from a grid of
multiple air speed measurements across the opening. The distribution of airflow through the
opening as indicated by the variation of velocities across the opening is referred to as spatial
19
variation or sometimes referred to as uniformity of flow across the opening. Turbulence is
dependent on flow rate and hood design, resulting in differences in face velocity over time
(sometimes called temporal variation). Escape at any given average face velocity can be expected to
increase as spatial and temporal variations exceed 20%.
Escape from the hood can occur at any location across the opening. However, certain areas are
more prone to escape including the horizontal and vertical edges of the sash panels along the
vertical edge of the side posts above the horizontal top of the airfoil sill. Escape is exacerbated by
the presence of a person standing in the opening. The photo in Figure 11 shows escape below the
sash and above the airfoil using smoke to visualize airflow patterns and a mannequin located at the
hood opening simulating a hood operator. The aerodynamic design of the sash handle, airfoil sill
and side posts are primary factors affecting distribution, turbulence and escape at those locations.
Visualization of escape using a smoke source located in the hood is best done both with and without
a person standing at the opening.
Figure 11 Image of Hood Depicting Areas Prone to Escape
Additional factors that affect the spatial and temporal variations of face velocities include room air
currents (cross drafts) and temperature gradients in the lab near the hood opening. Cross drafts
from supply diffusers or people walking by the hood easily disrupt containment. Many times,
escape from hoods is caused by improper supply of air through diffusers located too close to fume
hoods. The discharge temperature of the air from the diffuser can also skew airflow through the
opening and create excessive turbulence. See section 6.2 for additional information regarding
appropriate diffuser types and locations.
6.1.2
Sash Opening Configurations
Fume hoods are equipped with moveable sash panels to vary the opening area. Depending on the
design of the hood, sashes can consist of single or multiple panels that sometimes slide vertically
20
(vertical sash) or slide horizontally (horizontal sash) to increase or decrease the access opening.
Sashes should be configured to provide the minimum area necessary to safely conduct the work
performed in the hood. ECT. Inc. studies indicate the potential for escape is proportional to the size
of the opening.
The design opening area is the area of the opening where the hood is intended or designed for use.
The design opening may be less than the maximum achievable opening (100% full open) and is
sometimes different than the preferred user opening. The Hazard Demand Ventilation Assessment
must identify the opening areas required for the user to access and safely conduct procedures in the
hood.
The design opening should be clearly indicated and a mechanical stop installed to remind the users
of the opening restrictions. Under the vertical sash configuration, the user can access the entire
width of the hood opening, but access to the top of the hood chamber is limited by the sash panels
(See Figure 12 below). In Figure 13, the hood user is operating the hood in the right, horizontal, sash
opening configuration. In a horizontal sash configuration, the user has access to the top of the hood
chamber, but has limited access from side to side. Hood containment can be equivalent at either
sash configuration, but hood performance improves at smaller openings.
Vertical design openings are typically limited to a height below the breathing zone of the user and
results of performance tests conducted by ECT, Inc. have demonstrated that the maximum width of
horizontal sash opening should not exceed 30 inches. Operating a fume hood at sash openings
larger than the design opening can result in escape from the hood due to insufficient face velocities
or increased spatial and temporal variations.
Figure 12 Fume Hood with Vertical Sash at Restricted Height Design Opening
21
Figure 13 Example of Fume Hood with Horizontal Sash Opening
6.1.3
Airfoil Sills
All bench-top fume hoods should be equipped with an airfoil sill (Figure 14). The airfoil sill
streamlines flow into the hood over the work surface and reduces turbulence and reverse flow
along the bottom of the opening. The airfoil sill minimizes vortex formation and reverse flow at the
bottom of the opening to improve hood containment.
A
B
Figure 14 Diagram of Fume Hood Work Surface Showing Airflow Patterns with and without Airfoil
Sill
6.1.4
Baffle Design and Configuration
22
The design of the baffle and configuration of the capture slots affects the direction and uniformity
airflow through the opening and capture of airborne materials within the hood. Improper baffle and
slot configuration can result in escape from the hood regardless of the average face velocity.
Contrary to popular belief, the baffles should not be adjusted to accommodate the density of the
materials used in the fume hood. The baffles and slots are adjusted to achieve the flow patterns
that ensure satisfactory hood containment and contaminant removal from the hood.
The diagram in Figure 15 presents a side view of the hood showing the baffle and slots in the baffle.
Baffle panels and with adjustable slot widths can change the direction and distribution of flow
through the opening. The hood shown in the middle diagram has the top slot open creating an
upward flow of air through the opening. Conversely, the diagram of the hood on the right shows a
downward flow of air through the top of the opening and increased directional flow across the work
surface with the top slot nearly closed.
Qe
Qe
Qe
Baffle
Top
Plenum
Slots
Velocity
Middle
Bottom
Top Slot Open
Top Slot Closed
Figure 15 Design and Configuration of Baffle Panels and Capture Slots
Ensure baffle panels are properly installed and adjusted to achieve proper airflow distribution and
hood containment. The baffles should be adjusted by qualified personnel during hood
commissioning tests and evaluated following installation of equipment and apparatus in the hood.
Equipment and apparatus in the hood can disrupt airflow patterns and adjustments of the baffle
may be necessary to ensure containment.
Figure 9 shows a photo of smoke flow in a hood with the top slot of the baffle fully open. The
upwardly directed airflow combined with reduced flow across the work surface results in reverse
flow and escape over the airfoil sill downstream of the mannequin at the opening. The photo of the
hood on the right of Figure 16 shows airflow patterns when the top slot was nearly closed. The
closed top slot creates a slight downward flow through the opening at the top of the hood and
increased flow across the work surface that reduced reverse flow in front of the mannequin and
enabled satisfactory hood containment.
23
Figure 16 Fume Hood Showing Reverse Flow and Escape Near Airfoil Sill With Top Slot Fully Open
(Left). Fume Hood Showing Capture at Bottom Slot With Top Slot Closed (Right)
6.1.5
Fume Hood Specifications
6.1.5.1 Functional Requirements and Performance Criteria
A laboratory hood must meet the functional requirements and performance criteria defined by the
Hazard Ventilation Demand Assessment in section 3. In general, a laboratory fume hood system
should prevent overexposure of personnel to hazardous airborne materials generated in the hood
by capturing and exhausting contaminants from the lab environment. Meeting the performance
criteria are the expected result of operating the systems in accordance with the operating
specifications. Performance criteria can be specific such as “the laboratory hood system shall
minimize the concentration of contaminant x below permissible exposure limits or the criteria can
be more generic such as “escape shall not exceed a specified concentration of a tracer gas
generated during containment tests”. The operating specifications define how the systems operate
to provide the given level of performance. For example, meeting the performance criteria for
containment requires operating the fume hood at a specified exhaust flow to achieve the average
face velocity at the design sash opening. Performance criteria for each laboratory hood should be
appropriate for the intended function and specified prior to conducting functional tests.
Performance criteria for different laboratory hoods and performance tests are described in Table 4
below.
24
Table 4 Performance Criteria for Select Hoods and Tests
Laboratory Hood
Performance Test
Recommended Performance Criteria
General Safety
Containment must prevent overexposure to materials
generated within the hood.
ASHRAE 110 Airflow
Visualization see note 1
Hood must completely contain smoke inside the plane
of the sash at the design opening.
Containment Test
Hood must prevent escape below 0.1 ppm at a 4 lpm
generation rate at the design sash opening.
General Safety
Containment must prevent overexposure to materials
generated within the hood.
Tracer Gas
Containment Test
Glovebox must prevent escape of tracer gas to below
5x10-7 cc/sec see note 2.
Canopy Hoods
General
Canopy hoods are not recommended for personnel
protection. Canopy hoods should remove heat and
prevent increase in lab temperatures to less than 1
degree.
Slot Hoods
General Safety
Capture must prevent overexposure to materials
generated within design capture area.
Snorkel Hoods
General
Capture at contaminant source must prevent
overexposure and accumulation of concentrations to
unsafe levels within the lab.
General
Capture must prevent overexposure to materials
generated on the table.
Airflow Visualization
Test
Smoke must be captured by the table exhaust when
generated less than six inches above and within the
perimeter of the table.
Chemical Fume
Hood
Class III Glovebox
Downdraft
Necropsy Tables
Notes: (1) - The ANSI/ASHRAE 110 methods are described in more detail below.
(2) - Tracer Gas Test Performance Criteria per Protocol.
25
6.1.5.2 Laboratory Hood Operating Specifications and Test Criteria
Appropriate operating specifications must be established for every laboratory hood system.
Specifications for operating a laboratory hood system are based on satisfying the performance
criteria and can be unique to the laboratory hood system. Parameters included in specifications can
include:

Operating Modes

Opening Configuration

Range of Flow and Velocity

Differential Pressure and System Static Pressure

Maximum Cross Draft Velocities

VAV Speed of Response and Flow Stability

Monitor Accuracy

Qualitative and Quantitative Containment Requirements
Table 5 lists test requirements for various ECD. Table 6 presents recommended operating and
performance criteria.
26
Table 5 ECD Test Requirements
CAV Fume
Hood
VAV
Fume
Hood
Biosafety
Cabinet
VBE
FSE
Canopy
Slot Hood
VE
Down
draft
table
Filtered
Ductless
Hood
Inspection
X
X
X
X
X
X
X
X
X
X
Flow
X
X
X
X
X
X
X
X
X
X
Hood Static Pressure
X
X
X
X
X
X
X
X
X
X
Capture or Face
Velocity
X
X
X
X
X
X
X
X
X
X
Cross Draft Velocity
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Functional and
Performance Tests
VAV Response
X
VAV Stability
X
Smoke Test
X
X
X
X
X
Alternative Tracer Gas
X
X
Filter Leak Tests
X
X
Auxiliary Air Test
X
X
X
X(1)
Note: Auxiliary air test should be done on all fume hoods equipped with auxiliary air.
27
Table 6 Recommended Operating Specifications and Performance Criteria
Device
Test /Parameter
Industry Recommended Criteria/Specs
(Unless otherwise specified in the Design Documents)
Notes
Sash Design
Opening
N/A
Cross Draft Test
Vcd  50 fpm
Tracer Gas
Containment
AI, AU = <0.1 ppm
Peak = 30 second rolling average < 0.5 ppm
Face Velocity
100% Open Sash
Vfavg = 100 fpm
Vfmin  90 fpm
Vfmax  110 fpm
Face Velocity
Design Sash
Opening
Vfavg = 100 fpm
Vfmin  90 fpm
Vfmax  110 fpm
Mechanical sash stop installed.
Monitor must indicate within 5% of actual face velocity
Unoccupied mode with sash open (occupancy sensor)
Variance Fume
Hoods
N/A
The hoods covered by the variance shall operate with an
average face velocity of at least 80 fpm with a minimum of
61 fpm at any point and with a maximum sash height of 18”
High
Performance
Fume Hood
Face Velocity
100% Sash Opening
Vfavg  60 fpm
Criteria applicable to high performance hood or equivalent
design.
High
Performance
Fume Hood
Face Velocity Design
Sash Opening
Vfavg  60 fpm
Retro-Fit Fume
Hoods
Face Velocity
Maximum Sash
Opening
See Manufacturer Recommended
Operating Specifications
All Fume Hoods
Traditional
Fume Hood
Affects Hoods equipped with Vertical Sash, Horizontal
Sashes or Combination Sash.
At Design sash opening
From any direction using average over 30 seconds at each
test location
Sash Closed – No detectable escape from hood,
Hood interior vortex concentration less than 3 times steady
state exhaust duct concentration
VAV hoods can have 100 fpm face velocity at 100% sash full
open
± 10% prevents significant exhaust variation and room
pressure issues.
28
Device
Hood Flow, Face
Velocity or
Pressure
Monitor
VAV Controls
Fume Hood
Minimum Flow
or Min. ACH
Test /Parameter
Face Velocity
Design Sash
Opening
See Manufacturer Recommended
Operating Specifications
6” opening to Full
Open
Monitor must indicate within 5% or 5 fpm.
Based on 10 second average velocity or flow reading
VAV Response for
fume hoods.
Achieve 90% of the face velocity set-point within 5
seconds from the time the sash is opened.
Includes determination of steady state flow at minimum and
maximum to determine start and 90% of final flow.
Stability Test
Coefficient of Variation
COV< 20%
COV% = (3*Std.Dev.)/SSTAvg.flow
Min. Flow at Sash
Closed via Pitot
Tube Exhaust
Ensure contaminants are properly diluted and
exhausted from the hood.
ANSI/AIHA Z9.5 suggests that 150 ACH to 375 ACHfh
may be appropriate.
Flow must be controllable within stability requirements and
subject to minimum duct velocities (see Note 1).
Offset Volume (i.e.
transfer air)
Lab
Notes
Difference between supply and exhaust flow for laboratory
to achieve directional flow and pressurization.
Differential Pressure
(-) to adjacent non-lab spaces(1)
If potential for generation of airborne hazardous material.
(+) to adjacent non-lab spaces (2)
If no potential for generation of hazardous airborne
materials
100% outside air w/no recirculation
Air can be recirculated within a lab unit for local
conditioning.
Air may be recirculated when monitored for airborne
concentrations.
Air may be recirculated when no hazardous materials are
present.
Recirculation of Lab
Air
29
Device
Lab:
Tissue Culture,
Cleanroom
Exhaust Duct
Velocities
Test /Parameter
Notes
(+) to vestibule (anteroom)
and/or
(-) to adjacent non-lab spaces
If potential for generation of hazardous airborne materials,
but requires isolation or no infiltration to main lab
Vapors, Gases,
Smoke and Sub
Micron Particles
ACGIH – Industrial Ventilation Manual
1,000-2,000 fpm or any desired velocity
See Note 1 below
Criteria for duct velocity or hood ACH may be affected by
exhaust duct size.
Fumes: i.e. Zinc and
Aluminum Oxide
Fumes
Very Light Dust: i.e.
Cotton Lint, Wood
Flour, Litho-Powder
Dry Dust and
Powders Cotton
Dust
Average Industrial
Dust Shavings
Sawdust, Grinding
Dust
2,000-2,500 fpm
2,500-3000 fpm
3,000 -3,500 fpm
3,500-4,000 fpm
Heavy Dusts: i.e.
Metal Turnings,
Lead
4,000-4,500 fpm
Heavy Moist Dust:
i.e. Buffing Lint
(Sticky), Lead Dust
with Small Chips
> 4,500 fpm
30
Device
Lab Hood
Exhaust
Test /Parameter
Stack Discharge
Velocity or Criteria
3,000 fpm + 10 ft above roof, or
< 100 µg/m³ per g/s or 10,000:1 dilution factor.
Notes
Criteria for stack design should be based on preventing
exposure and re-entrainment rather than discharge velocity.
Notes:
1. Minimum duct velocities must be capable of transporting effluent out of system and preventing accumulation of materials within the duct system. The
minimum flow must also be sufficient to permit accurate and precise measurement and control within acceptable tolerances. The minimum flow through VAV
fume hoods can be a function of the fume hood internal ACH and the resulting capture and duct transport velocity.
31
6.1.5.3 Operating Mode
Depending on the design of the ventilation system, a laboratory hood can have multiple modes of
operation to meet changing demands for ventilation. Operating modes should be well defined and
assigned appropriate performance criteria and operating specifications. The operating modes for a
laboratory fume hood can be simple or complex depending on the capability of the controls. Simple
CAV systems have only one mode of operation where the hood operates continuously at full flow
regardless of use. More complex VAV control systems enable multiple modes of operation that
might vary flow depending on the position of the sash or whether someone is standing at the
opening.
Operating modes for a VAV fume hood equipped with sash sensors and an occupancy detector could
include:

Sash Open;

Sash Closed;

Sash Open – Occupied (person at hood opening); and

Sash Open – Unoccupied (person not at the hood opening).
For other hood types the operating modes may vary depending on the function. For example, the
operating modes for a FSE might include only two operating modes such as operating and not
operating.
6.1.5.4 Flow and Velocity Specifications
The design opening area for each hood type and the required face velocity or capture velocity must
be known to determine the exhaust flow. Flow (Q) is the product of opening area (A) multiplied by
the average velocity (V) where Q = V x A. The design face velocity is typically 100 fpm for traditional
fume hoods and 60 fpm for high performance fume hoods.
Exhaust flow for a VAV fume hood can range from a minimum with the sash closed to a maximum
with the sash full open (100%). The flow at a given sash configuration is equal to the design face
velocity multiplied by the opening area. However, the exhaust flow can be reduced when the sash
opening is reduced without sacrificing containment. See Figure 17 for the difference between flow
with the sash open and sash closed.
32
Figure 17 Laboratory Hood Flow Specifications at Sash Open and Sash Closed
Establishing the minimum flow for a VAV fume hood is more complicated than the simple Q = V x A
calculation, as the minimum exhaust must ensure containment with the sash closed and prevent
accumulation of unsafe concentrations within the fume hood.
The 2012 ANSI/AIHA Z9.5 American National Standard for Laboratory Ventilation requires the
minimum exhaust volume ensures that contaminants are properly diluted and exhausted from a
hood. From the standard:
"The following considerations shall be taken into account (as applicable) when setting the
minimum hood flow rate for each hood:

Control of ignition sources within the hood,

Design of the hood, the materials used in the hood and the anticipated maximum
generation rates,

Potential for increased hood interior corrosion,

Effect on exhaust stack discharge velocity,

Fume hood density,

Need to affect directional airflows, and the

Operating range of the hood exhaust equipment and the associated control system."
33
The standard also uses the internal volume of the hood and air changes per hour (ACH) to help
specify the minimum flow. See Figure 18 for a diagram of the critical measurements to calculate the
internal ACH.
The standard suggests that 150 ACH to 375 ACH is typically adequate but does not define a specific
acceptable minimum ACH. The minimum exhaust flow in cfm can be calculated by multiplying the
appropriate ACH by the internal hood volume and dividing by 60 minutes per hour (Q = ACHhood x
Vol.hood/60). Selecting the appropriate internal ACH depends on:

Understanding the Hazards and Processes

The lower explosion limit (LEL) and the safety factor (most facilities use 10-25% of the LEL)

Hood design, internal airflow patterns and the mixing factor

Capability of the VAV controls to ensure stable flow at reduced rates

Conducting dilution tests to determine the minimal flow acceptable for the hood

Maintaining appropriate duct transport velocity
Figure 18 Diagram of Hood Showing Dimensions for Calculating the Hood Air Change Rate
Table 7 contains specifications and criteria for dilution tests.
34
Table 7 Specifications and Criteria for Dilution Tests
Test
Criteria
Notes
Pitot traverse and calculated flow based on sash
height opening
 Sash heights to minimal spec. calculate and
confirm minimum exhaust set point for protocol.
 Measure to confirm minimum flow to provide minimum of 150 ACH
Exhaust Flow
 Exhaust flow should be within 5% of BAS reported
flow.
 Calculation of flow using average face velocity increases error for
flow.
 Measurement by Pitot tube is preferred with sufficient length of
straight duct.
Dynamic Response and Stability Test
 VAV Response Test:
 Time required for VAV to modulate flow with sash  The response time includes the time required to raise the sash.
 Sash is raised at approximately 1.5 ft/sec
closed to 90% of steady state flow with sash at
design opening must be less than or equal to 5
seconds.
 VAV Stability Test:
 The coefficient of variation is calculated as:
 The variation determined by the coefficient of
variation shall be less than 10% of the steady state
%COV = 100 × (3 × standard deviation) / average steady state flow
flow with the sash closed or with the sash at the
design sash opening.
Tracer Gas Containment Tests (static mannequin and
Sash Movement Effect Test (VAV Tracer Gas
Containment Tests)
 The maximum 5-minute average BZ concentration
 The maximum 5-minute average concentration applies to any test
must be 0.05 ppm.
configuration or mannequin position.
 The maximum 30-second rolling average shall be
 30-second rolling averages shall be calculated during opening scan
less than 0.1 ppm. Rolling average is the average
and sash movement tests. The 30-second rolling average negates
of any consecutive 30-second period.
instrument detection methods and replaces peak escape.
 The peak concentration shall not exceed 0.5 ppm.
Tracer Gas Dilution Tests
 The internal concentration shall not exceed 25% of  The dilution tests determine the hood dilution factor that is used to
the Lower Explosion Limit (LEL) for the worst
calculate potential concentrations inside the hood knowing the
flammable material used in the hood.
exhaust flow and contaminant generation rate.
Definitions: Vcd – Cross-draft velocity, Vfavg – Average face velocity, Vfmin – Minimum face velocity, Vfmax – Maximum face velocity, COV – Coefficient of variation.
35
6.1.5.5 Laboratory Hood Monitors
ANSI/AIHA Z9.5 requires that all hoods be equipped with a hood monitor (Figure 19) that indicates
flow, pressure or face velocity and provides both audible and visual alarms to provide the hood user
with information about the operation of the fume hood system. The audible and visual alarms alert
users to improper exhaust flow or low face velocity.
The hood monitor should be capable of indicating the airflow is in the desired range and capable of
indicating improper flow or face velocity is high or low by 10%.
Fume hood monitors should be calibrated annually and/or whenever hood airflow is modified,
within a tolerance of + -5%.
Figure 19 Example of Through-the-Wall Velocity Sensor
6.1.6
Distillation Laboratory Fume Hood Specifications
6.1.7
Walk-in Fume Hood Specifications
6.1.8
Perchloric Acid Fume Hood Specifications
Heated perchloric acid should only be used in a laboratory hood specifically designed for its use and
identified as “For Perchloric Acid Operations”.
Perchloric acid fume hoods and exhaust duct work shall be constructed of materials that are acid
resistant, noreactive, and impervious to perchloric acid.
36
Ductwork for perchloric acid hoods and exhaust systems shall take the shortest and straightest path
to the outside of the building and not be manifolded with other exhaust systems. A water wash
down system shall be provided for washing down the hood interior behind the baffle and the entire
exhaust system.
Hood work surface shall be watertight with a minimum depression of 13 mm at the front and sides
with an integral trough at the rear of the hood to collect wash down water.
Exhaust fans supporting perchloric hoods should be acid and spark resistant. The exhaust fan motor
should not be located within the ductwork.
Hood surfaces should have all welded construction and have accessible round corners for ease of
cleaning.
6.1.9
Radioisotope Fume Hood Specifications
Hoods designated for use with radioactive materials shall be identified with the radiation hazard
symbol.
Hoods intended for use with radioactive isotopes must be constructed of stainless steel or other
materials that will not be corroded by the chemicals used in the hoods.
The hood interiors must have coved corners to facilitate decontamination.
Radioisotope hoods equipped with HEPA or Charcoal/HEPA filters require a bag-out plenum for
mounting such filters and fan capacity for proper operation of the hood with the filter installed.
Cabinets that may be supporting radioisotope hoods shall be adequate to support shielding for the
radioactive materials to be used in the fume hood.
6.1.10 Ductless Fume Hood Specifications
6.1.11 Laminar Flow Fume Hood Specifications
6.2
Ventilated Balance Enclosures (VBE)
Weighing of hazardous materials should be conducted in a low volume exhaust hood designed to
enclose sensitive analytical balances. VBE (Figure 20, also called Weighing Enclosure) includes many
of the same components of a typical chemical lab hood. However, weighing enclosures generally do
37
not include double wall construction (interior liner and exterior hood enclosure panels) or sliding
sashes. They are operated at lower face velocities than chemical lab hoods to reduce turbulence
that disturbs the balance and increases unwanted loss of material (approximately 60 fpm or less).
The design of a balance enclosure and exhaust flow (face velocity) must be sufficient to prevent
unacceptable escape into the lab space. Exhaust from balance or weighing enclosures should be
appropriately discharged from the lab space or filtered prior to recirculation.
Figure 20 Typical VBE (Weighing Enclosure) Station
6.2.1
Ventilated Balance Enclosure Specifications
A balance enclosure is a ventilated enclosure designed to specifically house a laboratory balance.
Typically made of transparent materials, balance enclosures are designed to protect users and the
laboratory environment by directing airflow away from the breathing zone of the user.
Testing protocol and criteria should be provided by the manufacturer, including testing filter
integrity if a filter is a component of the system.
6.3
Canopy Exhaust Hoods
Canopy exhaust hoods (Figure 21) are receiving hoods provided for the removal of heat and
negligible hazards from specific laboratory apparatus such as furnaces, ovens, and sterilizers.
Canopy hoods should not be relied upon for personnel protection where processes could be
enclosed and containment better assured.
38
Figure 21 Photo of Canopy Hood
Canopy hoods can be enclosed to improve capture and minimize flow requirements. Use of canopy
hoods should be carefully scrutinized as occupant safety is limited and airflow requirements result in
high operating costs. Figure 22 shows a large canopy hood in an improper configuration, used to
capture hazardous emissions generated outside the enclosure.
Figure 22 Improperly Configured Canopy Hood Located Over Apparatus
6.3.1
Canopy Exhaust Hood Specifications
6.4
Flexible Spot Exhausts (FSE)
Flexible Spot Exhausts (Figure 23, also called snorkel hoods) are point source extraction hoods used
to remove chemical fumes or heat from laboratory instrumentation or processes that are not readily
conducted in a fume hood or other ventilated enclosure. Some examples include high-performance
liquid chromatography (HPLC), gas chromatography/mass spectroscopy (GC/MS), and atomic
39
absorption (AA) equipment. The flow through a FSE is often limited by the duct size and the system
static pressure; capture effectiveness is a function of the proximity to the contaminant source and
the design of the hood inlet. Generally, flanged inlets will provide better capture than un-flanged
openings.
Figure 23 Flexible Snorkel Exhausts
FSE are most commonly employed in fixed positions over equipment or applied to partial enclosures
associated with sonicators and balances, microscopes, tissue photography or surgical laser plumes.
Successful FSE bench applications are highly specific to the mass of the contaminant and the velocity
and angle of emission. These factors require a high level of user knowledge and often require readjustment of the FSE during use to ensure efficient capture. Investigate the intended use of the
FSE and evaluate the design and location of the exhaust inlet to ensure satisfactory capture of
hazardous materials.
6.4.1
Flexible Spot Exhaust Specifications
6.5
Slot Hoods
Slot hoods have limited application in research laboratories and are designed to capture emissions
generated with marginal velocities near the slot openings. Slot hoods provide a limited range of
capture. The capture is a function of the hood dimensions, slot aspect ratio, exhaust flow (capture
velocity) and contaminant emission characteristics. In addition, the orientation of the user with
respect to the opening can also influence capture. Locate a slotted hood so that the direction or
airflow is not around the operator; see Figure 24 for a diagram of airflow patterns and orientation of
the user. In laboratory programs, slot hoods are most commonly used to control vapors from tray
photo processing. Historically, slot hoods have also been used to control formaldehyde during
40
preserved tissue sorting. The American College of Governmental Industrial Hygienists (ACGIH)
Ventilation Manual should be used as a guide to the design of slot hoods1.
Figure 24 Front and Side View of Slot Hood
6.5.1
Slot Hood Specifications
6.6
Downdraft Necropsy Tables
This special vent application (Figure 25) allows unobstructed top access while limiting release of
preservative chemicals and odors into the room air. It must be carefully cleaned to prevent
blockage of vents. It is intended only for necropsy or similar animal studies should not be used
where other vent hoods would be more appropriate.
1
®
th
ACGIH : Industrial Ventilation: A Manual of Recommended Practice for Design, 27 Edition. Cincinnati, Ohio:
American Conference of Governmental Industrial Hygienists, 2010.
41
Figure 25 Downdraft Necropsy Table
6.6.1
Downdraft Necropsy Table Specifications
6.7
Glove Boxes
Glove boxes (Figure 26) are tightly sealed, fully enclosed systems often required to ensure total
containment of chemical and biological contaminants.
Such enclosures permit manual
manipulations within the box by means of armholes provided with thick gloves, which are sealed to
the box at the armholes. Depending on the application, the glove material may be susceptible to
cracking and wear (especially where they are joined to the box) and must be carefully inspected.
Figure 26 Glove Box
6.7.1
Glove Box Specifications
42
6.8
Biological Safety Cabinets
Laminar-flow biological safety cabinets shall meet minimum standards for cabinet classifications in
NSF 49 for personnel, environmental, and product safety and shall be listed and identified by a
distinctive NSF seal. Field re-certification, performed by an NSF 49-listed, competent technician and
conducted according to the procedures outlined in NSF 49, will be required once the cabinet(s) is
installed. Cabinet classification shall be determined in consultation with the laboratory managers.
These types of cabinets have special design requirements depending on their intended use:

Protecting personnel from harmful agents inside the cabinet

Protecting the work product, experiment, or procedure from contamination by the
laboratory environment, leading to invalidated test results

Protecting the laboratory environment from contaminants inside the cabinet.
There are three different types of cabinets, categorized as Class I, II or III. Each type of cabinet
operates differently with a limited range of application and include:

Class I cabinets provide environmental protection, limited personnel protection, and no
product protection. Class I cabinets may be appropriate for use with low to moderate risk
biological agents.

Class II cabinets are designed to provide environmental protection, product protection and
varying degrees of personnel protection. Class II cabinets are subcategorized according the
types A, B and 100% Total Exhaust. Class II Type A cabinets are typically exhausted to the
room and use of volatile chemicals is restricted. Type B and Total Exhaust cabinets are
ducted to the outside and enable limited use of volatile materials.

Class III cabinets, sometimes called glove boxes, provide the highest level of protection for
product, personnel and the environment.
For more information, U.S. Department of Health and Human Resources, Primary Containment
for Biohazards: Selection, Installation and Use of Biological Safety Cabinets. Table 8 below
provides information about different biological safety cabinets.
Table 8 Biological Safety Cabinets
Type
% Cabinet Air
Recirculated
% of
Exhaust
Minimum
Face
Velocity
Exhaust
Connection
Suitable for use
with toxic
chemicals and
radionuclides?
43
Class I
0%
100%
75 fpm
Hard Duct
No
Class II
Type A1
70%
30%
75 fpm
None or
Thimble
No
Class II
Type B1
30-50%
50-70%
100 fpm
Hard Duct
Minute
Quantities
Class II
Type B2
Total Exhaust
0%
100%
100 fpm
Hard Duct
Minute
Quantities
Class II
Type A2
70%
30%
100 fpm
Thimble or
Hard Duct
Minute
Quantities
Hard Duct
Minute
quantities,
No volatile
chemicals
Class III
6.8.1
0%
100%
N/A
Class I Biological Safety Cabinet
44
Figure 27 Diagram of Class I Biological Safety Cabinet
The Class I biological safety cabinet is applicable for low to moderate risk agents and where product
protection is not required. The cabinet protects the user in similar fashion to a fume hood with the
exception that exhaust air may be filtered prior to being exhausted (see Figure 27 above). Some
Class I cabinets are exhausted through a HEPA filter to the lab. However, cabinets should be hard
ducted to exhaust air outdoors. It is not recommended to return exhaust air to the room.
6.8.1.1 Class I BSC Specifications
6.8.2
Class II, Type A Biological Safety Cabinet
45
Figure 28 Class II, Type A1 Biological Safety Cabinet
The Class II, Type A1 biological safety cabinet is applicable for low to moderate risk agents and
where there is no use of volatile, toxic chemicals or volatile radionuclides. A Class II, Type A1
cabinet provides personal protection, product protection and environmental protection.
Class II, Type A cabinets re-circulate approximately 70% of the cabinet air after it passes through a
HEPA filter. The remaining 30% of the cabinet air is HEPA filtered and exhausted to the laboratory
room or to the outdoors. Refer to the Figure 28 for Class II, Type A biological safety cabinet for
airflow patterns.
Airflow through the face into the front grille provides personnel protection. Class II, Type A1
cabinets are designed for a 75 fpm-100 fpm inflow velocity. HEPA filtered down-flow (vertical
laminar flow) provides product protection with 50% of the air exhausted through the front grille and
50% of the air exhausted through the rear exhaust grille. Volatile chemical should not be used in a
Type A cabinet due to the volume of re-circulation and potential for accumulation of concentrations
in the work area.
6.8.2.1 Class II, Type A BSC Specifications
46
6.8.3
Class II, Type A2 Biological Safety Cabinet
Figure 29 Class II, Type A2 Biological Safety Cabinet
The Class II, Type A2 cabinet has nearly identical flow patterns as a Type A cabinet (see Figure 29
above). However, there are three main differences between the Type A2 and Type A cabinet:

A Type A2 cabinet requires 100 fpm inflow velocity while a Type A cabinet requires only 75
fpm

Contaminated areas within a Type A2 cabinet are maintained under negative pressure with
respect to the cabinet exterior or are surrounded by a negative pressure area. In
comparison, a Type A cabinet can have contaminated positive pressure areas adjacent to
the hood exterior

Type A2 cabinets are exhausted to the outdoors. Type A cabinets can be exhausted to the
laboratory given the right conditions of use
47
Type A2 cabinets can be used for low to moderate risk agents involving minute quantities of toxic
chemicals and trace radionuclides. The cabinet protects the user by maintaining a continuous flow
of room air into the front exhaust grille at a minimum of 100 fpm inflow velocity. The work opening
is generally limited to a height of 8 inches and the sash is not moveable. The biological substance is
protected from airborne impurities by a continuous down flow of HEPA filtered air. As in a Class II,
Type A cabinet, approximately 70% of the cabinet air is re-circulated after it passes through the
HEPA filter. The remaining cabinet air, 30%, is passed through another HEPA filter prior to exhaust
to the outside.
6.8.3.1 Class II, Type A2 BSC Specifications
6.8.4
Class II, Type B1 Biological Safety Cabinet
Figure 30 Class II, Type B1 Biological Safety Cabinet
The Class II, Type B1 biological safety cabinet is applicable for low to moderate risk agents and
minute quantities of toxic chemicals and trace radionuclides that will not affect interior cabinet
components. The cabinet provides protection for the user by providing a continuous flow of air into
the cabinet at a minimum velocity of 100 fpm through an 8 inch opening height. Approximately 30%
48
of the cabinet air is re-circulated after passing through a HEPA filter (see Figure 30 above). The
majority of cabinet air (70%) passes through another HEPA filter prior to exhaust to the outdoors.
The biological agents are protected from airborne impurities by a descending vertical laminar air
from a HEPA filter mounted above the work surface. The laminar supply flow splits above the work
surface with approximately 70% flowing toward the rear exhaust grille and 30% flowing into the
front exhaust grille. All exhaust air captured by the rear exhaust grille flows through a HEPA filter
for discharge to the outdoors. All potentially contaminated plenums and ducts are under negative
pressure with respect to the laboratory.
6.8.4.1 Class II, Type B1 BSC Specifications
6.8.5
Class II, Type B2 (Total Exhaust) Biological Safety Cabinet
Figure 31 Class II, Type B2 (Total Exhaust) Biological Safety Cabinet
The Class II, Type B2 biological safety cabinet is applicable for use with higher risk agents, toxic
chemicals and radionuclides where product protection is of concern. Product protection from
airborne impurities is provided by a continuous down flow of HEPA filtered air. Protection of the
user is provided by a continuous flow of air into the cabinet at a velocity of 100 fpm through a
typical 8 inch opening.
49
Supply air to the cabinet for product protection passes through a HEPA filter to provide a
descending vertical laminar flow over the work surface. Inflow and supply down-flow are exhausted
to the outdoors with no re-circulation (see Figure 31 above). All internal plenums and ducts are
under negative static pressure with respect to the cabinet exterior. The work opening is typically
limited to a height of 8 inches.
6.8.5.1 Class II, Type B2 BSC Specifications
6.8.6
Class III Biological Safety Cabinet
The Class III biological safety cabinet is a gas tight enclosure that is sometimes referred to as a glove
box. Reference section 6.7 Glove Boxes for more information. Caution is advised when using
volatile chemicals due to the low exhaust flow and risk of accumulating potentially explosive
concentrations.
6.8.6.1 Class III BSC Specifications
6.9
Ventilated Enclosure
A ventilated enclosure (Figure 32) is suitable for operations that are largely unattended but will emit
small volumes of potentially hazardous materials or excessive heat. The enclosure should be
constructed to contain the process and designed to provide effective dilution and removal of
materials and heat generated within the enclosure. Ventilation Enclosures are appropriate for a
variety of applications such as:

Robotic Sampling Equipment

Test Instrumentation such as laser diffractometers

Rotary Evaporators

Drying Ovens

Closed process equipment
50
Figure 32 Example of a Ventilated Enclosure Containing a Laboratory Oven
6.9.1
Ventilated Enclosure Specifications
6.10 Canopy Hoods
A canopy hood is a ventilated enclosure used to collect and disperse heat and non-hazardous
effluent. Canopy hoods are receiving hoods and as such, shall be used when there is a force, such as
heat, to deliver the contaminant to the receiving hood. Often custom-sized and constructed for use
in specific applications, canopy hoods are not typically efficient and should be installed for use only
under specific conditions, when other more efficient options are not available.
6.10.1 Canopy Hood Specifications
6.11 Gas Cabinets
Gas cabinets or special exhaust cabinets could be required to house individual toxic/pyrophoric gas
cylinders. Leak detectors and low-exhaust flow alarms, as well as a gas purge system, should be
required to provide for safe exchange of cylinders.
6.11.1 Gas Cabinet Specifications
51
6.12 Flammable Liquid Storage Cabinets
Venting of storage cabinets is not required for fire protection purposes, but venting may be required
to comply with local codes or authorities having jurisdiction. Non-vented cabinets should be sealed
with the bungs supplied with the cabinet or with bungs specified by the manufacturer of the
cabinet. If cabinet venting is required, the cabinet should be mechanically vented to the outside
and:

Both metal bungs must be removed and replaced with flash arrestor screens (normally
provided with cabinets). The top opening serves as the fresh air inlet.

The bottom opening must be connected to an exhaust fan by a length of rigid steel tubing
that has an inside diameter no smaller than the vent opening.

The fan should have a non-sparking fan blade and non-sparking shroud.

The cabinet should exhaust directly to the outside (the cabinet should not be vented
through the fume hood).

The total run of exhaust duct should not exceed 25 feet.

The design velocity of the duct should not be less than 2,000 fpm.

The cabinets should be conspicuously marked, “Flammable - Keep Fire Away.”
6.12.1 Flammable Liquid Storage Cabinet Specifications
6.13 Special Purpose Hoods
Special purpose hoods are defined as any hood that does not conform to the specific types
described above. Special hoods may be used for operations for which other types are not suitable
(e.g., robot sampling equipment, liquid nitrogen dewars, ETO sterilizers). Other applications might
present opportunities for achieving contamination control with less bench space or less exhaust
volume (e.g., using the hoods as special mixing stations, evaporation racks, heat sources, or
ventilated worktables).
6.13.1 Special Purpose Hood Specifications
7
Types of Laboratories
52
7.1
Categorization and Risk Control Bands
7.2
Bio-Safety Levels
7.2.1
BSL 1
7.2.2
BSL 2
7.2.3
BSL 3 and Higher Labs
7.3
Teaching Laboratories
7.4
Necropsy Laboratories
7.5
Radiation Laboratories
7.6
Gross Anatomy Laboratories
8
Laboratory Design and Layout Specifications
Given the high costs of conditioning air in laboratories, it is prudent to minimize the supply air
quantity into the space whenever possible while complying with the primary objectives of providing
safe and productive laboratories. The design goals should be to maximize the utility of the exhaust
and air supply systems such that they:

Satisfy the exhaust flow requirements of exposure control devices under all modes of
operation
53

Provide a healthy environment without negatively impacting performance of laboratory
hoods

Provide comfortable and productive work environments for occupants
If performance conflict arises, the occupant and general public safety requirements take priority.
The performance aspect of secondary laboratory containment must also be evaluated as a
component of the cascading principle of risk, where primary containment occurs in the laboratory
hood and the lab space provides secondary containment.
The primary components are the exhaust air devices and the supply air devices. Exhaust side
components include the laboratory hoods, general exhaust, ductwork and controls. On the supply
side are air supply diffusers, ductwork, controls, thermostat, reheat valves and coils. The
components of a typical laboratory and associated ventilation systems are shown in Figure 33.
Figure 33 Diagram of a Laboratory Depicting Supply and Exhaust Flow Components
8.1
Laboratory Systems and Operating Modes
The type of system influences the design decisions about type and location of supply diffusers,
location of hoods and resultant airflow patterns under different modes of operation. Modulating air
supply volume and discharge air temperatures can influence airflow patterns by affecting throw
patterns, terminal velocities and temperature gradients within the lab.
54
With the advent of Variable Air Volume (VAV) systems, Usage Based Controls (UBC), Occupied/UnOccupied modes, and Energy Recovery Units (ERU), the control of air distribution becomes very
complex due to the inter-dependency of the system components and variable operating conditions.
The harmonious integration of the air distribution components with laboratory hoods becomes a
challenge to the laboratory designer. The performance of many laboratory hoods especially
chemical fume hoods, are dependent on the lab environment and the air supply conditions near the
opening face of a laboratory hood.
8.2
Hood Location
Proper placement of fume hoods in a laboratory is critical to their safe and efficient operation. Poor
location with respect to sources of cross drafts can cause turbulence at the plane of the sash and
increase the possibility of contaminant escape. Undesirable airflow patterns affecting the
uniformity of flow into the hood sash opening can be produced when hoods are located too close to
one another.
Adherence to the following guidelines for properly locating chemical fume hoods will minimize the
adverse effects caused by excessive supply air velocities and proximity to personnel traffic. The
lettered points below are graphically represented in Figure 34.
A. Locate hoods at the back of labs or in alcoves.
B. There should be a minimum clearance of 4 ft. between a fume hood and the nearest door.
C. A minimum clearance of 8 ft. is required between a fume hood and door opposite the fume
hood.
D. Hoods should not be located within 3 ft. of obstructions that cause undesirable airflow
patterns at the plane of the sash. Obstructions include walls, partitions, and large
equipment such as freezers.
E. Hoods should be located at least 4 ft. from a main traffic aisle.
F. Hoods should be located at least 4 inches from adjacent walls unless the design of the hood
prevents spatial variations in face velocity from wall effects.
G. Hoods should not face each other within distances of less than 5 ft. from sash plane to sash
plane or the distance equal to the nominal length of the largest hood, whichever is greatest.
H. There is no recommendation for distances between laboratory hoods adjacent to one
another unless the location causes face spatial velocity variances greater than 20%. The
spatial variation is a measure of the uniformity of airflow through the opening and
distribution of velocities across the opening.
55
I.
The distance from the hood to a diffuser depends on the type of diffuser, throw pattern and
terminal velocities resulting over the range of temperature and supply volume. See section
3.2.3 for additional information regarding effective diffuser location.
4'
Min.
B, D
D
HW
HW
Supply Diffuser
8' Min.
3'
X = HW (Min)
I
(Min)
Freezer
A
C
F
Traffic Aisle Way
4" Min.
E
4'
G
Min.
H
G
Hw
X = Hw
Min.
A
A
Figure 34 Diagram of Laboratory Showing Location of Laboratory Hoods
8.2.1
Air Distribution Effectiveness
Distribution effectiveness can be affected by people, movement within the room, location of
obstructions and equipment, heat sources, and differences in HVAC system operating modes. The
design of the air distribution systems must take into account all of these factors for maximum
effectiveness. Selection of diffusers for VAV laboratories is particularly challenging due to the
changing supply volume and discharge temperatures. The air supply from supply diffusers in labs
must not affect the operation of the fume hoods when the sashes are open regardless of the
discharge temperature and must provide adequate room air mixing at low volumes when the sashes
are closed. As such, the air distribution systems must properly condition the space, compliment
hood performance at all operating modes and minimize installation and operating costs.
56
The effectiveness of the air distribution system can be judged by several factors including:
8.2.2

Utilizing the maximum percentage of air to condition the space and minimizing or
eliminating “short circuiting” with little or no utility

Causing minimal or no effect on the operation of the laboratory hood

Maintaining Indoor Air Quality (IAQ)

Providing minimal “First Cost” and subsequent operational costs

Maintaining differential pressure relationship to adjoining spaces
Doors and Traffic Aisles
Doors and traffic aisles provide the means of access and egress for both equipment and laboratory
personnel. Both the location and size of the doors and traffic aisles in the laboratory influence
airflow patterns and must be accounted for when investigating overall air balances and occurrence
of undesirable airflow patterns. The swing of a door or traffic past a hood can produce considerable
cross drafts in excess of 200 fpm and must be located to minimize impact on hood performance. It
is recommended to locate laboratory hoods at least 4 ft. from doors or traffic aisles.
Doors located between laboratories and adjoining spaces shall be equipped with automatic door
closers to optimize secondary containment and design pressurization. Self-closing doors are to be
able to be opened with a minimum of effort as to allow access and egress for physically challenged
individuals.
8.2.3
Location and Type of Supply Diffusers
Conditioned air is introduced to laboratories through supply diffusers. Supply diffusers come in
many sizes and types and can be mounted in the ceiling, walls or floor. The type of diffuser and
volume of air supplied at a given temperature generally determines the throw pattern and terminal
velocity. The terminal velocity is the resultant velocity at a given distance from the diffuser under a
specific set of conditions. Improper sizing, selection and location of diffusers when combined with
location of the hoods and laboratory furniture can dramatically affect room airflow patterns and
ability to satisfy the design objectives.
The hood density or number of fume hoods that can be placed within a laboratory space is
constrained by several factors including:

Distance between fume hoods and air diffusers

Physical size of the fume hoods

Available ceiling space for the installation of supply diffusers
57

Type of air diffuser and discharge characteristics
These factors result in a complex interaction of numerous variables that affect performance of
laboratory fume hoods and must be considered to minimize potential problems. Locating properly
sized diffusers at least 5 ft. from laboratory fume hoods reduces hood turbulence due to cross drafts
and variations in air supply temperature. The distance of 5 ft. from the front and sides of the fume
hood defines a zone (No Diffuser Zone, NDZ). Placement of any diffuser within the NDZ should be
avoided unless the diffuser is required for room air circulation and air supply from the diffuser does
not impact fume hood performance. High velocity diffusers should be avoided near laboratory fume
hoods.
When the placement of diffusers is close to this zone, certain locations may be preferred as shown
in Figure 35 below.
5' 0"
45°
6 FT
Diffuser
Zone 1
Diffuser
Zone 1
Diffuser
Zone 2
Diffuser
Zone 2
Diffuser
Zone 3
Figure 35 Good, Better, and Best Locations for Supply Diffusers
Three zones are identified surrounding the NDZ. Diffuser Zone 3 is a good location for locating a
supply diffuser, Diffuser Zone 2 is a better location and Diffuser Zone 1 is the best location. Lab
designers should use caution when locating diffusers in Zone 3 in front of a hood opening. Air
directed perpendicular to the plane of the sash can be more detrimental to hood performance than
cross drafts of similar velocity directed parallel to the opening.
58
As the NDZ extends five feet from the front and sides of the hood, the size or area of the NDZ is a
function of the size of the fume hood as shown below in Figure 36.
8 FT
6 FT
6 Foot Fume Hood
NDZ = ~79 Ft2
8 Foot Fume Hood
NDZ = ~84 Ft2
4 Foot Fume Hood
NDZ = ~64 Ft2
10 Foot Fume Hood
NDZ = ~89 Ft2
4 FT
10 FT
Figure 36 Diagram Showing No Diffuser Zone (NDZ) as a Function of Hood Size
To minimize restrictions caused by the size of the NDZ, fume hoods may be placed such that the
NDZs overlap (Figure 37) or extend outside the laboratory envelope. This recommendation is
compliant with the guidelines for placement of adjacent fume hoods established previously.
6 FT
Total NDZ
Overlapping
= 124 Ft2
8 FT
As Depicted
6 Foot Fume Hood
NDZ
= ~79 Ft2
6 FT
+
8 Foot Fume Hood
NDZ
= ~84 Ft2
=
Total NDZ
Non
Overlapping
= 163 Ft2
8 FT
Figure 37 Diagram of Laboratory Hoods Showing Adjacent and Overlapping NDZs
As the fume hood density in a lab space increases, the effective area of the combined NDZ(s) also
increases. As such, the amount of ceiling space available for the installation of diffusers, lighting
fixtures, or other furnishings decreases accordingly.
59
Once the fume hoods have been selected, the air flow requirements must be specified and the lab
designer must select air diffusers that have performance characteristics capable of delivering the
required air volume, provide adequate mixing for space conditioning and minimize effects on fume
hood performance. Ideally cross drafts at the plane of the sash should be limited to a maximum of
50% of the design face velocity.
Air diffusers create airflow patterns with velocities that are directly proportional to the volume of air
being delivered. As the air is distributed into the space, the supply velocities will degrade due to
expansion of the discharge plume. The degradation of the velocity is expressed by the term,
Terminal Velocity (TV). TV is usually set at 50 fpm for ceiling diffusers and 100 fpm for slots.
The terminal throw is the distance from the diffuser at which the air velocity meets the TV.
Matching the diffuser TV and terminal throw to the hood face places constraints on the placement
of diffusers. The discharge characteristics are particularly important when diffusers are not
mounted flush to the ceiling or are free standing in labs with high ceilings. Diffusers that are flush
mounted in ceiling grids depend on the ceiling surface to produce the mixing characteristics for the
diffuser. Air diffusers should be selected and placed that can deliver the maximum volume of air
while minimizing the distance from the diffuser for achievement of the maximum TV.
In addition to locating diffusers at least 5 feet from laboratory hoods, the outlet area of the diffuser
should be sufficient (approximately 2 times the area of the fume hood design openings). The 2:1
ratio can help determine the number of diffusers required to provide adequate make-up air to the
lab. The number and size of the diffusers together with the area of the NDZ indicates the limit of
fume hood density (# of hoods/lab).
8.2.4
Type of Air Supply Diffusers
Terminal ceiling diffusers or booted-plenum slot diffusers should be specifically designed for VAV air
distribution, where applicable. Booted plenum slots should not exceed 4 ft. in length, unless more
than one source of supply is provided. “Dumping” action at reduced air volume and sound power
levels at maximum delivery should be minimized. For VAV systems, the diffuser spacing selection
should not be based on the maximum or design air volumes, but rather on the air volume range that
the system is expected to operate within the majority of the time. The designer should consider the
expected variation in the range of the outlet air volume to ensure that the Air Diffusion Performance
Index (ADPI) values remain above the specified minimum for the project. This is achieved by
minimizing temperature variation, ensuring effective air mixing between supply and return air
streams, and preventing objectionable drafts in the occupied space.
The construction, sizing and positioning of the supply air diffusers is one of the most important tasks
of transmission and distribution of air in the laboratory. Numerous factors must be considered to
maximize the utility of the air supply to provide a safe and comfortable lab environment at
60
minimum airflow. A mismatched sizing of ductwork connections (round, rectangular, or elliptical)
ending with placing improperly selected diffusers may cause the entire system to produce
undesirable airflow patterns. The following guidelines are to assist with the proper selection,
specification, placement and operation of supply diffusers:

The supply duct should be designed to provide satisfactory flow at the inlet of the diffuser
and follow the diffuser manufacturer’s requirements for inlet design. The ducts to each
diffuser must include a quality damper to ensure proper air balance and distribution of flow
between supply diffusers in a lab.

Terminal velocities from supply diffusers should not exceed 50% of the face velocity or
capture velocity of the laboratory hood at the plane of the sash regardless of supply volume
or discharge temperature resulting at different operating modes. For fume hoods operating
at an average face velocity of 100 fpm, the terminal throw velocity at the plane of the sash
should not exceed 50 fpm.

Perforated laminar flow diffusers or radial face diffusers are preferred over linear slot or
rectangular high velocity, high aspirating diffusers.

The diffusers should be selected and located to minimize areas of flow stagnation in the lab
and promote purging of flow and flow from areas of low hazard to high hazard.
Slot Diffuser - These diffusers are routinely used to provide an air curtain which will provide a
thermal barrier adjacent to windowed exterior walls. Horizontal throw of this type of diffuser
will range from 16-28 ft. to achieve a terminal velocity of 50 FPM with air volumes ranging from
300-500 cfm.
Perforated Diffuser with Modular Core – This type of diffuser is routinely used in laboratory and
office spaces. The modular core can be specified to deliver air in 1, 2, 3, or 4 directions.
Directional flow characteristics allow placement of diffusers near walls and corners of the space.
Horizontal throw of this type of diffuser will range from 9-13 ft. to achieve a terminal velocity of
50 fpm with air volumes ranging from 300-500 cfm.
Swirl Pattern Diffuser – This type of diffuser is specified for applications requiring reduced
horizontal throws. Horizontal throw of this type of diffuser will range from 5-13 ft. to achieve a
terminal velocity of 50 fpm with air volumes ranging from 300-500 cfm.
Radial Diffuser or Hemispherical Diffuser – Designed for critical space applications and
laboratories where turbulence due to air jets must be minimized. Horizontal throw of this type
of diffuser will range from 4-8 ft. and vertical throws of 6-7 ft. to achieve a terminal velocity of
50 fpm with air volumes ranging from 300-500 cfm. Radial and Hemispherical diffusers are most
appropriate for laboratories with fume hoods.
61
Louvered Diffuser – These diffusers are generally high velocity diffusers routinely used in office
or commercial buildings where larger volumes of air and terminal velocities are a not a primary
concern. Horizontal throw from this type of diffuser will range from 16-28 ft. to achieve a
terminal velocity of 50 fpm with air volumes ranging from 300-500 cfm. Louvered diffusers are
not normally appropriate for use in laboratory environments.
8.3
Ventilation Effectiveness (Air Change Rates in Laboratories)
The preponderance of information indicates that reliance on a single airflow rate or specification of
a minimum Air Change per Hour (ACH) standard for laboratory safety is imprudent and can lead to a
false sense of safety. In reality, laboratory scale procedures with even modest emissions within the
laboratory (not captured by an exhaust device) can result in odorous or hazardous concentrations
that can exceed acceptable limits of concern (LOC) at any reasonable or recommended ACH. Table 9
below is a list of generally recommended ACHs from other guides and organizations, illustrating the
wide variety of opinions and recommendations for appropriate minimum ACH.
Table 9 List of Generally Recommended Ventilation Rates for Labs
Agency
Ventilation Rate
OSHA 29 CFR Part 1910.1450
4-12 ACH
ASHRAE Lab Guides
4-12 ACH
Universal Building Codes – 1997 (UBC)
1 cfm/ft2
International Building Code – 2003 (IBC)
1 cfm /ft2
International Mechanical Code – 2003
(IMC)
United States Environmental Protection
Agency ( U.S. EPA)
4 ACH Unoccupied Lab
8 ACH Occupied Lab
American Institute of Architects (AIA)
4-12 ACH
National Fire Protection Association 452004 (NFPA)
Nuclear Regulatory Commission Prudent
Practices
4 ACH Unoccupied Lab
8 ACH Occupied Lab
ANSI/AIHA Z9.5
ACGIH 24th Edition, 2001
1 cfm/ft2
4-12 ACH
Standard states that ACH is not an appropriate concept
for designing containment control systems. The specific
room ventilation rate should be established by the
owner.
The required ventilation depends on the generation
rate and toxicity of the contaminant and not the size of
the room in which it occurs.
62
Effective airflow distribution in laboratories is important to laboratory occupants as it helps ensure a
healthy, productive and energy efficient environment for research and development. The process of
designing, specifying, and testing air distribution systems and components for laboratories is a
critical function of the architects, engineers, test and balance firms, and facility commissioning
agents. Lab air distribution systems need to minimize energy consumption, distribute sufficient
quantities of air to meet indoor air quality (IAQ) standards, provide occupants with a comfortable
work environment, and most importantly, effectively distribute air that will support the operation of
laboratory hoods. Furthermore, proper airflow distribution improves energy efficiency by ensuring
effective mixing, distribution and maximum utility of expensive conditioned air.
8.4
Specification of Airflow Rates for Laboratories
The minimum ACH specification for laboratories shall be derived rather than randomly selected and
specified based on historical standards. In place of a required minimum, the following guidelines
are recommended to derive the minimum required airflow rates in laboratories2:

An exposure control device (ECD) and laboratory risk assessment shall be conducted.
Potential sources of contaminant emissions shall be identified and ECDs including laboratory
exhaust hoods should be specified as appropriate to control emissions at the source. All
potential emission sources and assumptions should be clearly defined at the time of design.

Laboratory airflow rates should be based by definition on total exhaust flow for negatively
pressurized laboratories and total supply flow for positively pressurized laboratories. All lab
areas having potential for release of hazardous airborne contaminants should operate under
negative pressure with respect to adjacent non-laboratory spaces. The required pressure
differential between the spaces should be defined by the design team, or as specified on the
design documentation approved and released for construction.

The required exhaust flow should be sufficient to satisfy the exhaust demands of all
laboratory hoods and ECDs (within the lab) operating under all modes of operation;
including occupied and unoccupied operation modes (chemical fume hood sashes open or
closed), full heating and cooling modes, and emergency modes of operation. Emergency
modes of operation may include fire, smoke or “shelter in place” scenarios.

The volume of air supply to the laboratory should be sufficient to meet indoor air quality
(IAQ) requirements as specified by ASHRAE and other applicable codes and standards
2
Smith, T.C. and Yancey-Smith, S.L: “Specifying Airflow Rates for Laboratories.”, Journal of
Chemical Health and Safety 16(5): September/October 2009.
63
including the International Mechanical Code (IMC) and applicable State or local Indoor Air
Quality Code. The laboratory should operate with 100% outside air for the supply flow.

The quality, quantity and conditioning of the air supply should maintain the lab
environment’s comfort, temperature, and humidity specifications accounting for seasonal
fluctuations.

The accuracy and precision of the airflow control systems should be sufficient to maintain
the required specifications for exhaust, air supply and transfer air volumes (difference
between supply and exhaust). The airflow requirements of the exposure control devices
should never be compromised regardless of operating mode.
The transfer air should be mechanically supplied, of equal quality to lab supply air, and free of hazardous
contaminants. The control of transfer air quantities should prevent the spread of contamination
between laboratories in the event of spill or other emergency conditions.
8.5
Calculating Air Change per Hour Rate (ACH)
Following the above guidelines, the required exhaust and supply airflow should be established to
calculate and report the resultant ACH rate for each mode of operation. In the following formulas,
ACH has units of Cubic Feet per Minute (CFM) and Room Volume is in Cubic Feet (FT3). The value 60
has units of Minutes per Hour and is used for conversion.
ACH rate for a negatively pressurized lab:
ACH = (  of Exhaust Volumes / Room Volume ) x 60
ACH rate for a positively pressurized lab:
ACH = (  of Supply Volumes / Room Volume ) x 60
When combined with adherence to good work practices, establishment of minimum airflow rates in
accordance with the above guidelines will provide safe and comfortable lab environments.
However, the airflow rates or use of recommended ACH will not guarantee adequate dilution of
chemicals to safe levels that may be produced during:
8.6

Accidental spills in the lab

Serious breach in hood containment

Failure of gas cylinders

Contaminates generated outside an approved exposure control device
Laboratory Pressurization
64
Research laboratories should be under "negative" pressure with respect to surrounding spaces to
ensure secondary control of hazardous emissions. A laboratory under negative pressure will reduce
the potential for materials to escape from the laboratory into surrounding areas.
For R&D facilities where product contamination or cross-contamination is of major concern, the
laboratory space is may be maintained under a positive pressure relative to external barometer or
static pressure in the facility. This approach will reduce the likelihood of particulate infiltrating the
space and potentially contaminating the research products. However, a positively pressurized lab
will not serve to provide secondary containment and hazardous airborne contaminants that escape
capture within the space can escape to adjacent areas. To mitigate this hazard, an anteroom or
airlock may be required to provide a negative pressure zone.
The magnitude of the “negative” and “positive” pressure is a function of the difference between
supply and exhaust volume and the room tightness. As room tightness can vary and is difficult to
specify, specifications to achieve positive or negative pressurization must include either room offset
volume or the desired room pressurization. When specifying pressure, it is recommended that the
differential pressure be 0.005 to 0.05 inches of water gage (W.G.). As a reference, 1.0” W.G.
pressure differential equals approx. 5.2 lbs. of force on the architectural components (walls,
fenestration, etc.). In Figure 38, the lab is under negative pressure to adjacent spaces when the
exhaust is greater than supply. Conversely, a positively pressurized room results from supply
exceeding exhaust.
Figure 38 Laboratory Pressurization and Direction of Airflow Resulting From Differences In Air
Supply and Exhaust Volumes
8.6.1
Lab Offset Volume
65
The specifications for offset volume is dependent on the available transfer area, but is typically 100
cfm per door. The offset volume must be sufficient to achieve the desired pressurization. The
equation of air leakage from or to the laboratory is:
Ql = A · 776 · CD ( 2 · Δp / δa ) 0.5, where
Ql = Outflow or Inflow, from or to the space in ft3/min
A = Gap Area, ft2
Δp = Pressure Differential, inch W.G.
δa = Actual Air Density, lb/ft3
CD = Coefficient of Discharge (Dimensionless, usually between 0.6 to 0.8)
The offset volume should be at least two times the maximum error of the supply and exhaust
controls or approximately 10% of the maximum exhaust flow.
8.7
Airflow Controls
Many factors associated with the design of the laboratory can affect the ability of hoods to contain
hazardous chemicals. The location of the hoods in the laboratory, location and type of air supply
diffusers and terminal velocity of supply air can affect hood performance. The following sections
provide general guidelines for ensuring proper design of laboratories and reduction of factors
affecting hood performance. The type of system, constant air volume (CAV) or variable air volume
(VAV), influences the design decisions about type and location of supply diffusers, location of hoods
and resultant airflow patterns under different modes of operation.
8.7.1
CAV
8.7.2
VAV
8.7.2.1 Direct Pressure
8.7.2.2 Airflow Tracking
8.7.3
Demand Control Ventilation (DCV)
66
8.7.4
Occupancy Based Control Schemes
8.7.5
Purge Modes
8.8
Laboratory Temperature Control
Maintaining proper environmental conditions expressed in both dry-bulb (DB) temperature and
relative humidity (RH) are goals of the air supply system. Diffuser selection and location along with
the air supply temperature, thermostat and reheat controls can affect the ability to properly control
lab conditions. Temperature control systems in a laboratory can affect hood containment3.
Maintaining constant lab temperatures often requires modulating the temperature and volume of
air supply to the lab. The change in discharge temperature and volume of air from a diffuser can
affect the throw patterns and room air currents near hood openings. The effects are particularly
problematic when diffusers are located near hoods (<6 ft.) and discharge temperatures vary more
than 5°F to 10°F in less than 5 minutes. The change in temperature or the temperature gradient can
cause excessive turbulence at the plane of the hood opening and potential for escape. Temperature
stratification within the space should be limited through proper selection of diffusers and limiting
the change in discharge temperatures to less than 5°F over a five minute period when diffusers are
located less than 6 ft. from a laboratory hood.
9
Lab Ventilation
9.1
Laboratory Exhaust Ventilation
This section includes guidelines for evaluating the design of the laboratory ventilation systems to
ensure compliance with standards and guidelines, and information to evaluate different system
configurations and operation of the flow control systems. Ensuring proper functioning of a
laboratory hood requires proper design and operation of all system components. The ability to
increase or decrease flow through the hoods and the laboratories requires the ability to modulate
flow through the exhaust and air supply systems. The increase and decrease in flow must be
3
Smith, T.C.: “The Unintended Practice of Using Employee Health as an Indicator of Proper Hood
Performance”, Journal of Chemical Health and Safety, January/February, 2004.
67
synchronized for both the exhaust and supply systems to avoid air balance and space pressurization
issues.
Figure 39 illustrates the exhaust fans and air handlers connected to plenums and ductwork for
exhausting air from the laboratory hoods and supplying make-up air to the laboratory.
Figure 39 Diagram of a Laboratory Ventilation System
9.1.1
Materials of Construction
This section covers the ductwork installation and materials used in combined laboratory exhaust
systems, including duct and duct accessories (plenums, manifolds, connectors, louvers and dampers,
access doors, dampers, wall and roof penetrations, and cleaning). Ensuring proper materials of
construction prevents premature degradation of the ducts and system components.
The construction of the exhaust system and selection of materials are based on:

Nature of the hood effluents,

Ambient conditions (dry-bulb and wet-bulb temperatures, barometric pressure),

Potential for particulate loading,

Lengths and arrangement of duct runs,
68

Exhaust fan drive and operational controls,

Flame and smoke spread rating, and

Resulting air velocities and pressure drops.
When selecting materials and designing ducts, the designer should take into consideration effluents
that are known or may be generated in the future. The laboratory fume hood effluents may vary in
temperature and general hazard classification including organic and inorganic chemical gases,
vapors, fumes, or smokes, and qualitatively as acids, alkalis, and solvents. Exhaust system ducts,
accessories, and coatings are subject to attack from such effluents by corrosion, which is the
destruction of metal by chemical, or electrochemical action; by dissolution (especially for coatings
and plastics), and melting which can occur with certain plastics and coatings at elevated operating
temperatures.
Ambient temperature of the space where ducts and fans operate may affect the vapor condensation
in the exhaust system and thus the metal corrosion with or without the presence of chemical agents
or hazardous gases. The ductwork and duct accessories are subject to a lesser attack when the
lengths of duct runs are relatively short and the air velocities are relatively high (but not excessively
high so that the velocity pressures would also be unreasonably high and cause failure or degradation
due to pressure on the components). The designer should also consider issues of engineering
economics such as the impact of cross sectional duct areas and duct pressures on first cost and
subsequent operating costs.
Horizontal duct runs create more surfaces for contaminant accumulation and moisture deposition
than vertical duct installations. Where the potential for condensation exists, the ducts should be
sloped and condensate drains should be utilized (the recommended slope of the horizontal runs is 1
inch per 10 ft. of duct length). Duct condensate may contain hazardous materials and acids in
solutions. As such, the design and construction of the duct manifold should prevent air and liquid
leaks.
If the hoods will be used for acid digestion or used with concentrated acids that are highly corrosive
to stainless steel, the hood, duct, and fan must be made of fiberglass reinforced plastic or material
with similar acid resistance. However, the Architect/Engineer must confirm design acceptability
with both the Fire Engineer and the local fire authority having jurisdiction prior to the Design
Development Phase.
Under all circumstances, the contaminated air stream should be diluted to prevent concentrations
exceeding 25% of a lower explosion limit (LEL). This provides an adequate safety factor.
The ductwork material selection depends on several factors, including:

Laboratory exhaust mode,

The size of the system (number of labs, hoods, etc.),
69

The amount and concentrations of the fumes, gases and particulates,

Exhaust stream heat recovery,

Projected length of facility life cycle, and

Allowable cost.
Stainless steel (S.S.) is one of the most common laboratory exhaust materials. High corrosion
resistance, durability and appearance make it a preferred duct material. S.S. is environmentally
friendly and can be purchased with high recycled content.
Drawbacks to the use of stainless steel duct is its high cost and possible degradation resulting from
high concentrations and/or heating of hydrochloric acid or other mineral acids. A summary of
applications, advantages, limitations, and compatibility of various duct materials are shown in Table
10 below.
Table 10 Duct Materials and Compatibility
Materials
Applications
Galvanized Steel
Widely used for most
non-lab air handling
systems. Not
recommended for
corrosive product
handling, or
temperatures above
400°F (200°C)
Stainless Steel
Duct systems for kitchen
exhaust, moisture-laden
air, fume exhaust.
Fiberglass
Reinforced Plastic
(FRP)
Chemical exhaust,
scrubbers, underground
duct systems.
Polyvinyl Chloride
(PVC)
Exhaust systems for
chemical fumes and
hospitals, underground
duct systems.
Advantages
Relatively low cost, high
strength, rigidity,
durability, rust resistance
in ordinary conditions,
availability, non-porous,
workability.
Limitations
Limited corrosion
resistance, inability
to be welded
(requiring
mechanical joining
of sections) or
painted.
High resistance to many
common forms of
High material cost,
corrosion (but care is
workability,
definitely required in alloy availability.
selection).
Cost, weight, range
of chemical and
Corrosion resistant, ease physical properties,
of modification.
brittleness,
fabrication, code
acceptance.
Cost, fabrication,
Corrosion resistance,
code acceptance,
weight, weldability, ease
thermal shock,
of modification.
weight.
70
Materials
Applications
Breechings, Flues, stacks,
hoods, other high
Carbon Steel (Black temperature duct
Iron)
systems, kitchen exhaust
systems, ducts requiring
paint or special coating.
Duct systems for
moisture-laden air,
louvers, special exhaust
systems, ornamental duct
Aluminum
systems. Often
substituted for galvanized
steel in HVAC duct
systems.
Copper
Duct systems for
exposure to outside
elements and moistureladen air.
Polyvinyl Steel
(PVS)
Underground duct
systems, moisture-laden
air and corrosive air
systems.
Concrete
Underground ducts, air
shafts.
Rigid Fibrous Glass
Interior HVAC lowpressure duct systems.
Advantages
Limitations
High strength, rigidity,
durability, availability,
paintability, weldability,
non-porous.
Corrosion
resistance, weight.
Weight, resistance to
some forms of corrosion,
availability.
Low strength,
material cost,
weldability, thermal
expansion.
Cost, electrolytic
Accepts solder readily,
action of in contact
durable, resists corrosion, with galvanized
non-magnetic.
steel, thermal
expansion, stains.
Susceptible to
coating damage,
Corrosion resistance,
temperature
weight, workability,
limitations (250°F or
fabrication, rigidity.
120°C max.),
weldability, code
acceptance.
Compressive strength,
Cost, weight,
corrosion resistance
porous, fabrication
(although steel
(requires forming
reinforcement in concrete
processes).
must be properly treated).
Weight, thermal insulation Cost, susceptible to
and vapor barrier,
damage, system
acoustical qualities, ease pressure, code
of modification,
acceptance,
inexpensive tooling for
questionable
fabrication.
cleanability.
71
Materials
Gypsum Board
Applications
Advantages
Ceiling plenums, corridor
Cost, availability.
ducts, airshafts.
Limitations
Weight, code
acceptance, leakage,
deterioration when
damp.
Laboratory ventilation system ductwork shall not be internally insulated. Sound baffles or external
acoustical insulation at the source should be used for noise control.
Air exhausted from laboratory work areas shall not pass un-ducted through other areas.
72
9.1.2
Manifolds and Duct Design
Laboratory hoods and the general exhaust from laboratories can be combined into an integrated
common manifold exhaust system. Two major considerations must be taken into account when
considering an integrated exhaust system:

hazardous materials generated in the laboratory hoods could be toxic, flammable,
pyrophoric, or highly corrosive

ductwork and duct accessory material must be compatible
The materials used in laboratories may have a profound influence on the design and operation of
integrated exhaust systems including, but not limited to, control of hazardous energy (lock-out/tagout), hazard communication, maintenance provisions, filter loading, international building codes and
fire code implications such as NFPA 45 and 50A. The design should include a Ventilation Risk
Assessment that provides a mechanism for identifying risks and evaluating their magnitude. Issues
to address during design or renovations may include:

Type and quantity of hazards

Need for fire detection and suppression

Ventilation system arrangement and construction

Ventilation sensors and controls

Emergency safeguards and procedures

Manifolded fume hoods should meet the requirements of NFPA 45

Ducts used on systems involving flammable or explosive mixtures require analysis and meet
applicable NFPA 45 standards

The duct joint used to connect the hood to the exhaust ductwork must be flanged and sized
to mate with the fume hood exhaust collar and flange

Duct construction should be sufficient to prevent duct leakage of more than 1%

The manifold must be maintained under negative pressure at all times during hood use

A manifold designed to operate as a plenum must have a relatively constant pressure
throughout the plenum

Effluent streams from multiple hoods must be compatible and non-reactive

Unless the use of all hoods on the system can be safely and completely stopped, the static
pressure in the plenum must be maintained throughout the duration of use

Use of redundant fans and bypass dampers are highly recommended for use as backups and
meeting above conditions
73
9.1.3
Dampers
The damper must have an external indicator showing the position of the damper blade. Electronic
dampers should provide feedback of damper position. The damper position and flow characteristics
must be known. Operation of the damper should exhibit a linear response for flow versus position
across the acceptable range of flow required for proper functioning of the hood. Damper housing
and shaft openings must be sealed to prevent leakage of materials from the duct interior.
Fire dampers are not allowed on fume hood exhaust systems and dampers must be resistant to
attack by hood effluents.
9.1.4
Duct Pressures
Ducts located within the building envelope should be under negative pressure and leak tight as
subject to duct leak testing and Sheet Metal and Air Conditioning Contractor’s National Association
(SMACNA) standards. The degree of leak tightness must be appropriate to hazards identified as part
of a ventilation risk assessment. Positively pressurized ducts on the downstream side of the exhaust
fan must be leak tight and located within properly ventilated areas (penthouses) or located exterior
to the building.
9.1.5
Duct Velocities
Duct transport velocities should be sufficient to prevent accumulation of materials within the ducts
that could potentially affect duct integrity or react with other effluents. Ranges of exhaust duct
velocities (ft./min.) depend on the nature of the contaminants and are summarized in Table 11.
Table 11 Ranges of Recommended Exhaust Duct Velocities
Nature of Contaminants
Vapors, gases, smoke, and
sub-micron size particles
Fumes
Very fine light dust
Dry dust and powders
Average industrial dust
Heavy dusts
Heavy moist dust
Examples
Velocity Range
(fpm)
All forms
500(see note 1) – 2,000
Zinc and aluminum Oxide fumes
Cotton lint, wood flour Lithopowder
Cotton dust
Shavings Sawdust, grinding dust
Metal turnings, lead
Buffing lint (sticky) Lead dust w/
small chips
1,000 – 2,000
2,000 – 2,500
2,500 – 3,000
3,500 – 4,000
4,000 – 4,500
4,500 or more
From "Industrial Ventilation: A Manual of Recommended Practice for Design", ACGIH
74
Note 1: Where sufficiently dilute, materials will be transported by the exhaust air. A lower limit of 500 fpm
provides the ability to accurately measure flow in the duct using commonly applied techniques including Pitot
tube traverse.
9.1.6
Exhaust Fans
Proper design, operation and maintenance of the exhaust fan is critical to safe use of laboratory
ventilation equipment. The following guidelines summarize important concepts:

Exhaust fans should be backward curved blade centrifugal or venturi-type fans.

Fan wheels and housings should be constructed of materials compatible with chemicals
being transported in the air through the fan. Fans should be spark-resistant construction in
accordance with the Air Moving and Control Association (AMCA) Standard 401. The fan
should be constructed so a shift of the wheel or shaft will not permit ferrous parts to rub or
strike. Bearings must not be placed in the air stream.

Fans must be direct drive or belt driven using fixed pitched sheaves. Variable pitch sheaves
are not recommended.

Fans used to exhaust flammable or explosive mixtures (i.e. perchloric acid) require special
analysis to determine the construction required, pressure relief, grounding etc. The fans’
construction should be as recommended by AMCA's Classification for Spark Resistant
Construction.

A one-inch NPT drain should be provided in the bottom of the fan scroll.

The fans should be placed to prevent positively pressurized ductwork inside the occupied
building interior.

The direction of fan rotation must be clearly marked and proper rotation direction
confirmed.

The fan speed must be within manufacturer's specifications for optimum performance
characteristics.

At least eight duct diameters of straight duct must precede the inlet to the fan.

Inlet duct diameter must not vary more than one inch from the fan inlet diameter.
9.1.6.1 VAV System Fans
VAV systems should be designed with control devices that sense ductwork static air pressure and
velocity air pressure. The measurements collected by these sensors should be used to control fan
airflow and static pressure output by modulating any combination of the following:

Variable inlet vanes
75

Inlet/discharge dampers

Scroll dampers

Bypass dampers

Variable pitch blades

Variable frequency electric drive controls.
The control systems should have a minimum of one static pressure sensor mounted in ductwork
downstream of the fan and one static pressure controller to vary fan output through either the inlet
vane, the damper, the belt modulator, or the speed control. The VAV control systems should be
capable of maintaining the minimum outdoor air ventilation requirements set forth in ASHRAE 62.1
and other applicable standards under all modes of operation.
The VAV exhaust and supply fans should be capable of operating at the following three design
conditions, without significant noise or vibration and without overloading:

Normal peak load (including diversity)

Maximum cooling load (no diversity and with terminal box dampers open), and

Minimum cooling load (with terminal boxes at the minimum flow condition).
The minimum supply volume setting of the VAV terminal boxes should equal the largest of the
following:

30% of the peak supply volume

0.4 cfm/ft2 of conditioned zone area

The minimum outdoor airflow to satisfy ASHRAE Standard 62.1 ventilation requirements.
9.1.6.2 VAV Diversity
Diversity should be based on the unique characteristics and needs of the individual facility. Diversity
less than 80% must be supported by an assessment of researcher practice and consider the
effectiveness of both administrative and engineering controls.
9.1.6.3 VAV Sensitivity
VAV Sensitivity is a measure of the ability of the ventilation systems to detect, resolve and modulate
flow equivalently or in proportion to modulation of flow through individual terminal units. A system
with a VAV Sensitivity of 100% has perfectly linear response where a change of 1 cfm at a fume hood
76
exhaust terminal is matched at the exhaust fan or air handling unit. Large systems tend to be less
sensitive where flow modulation at an individual terminal is less than 5% of total system flow.
9.1.7
Exhaust Stack
Unless otherwise specified, fume hood exhaust stacks must be in the vertical-up direction at a
minimum of 10 ft. above the adjacent room line. The height of the stack must be sufficient to
ensure contaminated exhaust air does not re-enter the building.
The effluent must be discharged in a manner and location to avoid reentry into the building at
concentrations greater than the allowable breathing zone concentrations under any wind or
atmospheric conditions. Air intakes should be located at least 30 ft. from the exhaust discharge. Per
ANSI/AIHA Z9.5, the "stack discharge velocity shall be at least 3000 fpm unless it can be
demonstrated that a specific design meets the dilution criteria necessary to reduce the
concentration of hazardous materials in the exhaust to safe levels at all potential receptors". A wind
wake model can be used verify dilution at velocities less than 3000 fpm.
Aesthetic considerations concerning external appearance should not overcome the requirements
set forth above. If applicable, a masking structure must not reduce the effectiveness of the exhaust
stack.
9.1.8
General Exhaust
This can be used for temperature control on VAV systems. General exhaust may be used to
augment laboratory exhaust where air supply rates significantly exceed the hood exhaust air
volumes and room differential pressure requirements cannot be met. The air exhausted from the
laboratory through the general exhaust must not be re-circulated unless the air is adequately
filtered and meets the requirements set forth in ANSI Z9.5 for re-circulation of laboratory exhaust
air.
9.1.9
Fire Dampers
Fire dampers should be provided in accordance with NFPA guidelines and local codes, except in the
exhaust systems from laboratory areas.
9.2
Air Supply Systems
Proper design and operation of the air supply system is critical to achieving acceptable indoor air
quality and important for achieving proper functioning of fume hoods. The laboratory air supply
system must be in compliance with ANSI/ASHRAE 62, American National Standard for Ventilation for
77
Acceptable Indoor Air Quality. In addition the system must be capable of providing sufficient air to
the laboratory to meet climatic requirements (i.e. temperature, humidity, etc.) and ensure proper
room air balance and space pressurization under all operating modes.
ANSI/AIHA Z9.5 does not allow air exhausted from laboratory spaces to be recirculated to other
areas unless certain criteria are met as defined in section 5.4.7.1.
9.2.1
100% OA vs. Recirculated (can you recirculated GEX and when)
9.2.2
Outside Air Intakes
9.2.3
Airflow Measurement
9.2.4
Humidity Control
9.2.5
Supply Air Temperature
9.2.6
Fire Dampers
9.2.7
Noise
9.2.8
Insulation
9.2.9
Filtration
From VHA doc
Filters should be sized for a maximum face velocity of 500 fpm. Filter media should be
fabricated such that fibrous shedding does not exceed levels specified in ASHRAE 52.2. The filter
78
housing and all air-handling components downstream should not be internally lined with fibrous
insulation. Double-wall construction or an externally insulated sheet metal housing is
acceptable. The filter change-out pressure drop, not the initial clean filter rating, must be used
in determining fan pressure requirements. Pressure gauges and sensors should be placed across
each filter bank to allow rapid and accurate assessment of filter dust loading, as reflected by air
pressure drop across the filter. All such sensors should be connected to, and feed real-time
readings to, the BAS. Additional considerations include:
9.3

Contaminated air at concentrations higher than the allowable breathing zone
concentrations should be treated to the extent necessary to ensure compliance with
applicable federal, state or local regulations with respect to air emissions.

All filters should have a monitor capable of indicating filter effectiveness. A pressure
gauge must be installed across filters to ensure proper pressure drop.

The range of operating pressures across the filter must be known.

Air supply should be filtered to meet the cleanliness requirements for the laboratory.
Filtration includes use of 85% efficient filters to HEPA filters. Unless otherwise specified,
air supply systems must be equipped with 85%-95% efficient filters.

Where required in fume hood exhaust systems, absolute filters will have an efficiency of
99.97 percent, as determined by the dioctyl phthalate aerosol test for absolute filters
and should satisfy ASHRAE 52.2. (Note – An “absolute” filter is one capable of removing
as near as possible to 100 percent by weight of solid particles greater than a stated
micron size).
Energy Recovery
9.4
Smoke and Fire Control
9.5
Noise
9.5.1
Criteria
There are two important criteria requirements for laboratories; background noise, and speech
intelligibility.
Background noise is quantified in several ways. The most commonly used form is the noise criteria
(NC) method defined by ASHRAE. Other methods available and also described by ASHRAE include
the RC, dBA, NCB, and RC Mark II methods. Each of these has different advantages. The guidelines
listed below are applicable to the NC, NCB, RC and RC Mark II (when applicable to the criteria used,
79
the guidelines recommend a neutral spectrum). Some interpretation of noise data is required to
understand the impacts, and this is best addressed by an acoustical consultant.
Laboratory background noise levels are dependent on the intended use of the space. Background
noise requirements presented in the ASHRAE Handbook HVAC Applications lists common laboratory
types, each of which has different background noise requirements.
It is not enough to only look at background noise within a laboratory. Sound absorptive surfaces are
required for good speech communication is an integral part of noise control within a laboratory
space.
For smaller teaching laboratories (<750 sq.ft.) it is recommended that the ceiling be finished with an
acoustical lay-in tile ceiling (NRC ≥ 0.8) or equivalent wall/ceiling treatment.
For larger teaching laboratories (> 750 sq.ft.), a combination of ceiling and wall treatment is
recommended to improve speech intelligibility. The total area of treatment should be equal to or
greater than the plan area of the space, but should be evenly distributed on the ceiling and two
walls. If there is a predominant lecturing position, the surface behind the lecturer should remain
untreated, but the opposite wall should be treated acoustically (approximately 20% coverage with
NRC ≥ 0.8 material).
For non-teaching laboratories, it is recommended that some acoustically absorptive materials are
included in the finish schedule to control reverberation; this will improve background noise levels
and speech intelligibility. As a minimum, it is recommended that mineral lay-in tile ceilings (NRC ≥
0.5) or an equivalent wall/ceiling treatment be used.
9.5.2
Equipment
Laboratories place high demands on the mechanical systems that serve them and often require
large, noisy equipment. Table 12 below lists typical equipment associated with laboratory
ventilation systems and recommendations for equipment selection.
Table 12 Recommendations for Selection of Equipment
Equipment
Recommendations


Fans


Choose quiet fans (slow and large diameter are better for
noise)
Airfoil and forward curved designs are typically 10 dB quieter
than straight blade radial or vane-axial fans (10 dB is
perceived to be a 50% noise reduction).
Plug-type fans are typically quieter than enclosed centrifugal
fans
Multiple fan, wall-type systems are generally quieter than
80



Silencers




Ducts (general)






Valves




Flex Duct



single large fan systems.
Reserve at least 5 feet of straight duct space for silencers on
intake and outlet for all fans.
Elbow silencers provide improved attenuation at low
frequencies.
For a laboratory setting, exposed fibrous liners are rarely
acceptable, particularly in exhaust silencers susceptible to
entrapment of chemicals, particulates or bacteria.
Hospital-type silencers are available with protective plastic
films that protect the fibrous materials from the air flow.
No-media (packless) silencers are also available, but provide
less attenuation than typical media-type silencers, therefore
additional silencer length may be required.
Good transitions are essential to avoid rumble in duct
systems. This typically requires straight sections of a
minimum 3 duct diameters in length between transitions.
Duct velocities are discussed further in the section below,
but in general larger ducts with lower flow rates are best for
avoiding flow induced noise and rumble.
Large pressure drops across various duct components
typically create turbulence and noise. Lower pressure drops
are desirable from a noise perspective.
Acoustical duct linings protected by a plastic film and a
perforated metal cover can be considered for reducing noise
transmission in some systems. This must be evaluated on a
case-by-case basis.
Valves are a major source of sound in HVAC systems.
Valve noise is difficult to attenuate because of the close
proximity to the room inlet/outlet.
Sound characteristics are highly dependent on flow volume
and pressure drop.
Where possible choose quieter valves.
Aerodynamic
(venturi) valves are preferred over opposed blade dampers.
Over-sizing valves (running them at low flow ratings) or
running multiple valves can be an effective means of
reducing valve noise.
Pressure drops below 1 inch are preferred.
Integral valve silencers provide benefit to attenuating valve
noise, but are not always adequate to meet desired
background noise levels.
Duct space should be made available for a minimum of a 3foot silencer on the room side of valves.
Reduces noise significantly when installed properly.
Best placed above ceilings with good acoustic transmission
loss (noise breaks out and is absorbed in ceiling plenum).
Avoid tight bends that create noise through turbulence.
81



Terminals (diffusers and
grilles)


Equipment in the laboratory
(not necessarily ventilation
equipment)
9.5.3


Can be the most significant source of background noise.
Difficult to attenuate.
Square or round diffusers are quieter than strip diffusers due
to slower velocities.
Sock diffusers are quietest because of a low throw/low
speed supply.
Should be selected at 10 NC points below the target
background noise level.
Choose quiet lab equipment whenever possible (centrifuge,
refrigerators, autoclave (blower fan), bio-safety cabinet, etc.)
Consider pressure drops of selected equipment (hoods, biosafety cabinets)
Ventilation System Layout
For any noise source it is beneficial to separate the source from the receptor by distance, or by
blocking (attenuating) the sound through some form of barrier. This is true for duct layouts as well.
Longer duct runs provide greater separation between noisy equipment and the spaces that they
service. However, even with longer duct runs, silencers are often required to attenuate the sound.
Mechanical rooms should be separated from noise sensitive spaces, ideally with buffering spaces
(e.g., storage space, restrooms) between the mechanical room and noise sensitive spaces. Where
this is not possible, anticipate cavity wall construction, floating floors and/or resiliently suspended
sound barrier ceiling systems.
It is important to leave space for silencers in the ductwork, preferably immediately outside
mechanical rooms. If the silencers must go inside a mechanical room, they require a high sound
transmission loss (TL) casing, or must be enclosed with a drywall enclosure to prevent the ‘quiet
side’ from being impact by mechanical room noise. All ‘quiet side’ ducts in the mechanical room
must also be enclosed.
Silencer lengths will increase where shorter duct runs are present. Options exist for both straight
and elbow type silencers. Leave 3 duct diameters of straight duct between silencer and fans or
transitions (e.g., elbows).
Main ducts should be placed over spaces that are less sensitive to noise (e.g., corridors, storage,
restrooms). Where this is not possible, duct flow velocities should be limited and duct enclosures
may be required. The ASHRAE Handbook HVAC Applications contains recommendations for
maximum airflow velocities.
82
Branch and final run-out ducts flow velocities must also be limited. The ASHRAE Handbook HVAC
Applications contains recommendations for maximum air speeds for different conditions and noise
criteria.
VAV terminals should be placed outside spaces requiring NC 35 or less. If they must be placed in a
space requiring NC 35 or less, they must be equipped with a silencer, and may require an enclosure.
VAV terminals should be as far from the outlet/inlet as possible with silencers located between the
terminal and outlet/inlet to control noise.
Where possible, it is recommended that insulated flex duct be used for the final elbow connecting
the duct to the terminal unit (e.g., diffuser, grille, etc.). The flex duct should be above an acoustical
ceiling and should be well aligned with a smooth corner to avoid creating turbulence (noise) in the
airflow. The flex duct must be well aligned with the terminal unit to avoid excessive noise at the
connection.
Terminal units should be selected to be 10 NC points below the target background noise level for
the design flow volume, and should be located away from areas of communication (i.e., away from
lecturing position and away from student seating area). Placing terminal units around the perimeter
of the room is best with students seated centrally for lectures.
9.5.4
Layout of Laboratory
Laboratories are best set up with all noise producing equipment located around the perimeter
rather than above students or teachers. This allows for better communication for teaching purposes
within a central area. Noise producing equipment includes exhausts and intakes, fume hoods, and
any other lab equipment (e.g., refrigerators, centrifuge, autoclave (blower fan), bio-safety cabinet,
etc.).
For teaching purposes, fume hoods are best located around the perimeter rather than as a central
cluster where they become obstructions for teaching and students cannot sit away from the fume
hoods. This also provides the benefit of clear visual sightlines, which can improve safety through
improved supervision, ability to provide visual cues or non-verbal communication, and for
emergency egress.
Alcoves for fume hoods typically create a quieter space by separating the fume hoods from teaching
areas, but also create barriers that impair supervision and communication while in use.
Smaller labs put students and teachers closer together which is a benefit for speech intelligibility
(i.e., less strain on teachers and better attention and comprehension from students). Larger
laboratories can provide a similar benefit by placing the lecturing position at the center of one of the
longer walls (in rectangular plans), which reduces the student to teacher distance.
83
Higher ceilings are undesirable due to an increase in the volume of the space and an increase in
unwanted reverberation.
Acoustically absorptive finishes for the ceiling and walls are recommended as described in the
criteria section above. While such finishes help to improve communication by reducing
reverberation and background noise, they can collect chemicals, particulate, and bacteria.
Additional costs should be anticipated for available washable finishes, where required.
9.5.5
External Noise
Most laboratory buildings have significantly more ventilation equipment than buildings supporting
offices and teaching space only. The higher volume of air required demands larger fans and
heating/cooling equipment. Larger equipment typically produces more noise, which not only
impacts the indoor environment, but can also impact the outdoor environment.
Noisy intakes and exhausts can impact labs and nearby buildings, especially where equipment or
intakes/exhausts are in close proximity to windows. Allow for space in mechanical rooms and in
duct runs for silencers on exhausts and intakes. Other means of mitigating external noise emissions
may include use of plenums, acoustic louvers and noise barriers. Windows are usually the limiting
factor for indoor/outdoor noise transmission. Upgrading to better acoustical performance windows
is a means of mitigation. As with duct systems within the building, separation through distance,
duct length, or by creating noise barriers/attenuators is necessary to reduce noise levels. It is
important to note that barriers can conflict with exhaust re-entrainment requirements and should
be reviewed with a re-entrainment consultant..
Impacts on nearby buildings and outdoor pedestrian areas are important considerations. It is
important to check local legislation, codes, regulations, and/or ordinances to determine the site
requirements. City regulations provide a “do not exceed” limit for daytime and night-time noise
that varies with property use (see Seattle Municipal Code, Chapter 25.08 - Noise Control,
Subchapter III - Environmental Sound Levels for requirements in Seattle and King County).
It is often prudent to establish more stringent guidelines that target limiting impacts on neighbors
by setting criteria that minimize the change in background noise levels at nearby receptors. While
not required, it is a good strategy for maintaining relations with the surrounding community. A
noise impact study requires a baseline noise survey to determine pre-construction noise levels,
which can be compared to the future condition to determine change/impacts.
External noise modeling should be done early in the design of the building using proper modeling
techniques to determine impacts on surroundings and the building on itself. Models such as
84
Cadna/A, SoundPlan, ENM, etc. can be used. Noise model studies are often required in building
construction permitting.
9.5.6
Vibration
Vibration isolation of all mechanical and electrical equipment (including ducting, piping and conduit)
is an important part of controlling noise and vibration within a building. The primary purpose of
vibration isolation systems is to limit the transmission of vibration into the structure, which is
carried through the structure as structure-borne noise and re-radiated acoustically in spaces that
can be distantly separated from the source. Structure-borne noise is very difficult to attenuate by
means other than vibration isolators.
Proper selection and installation of vibration isolation systems (which may include but is not limited
to spring isolators, rubber/neoprene isolators, inertia bases, and hangers with spring or neoprene
elements) is an essential part of a complete noise control system.
9.5.7
Other Considerations
For teaching labs, there are other means of improving the function of the space without requiring
more stringent background noise limits. Noise can also be limited by operational controls such as:

Keeping sashes closed when not in use, and particularly while teaching,

Providing areas for pre-lab lectures away from fume hoods or in separate rooms,

Providing audio/video alternatives such as; screens to show demos, cameras to monitor
students, or by pre-recording laboratory demonstrations and having students view them
before labs (pre-lab quizzes provide confirmation of viewing).
In a cutting edge research environment where critical funding is highly dependent on maintaining a
competitive edge, privacy is often of significant concern. Where privacy is required, it must be
considered that communication within a loud space requires increased vocal effort that may be
heard clearly in quieter adjacent spaces such as corridors or offices. Limiting background noise
within the laboratory is an important part of maintaining privacy, but partition construction
(including doors, windows, penetrations, and duct layouts to control “cross-talk”) should also be
considered in this type of environment to maintain privacy and/or security.
Noise from laboratories can impact more sensitive adjacent spaces such as offices, conference
rooms, or classrooms. Transfer of noise should be controlled through proper partition design and
construction. Penetrations through walls, floors, and ceilings should be sleeved and sealed as
appropriate. Direct duct runs between spaces should be avoided. It is preferred to have central
supply and return ducts with individual duct runs into each room to avoid “cross-talk” issues.
85
While many of the topics covered within this document could be addressed by the architect or the
mechanical system designer, without due consideration of the interaction of the individual
components, there is potential for a detrimental combination of factors to be overlooked. An
acoustical consultant is required to review the ventilation system and room design and their
interaction with the building in a holistic way. This input is required early in a project, while it is still
possible to allocate space for necessary silencers, and to keep noise and vibration sources
sufficiently separated from sensitive receptors.
Systems should satisfy the noise criteria recommended for various types of spaces and the vibration
criteria listed in the ASHRAE Handbook Fundamentals. The combined noise level generated by
mechanical and electrical building equipment should not exceed 70 decibels (dBa) in mechanical
rooms. Where air handling equipment and air distribution systems cannot meet these
requirements, sound- and vibration-attenuation devices should be installed.
The noise exposure at the working position in front of the hood should not exceed 70 dBa with the
system operating and the sash open, nor should it exceed 55 dBA at bench-top level elsewhere in
the laboratory room. Total room performance with respect to noise levels must meet permissible
occupational limits specified in 29 CFR 1910.95.
9.6
Insulation
Laboratory ventilation ductwork should not be internally insulated. Fiberglass duct liners can
deteriorate with age and shed into the space resulting in Indoor Air Quality (IAQ) complaints,
adverse health effects, maintenance problems and significant economic impact.
9.7
Filtration
Filters should be sized for a maximum face velocity of 500 fpm. Filter media should be fabricated
such that fibrous shedding does not exceed levels specified in ASHRAE 52.2. The filter housing and
all air-handling components downstream should not be internally lined with fibrous insulation.
Double-wall construction or an externally insulated sheet metal housing is acceptable. The filter
change-out pressure drop, not the initial clean filter rating, must be used in determining fan
pressure requirements. Pressure gauges and sensors should be placed across each filter bank to
allow rapid and accurate assessment of filter dust loading, as reflected by air pressure drop across
the filter. All such sensors should be connected to, and feed real-time readings to, the BAS.
Additional considerations include:

Contaminated air at concentrations higher than the allowable breathing zone
concentrations should be treated to the extent necessary to ensure compliance with
applicable federal, state or local regulations with respect to air emissions.
86
9.8

All filters should have a monitor capable of indicating filter effectiveness. A pressure gauge
must be installed across filters to ensure proper pressure drop.

The range of operating pressures across the filter must be known.

Air supply should be filtered to meet the cleanliness requirements for the laboratory.
Filtration includes use of 85% efficient filters to HEPA filters. Unless otherwise specified, air
supply systems must be equipped with 85%-95% efficient filters.

Where required in fume hood exhaust systems, absolute filters will have an efficiency of
99.97%, as determined by the dioctyl phthalate aerosol test for absolute filters and should
satisfy ASHRAE 52.2. (Note – An “absolute” filter is one capable of removing as near as
possible to 100 percent by weight of solid particles greater than a stated micron size).
Energy Recovery
10 Laboratory Ventilation Construction, Renovation and Commissioning
10.1 Lab Designer's Checklist
10.2 TAB Plan
10.3 Commissioning Plan (building and lab)
10.4 ECD Commissioning
10.5 Laboratory Environment Tests (LETs)
10.6 System Mode Operating Tests (SOMTs)
11 Laboratory Ventilation Management Program
87
11.1 LVMP and the Design Process
11.2 Routine Testing
11.3 Management of Change
11.4 BAS Trends and Reports
88
12 References
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
ANSI/AIHA Z9.5, American National Standard for Laboratory Ventilation
NFPA 45, Fire Protection for Laboratories Using Chemicals
SEFA, Laboratory Fume Hoods, Recommended Practices
ACGIH, Industrial Ventilation Manual, 21st Edition
ASHRAE 90.1 Energy Standard for Buildings Except Low-Rise Residential Buildings
ASHRAE 62, Ventilation for Acceptable Indoor Air Quality
ACGIH®: Industrial Ventilation: A Manual of Recommended Practice for Design, 27th Edition.
Cincinnati, Ohio: American Conference of Governmental Industrial Hygienists, 2010.
ACGIH®: Threshold Limit Values (TLV®) for Chemical Substances and Physical Agents. Cincinnati,
Ohio: American Conference of Governmental Industrial Hygienists, 2002.
AGS-1998-001: Guideline for Gloveboxes, 2nd Edition. Santa Rosa, Calif: American Glovebox
Society, 1998.
ANSI/ASHRAE 41.2-1987 (RA 92): Standard Methods for Laboratory Air Flow Measurement.
Atlanta, Ga.: American Society of Heating, Refrigerating and Air Conditioning Engineers, 1992.
ANSI/ASHRAE 41.3-1989: Standard Method for Pressure Measurement. Atlanta, Ga.: American
Society of Heating, Refrigerating and Air Conditioning Engineers, 1989.
ANSI/ASHRAE 41.7-1984 (RA 00): Method of Test Measurement of Flow of Gas. Atlanta, Ga.:
American Society of Heating, Refrigerating and Air Conditioning Engineers, 2000.
ANSI/ASHRAE 110-1995: Method of Testing Performance of Laboratory Fume Hoods. Atlanta,
Ga.: American Society of Heating, Refrigerating and Air Conditioning Engineers, 1995.
SMACNA: HVAC Duct Construction Standards: Metal and Flexible, Merrifield, Va.: Sheet Metal
and Air Conditioning Contractors’ National Association, 1995.
Smith, T.C. and Yancey-Smith, S.L: “Specifying Airflow Rates for Laboratories.”, Journal of
Chemical Health and Safety 16(5): September/October 2009.
Smith, T.C., and Crooks, S.M.: “Implementing a Laboratory Ventilation Management Program.”
Journal of Chemical Health and Safety 3(2):12–16 (1996).
Smith, T.C.: “The Unintended Practice of Using Employee Health as an Indicator of Proper Hood
Performance”, Journal of Chemical Health and Safety, January/February, 2004.
Laboratories for the 21st Century, Best Practice Guide Optimizing Laboratory Ventilation Rates,
Draft, September 2008, Pg 1.
Heinsohn, Robert J., Industrial Ventilation Engineering Principles, University Park, PA 1991;
Diberardinis, Louis J., Guidelines for Laboratory Design, 2nd ed, 1993; pg 100.
Exposure Controls Technology Inc. data obtained from various ventilation studies.
American Conference of Governmental Industrial Hygienists (ACGIH). 2010. Industrial
Ventilation: A Manual of Recommended Practice for Design, 27th Edition. Cincinnati, Ohio.
ASHRAE Handbook Fundamentals
ASHRAE Handbook HVAC Applications.
Exposure Control Technologies, Inc. and Rowan William Davies & Irwin, Inc. : "Ventilation Noise
Issues".
89
Table 1 Document Section Status Section 1 2 3 4 4.1 4.2 4.2.1 4.2.2 4.2.3 4.3 4.4 5 5.1 5.2 5.3 5.3.1 5.3.2 5.3.3 5.3.4 5.3.5 5.3.6 5.3.7 5.3.8 5.3.9 5.3.10 5.3.11 5.3.12 5.3.13 5.3.14 5.3.15 6 6.1 6.1.1 6.1.2 6.1.3 6.1.4 6.1.5 6.1.5.2 Topic Purpose and Introduction Energy and Sustainability The Laboratory Design Process Laboratory Demand for Ventilation Types of Hazardous Procedures Risk Assessment Quantity of Materials Used and Generation Rates Effluent Characteristics Control Banding Lab Air Quality and Conditioning Occupancy and System Utilization Exposure Control Device Selection Description of Exposure Control Device ECD Risk Matrix Types of ECDs (need to harmonize names/descriptions with current SEFA standard) Laboratory Fume Hoods Constant Air Volume (CAV), Conventional Fume Hood CAV, Bench‐Type, Bypass Fume Hood Auxiliary Air Bypass Fume Hood CAV – High Performance Fume Hoods (HP Fume Hoods) Variable Air Volume (VAV) Fume Hood Systems Distillation Laboratory Fume Hoods Floor Mounted Laboratory Fume Hoods Perchloric Acid Laboratory Fume Hoods Radioisotope Fume Hoods Pass Through Hood California Hood Teaching Lab Hood Ductless Fume Hood Laminar Flow Fume Hood Exposure Control Device Operation Laboratory Hood Operation Escape of Contaminants Sash Opening Configurations Airfoil Sills Baffle Design and Configuration Fume Hood Specifications Laboratory Hood Operating Specifications and Test Criteria Status Complete Complete Incomplete Complete Complete Incomplete Complete Complete Complete Incomplete Incomplete Incomplete Incomplete Incomplete Incomplete Complete Complete Complete Complete Complete Complete Complete Complete Complete Complete Incomplete Incomplete Incomplete Incomplete Incomplete Incomplete Complete Complete Complete Complete Complete Incomplete Complete 6.1.5.3 6.1.5.4 6.1.5.5 6.1.6 6.1.7 6.1.8 6.1.9 6.1.10 6.1.11 6.2 6.2.1 6.3 6.3.1 6.4 6.4.1 6.5 6.5.1 6.6 6.6.1 6.7 6.7.1 6.8 6.8.1 6.8.1.1 6.8.2 6.8.2.1 6.8.3 6.8.3.1 6.8.4 6.8.4.1 6.8.5 6.8.5.1 6.8.6 6.8.6.1 6.9 6.9.1 6.10 6.10.1 6.11 6.11.1 Operating Mode Flow and Velocity Specifications Laboratory Hood Monitors Distillation Laboratory Fume Hood Specifications Walk‐in Fume Hood Specifications Perchloric Acid Fume Hood Specifications Radioisotope Fume Hood Specifications Ductless Fume Hood Specifications Laminar Flow Fume Hood Specifications Ventilated Balance Enclosures (VBE) Ventilated Balance Enclosure Specifications Canopy Exhaust Hoods Canopy Exhaust Hood Specifications Flexible Spot Exhausts (FSE) Flexible Spot Exhaust Specifications Slot Hoods Slot Hood Specifications Downdraft Necropsy Tables Downdraft Necropsy Table Specifications Glove Boxes Glove Box Specifications Biological Safety Cabinets Class I Biological Safety Cabinet Class I BSC Specificiations Class II, Type A Biological Safety Cabinet Class II, Taype A BSC Specifications Class II, Type A2 Biological Safety Cabinet Class II, Type A2 BSC Specifications Class II, Type B1 Biological Safety Cabinet Class II, Type B1 BSC Specifications Class II, Type B2 (Total Exhaust) Biological Safety Cabinet Class II, Type B2 BSC Specifications Class III Biological Safety Cabinet Class III BSC Specifications Ventilated Enclosure Ventilated Enclosure Specifications Canopy Hoods Canopy Hood Specifications Gas Cabinets Gas Cabinet Specifications Complete Complete Complete Incomplete Incomplete Complete Complete Incomplete Incomplete Complete Complete Complete Incomplete Complete Incomplete Complete Incomplete Complete Incomplete Complete Incomplete Complete Complete Incomplete Complete Incomplete Complete Incomplete Complete Incomplete Complete Incomplete Complete Incomplete Complete Incomplete Complete Incomplete Complete Incomplete 6.12 6.12.1 6.13 6.13.1 7 7.1 7.2 7.2.1 7.2.2 7.2.3 7.3 7.4 7.5 7.6 8 8.1 8.2 8.2.1 8.2.2 8.2.3 8.2.4 8.3 8.4 8.5 8.6 8.6.1 8.7 8.7.1 8.7.2 8.7.3 8.7.4 8.7.5 8.8 9 9.1 9.1.1 9.1.2 9.1.3 9.1.4 9.1.5 Flammable Liquid Storage Cabinets Flammable Liquid Storage Cabinet Specifications Special Purpose Hoods Special Purpose Hood Specifications Types of Laboratories Categorization and Risk Control Bands Bio‐Safety Levels BSL 1 BSL 2 BSL 3 and Higher Labs Teaching Laboratories Necropsy Laboratories Radiation Laboratories Gross Anatomy Laboratories Laboratory Design and Layout Specifications Laboratory Systems and Operating Modes Hood Location Air Distribution Effectiveness Doors and Traffic Aisles Location and Type of Supply Diffusers Type of Air Supply Diffusers Ventilation Effectiveness (Air Change Rates in Laboratories) Specification of Airflow Rates for Laboratories Calculating Air Change per Hour Rate (ACH) Laboratory Pressurization Lab Offset Volume Airflow Controls CAV VAV Demand Control Ventilation (DCV) Occupancy Based Control Schemes Purge Modes Laboratory Temperature Control Lab Ventilation Laboratory Exhaust Ventilation Materials of Construction Manifolds and Duct Design Dampers Duct Pressures Duct Velocities Complete Incomplete Complete Incomplete Incomplete Incomplete
Incomplete
Incomplete
Incomplete
Incomplete
Incomplete
Incomplete
Incomplete
Incomplete
Incomplete Complete Complete Complete Complete Complete Complete Complete Complete Complete Complete Complete Complete Incomplete Incomplete Incomplete
Incomplete
Incomplete
Complete Incomplete Complete Complete Complete Complete Complete Complete 9.1.6 9.1.6.1 9.6.1.2 9.6.1.3 9.1.7 9.1.8 9.1.9 9.2 9.2.1 9.2.2 9.2.3 9.2.4 9.2.5 9.2.6 9.2.7 9.2.8 9.2.9 9.3 9.4 9.5 9.5.1 9.5.2 9.5.3 9.5.4 9.5.5 9.5.6 9.5.7 9.6 9.7 9.8 10 10.1 10.2 10.3 10.4 10.5 10.6 11 11.1 11.2 Exhaust Fans VAV System Fan VAV Diversity VAV Sensitivity Exhaust Stack General Exhaust Fire Dampers Air Supply Systems 100% OA vs. Recirculated (can you recirculated GEX and when) Outside Air Intakes Airflow Measurement Humidity Control Supply Air Temperature Fire Dampers Noise Insulation Filtration Energy Recovery Smoke and Fire Control Noise Criteria Equipment Ventilation System Layout Layout of Laboratory External Noise Vibration Other Considerations Insulation Filtration Energy Recovery Laboratory Ventilation Construction, Renovation and Commissioning Lab Designer's Checklist TAB Plan Commissioning Plan (building and lab) ECD Commissioning Laboratory Environment Tests (LETs) System Mode Operating Tests (SOMTs) Laboratory Ventilation Management Program LVMP and the Design Process Routine Testing Complete Complete Complete Complete Complete Complete Complete Complete Incomplete Incomplete
Incomplete
Incomplete
Incomplete
Incomplete
Incomplete
Incomplete
Incomplete
Incomplete
Incomplete
Incomplete Complete Complete Complete Complete Complete Complete Complete Complete Complete Incomplete Incomplete
Incomplete
Incomplete
Incomplete
Incomplete
Incomplete
Incomplete
Incomplete
Incomplete
Incomplete
11.3 11.4 12 Management of Change BAS Trends and Reports References Incomplete
Incomplete
Incomplete

Lab Ventilation Design Manage

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