Hospital Guidelines - Electronic Systems Group

Transcription

Phase 1
Brief of the Physical
Environment & Interior
Design of Hospitals
Literature Research on
Hospital Health & Comfort
Guidelines
Brief of the Physical
Environment & Interior
Design of Hospitals
Literature Research on
Hospital Health &
Comfort Guidelines
Nov 2009
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Phase 1
Research on Environmental & Architectural Hospital Design Requirements
Contents
Page
1
2
3
Research Content & Methodology
2
1.1
Introduction
2
1.2
Requirement Categories
2
1.3
Hospital Departments
2
1.4
Selection of Papers & Guidelines
2
1.5
Output Presentation
2
ICU Recommendations
2
2.1
Sleep
2
2.2
Stress & Depressives
7
2.3
Visual Environment - Lighting
8
2.4
Visual Environment – View/ Aesthetics
10
2.5
Acoustic Environment
11
2.6
Thermal Environment
12
2.7
Indoor Air Quality
12
2.8
Spatial Environment
15
Hospital Acquired Infections (HAI)
15
3.1
Types of Hospital Acquired Infections
15
3.2
Airborne Transmission of Pathogens
17
3.3
Contact Transmission of Pathogens
21
3.4
Waterborne Transmission of Pathogens
25
3.5
Influence of HAI
26
3.6
Survival of pathogens in air
27
3.7
Ventilation Rate & Speed vs. survival of pathogens in air
27
3.8
Ventilation System vs. survival of pathogens in air
27
3.9
RH and temperature vs. survival of pathogens in air
31
3.10
Air Disinfection Techniques vs. survival of pathogens in air
31
3.11
Single Occupancy Rooms vs. survival of pathogens in air
36
3.12
Natural Ventilation vs. survival of pathogens in air
39
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1
Research Content & Methodology
1.1
Introduction
This document contains the literature research done for master project 3, as an introduction
to the graduation project, at Eindhoven University of Technology. The introduction to the
graduation project consists of a literature research on environmental health and comfort
requirements of the entire hospital in general, resulting in a brief with a comparison of the
requirements given by each guideline or paper per hospital department and a description on
the environmental health and comfort levels. The results are presented online at
http://www.ics.ele.tue.nl/~akash/maartje/nameSearchGuideline.php. The goal, problem
definition, etc. are described in afstudeerplan_30102009.doc.
To be able to give an overview of all requirements per hospital function, we need to define a
categorization of these requirements according to comfort levels and a categorization of the
hospital departments according to the ‘Shell model’ of the ‘College Bouw
Ziekenhuisvoorzieningen’. The last part of this chapter contains a selection of papers and
guidelines used for this research and a description of the presentation of results.
1.2
Requirement Categories
The requirements can be ordered using the following categories.
i. Spatial Comfort
1.
Location [-]
a.
b.
c.
d.
e.
f.
2.
Ground Floor versus Higher
In the Middle or on the Side of the Plan
Near Highway (Emergency)
Quiet Location
North/ East/ South/ West
Functional Relation to Other Spaces [-]
2
Minimum Floor Area [m ]
Minimum Height [m]
3.
ii. Indoor Air Quality
1.
2.
3.
4.
Natural Ventilation Allowed? [-]
Locked Chamber Required? [-]
Overflow Grids Allowed/Required? [-]
Pressure Relationship to Adjacent Areas [-]
5.
6.
7.
Minimum Air Changes of Outdoor Air per Hour [1/h]
Minimum Total Air Changes per Hour [1/h]
All Air Exhausted directly to Outdoors [-]
a.
a.
Nominal Pressure [Pa]
Energy-recovery allowed? [-]
8.
9.
Air Recirculated Within Room Units [-]
Air Inlet
a. Location Air Inlet versus Location Air Exhaust [-]
2
b. Air Inlet Plenum Size [m ]
c. Type of Air Inlet [-]
10. Amount of Particles? [-]
a.
b.
c.
d.
[KVE/m3]
[KVE/m2/hour]
[Particles/m3]
MAC-value [-]
11. Filter Type [-]
a.
Particles Capture Percentage [%]
iii. Thermal Comfort
o
1.
2.
3.
4.
5.
Design Temperature [ C]
o
Air Temperature [ C] – Air Inlet versus Air Outlet
Individual Control of Temperature [-]
o
Radiant Temperature [ C] - Assymetry
Relative Humidity [%]
6.
7.
Air Speed [m/s]
Heating Device [-]
a.
a.
b.
Humidification Required? [-]
Air
Water
iv. Visual Comfort - Lighting
1.
Daylight Required [-]
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2.
3.
4.
Laminar Flow Index [-]
Location of Light sources [-]
Illuminance [lux]
5.
6.
7.
8.
Luminance (contrast) [cd/m2]
Color-Appearance Index [Ra]
Color Temperature [K]
Light Colors [-]
a.
Position of measurement
v. Visual Comfort – View/ Aesthetics
1.
2.
3.
4.
View Outside Required [-]
Greenery Inside/Outside [-]
Art [-]
Room Materials [-]
a.
b.
c.
5.
Recommended Color Finishes [-]
a.
b.
c.
6.
Easy to Clean
Natural versus Artificial
Warm versus Cold Atmosphere
Ceiling
Walls
Floor
Recommended Reflectance [-]
a.
b.
c.
Ceiling
Walls
Floor
vi. Acoustic Comfort
1.
2.
Perceived Sound Level by Human Ear [dB(A)]
Frequency of this Sound Level [1/s] indicating Rhythm/ Pattern
vii. Safety & Sustainability
1.
2.
3.
1.3
Security Diffuser [-]
Medical Gas Installations [-]
Night Switch For Energy Reduction [-]
Hospital Departments
The so called ‘shell method’ from the Dutch ‘College bouw zorginstellingen’ divides the
functions depending on specific building requirements in 4 building typologies, also called
‘shells’. The first shell, the hot floor, includes the high-tech, expensive functions that are
specific for hospitals. In the hotel are all functions that allow patients to stay over. The
functions for interviews and not elaborate checks and treatment are in the office. The office
also includes offices, such as administration. The factory includes all additional medical
functions and facilities.
The shells [CBZ’07]:
• Hot floor Operation Department, emergency, general patient facilities
• Hotel Nursing, rooms for patients
• Office Administration, interviews, not elaborate checks and treatments
• Factory Medical additional functions and facilities
The guidelines [ASH’07], [ASH’03], [AIA’01], [AIA’97] give the following departments for
hospitals in general.
•
Hot floor
•
Hotel
•
Office
•
a.
Surgery and Critical Care
a.
Nursing
a.
b.
c.
Administration
Sterilizing and Supply
Service
a.
b.
Ancillary
Diagnostic and Treatment
Factory
A further description of rooms per department, according to [ASH’03], is given below:
–
Surgery and Critical Care
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The general acute care hospital has a core of critical-care spaces, including operating
rooms, emergency rooms, delivery rooms, and a nursery. Usually the functions of radiology,
laboratory, central sterile, and pharmacy are located close to the critical care space.
Inpatient nursing, including intensive care nursing, is in the complex. The facility also
incorporates a kitchen, dining and food service, morgue, and central housekeeping support.
Operating room (recirculating air
system) (e) (r)
Operating/ surgical cystoscopic
rooms (e), (p), (q) (r)
Plaster room
Scrub bay
Scrub room
Eye Surgery
Cardiac Surgery
Neuro-Surgery
Delivery room (p) (r)
Recovery room (p)
Critical and Intensive Care
Newborn Intensive Care
–
Treatment room (s)
Nursery suite
Trauma room (crisis or shock) (I) (s)
Trauma room (conventional ED or
treatment) (I) (s)
Anesthesia gas storage
Endoscopy
Bronchoscopy (q)
ER waiting rooms
Triage
Radiology waiting rooms
Class A Operating (procedure) room
(e) (r)
Outpatient Surgery
Outpatient surgery is performed with the anticipation that the patient will not stay overnight.
An outpatient facility may be part of an acute care facility, a freestanding unit, or part of
another medical facility such as a medical office building.
–
Nursing Facilities
Nursing facilities have fundamental requirements that differ greatly from those of other
medical facilities.
Patient
room/
resident
room
(holding room)
Resident gathering (dining, activity)
Toilet room (g)
Newborn nursery suite
Protective environment room (i). (q),
(w)
–
Airborne infection isolation room
(h),(q), (x)
Isolation alcove or anteroom (w) (x)
Labor/delivery/recovery/postpartum
(LDRP)
Public Corridor
Patient corridor / resident corridor
Ancillary
RADIOLOGY (y)
• X-ray
(diagnostic
and
treatment)
• X-ray (surgery/ critical care and
catheterization)
• Darkroom
Laboratory, general (y)
Laboratory. bacteriology
Laboratory, biochemistry (y)
Laboratory, cytology
Laboratory, glasswashing
Laboratory, histology
–
Microbiology (y)
Laboratory, nuclear medicine
Laboratory, pathology
Laboratory, serology
Laboratory, sterilizing
Laboratory, media transfer
Autopsy room (q)
Non-refrigerated body-holding room
(k)
Pharmacy
Administration
Admitting and waiting rooms
–
Interview spaces
Diagnostic and Treatment
Bronchoscopy,
sputumcollection,
and pentamidine, administration
Examination room
Medication room
Treatment room
–
Physical, occupational, and hydrotherapy
Soiled workroom or soiled holding
Clean workroom or clean holding
Sterilizing and Supply
Sterile Preparation
• Lay-up
• Sterile pack storage
ETO-sterilizer room
Sterilizer equipment/exhaust room
Central medical and surgical supply
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• Soiled or decontamination room
• Clean workroom
• Sterile storage
Endoscope cleaning room
Changing room
Shower
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Locked Chamber (sluis)
Packing area
Office room
–
Coffee-room/ instruction
Toilets
Closet
Service
Food preparation center (I)
Warewashing
Dietary day storage
Laundry, general
Soiled linen sorting and storage
Clean linen storage
Linen and trash chute room
Bedpan room
Bathroom
–
Janitor's closet
Hazardous material storage
Personal Services
Hemodialysis/ Renal Dialysis
Psychiatry
Dirty utility/ disposal room
Disposal corridor
Dental Facilities
Requirements for these facilities differ from those of other health care facilities because
many procedures generate aerosols, dusts, and particulates. [ASH’07]
1.4
Selection of Papers & Guidelines
I assume that the quality of guidelines and papers can be based on the following:
• Date of publication
o Since I assume that technologies and knowledge improves over time
• The quality of journal/ conference
o Examples of good quality:
All papers published in ScienceDirect
• The quality of guideline/ institution
o Examples of guidelines/ institutions which are generally known to be good
quality:
USA
• AIA
• ASHRAE
UK
• CIBSE; the Chartered Institute of Building Services
Engineers
o CIBSE’s (2005) Applications Manual AM10 –
‘Natural ventilation in non-domestic buildings’.
o CIBSE’s (2000) Applications Manual AM13 –
‘Mixed mode ventilation’ gives guidance.
• HTM 2025, 0305, 0401(Legionella)
o Health Technical Memorandum 55 – ‘Windows’, BS
5925
• International and British Standards (ISO and BS EN)
• the Building Services Research and Information
Association (BSRIA)
• trade associations such as the Heating and Ventilating
Contractors’ Association (HVCA)
• Health and Safety Commission’s Approved Code of
Practice and guidance document ‘Legionnaires’ disease:
‘the control of Legionella bacteria in water systems’
(commonly known as L8)
•
NHS
o
The Department of Health publication ‘The Health
Act 2006: code of practice for the prevention and
control of healthcare associated infections’
The Netherlands
• NEN and ISSO norms
• TNO
• Beheersplan Luchtbehandeling voor de Operatie-afdeling
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•
•
•
1.5
Bouwmaatstaven
CBZ
Ziekenhuisvoorzieningen)
Arbo
Senter Novem
(College
Bouw
Output Presentation
This report contains a description of the ICU requirements according to guidelines. The
measurement results from the measurements that will be done during my graduation project
will be compared with these standards to analyse their satisfaction of guideline
recommendations. A complete overview of hospital requirements according to guidelines is
given in an excel sheet with the following layout and is also provided online at
http://www.ics.ele.tue.nl/~akash/maartje/nameSearchGuideline.php. Using this layout online
several search methodologies can be applied, e.g.:
• Search per department or per room
• Search per comfort level
• Search per guideline (e.g. only Dutch guidelines or International guidelines)
Figure: Example of layout of brief of hospitals
Besides this a description on (techniques to improve) indoor air quality and Hospital
Acquired Infections is given in this report.
2
ICU Recommendations
There are no concrete rules or requirements by law according the thermal internal climate in
buildings, except ‘that the climate at places where people work cannot cause any damage
to the health of the employee’. The values that are mentioned are no rules by law but
guidelines. Specific requirements for the Intensive Care Units are a limited number in the
Dutch guidelines. In the building guidelines for hospitals more detailed information is given
about the required internal climate. For some guidelines the desired conditions are
mentioned per room. Using literature and guidelines I got the following list of ICU internal
climate and spatial design recommendations.
2.1
Sleep
2.1.1
Quantity of Sleep Required
The amount of sleep each person needs depends on many factors, including age. Infants
generally require about 16 hours a day, while teenagers need about 9 hours on average.
For most adults, 7 to 8 hours a night appears to be the best amount of sleep, although some
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people may need as few as 5 hours or as many as 10 hours of sleep each day. Much less
or more sleep than 7 to 8 hours is bad for health. People tend to sleep more lightly and for
shorter time spans as they get older, although they generally need about the same amount
of sleep as they needed in early adulthood. The total sleep time should be similar to the
mean total sleep time per 24 h period, this means that it should be within the normal
range (8.8 ± 5.0 h) [Car’94].
2.1.2
Sleep architecture in ‘normal’ human beings
Brief arousals are clinically important and increasingly scored during polysomnography.
Although highly variable both among different individuals and on different nights, some
generalizations can be made about typical sleep architecture. Normal subjects will fall
asleep within about 20 min., and enter successively deep stages (non-REM) of sleep, with a
deepest sleep period (REM period) occurring in about 90 min. and every 90-120 min.
thereafter. Typically, deeper non-REM sleep is seen in the first half of the sleep period, and
more REM in the second half. Brief episodes of wakefulness are seen normally during the
sleep period, particularly in older subjects. However, any condition that causes frequent
awakenings or arousals can lead to daytime sleepiness.
[Mar’95] performed overnight polysomnography in 55 control subjects to find the frequency
of arousals during routine polysomnography in the normal population, which can be used as
a guideline for how the sleep architecture of patients should ideally be. Awakenings were
scored according to the criteria of Rechtschaffen and Kales and briefer arousals according
to three different criteria, including the American Sleep Disorders Association (ASDA)
definition. The high upper limit of the frequency of brief arousals was not altered by
exclusion of patients who snored or had witnessed apneas or daytime sleepiness.
• There was a mean of 4 [95% confidence interval (CI), 1-15] Rechtschaffen and Kales
awakenings per hour, whereas the ASDA definition gave 21 (95% CI, 7-56) per
hour slept.
• Arousal frequencies increased significantly (p < 0.001) with age in the subjects,
who ranged from the late teens to early 70s.
• It is important that those scoring arousals on routine polysomnography recognize that
high arousal frequencies occur in the normal population on 1-night polysomnography.
[Mar’95]
[Bon’07] scored the occurrence of brief arousals systematically during sleep for more than
20 years. Seventy-six normal subjects (40 men) without sleep apnea or periodic limb
movements of sleep, aged 18 to 70 years, slept in the sleep laboratory for 1 or more nights.
Sleep and arousal data were scored by the same scorer for the first night (comparable to
clinical polysomnograms) and summarized by age decade. The result is significant
knowledge concerning the importance of arousals for the sleep process in normal subjects
and patients, and comprehensive age norms.
• There were no statistically significant differences for sex or interaction of sex by
age (p > 0.5 for both).
• The mean arousal index increased as a function of age. Newman-Keuls
comparisons (0.05) showed arousal index in the 18- to 20-year and 21- to 30-year age
groups to be significantly less than the arousal index in the other 4 age groups. Arousal
index in the 31-to 40-year and 41-to 50-year groups was significantly less than the
arousal index in the older groups. [Bon’07] concludes that brief arousals are an integral
component of the sleep process and that they increase with other
electroencephalographic markers as a function of age. Besides, age-related norms may
make identification of pathologic arousal easier.
• The arousal index was significantly negatively correlated with total sleep time and
all sleep stages (positive correlation with stage 1 and wake). Brief arousals are highly
correlated with traditional sleep-stage amounts and are related to major demographic
variables.
Table [Bon’06]
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Sleep architecture across lifespan in ‘normal’ human beings
l. Premature Neonates
• Two sleep stages: “Quiet” sleep and “Active” sleep
o Active sleep develops first, may be up to 75% of TST
2. Neonates (full term)
• TST = 16-17 hours/24
• Quiet sleep – 50% & gradually increases in amount as S matures
o Seen at SO if 3 months or older
o Immature version of NREM/SWS
• Active sleep – 50% & gradually decreases in amount as S matures
o See at SO from birth to 3 months of age
o Presumed activation of “central motor programs”
3. Six months of Life
• 70% Quiet sleep + 30% Active sleep
4. Sleep during First Year of Life
• At birth, infant sleeps a lot, mostly in active sleep, with brief bursts of quiet sleep
• Sleep is interspersed with brief bouts of wake
• Gradual consolidation of wake into one period of time
• Gradual consolidation of sleep into several periods of time, nocturnal plus long naps
“polycyclic” sleep
4. Sleep during First Year of Life (cont.)
• Gradual maturation of sleep EEG patterns
• Delta waves and sleep spindles emerge
• Gradual decrease in active/REM sleep
• Gradual decrease in TST
5. Sleep during Early Childhood (1-5 years of life)
• TST = 10-12 hours/24, consolidated into nocturnal sleep plus one afternoon nap by 2
years of age
• Full EEG sleep staging by 5 years of age
• Boys sleep mean average of 611 minutes, girls 576 minutes
• Sleep “architecture”: Stage l = 2%, Stage 2 = 46%, Stage ¾ = 20%, Stage REM = 31%
Lots of Stages 3&4 sleep, difficult to arouse S, more parasomnias
6. Sleep in Middle Childhood (5-12 years of life)
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• By 6 years, TST = 9-12 hours, consolidated, no afternoon naps
• Boys sleep mean average of 573 minutes, girls 589 minutes
• Sleep architecture: Stage 1 = 2%, Stage 2 = 48%, Stage ¾ = 20%, Stage REM = 28%
• Importance of growth hormone, parasomnias still frequent
7. Sleep in Adolescence (12-18 years of life)
• Decreasing TST, mean average 8.5 hours (may need more)
• Decreasing number of REM periods
• Growth hormone and sexual hormones
• Orgasm and ejaculation seen in REM sleep
• Generally poor sleep hygiene, likely to develop delayed sleep phase increase in EDS…
8. Sleep in Early Adulthood (18-30 years)
• TST = 7.5 to 8 hours (range 4.5 to 10.5)
• Sleep efficiency: 91-99% males, 94-98% females
• Awakenings: 0-6 males, 0-2 females (> 2 minutes duration)
• Sleep architecture: Stage 1 = 2-6%, Stage 2 = 41-51% males, 46-58% females,
• Stage ¾ = 6-26% males, 11-25% females
• Stage REM = 22-34% males, 21-29% females
• Again, may be shorting sleep…
9. Sleep in Early Middle Age (30-45 years)
• TST = 399-436 minutes in males, 394-448 minutes in females
• SE: 85-99% males, 90-99% females
• Awakenings: 1-7 males, 0-5 females
• Sleep architecture:
• Stage 1 = 3-11% males, 2-8% females
• Stage 2 = 45-66% 45-63%
• Stage ¾ = 2-18% 4-21%
• Stage REM = 19-27% 21-31%
• Parasomnias are very rare
• Increasing frequency of sleep disorders (OSA, PLMD, snoring, Insomnia, etc)
10. Sleep in Later Middle Age (45-60 years)
• TST = 340-440 minutes in males, 396-466 minutes in females
• SE = 88-96% males, 86-100% females
• Awakenings: 4-7 males, 3-7 females
• Stage 1 = 4-12% males, 3-7% females
• Stage 2 = 52-72% 51-65%
• Stage ¾ = 0-12% 5-17%
• Stage REM = 17-25% m 19-25% f
11. Sleep in Old Age (60 years +)
• TST = 5-6 hours/24 + afternoon nap (1 hour usually)
• Cannot keep sleep consolidated at night
• 286-460 minutes in males, 349-461 minutes in females
• SE: 57-97% males, 73-96% females
• Stage 1 – 6-14% males, 4-12% females
• Stage 2 – 38-72% 44-64%
• Stage ¾ - 0-3% 0-18%
• Stage REM – 11-27% 15-25%
• Increased numbers of awakenings: medical problems + sleep changes?
o Ages 60-69: 4-11 in males, 2-7 in females
o Ages 70-79: 1-10 in males, 3-14 in females
• Greater tendency to phase advance
• Greater amounts of daily exercise & greater durations of daylight exposure --- better
sleep
Summary of Sleep Requirements
2.1.3
The following table indicates a summary of the reference sleep architecture with which the
sleep architecture of the ICU patients will be compared. Since I will measure the sleep
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pattern in BIS values and not directly in sleep stages, the BIS values related to each sleep
stage are also indicated in the following table.
Table: Overview of Sleep Architecture in ‘Normal’ Human Beings
Age
Arousal
TST
Sleep
Arousal
Awakenings
Awakenings
Stage
Index AI
[hours]
Efficiency [%]
(3-15
per
hour
(>2
[%]
sec.)
(>15
sec.
Duration) =
BIS>90
Duration) =
(usually
BIS=98
min.
1
BIS=98
Stage 2 [%]
Stage
3/4
Stage REM
=
[%] =
[%] =
BIS 75-90
BIS 20-70
BIS 75-92
M
F
M
F
M
F
46-
6-26
11-25
22-
21-
34
29
19-
21-
27
31
17-
19-
25
25
11-
15-
27
25
96)
M
F
M
F
11+/-4
4
per
schaffen
(Recht-
hour
and Kales),
M
F
M
0-6
0-2
2-6
F
21 (ASDA)
18-30
10.8+/-
7.5-8
91-99
4.6
30-45
45-60
60+
94-
83+/-33
22.9
41-51
98
16.8+/-
6
40m-7
6.2
20m
16.5+/-
6
5.6
20m
21.9+/-
5-6/24
6.8
after-noon
40m-7
nap
+
85-99
88-96
57-97
58
90-
116+/-
99
44
86-
109+/-
100
22
73-
130+/-
96
42
29.8
1-7
0-5
3-
2-8
45-66
11
34.7
4-7
3-7
4-
4-10
2-18
4-21
63
3-7
52-72
12
42
45-
51-
0-12
5-17
65
3-
6-
4-
12
14
12
38-72
44-
0-3
0-18
64
(1
hour)
In this table we see the following:
•
The Total Sleep Time (TST) decreases as the individual grows older, from 7.5-8
hours continuously in the age range 18-30 to 5-6 hours in short terms at the age
60+.
•
The Sleep Efficiency decreases from 94-98% to 60-90%.
•
Awakenings occur more once we grow older, starting with 0-4 awakenings in the
age range 18-30 to 4-7 awakenings in the age range 45-60.
If the arousal occurred during or within 3s after the completion of an
environmental noise increase of >10 dB(A) than the arousal is a soundinduced arousal (an arousal caused by sound).
Stage 1 sleep typically occupies 4-10% and stage 2 sleep (BIS 75-90) typically
occupies 44-60% of nocturnal sleep time in normal individuals and remains
relatively stable throughout the life span.
o
•
•
Stage ¾ sleep (BIS 20-70) occupies 8-25% in the age range 18-30 and 0-10% in
the age 60+, which indicates that stage ¾ sleep is not stable throughout the life
span.
•
REM sleep (BIS 75-92) typically occupies 20-25% of nocturnal sleep time in
normal individuals and unlike delta sleep, REM distribution remains relatively stable
throughout the life span [Car’94]. [Gaz’01]
•
Comparing the RASS scale with the sleep levels, a RASS score of -4 to -5
would be similar to deep sleep and would therefore be preferred. Where a
RASS score of -1 to -2 is similar to light sleep.
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2.2
Stress & Depressives
2.2.1
Blood Pressure and Heart Beat
For each heartbeat, the blood pressure varies between maximum and minimum blood
pressure, which for a normal, resting, healthy adult human is respectively 115mmHg and
75mmHg, which is written as 115/75mmHg. While average values for arterial pressure could
be computed for any given population, there is often a large variation from person to person;
arterial pressure also varies in individuals from moment to moment. Additionally, the
average of any given population may have a questionable correlation with its general health,
thus the relevance of such average values is equally questionable. However, in a study of
100 subjects with no known history of hypertension, an average blood pressure of
112/64 mmHg was found [Pes’01], which is in the normal range. In children the normal
ranges are lower than for adults [NHLBI]. In the elderly, blood pressure tends to be higher
than normal adult values, largely because of reduced flexibility of the arteries. Factors such
as age and gender [Rec’01] influence blood pressure values. Pressure also varies with
exercise, emotional reactions, sleep, digestion and time of day.
Pulse pressure is the difference between max. and min. value, so in this case 115-75=40.
The max. (systolic) and min. (diastolic) blood pressures are not static but undergo natural
variations from one heartbeat to another and throughout the day (in a circadian rhythm).
They also change in response to stress. [wiki blood pressure]
Table: Classification of blood pressure for adults [wiki blood pressure]
Category
Hypotension
Normal
Prehypertension
Stage 1 Hypertension
Stage 2 Hypertension
Max. (systolic) [mmHg]
<90
90-119
120-139
140-159
>160
Min. (diastolic) [mmHg]
Or <60
And 60-79
Or 80-89
Or 90-99
Or >100
Heart rate (HR) is a measure of the number of heart beats per minute (bpm). The average
resting human heart rate is about 70 bpm for adult males and 75 bpm for adult females. A
heart rate of 60-80 bpm is normal for an adult in rest. Heart rate varies significantly between
individuals based on fitness, age and genetics. Endurance athletes often have very low
resting heart rates. Heart rate can be measured by monitoring one's pulse. Pulse
measurement can be achieved using specialized medical devices, or by merely pressing
one's fingers against an artery (typically on the wrist or the neck). [wiki heart rate]
Table: Classification of normal heart rate per age group [wiki heart rate] [UMHC]
Age
Newborn
Older Child
Adult
Normal heart rate [beats per minute]
120
90-110
50-100 (60-80 for average person in rest)
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Figure: Heart Beat
2.2.2
Reduced pain medication
A normal amount of pain medication is different for a patient in pain at the ICU, as
compared to a healthy person, who usually doesn’t take any pain medication. To the best of
our knowledge, there are no standards available for normal pain medication consumption at
the ICU. However, the following research is found as an indicator for the amount of pain
medication. [Yor’04] A study at the cardiothoracic intensive care unit of a major teaching
hospital in Sydney, Australia, with 102 subjects indicated that patients received limited total
amounts of morphine during their critical care stay (mean = 26.7 mg; SD = 13.3; range: 068).
2.3
Visual Environment - Lighting
2.3.1
Dutch Requirements for ICU Design
The basis for the majority of norms and guidelines in which light is treated is that people
should be able to do work under good visual circumstances. In NEN-EN 12464-1 (‘Licht en
verlichting – werkplekverlichting – Deel 1: Werkplekken binnen’), for example, there are
guidelines for the illuminance and the color-appearance index (see following table) for
several tasks. The SBR guideline ‘gezonde verlichting in gebouwen’ aimed to provide
guidelines for which the biological effects and the wellbeing of human beings is taken as a
focus. For a patient at the ICU, however, we expect different aspects to be of importance.
The measurements will be done as described in NEN 1891, Binnenverlichting –
Meetmethoden voor verlichtingssterkten en luminanties.
Table; Lighting requirements for the ICU according to EN 12464-1:2003
Em
UGRL
Ra
Type of room/ task / activity
Lux
-
-
General Lighting
100
<19
>90
Remark
At floor height
Simple/short Medical Research/Reading
300
<19
>90
At bed height
Research and threatment
1000
<19
>90
At bed height
20
<19
>90
Night Security
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•
•
Max. luminance ratio 1:3:10
o
Between the visual task (e.g. paper) and the immediate environment (e.g.
the table) the luminance-ratio should not be more than 3.
o
Between the visual task and the periphery (surfaces in the rest of the room)
the luminance-ratio should not be more than 10.
Uniformity average u0>=0,3 at floor height, u0>=0,7 in reading area
2.3.2
American Guidelines on Intensive care lighting
The following American guidelines provide recommendations on maximum illuminance
levels besides recommendations of minimum illuminance levels.
General overhead illumination
General overhead illumination plus light from the surroundings should be adequate for
routine nursing tasks, including charting, yet create a soft lighting environment for patient
comfort. Total illuminance should not exceed 30 foot-candles (fc). (1 fc= 10.764 lux) So total
2
illuminance ≤322,920lux (lumen/m ) On surface for reading or research/treatment the
illuminance can exceed 322,920lux temporarily. [CCM’95]
Night light
Night lighting should not exceed 6.5 fc (1 fc= 10.764 lux) for continuous use or 19 fc for
short periods. So nightlight ≤ 70lux. [CCM’95]
Emergency/ treatment
Separate lighting for emergencies and procedures should be located in the ceiling directly
above the patient and should fully illuminate the patient with at least 150 fc shadow-free.
150 fc=1614,6lux. [CCM’95] So this guideline gives a somewhat higher illuminance
requirement than the Dutch NEN guidelines which recommend 1000lux for research and
treatment.
Reading
A patient reading light is desirable, and should be mounted so that it will not interfere with
the operation of the bed or monitoring equipment. The luminance of the reading lamp
should not exceed 30 fc. [CCM’95]
Lighting control
Control of illumination should be accessible to staff and families, and capable of adjustment
across the recommended range of lighting levels. Use of multiple light switches to allow
different levels of illumination is one method helpful in this regard, but can pose serious
difficulties when rapid darkening of the room is required to permit transillumination, so a
master switch should also be provided. It is preferable to place lighting controls on variablecontrol dimmers located just outside of the room. This permits changes in lighting at night
from outside the room, allowing a minimum disruption of sleep during patient observation.
[NICU]
Light quality
Perception of skin tones is critical in the ICU; light sources that meet the CRI, FSCI, and GA
values identified above provide accurate skin-tone recognition. Light sources should be as
free as possible of glare or veiling reflections. When the light sources to be used are linear
fluorescent lamps, these color criteria can be met by using lamps that carry the color
designation “RE80”. [NICU]
Lighting requirements for staff
Illumination should be adequate in areas of the ICU where staff perform important or critical
tasks; the IESNA specifications in these areas are similar to but somewhat more specific
than the general guidelines recommended by AAP/ACOG. In locations where these
functions overlap with care areas (e.g., close proximity of the staff charting area to patient
beds), the design should nevertheless permit separate light sources with independent
controls so the very different needs of sleeping patients and working staff can be
accommodated to the greatest possible extent. Care must be taken, however, to insure that
bright light from these locations does not reach the patients’ eyes.
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Consideration should be given to providing a space easily accessible to all staff that will
provide an opportunity for exposure to higher-intensity light levels for at least 15 minutes a
shift in order to ameliorate the effects of working at night and Seasonal Affective
Disorder(13). This space can be illuminated with white light to produce 300-500 lux at the
eye, which is produced by approximately 1500-2500 lux at the work plane. If a blue local
lighting system is used, the illumination should be from a spectrally narrowband source such as a blue LED – with a peak wavelength at or near 470 nanometers, and should
produce at least 30 lux at the eye. These requirements are for operation rooms. [NICU]
Daylighting
At least one source of daylight shall be visible from patient care areas, either from each
patient room itself or from an adjacent staff work area. When provided, external windows
in patient care rooms shall be glazed with insulating glass to minimize heat gain or
loss, and shall be situated at least 2 feet (0.6 meters) away from any part of a patient's
bed to minimize radiant heat loss. All external windows shall be equipped with shading
devices that are neutral color or opaque to minimize color distortion from transmitted
light.
Windows provide an important psychological benefit to staff and families in the ICU.
Properly designed daylighting is the most desirable illumination for nearly all care-giving
tasks, including evaluation of patient skin tone. However, placing patients too close to
external windows can cause serious problems with radiant heat loss or gain and glare, so
provision of windows in the ICU requires careful planning and design. Shading devices
should be easily controlled to allow flexibility at various times of day, and should either be
contained within the window or easily cleanable. These should be designed to avoid direct
sunlight from striking the patient, IV fluids, or monitor screens. [NICU]
2.4
Visual Environment – View/ Aesthetics
2.4.1
Nature & other Positive Distractions
When possible, views of nature shall be provided in at least one space that is accessible
to all families and one space that is accessible to all staff. Other forms of positive distraction
shall be provided for families in infant and family spaces, and for staff in staff spaces.
Provision should be made for direct access to nature and other positive distractions within
the hospital complex. These nature environments may consist of outdoor spaces such as
gardens or walking paths or indoor spaces such as greenhouses and atria. Amenities within
the nature environment might include water features, plant and animal life and solitary and
group seating. Other positive distractions might include fitness centers and access to music.
Culturally appropriate positive distractions provide important psychological benefits
to staff and families in the ICU. Looking out a window, viewing psychologically supportive
art, or taking a stroll in a garden may help to reduce stress or increase productivity.
When possible, windows should have views of nature environments. These environments
might consist of trees, plants, human and animal activity, gardens, and landscapes. In
urban settings, appropriate nature elements might include planters or water features.
When such views are not possible, artwork with nature images or other nature
simulations (e.g., video and artificial representations) should be provided throughout
the unit. Family and staff lounge spaces are ideal locations for views of nature and
other positive distractions.
[NICU]
Interior Finishes
2.4.2
Floor surfaces
Floor surfaces shall be easily cleanable and shall minimize the growth of microorganisms.
Flooring material with a reflectance of no greater than 40%(9) and a gloss value of no
greater than 30 gloss units shall be used, to minimize the possibility that glare reflected
from a bright procedure or work-area light will impinge on the eyes of infants or caregivers.
Floors shall be highly durable to withstand frequent cleaning and heavy traffic. Flooring
materials shall be free of substances known to be teratogenic, mutagenic, carcinogenic, or
otherwise harmful to human health.
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While ease of cleaning and durability of ICU surfaces are of primary importance,
consideration should also be given to their glossiness (the mirror-like reflectivity of a
surface), their acoustical properties, and the density of the materials used. Reduced
glossiness will reduce the risks from bright reflected glare; acoustic and density properties
will directly affect noise and comfort. Materials should permit cleaning without the use of
chemicals that may be hazardous, since it may not be possible to vacate the space during
cleaning. Transition surfaces that do not obstruct mobility, are durable, and minimize noise
and jarring of equipment should be provided at the intersection of different flooring
materials.
Materials suitable to these criteria include resilient sheet flooring (medical grade rubber or
linoleum) and carpeting with an impermeable backing, heat- or chemically-welded seams,
and antimicrobial and antistatic properties. Carpeting has been shown to be an acceptable
floor covering in the hospital and the ICU and has obvious aesthetic and noise reduction
appeal, but it is not suitable in all areas (e.g., around sinks or in isolation or soiling
utility/holding areas). Small floor tiles (e.g., 12 inch squares) have myriad seams and areas
of non-adherence to the sub-floor. These harbor dirt and fluids and are a potential source of
bacterial and fungal growth. Much is known regarding the effects of chemicals such as
mercury on human health and development. Additional efforts should be made to exclude
persistent, bioaccumulative toxic chemicals (PBTs) such as polyvinyl chloride (PVC) from
healthcare environments. PVC or vinyl is common in flooring materials including sheet
goods, tiles, and carpet. The production of PVC generates dioxin, a potent carcinogen, and
fumes emitted from vinyl degrade indoor air quality. Dioxin releases are not associated with
materials such as polyolefin, rubber (latex), or linoleum.
Volatile organic compounds (VOCs) such as formaldehyde and chlorinated compounds
such as neoprene also should be avoided when selecting adhesives or sealants for floor
coverings. Specify low- or no-VOC and non-toxic and non- carcinogenic materials. Flooring
containing natural rubber (latex) should be certified non-allergenic by the manufacturer.
Infants should not be moved into an area of newly installed flooring for a minimum of two
weeks to permit complete off-gassing of adhesives and flooring materials. [NICU]
Wall & ceiling surfaces
Wall surfaces shall be easily cleanable and provide protection at points where contact with
movable equipment is likely to occur. Surfaces shall be free of substances known to be
teratogenic, mutagenic, carcinogenic, or otherwise harmful to human health.
As with floors, the ease of cleaning, durability, and acoustical properties of wall surfaces
must be considered. Although commonly used, vinyl wall covering contains PVC and will
degrade indoor air quality, and thus should be avoided. VOCs and PBTs such as cadmium
often are found in paints, wall-coverings, acoustical wall panels, and wood paneling systems
and also should be avoided. [NICU]
2.5
Acoustic Environment
In the rules there are mainly requirements about the maximum sound pressure level in a
space and the minimal sound insulation in a space. Besides this there are several
guidelines according the speech intelligibility and acoustics. In the ICU, however, we are
considering sound disturbance. Since this term is difficult to define, it is also difficult to make
rules or guidelines for this. The A-weighted equivalent sound level Laeq (an imaginary
constant sound level that within a certain time span gives the same amount of sound energy
as is given in reality) of machines is preferably not higher than 25 to 30 dB(A) in rooms
which are used for resting. [Zim’08]
The World Health Organization (WHO) provides guideline values for continuous maximum
background noise in hospital patient rooms, which are 35 dBA during the day and 30 dBA at
night, with nighttime peaks in wards not to exceed 40 dBA [Ber’99]. In evaluating these
noise levels, it should be noted that the decibel scale for quantifying loudness or sound
pressure intensity is logarithmic; each 10 dBA increase therefore represents a sound
pressure level that is 10 times higher.
For the analysis of the causes of certain sound levels and frequencies in the ICU it is useful
to know what the characteristics of the sound produced by human voice are. The voiced
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speech of a typical adult male will have a fundamental frequency from 85 to 155 Hz, and
that of a typical adult female from 165 to 255 HzError! Hyperlink reference not valid.. [Voice]
2.5.1
Standard 18 & 19: Floor, Wall & ceiling Surfaces
The choice of floor, wall and ceiling materials related to acoustic properties is described in
section 2.4.2.
2.6
Thermal Environment
o
The thermal comfort is best if the temperature is between 21 and 24 C and the relative
humidity is between 30 and 60%, and for the air speed no recommendations are given for
the ICU, according to the guidelines [ASH’07] [ASH’03] [ASHRAE manual] [AIA’01] [AIA’97].
According to the same guidelines, the air speed for the Operation Room should be between
0.3-.35m/s, which might be used as a reference, but not as a requirement for the ICU. For
normal comfort conditions the preferred air speed is less than 0.2m/s to prevent the feeling
of chilling.
Table: Indoor Thermal Climate Recommendations for ICU design per guideline
Source
NEN 6055, NEN 1822, 12464-1, 1891, Committee of the American College of
Critical Care Medicine
Bouwmaatstaven ziekenhuizen (College Bouw Zorginstellingen)
Temperature
°C
22
RH
%
22 – 25,5
>30
45 advised
30-60
30-60
ASHRAE HVAC design manual for hospitals and clinics
21-24
Heating and ventilation systems (department of Health)
Guidelines for design and Construction of hospitals and health care facilities
(The American Institute of Architects)
18-25
24
2.7
Indoor Air Quality
Air quality can be defined in terms of CO2-level and/or in terms of particles and bacteria’s.
[TNO’04] provides methods to measure air quality in terms of particles (size and number)
and in type and occurrence of micro-organisms. However, in this research we limit
ourselves to the measurement of CO2-levels, since we assume particles and microorganisms do not influence the sleep-pattern of patients immediately, but either only on the
long run or not at all, and since measuring particles and micro-organisms is quite
complicated.
CO2-level
As of March 2009, carbon dioxide in the Earth's atmosphere is at a concentration of 387
ppm by volume, and indoor climates should aim to keep their CO2-concentration at the
same level. Atmospheric concentrations of carbon dioxide fluctuate slightly with the change
of the seasons, driven primarily by seasonal plant growth in the Northern Hemisphere.
Concentrations of carbon dioxide fall during the northern spring and summer as plants
consume the gas, and rise during the northern autumn and winter as plants go dormant, die
and decay. CO2 is toxic in higher concentrations: 1% (10,000 ppm) will make some people
feel drowsy. Concentrations of 7% to 10% cause dizziness, headache, visual and hearing
dysfunction, and unconsciousness within a few minutes to an hour. Amounts above 5,000
ppm are considered very unhealthy, and those above about 50,000 ppm (equal to 5% by
volume) are considered dangerous to animal life. Even when greenhouses are vented,
carbon dioxide must be introduced into them to maintain plant growth, as the concentration
of carbon dioxide can fall during daylight hours to as low as 200 ppm (a limit of C3 carbon
fixation photosynthesis. [wiki]
The following are norms about particles in air in cleanrooms, given by the guidelines U.S.
Federal Standard 209, De Europese Richtlijn GMP 1997, NEN-EN-ISO 14644 and NENEN-ISO 14698, and ISO/TC 209.
Table: Cleanroom classification in particle’s size according to EU guideline GMP 1997
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Maximum allowed # particles/m
Class In rest
0.5micrometer
5micrometer
A
3.500
0
B
3.500
0
C
350.000
2.000
D
3.500.000
20.000
Working
0.5micrometer
3.500
350.000
3.500.000
5micrometer
0
2000
20.000
Table: Cleanroom classification in number of KVE’s according to EU guideline GMP 1997
Maximum allowed # KVE’s
Class Air sample
Sedimentation
Contact surfaces, Glove
surface, diameter diameter 55m
90mm
3
KVE/m
KVE/(4 hours)
KVE/surface
KVE/glove
A
<1
<1
<1
<1
B
10
5
5
5
C
100
50
25
D
200
100
50
-
Table: Classification according to ISO 14644-1
Selected airborne particulate cleanliness classes for cleanrooms and clean zones
3
ISO
Maximum concentration limits (particles/m of air) for particles equal to and
classification larger than the considered sizes shown below (concentration limits are
number (N)
calculated in accordance with 3.2)
0.1µm
0.2 µm
0.3 µm
0.5µm
1 µm
5µm
ISO Class 1
10
2
ISO Class 2
100
24
10
4
ISO Class 3
1000
237
102
35
8
ISO Class 4
10000
2370
1020
352
83
ISO Class 5
100000
23700
10200
3520
832
29
ISO Class 6
1000000 237000 102000 35200
8320
293
ISO Class 7
352000
83200
2930
ISO Class 8
3520000
832000
29300
ISO Class 9
35200000
8320000
293000
NEN-EN 779 provides the following filter qualification, and NEN-EN 1822-1 provides the
filter qualification for HEPA and ULPA filters.
Table: NEN-EN 779: Filter qualification for coarse and fine filters
Weight
Average Efficiency 0.4µm Filter
class Filter
efficiency [%] particles [%]
EN779
4/9
Am<65
G1
EU1
65<Am<80
G2
EU2
80<Am<90
G3
EU3
90<Am<
G4
EU4
40<Em<60
F5
EU5
60<Em<80
F6
EU6
80<Em<90
F7
EU7
90<Em<95
F8
EU8
95<Em
F9
EU9
class
Begin efficiency
0.4µm
<5%
<5%
15%
25%
63%
80%
>80%
Table: NEN-EN 1822-1: Classification for HEPA and ULPA filters
Filter
Efficiency [%] @ MPPS
Penetration [%] @ MPPS
Classification
EN1822
Overall Value
Local Vale
Overall Penetration Local Penetration
H10
85
15
H11
95
5
H12
99.5
0.5
H13
99.95
99.75
0.05
0.25
H14
99.995
99.975
0.005
0.025
U15
99.9995
99.9975
0.0005
0.0025
U16
99.99995
99.99975
0.00005
0.00025
U17
99.999995
99.9999
0.000005
0.0001
The required ventilation amount is given in the following table.
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Table: Recommendation ventilation amount for ICU design per guideline
Ventilation
1/h (* [dm3/s per m2])
Source
Bouwbesluit
B1
15
*
B2
6*
B3
2,4*
ASHRAE HVAC design manual for hospitals and clinics
2-6
Heating and ventilation systems (department of Health)
Guidelines for design and Construction of hospitals and
health care facilities (The American Institute of Architects)
10
6
B4
1*
B5
n.t
Standard 18 & 19: Floor, Wall & ceiling Surfaces
2.7.1
The choice of floor, wall and ceiling materials related to indoor air quality properties is
described in section 2.4.2.
2.8
Spatial Environment
Patients must be situated so that direct or indirect (e.g. by video monitor) visualization by
healthcare providers is possible at all times. This permits the monitoring of patient status
under both routine and emergency circumstances. The preferred design is to allow a direct
line of vision between the patient and the central nursing station. In ICUs with a modular
design, patients should be visible from their respective nursing substations. Sliding glass
doors and partitions facilitate this arrangement, and increase access to the room in
emergency situations. [CCM’95]
3
Hospital Acquired Infections (HAI)
Indoor air pollution has been recognized as one of the top environmental risks worldwide
[WHO’89] [EPA’90]. The risk of cross-infection is a psychological stress factor as well as a
health issue. It reduces the well-being of the population and has a powerful economical
impact due to absenteeism and reduced productivity. [Bol’09]
3.1
Types of Hospital Acquired Infections
Bacterial Infection
Examples of bacteria that are highly infectious and transported within air or air and
water mixtures are Mycobacterium tuberculoses and Legionella pneumophila. Wells
(1934) showed that droplets or infectious agents of 5 µm or less in size can remain
airborne indefinitely. [Iso’80] and [Luc’84] have shown that 99.9% of all bacteria present
in a hospital are removed by 90 to 95% efficient filters (ASHRAE Standard 52.1),
because bacteria are typically present in colony-forming units that are larger than 1
µm.
Viral Infection
Examples of viruses that are transported by and virulent within air are chicken pox
and measles. Epidemiological evidence and other studies indicate that many of the
airborne viruses that transmit infection are submicron in size; thus, there is no known
method to effectively eliminate 100% of the viable particles. HEPA and/or ultralowpenetration (ULPA) filters provide the greatest efficiency currently available. Attempts to
deactivate viruses with ultraviolet light and chemical sprays have not proven reliable
or effective enough to be recommended by most codes as a primary infection control
measure. Therefore, isolation rooms and isolation anterooms with appropriate ventilationpressure relationships are the primary means used to prevent the spread of airborne viruses
in the health care environment.
Molds
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Evidence indicates that some molds such as Aspergillis can be fatal to advanced
leukemia, bone marrow transplant, and other immunocomprised patients.
Category operations
We categorized operations into four classes; clean, clean/ contaminated, contaminated and
dirty/ infected wound operations, and we defined surgical site infections (SSI) as that
developing with any purulent discharge from surgical wounds or surgical drains
according to CDC Guidelines [Man’99]. SSI are often caused by MRSA. [Mas’01]
3.1.1
TB Tuberculosis
TB is a common and often deadly infectious disease caused by mycobacteria, mainly
Mycobacterium tuberculosis [Kum’07]. Tuberculosis usually attacks the lungs, but can also
affect the central nervous system, the lymphatic system, the circulatory system, the
genitourinary system, the gastrointestinal system, bones, joints, and even the skin. The
classic symptoms of tuberculosis are a chronic cough with blood-tinged sputum, fever, night
sweats, and weight loss. The diagnosis relies on radiology (commonly chest X-rays), a
tuberculin skin test, blood tests, as well as microscopic examination and microbiological
culture of bodily fluids. Tuberculosis treatment is difficult and requires long courses of
multiple antibiotics.
Tuberculosis is spread through the air. When people who have the disease cough, sneeze,
or spit, they expel infectious aerosol droplets 0.5 to 5 µm in diameter. A single sneeze
can release up to 40,000 droplets [Col’98]. Each one of these droplets may transmit the
disease, since the infectious dose of tuberculosis is very low and the inhalation of just a
single bacterium can cause a new infection [Nic’05] [Haa’00]. A person with active but
untreated tuberculosis can infect 10–15 other people per year [Kum’07][WHO’06]. Others at
risk include people in areas where TB is common, people who take immunosuppressant
drugs, and health care workers serving these high-risk clients [Gri’96]. [wiki]
3.1.2
MRSA Methicillin-resistant Staphylococcus Aureus
(MRSA) is a bacterium responsible for difficult-to-treat infections in humans, and a strain of
Staphylococcus aureus that is resistant to a large group of antibiotics. MRSA is
especially troublesome in hospital-associated (nosocomial) infections. In hospitals, patients
with open wounds, invasive devices, and weakened immune systems are at greater risk for
infection than the general public. A 2004 study showed that patients in the United States
with MRSA infection had, on average, three times the length of hospital stay (14.3 vs.
4.5 days), incurred three times the total cost ($48,824 vs $14,141), and experienced five
times the risk of in-hospital death (11.2% vs 2.3%) than patients without this infection
[Nos’05]. [wiki]
3.1.2.1
Airborne Transmission of MRSA
Scientific studies showing evidence of MRSA airborne transmission:
In [Bos’06] UK microbiology researchers wanted to know if filtering the air in a hospital
would lead to a decrease in MRSA found on horizontal surfaces. Ward rooms housing
“…heavy MRSA dispensers…” were supplied with portable HEPA filtration units. 95% of
settle plates placed in a variety of locations in the wards showed MRSA contamination.
When HEPA filtration was introduced, measurable MRSA decreased between 73%-95%.
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In [Dur’05] researchers proved that MRSA was airborne and that there is a link between
the concentration of these airborne pathogens and colonization in patients. It can be
concluded that, total number of airborne viable particles in the critical areas such as
operating theatres and intensive care units, seems to be a significant risk factor for the
development of nosocomial infections in immuno-compromised patients.
In [Udu’02] researchers determined that the reservoir of the deadly pathogen was the air
conditioning system that fed the NICU. Despite many typical infection control
interventions such as staff education, environmental cultures, isolation of colonized
patients, compliance with aggressive infection control measures and recognition of
the role of cross contamination the colonization of infants grew.
In [Shi’01] three patients in single occupancy rooms became infected with MRSA after
surgery. An epidemiological study demonstrated that clinical isolates of MRSA in our ward
were of one origin and that the isolates from the air and from inanimate environments were
identical to the MRSA strains that caused infection or colonization in the inpatients. The
conclusions of this study indicate that disinfecting the air circulated within their ward
could help reduce colonization of patients. In this study, it was confirmed that MRSA could
be acquired by medical staff and patients through airborne transmission. The findings
suggest the importance of protecting patients against cross-infectious agents existing in
aerosols. Laminar unidirectional airflow, air ventilation, and air filtration could also be
beneficial in hospital environments and should be considered.
[Kow’08]
Sources of HAI
3.1.3
[Spa’91] classified common indoor pollutant (VOC) sources into three categories [Yan’04]:
(1) Steady-state sources such as moth cakes.
(2) On/ff sources such as heaters.
(3) Decaying sources such as “wet” coatings and many dry materials.
3.2
Airborne Transmission of Pathogens
Sources and Environmental Routes of Airborne Infections
Airborne pathogens originate from different sources. Most pathogens in healthcare settings
originate from patients, staff, and visitors within the buildings, from such sources as infected
patients' respiratory tracts or skin squamae (scales). In order to save energy, the air
tightness of buildings has been improved and the supply of fresh air has been reduced
[Esm’85]. This has increased the indoor air pollutant levels signifcantly. A series of longterm studies of human exposure to air pollutants indicated that indoor levels of many
pollutants may be 25 times, and occasionally more than 100 times, higher than outdoor
levels [EPA’85].
Other pathogens can enter buildings from outside air through dust that harbours pathogens
such as aspergillus, streptococci, or staphylococci [Beg’03]. There are also less common
sources of airborne infections; for example, bird droppings or aerosols from contaminated
water in a warm-water therapy pool [Ang’05]. Several environmental factors and conditions
have been identified as frequent sources of airborne infection outbreaks. The malfunction or
contamination of ventilation systems and lack of cleaning and maintenance are commonly
cited [Kum’98], [Lut’03], [McD’98], [Sch’03]. In one MRSA outbreak, for example, the
ventilation grilles in two patient bays were found to be harbouring MRSA [Kum’98]. On
occasions when this ventilation system was shut down, it sucked air from the ward
environment into the system, contaminating the outlet grilles then it blew contaminated air
back into the ward when the system was restarted. Additionally, several studies have
identified hospital construction and renovation activities as the sources of airborne infection
outbreaks due to dust or particulate generation [Hum’91], [Iwe’94], [Loo’96], [Opa’86],
[Ore’01]. [Zim’08]
Airborne
Airborne pathogens are those pathogens generated in the respiratory system and released
in exhaled air as a way of propagation. There are 4 parts in the respiratory tract where
microorganisms may multiply and be dispersed in exhaled air: nose, oral cavity, throat and
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lungs (e.g. TB). The airborne transmission route has been shown to be predominant for
three respiratory diseases: measles, varicella and tuberculosis [Qia’06]. [Bol’09]
Although not well-documented, the airborne spread of MRSA has been reported by several
authors, especially from burn units and intensive therapy units [Far’90], [Wag’93], [Cot’96].
[Kum’98] According to [Dur], the major nosocomial pathogen MRSA is the most
frequently isolated airborne microbe. ‘During an outbreak, MRSA may be recovered
from various environmental sources such as dust on floors, beds, fans, mattresses
etc. [Bar’84], [Dun’95], [Nda’91] The major sources of MRSA in hospitals are septic
lesions and carriage sites, especially anterior nares and the perineal area, of patients
and personnel.
Most infections, including MRSA, are environmental [HIS]. This article showed how MRSA
was being distributed in a hospital via the ventilation system. Pennington's statement
that MRSA bacteria die when they hit the floor is contradicted by a large body of
research. [ICHE] contains a report on MRSA survival that is typical of this research,
determining the duration of survival of 2 strains of MRSA on 3 types of hospital fomites.
MRSA survived for 11 days on a plastic patient chart, more than 12 days on a laminated
tabletop, and 9 days on a cloth curtain."
Airborne transmission is known to be the route of infection for diseases such as
tuberculosis and it has also been implicated in nosocomial outbreaks of MRSA.
Although the principal mode of transmission is transiently contaminated hands of hospital
personnel for most infections, airborne micro-organism (e.g. MRSA), the contribution of
airborne micro-organisms to the spread of infection is likely to be greater than is currently
recognised [APIC]. This is partly because many airborne micro-organisms remain viable
while being non-culturable, with the result that they are not detected, and also because
some infections arising from contact transmission involve the airborne transportation of
micro-organisms onto inanimate surfaces.
Ventilation grilles
‘Environmental sources such as exhaust ducting systems have been increasingly
recognized as a source for MRSA outbreaks in intensive therapy units. Daily shut-down
of the system temporarily created a negative pressure (chimney effect), sucking air in
from the ward environment into the ventilation system and probably contaminating
the outlet grilles. It is likely that contaminated air is blown back into the ward when the
ventilation system was started, and probably this is the source of MRSA in the tested
patients in [Kum’98]. Thorough cleaning of the ventilation system and the entire ward with its
fittings and furniture together with appropriate infection control measures terminated the
outbreak. The ventilation system now (preferably) operates on a continuous cycle with the
outlet grilles maintained at a positive pressure.’ [Kum’98]
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Figure: Surfaces commonly contaminated by MRSA [Ulr’08]
Reducing Infections Caused by Airborne Pathogens
Airborne transmission refers to infections that are contracted from airborne microorganisms.
Reservoirs for airborne pathogens range from dust (e.g., spores of Clostridium Difficile or C.
Diff. and Aspergillus) to aerosol droplets (e.g., tuberculosis [TB], severe acute respiratory
syndrome [SARS], influenza, chickenpox), to skin scales shed by patients infected with
methicillin-resistant Staphylococcus aureus (MRSA) [Ulr’06]. Airborne transmission has also
been implicated in outbreaks of other infections such as Acinetobacter spp. and
Pseudomonas spp. [Beg’03], [Beg’06]. The relative importance of airborne transmission
remains somewhat controversial [Bau’90]. [Bra’70] estimated that airborne transmission
accounted for 10– 20% of nosocomial infections. [Beg’03] argued that the role of airborne
transmission may have been underestimated, due to the difficulty of culturing many airborne
organisms and the complexities of assessing the role such pathogens play in the
contamination of environmental surfaces and subsequent contact transmission. Recently
airborne infections have attracted more attention due to outbreaks of SARS in 2002–2003
and current concerns about an avian influenza (H5N1) pandemic. A few extensive research
reviews have been conducted, notably [Li’07] on the relationship between ventilation
systems and airborne transmission; [Tan’06] on airborne infection and ventilation control in
healthcare settings; and [Beg’03] on the importance of airborne transmission in healthcareacquired infections. This literature survey identified many studies that explicitly examine the
relationships between airborne infections and environmental factors in healthcare buildings.
There is a pattern of findings across these studies suggesting that hospital air quality plays
a decisive role in affecting the concentration of pathogens in the air, and thereby has major
effects on the frequency of airborne infectious diseases such as TB, aspergillosis,
chickenpox, influenza, and SARS. The research also clearly indicates that multiple
environmental approaches or interventions can be effective in controlling and preventing
airborne infections. Though a sizable amount of sound research is available, data on certain
aspects of air quality and infection are insufficient to permit the precise specification of, for
example, minimum ventilation and filtration requirements for certain patient groups and
treatment spaces [Li‘07], or the maximum tolerable level of spores per cubic meter [Bou’02]
for the prevention of airborne transmission. [Zim’08]
Environmental Approaches for Reducing Airborne Infections
The research literature strongly supports implementing several environmental approaches
for controlling and preventing airborne infections, including installing effective filters,
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specifying appropriate ventilation systems and air change rates, employing various control
measures during construction or renovation, and using single-bed rooms instead of multibed rooms to increase isolation capacity and reduce transmission from infected patients.
Also, limited research suggests that measures such as the use of ultraviolet irradiation can
be effective in reducing airborne pathogens [Gri’05] and lowering the incidence of asthma in
asthmatic children's homes [Ber’06].
High-efficiency particulate air (HEPA) filters
An effective way to control infections is to control their source. Filtration, the physical
removal of particulates from air, is often the first step in ensuring good air quality. One
experimental study of a commercial air purification system found that a chemical-coated
filter demonstrated 61.46% efficiency in destroying pathogens and reached 99.99%
efficiency when used in conjunction with ultraviolet lamps [Gri’05]. In acute healthcare
settings, a commonly used approach is the HEPA filter, which can be at least 99.97%
efficient for removing particulates as small as 0.3 µ in diameter (as a reference, Aspergillus
spores are 2.5 µ to 3.0 µ in diameter) [She’04]. This is adequate for most healthcare
settings in ambulatory care facilities and hospitals, including operating rooms (ORs)
[She’04]. [Bos’06] revealed a significant reduction in environmental contamination by MRSA
with the use of portable HEPA units in a clinical setting. In the CDC/HICPAC guidelines, the
use of HEPA filtration is recommended for healthcare facilities, and it is either required or
strongly recommended for all construction and renovation areas [She’04]. There is strong
evidence that immunocompromised and other high-acuity patients have a lower incidence of
infection when housed in HEPA-filtered isolation rooms. Bonemarrow transplant recipients
in one study showed a 10-fold greater incidence of nosocomial Aspergillus infection when
they were assigned beds outside a HEPA-filtered environment with laminar airflow (LAF), as
compared to similar patients housed in a HEPA-filtered unit [She’87]. A strong multisite
study by Passweg and colleagues (1998) found that the use of HEPA and/or LAF reduced
infections, decreased transplant-related mortality, and increased survival for leukemia
patients after bone marrow transplant.
Ventilation systems and airflow control
After air is filtered, effective ventilation systems are needed to achieve optimal ventilation
rates, airflow patterns, and humidity so that the spread of infections can be minimized. First,
ventilation rate is an important measure to control indoor air quality. In healthcare facilities, it
is usually expressed as room air changes per hour (ACH), where peak efficiency for particle
removal in the air space often occurs between 12 ACH and 15 ACH. In a study of SARS
infections, wards with the highest ventilation rate had a significantly lower infection rate
among healthcare workers as compared with other wards [Jia’03]. A study of 17 Canadian
hospitals found that the risk of healthcare workers acquiring TB was strongly linked with
exposure to infected patients in rooms with low ACH rates, such as waiting areas [Men’00].
Detailed ventilation standards are provided by the American Institute of Architects (AIA) and
Facilities Guidelines Institute (FGI) in the Guidelines for Design and Construction of Health
Care Facilities (AIA & FGI, 2006), and by the American Society of Heating, Refrigerating
and Air-conditioning Engineers (ASHRAE) in ASHRAE 62.1-2004—Ventilation for
Acceptable Indoor Quality (ASHRAE, 2004). Yet questions remain regarding the minimum
ventilation requirements needed for effective prevention of infections [Li’07]. A second key
aspect of ventilation is airflow direction. Negative pressure is preferred for rooms housing
infectious patients to prevent the dispersion of pathogen-laden aerosols, dust, and skin
scales from the locus of the infected patient to other spaces. Importantly, a review of 40
studies by [Li’07] concluded that there is strong evidence to support and recommend the
use of negatively pressurized isolation rooms. By contrast, if a care space houses an
immunocompromised patient (e.g., surgical patients, patients with underlying chronic lung
disease, or dialysis patients) or immunosuppressed patients (e.g., transplant patients or
cancer patients), positive airflow pressure is desirable to safeguard them from aerial
pathogens entering from adjacent spaces. Finally, an exceptionally effective ventilation
approach for maintaining indoor air quality is to use LAF, which is HEPA-filtered air blown
into a room at a rate of 90 ±?10 feet/min in a unidirectional pattern with 100–400 ACH
[She’04]. When combined with HEPA filters, LAF can reduce air contamination to the lowest
level; thus it is recommended for ORs and areas with ultraclean room requirements, such as
those housing immunocompromised patients [Alb’01], [Arl’89], [Dha’02], [Fri’03], [Hah’02],
[She’87]. A prospective cohort study found that the type of operating theater ventilation was
an independent risk factor for the incidence of sternal surgical site infections [Yav’06]. New
theaters with LAF and automatically closing doors showed significantly better results in
reducing infections than older theaters with conventional plenum ventilation. [Zim’08]
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Effective air quality control measures during construction and renovation
It is extremely important to employ effective control and prevention measures during
construction and renovation, because such activities have been frequently implicated in
outbreaks of airborne infection. Examples of such measures include using portable HEPA
filters, installing barriers between patient-care areas and construction/renovation areas,
generating negative air pressure for construction/renovation areas relative to patient-care
areas, and sealing patient windows. Strong evidence indicates that using HEPA filters for air
intakes near construction and renovation sites has positive effects on air quality and
reduces the risk of infection for patients [Bou’02], [Cor’99], [Loo’96], [Mah’00], [Opa’86],
[Ore’01]. For example, a study conducted during extensive hospital construction and
renovation documented an outbreak of invasive pulmonary aspergillosis (IPA) among acute
leukemia patients housed in wards with natural ventilation, soaring to an infection rate of
50% [Ore’01]. At this point some patients were moved to a hematology ward with HEPA
filters. During the following 3 years, none of the patients hospitalized in the hematology
ward developed IPA, although 29% of leukemia patients housed in the regular ward
contracted aspergillosis. However, one strong study demonstrated that HEPA filters were
not by themselves an Health Environments Research & Design, 1(3), 2008 adequate control
measure during construction; they should be employed in conjunction with other measures
such as sealing windows and installing barriers [Hum’91]. It was noted earlier that the
combination of LAF and HEPA filtration is capable of reducing air contamination to the
lowest level. During construction or renovation activities, however, LAF is more expensive
and especially difficult to achieve, because furnishings and other features can create
turbulence. There is currently a lack of cost benefit research to enable well-founded
evaluations of the expense versus effectiveness of LAF for patient-care areas near
construction and renovation sites. [Zim’08]
3.3
Contact Transmission of Pathogens
Although airborne transmission poses serious safety risks, contact contamination is
generally recognized as the principal transmission route of nosocomial infections, including
pathogens such as MRSA, C. difficile, and vancomycin-resistant enterococci (VRE), which
survive well on environmental surfaces and other reservoirs [Bau’90], [IOM’04]. The
prevention of contact-spread infections is of paramount importance in healthcare settings.
[Zim’08]
Sources and Environmental Routes of Contact-Spread Infections
Environmental routes of contact-spread infections include direct person-to-person contact
and indirect transmission via environmental surfaces. Healthcare workers' hands play a key
role in both direct and indirect transmissions. A staff member may touch two patients in
succession without washing his or her hands, or touch an environmental surface or feature
after direct contact with an infected patient. Other staff and the patient may then acquire the
pathogen by touching the same surface [Ulr’06]. Research indicates that there is an inverse
causal link between the hand-washing compliance rate of healthcare workers and contact
transmission of infectious diseases [Lar’88], [Lar’99]. It is well established that hand hygiene
is the most important single measure for preventing the spread of pathogens in healthcare
settings [Boy’02]. In this context, the fact that hand-washing compliance rates are often low
represents a very serious challenge to patient safety. [Mal’98] reviewed 38 studies and
reported that compliance rates were usually less than 40%. In more recent studies,
compliance rates were still low, with most ranging between 20% and 35%; rates above 40%
or 50% are the exception [Alb’81], [Gra’90], [Kuz’05], [Lar’05], [Ran’06], [Sab’05], [Sac’06],
[Tri’07]. Compliance rates usually are lower for indirect contact (through environmental
surfaces) than for direct person-to-person contact [McA’06]. There is a pattern that
compliance is worse in high-acuity units such as ICUs, because patient care in these units
is often more demanding than in lower-acuity units [Kar’05]. Meanwhile, guidelines require
staff to clean their hands more frequently when caring for sicker patients [Kar’05]. Hand
hygiene tends to be especially poor in units that are busy due to understaffing and/or a high
bed-occupancy rate or patient census [Arc’97]. High bed-occupancy rates have been
identified as a factor contributing to higher rates of infections such as MRSA [Bor’03].
Furthermore, environmental surfaces in healthcare settings often become extensively
contaminated by nearby patients or by healthcare workers' contaminated hands. [Boy’97]
found that in rooms housing patients infected with MRSA, 27% of all environmental surfaces
sampled were contaminated. Meanwhile, 42% of nurses who had no direct contact with
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MRSA patients but who had touched environmental surfaces contaminated their gloves with
MRSA. Other research reports even higher levels of MRSA surface contamination (74%) in
spaces previously occupied by colonized or infected patients [Fre’04]. The same study
found MRSA contamination in 100% of patient rooms sampled, regardless of whether or not
the previous occupant had been infected. Furthermore, patient rooms can become
contaminated with more than one type of MRSA, suggesting prolonged survival of MRSA
strains from prior room occupants [Fre’04]. It is not surprising that the risk of acquiring
antibiotic-resistant infections such as MRSA and VRE is significantly increased if a patient is
admitted to a room previously occupied by an infected individual [Hua’06]. Because many
nosocomial pathogens can survive on environmental surfaces for weeks or months
[Bon’96], [Kra’06], such contaminated surfaces act as pathogen reservoirs and can become
the source of infection outbreaks [Boy’93], [Lan’06]. Many of these environmental surfaces
and features have direct relevance to architectural design, including floors [And’82],
[Bey’00], [Boy’97], [Sko’94], work surfaces or furniture such as chairs [Nos’00], bed privacy
curtains [Pal’99], door handles [Rob’01], sink faucets [Bla’04], [Bur’00], bedside rails, overbed tables, bed linens and patients' gowns [Boy’97], clinical waste carts [Ble’06], computer
keyboards [Bur’00], bedside patient files [Pan’05], and even toys in healthcare settings
[Fle’06], [Mer’02]. Other very frequently contaminated surfaces and objects include medical
equipment such as infusion pumps [Ayg’02], blood pressure cuffs [Boy’97], laryngoscope
blades [Bea’99], stethoscopes [Mar’97], and electronic ear-probe thermometers [Por’01].
The pervasiveness of such contamination underscores the importance of hand- and
workplace hygiene in healthcare settings [Wil’06]. [Zim’08]
Environmental Approaches to Reduce Contact-Spread Infections
The research literature supports the effectiveness of certain environmental approaches for
controlling and preventing contact-spread infections. Examples of such approaches include
providing sufficient and accessible alcohol-based hand-rub dispensers, choosing easy-toclean furniture and wall finishes, and providing single- rooms rather than multi-bed rooms.
[Zim’08]
Reducing contact transmissions by increasing hand-washing compliance
Education programs to increase hand-washing compliance alone have yielded, at best,
mixed results [Bis’00]. Some investigations have found that education interventions
generate no increase in hand washing. Even intensive education or training programs, such
as classes and group feedback, may produce only transient increases in hand washing
[Dor’96], [Dub’90]. Recently, multifaceted interventions, in addition to education, have been
more successful at increasing hand washing. These interventions include environmental
measures such as providing localized availability of alcohol-rub dispensers and using
posters as reminders to staff [Cre’05], [Gor’05], [Joh’05], [Lam’04], [Pit’00], [Ran’06], [Tri’07].
There is mounting evidence that the type of hand-washing facility influences handwashing
compliance and infection rates. Compared with traditional soap and water, alcohol-based
hand-rub acts more rapidly and effectively, requires less time for staff to decontaminate their
hands adequately, and has a lower risk of side-effects and recontamination [Boy’02]. The
CDC/HICPAC guidelines define alcoholbased hand-rub as the standard of care for hand
hygiene practices in healthcare settings [Boy’02]. Several studies have shown that the
introduction of alcohol-based hand-rub boosted hand-washing compliance [Hug’02] [Joh’05]
[Tri’07]. Importantly, several other studies supported the effectiveness of alcohol-based
hand-rub, compared to soap and water, for improving the effectiveness of hand washing in
terms of reducing microbial counts on hands [Bis’00] [Coh’03] [Gir’02] [Gra’90] [Kar’05]
[Tve’05] and reducing infection rates [Gor’05]. [Mac’07] analyzed MRSA prevalence in more
than 100 hospitals across Europe and found that the use of alcohol-based hand-rub was the
single most important predictor of lower MRSA incidence after adjusting for other
confounding factors. These findings have implications for designers, because alcohol-based
hand-rub dispensers are small and inexpensive, and they do not require costly plumbing
systems and sinks. These characteristics afford more flexibility than soap-and-water
facilities, which in turn facilitates the distribution of dispensers to more locations, closer to
patient-care activities and work spaces, thereby making them more accessible to busy
clinicians and other staff.
The number and accessibility of hand-washing facilities also influence compliance and
infection rates. In particular, the evidence suggests that installing alcohol-based handrub
dispensers at the bedside usually improves adherence. Four studies examined the impact
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washing compliance [Bis’00] [Cre’05] [Pit’00] [Ran’06]. Another study made a statistical
adjustment for other known risk factors of poor hand-washing adherence; the positive
effects of the intervention remained significant and were accompanied by decreased
infection rates [Pet’00]. In an observation study, researchers compared the 3 years after the
installation of alcohol-based hand-rubs in all rooms with the 3 prior years with fewer soapand water sinks; they observed a 21% decrease in MRSA infections and a 41% decrease in
VRE infections. Although hand-washing compliance was not measured in this study, it is
likely that it may have played a role in this improvement. In contrast to the effectiveness of
locating hand-rub dispensers at the bedside, [Mut’00] found that installing dispensers in
hallway locations (near the doors to patient rooms) did not significantly increase the
frequency of hand washing. Other investigations focusing on traditional sinks (soap-andwater) have obtained mixed results concerning the impact of increasing the number and
accessibility of sinks, with a few studies reporting positive impacts [Kap’86]; one finding a
transient increase in compliance [Whi’04]; and other studies reporting no significant
changes [Lan’00] [Lan’03] [Ver’03]. Automated technology has also been examined for its
impact on hand-washing compliance for soap-and-water sinks and alcohol-based hand-rub
dispensers. For traditional soap-and-water hand washing, automated sinks or faucets have
shown mixed results [Lar’91] [Lar’97]. Simplicity of use seems to be important to the
success of automation. In this regard, limited research suggests that automated touch-free
alcohol-based rub dispensers are easy to use and are used more frequently than manual
dispensers [Lar’05]. [Swo’04] examined the effect on compliance of an automatic system
that monitored entries and exits from patient rooms, recorded usage of sinks and alcoholbased hand-rub dispensers, and incorporated voice-prompt devices that reminded
healthcare workers and visitors to wash their hands. The system improved hand-cleaning
compliance from 19% to 27% and was associated with a reduction in the nosocomial
infection rate. There are some limitations, however, in current hand-washing research
knowledge. Because many studies have employed multifaceted interventions, it is not clear
how much of the effectiveness of increased hand washing, reduced microbial counts, or
reduced infection rates can be attributed to the installation of more numerous and/or
accessible alcohol-based hand-rub dispensers. Future research should include prospective
controlled experiments, for example, that systematically vary the number and location of
alcohol hand-rub dispensers. There is also a conspicuous need for studies that define
accessible locations for hand-washing facilities in an evidence-based manner—that is, on
the basis of empirical analysis of staff movement paths, visual fields, interactions with
patients and families, and work processes. In this regard, the neglect of human factors and
research methods are major weaknesses of hand-washing research and of the infection
control literature in general. Research teams should include a human factors specialist and
sometimes an environmental psychologist. The urgent need to increase hand-washing
frequency underscores the high priority that should be accorded to this research direction.
Reducing contact transmission by controlling surface contamination.
As previously mentioned, contaminated environmental surfaces often serve as an
intermediate step in the contact spread of infections. Several design-related factors should
be considered to minimize the risk of infection stemming from contaminated surfaces.
Selection of appropriate floor and furniture coverings is an important step, where ease of
cleaning should be a key consideration. Some studies have examined flooring materials
[And’82] [Sko’94] and furniture coverings [Lan’06] [Nos’00] as they relate to environmental
contamination in healthcare settings. The use of carpet can be a controversial issue. On
one hand, many people believe that carpet is more difficult to clean than hard floor
coverings [Har’00]. A few studies have identified carpeting as susceptible to contamination
by fungi and bacteria [And’82] [Bey’00] [Boy’97] [Sko’94]. However, a recent rigorous study
suggests that certain serious pathogens such as VRE survive less well or for shorter
periods on carpet than on other floor coverings, including rubber tile, linoleum, vinyl sheet
goods, and vinyl composition tile [Lan’06]. In addition to discovering that carpet harbours
less VRE, this research found that carpeting transferred less VRE to hands via contact than
rubber and vinyl flooring and performed as well in cleaning as any other floor covering
tested [Lan’06]. There is limited research comparing the air above carpeted areas and hard
flooring with respect to concentrations of microorganisms, and the findings are conflicting.
[And’82] found higher concentrations above carpeted areas, whereas [Har’00] reported
higher particulate concentrations above hard flooring. In summary, the advantages and
disadvantages of carpeting versus other floor coverings with respect to infection control are
neither clear-cut nor fully resolved. However, in judging different floor coverings, it should be
kept in mind that carpeting, compared to hard floorings, offers important advantages
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unrelated to infection control, including noise reduction [Phi’02], greater ease of walking and
perceived safety for the elderly [Wil’86], a possible reduction in falls [Cou’00], longer family
visits in patient rooms, and more positive evaluations and emotional responses from
patients and families [Har’00]. It is worth mentioning that CDC/HICPAC guidelines do not
recommend against the use of carpeting in patient-care areas. However, the guidelines
suggest that carpeting should be avoided in areas where spills are likely to occur or where
patients are at greater risk of airborne infections [She’04]. Similarly, the EBD standards for
neonatal intensive care units (NICUs) of the National Perinatal Association state that
suitable flooring materials “include resilient sheet flooring (medical grade rubber or linoleum)
and carpeting with an impermeable backing, heat- or chemically welded seams and
antimicrobial and antistatic properties. Carpeting has been shown to be an acceptable floor
covering in the hospital and the NICU and has obvious aesthetic and noise reduction (NR)
appeal, but it is not suitable in all areas (e.g., around sinks or in isolation or soiled
utility/holding areas)” [Whi’06]. The selection of furniture-covering materials may also
influence the incidence of contamination and risk of infection. [Nos’00] identified fabriccovered furniture as a source of VRE infection in hospitals and suggested the use of easily
cleanable, nonporous material. Another study compared the performance of a variety of
furniture upholstery types with respect to VRE and Pseudomonas aeruginosa (PSAE)
contamination [Lan’06]. Performance was similar across different furniture coverings in
terms of reductions in VRE and PSAE after cleaning and the transfer of VRE and PSAE to
hands through contact. However, for the ability to harbour pathogens, although upholstery
types showed no differences with respect to PSAE, there was a difference related to VRE.
Vinyl upholstery performed the best for VRE—that is, the VRE pathogen survived less well
or for shorter periods on vinyl [Lan’06]. In addition, as with evaluating carpeting and other
floor coverings, it is worth considering that fabric-covered furniture might foster a more
home-like, less institutional feeling. The CDC/HICPAC guidelines for upholstery are broadly
similar to those for carpeting in that they do not recommend against using it in patient-care
areas, but they suggest minimizing its use in areas housing immunocompromised patients
[She’04].
A limited amount of research has compared different wall finishes and metals with respect
to their infection control properties. One study evaluated the effectiveness of copper, brass,
and stainless steel surfaces in reducing the viability of air-dried deposits of MRSA [Noy’06].
The results suggested that copper had a better antimicrobial effect than stainless steel. The
use of antimicrobial metals such as copper may not reduce the need for careful cleaning,
however, because dirt or dust on their surfaces may diminish or eliminate their antimicrobial
effects. [Lan’06] compared the performance of different wall finishes (latex paint with
eggshell finish, microperforated vinyl, vinyl with nonwoven backing, and Xorel® wall
covering), and reported that all harbored VRE and were capable of transferring the
pathogen through hand contact. No reduction in VRE was found 7 days after inoculation for
two of the wall products—Type II microvented vinyl with paper backing and Xorel® wall
covering—indicating that harbouring was a greater problem than for other wall products
tested. Latex paint with eggshell finish performed worse in cleaning and disinfection than
other wall finishes, indicating that cleaning produced inadequate reduction of VRE and
PSAE [Lan’06]. Proper cleaning and disinfection is another very important step in preventing
the spread of infections by contact. The limited and conflicting nature of research on
environmental surface materials poses a perplexing challenge to designers attempting to
select materials to help control infection. It appears that for each general category of
surfaces—flooring, upholstery, and wall finishes—no single material has yet been identified
that consistently outperforms others across diverse performance criteria (e.g., harbouring,
capacity to transfer) and for different pathogens. This underscores the importance of
selecting materials that are easily cleaned and of proper cleaning and disinfection
procedures [Ayg’02] [Bar’04] [Det’04] [Fre’04] [Gri’02] [Hot’04] [Mar’03] [Nee’05] [Wil’06]. As
noted, some research suggests that latex paint with eggshell finish does not perform
adequately in cleaning/disinfection for VRE and PSAE [Lan’06]. Detailed cleaning
recommendations for environmental surfaces are available in the CDC/HICPAC Guidelines
[She’04].
Notwithstanding the importance of cleaning, there is alarming evidence indicating that
conventional cleaning techniques often do not adequately eliminate contamination by
serious pathogens such as MRSA and C. difficile. This problem has led infection control
researchers to investigate the effectiveness of alternative decontamination methods or
technologies, notably hydrogen peroxide vapor (HPV). [Fre’04] conducted a prospective
study of multi-bed patient rooms contaminated with MRSA in the United Kingdom, assigning
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six rooms to be cleaned using conventional methods and six similar rooms using HPV.
Before cleaning, 70% of 359 sample swabs from the study rooms yielded MRSA. An
important and disturbing finding was that following conventional cleaning, 66% of swabs
taken from rooms decontaminated by traditional methods yielded MRSA, indicating that
conventional cleaning failed to remove most MRSA contamination. By contrast, following
HPV cleaning only 1.2% of swabs yielded MRSA, indicating that HPV was a far more
effective method for decontaminating patient rooms [Fre’04]. Another British study by
[Jea’05] found that even after an exceptionally intensive three-day period of deep cleaning
using traditional methods (detergent, steam cleaning, chlorine disinfectant), 16% of surfaces
sampled in a Nightingale ward were still cultured with MRSA. Following HPV
decontamination of the Nightingale ward, however, no MRSA at all was cultured from
surfaces. These studies support the effectiveness of HPV cleaning and have implications for
hospital architecture, because a key consideration in employing HPV is that no patients or
staff can be in a room during the process of vapour decontamination. Accordingly, the use
of HPV in multi-bed rooms or open bays necessitates temporarily removing all patients from
the space, shutting and sealing the space for several hours, and disrupting patient care and
flow. By comparison, evacuating persons from single-bed rooms following patient discharge
poses little hindrance to using HPV. [Zim’08]
3.4
Waterborne Transmission of Pathogens
Compared with airborne and contact transmission of infection, fewer studies were identified
on waterborne transmission in relation to hospital design factors. The literature nonetheless
makes it clear that waterborne infections can be a serious threat to patient safety. Many
bacterial and some protozoal micro-organisms can proliferate or remain viable in moist
environments or aqueous solutions in healthcare settings [She’04]. [Ana’02] reviewed
studies between 1966 and 2001 on waterborne nosocomial infections caused by microorganisms other than Legionella. The review identified 43 reported outbreaks and an
estimated 1,400 deaths each year in the United States alone resulting from waterborne
nosocomial pneumonia caused by Pseudomonas aeruginosa. A study of 115 randomly
selected dialysis facilities in the United States detected nontuberculous mycobacteria in
83% of centers [Car’88]. Contaminated water systems in healthcare settings (such as
inadequately treated wastewater) may lead to the pollution of municipal water systems,
enter surface or ground water, and affect residents [Ive’04]. [Zim’08]
Sources and Environmental Routes of Waterborne Transmission
The CDC/HICPAC guidelines [She’04] identify the following categories of environmental
routes or sources of waterborne transmission:
(1) direct contact, such as hydrotherapy [Ang’05];
(2) ingestion of water, such as drinking water [Con’04] [Squ’00];
(3) inhalation of aerosols dispersed from contaminated water sources, such as improperly
cleaned or maintained cooling towers, showers [Min’05], respiratory therapy equipment, and
room air humidifiers; and
(4) aspiration of contaminated water. [Zim’08]
Environmental Approaches to Reduce Waterborne Infection Transmission
The following environmental approaches that aid in controlling and preventing waterborne
infections were identified in literature;
Water supply system. The water supply system should be designed and maintained with
proper temperature and adequate pressure; stagnation and back flow should be minimized;
and dead-end pipes should be avoided [AIA & FGI, 2006] [She’04]. To prevent the growth of
Legionella and other bacteria, the CDC/HICPAC guidelines recommend that healthcare
facilities maintain cold water at a temperature below 68°F (20°C), store hot water above
140°F (60°C), and circulate hot water with a minimum return temperature of 124°F (51°C)
[She’04]. When the recommended standards cannot be achieved because of inadequate
facilities that cannot be renovated, other measures such as chlorine treatment, copper-silver
ionization, or ultraviolet lights are recommended to ensure water quality and prevent
infection [She’04]. For example, in a university hospital where endemic nosocomial
legionellosis was present and all previous disinfection measures had failed, the
implementation of a copper-silver ionization system substantially decreased environmental
colonization by Legionella, and the incidence of nosocomial legionellosis decreased
dramatically [Mod’07]. The review by [Ana’02] recognized the potential severity of
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waterborne infections and recommended that high-risk patients should not be exposed to
tap water, but should use sterile water instead.
Point-of-use fixtures. Water fixtures such as sinks, faucets, aerators, showers, and toilets
have been identified as potential reservoirs for pathogenic microorganisms [Bla’04] [Con’04]
[Min’05] [Squ’00]. Such fixtures produce aerosols that can disperse microbes, and they
have wet surfaces on which moulds and other microorganisms can proliferate. However,
empirical evidence linking these fixtures to nosocomial infections is still limited; no
consensus has been reached regarding the disinfection or removal of these devices for
general use [She’04]. Regular cleaning, disinfection, and good maintenance should be
provided, especially in areas housing immunocompromised patients.
Decorative fountains in healthcare settings. Decorative fountains increasingly are being
used by designers for healthcare facilities, because they can serve as landmarks and
wayfinding elements as well as positive distractions that reduce stress [Jos’06]. The
infection control departments of some hospitals may oppose the installation of fountains out
of concern for the possible generation of infectious aerosols. However, [Rog’06] found no
empirical study linking a waterborne infectious disease or nosocomial outbreak to the indoor
placement of a water fountain or water feature in hospitals. The only related case was an
outbreak of Legionnaires' disease among a group of older adults in a hotel. The source was
traced to a fountain in the lobby, which was not regularly maintained and which was heated
by underwater lighting [Hla’93]. Despite the absence of empirical documentation linking
properly maintained fountains to hospital-acquired infections, the AIA & FGI Guidelines
(2006) recommend that fountains not be installed in enclosed spaces in hospitals. [Zim’08]
3.5
Influence of HAI
The recent increase in hospital-acquired infections (HAIs) means increase in hospitalacquired pneumonia (HAP); the most common HAI contributing to death and affects
about 0.5–1% of all patients admitted to hospital. HAP significantly increases health
complications and extends the length of time patients stay in hospital by up to 13
days on average, thus impacting significantly on hospital resources. [HAP] represent one
of only two sets of evidence-based HAP guidelines in the world which deal with the trio of
prevention, diagnosis and treatment [Mas’07]. It has been estimated that 10-20% of HAIs
are transmitted via the airborne route [Beg’03] equating to a cost of £83-167m per
annum in England alone [Tho’04] [Rob’08] [Rob’06] [Rob, Arup Healthcare]. Besides,
despite advances in infection-control practices, SSI remain to be responsible for
morbidity and mortality among hospitalized patients [Emo’93], [Man’99].
3.5.1
HAP
HAP is defined as a respiratory infection that develops >48 h after admission, and is the
most common hospital-acquired infection contributing towards death [Gro’00] [Gro’80]. A
proportion of HAP cases are attributed to VAP where the infection has arisen following
mechanical ventilation (MV) [Cra’00]. VAP complicates the course of 8e28% of patients
receiving MV and has a mortality rate ranging from 24 to 50%, rising to 76% when the
infection is caused by high-risk pathogens [Cha’02]. VAP is the commonest sepsis
complication among patients admitted to intensive care units (ICU) and carries with it a
significantly increased risk of death [Vin’95]. In addition VAP is associated with prolonged
ventilation requirements and a greater duration of ICU stay, all of which contributes to the
significant financial burden that VAP exerts upon the health service [Hey’99]. Furthermore
VAP is often associated with a dramatic increase in the length of general hospital stay, with
the mean length of hospitalization for patients with VAP recorded as 34 days compared to
21 days for ventilator-assisted patients without VAP [Boy’91]. The excess cost associated
with each case of HAP is estimated to be $40 000 [Rel’02] though this varies depending
upon the complexity and setting of the disease. Measures are available that have proven
efficacy in reducing both mortality and cost [Kel’93]. Hand washing, barrier nursing and
increased isolation are methods aimed at tackling hospital-acquired infection. [CDC’04]
[Col’03] [Dod’04] [ATS’05] [Fre] [Gal] [Str]. [Mas’07]
3.5.2
Infection Control
Engineering solutions can be proposed in order to efficiently reduce the pathogen loads
released in air, disable their virulence, and make them harmless for healthy inhabitants. The
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methods applied should be neither life nor health threatening, nor should they reduce in any
way occupants’ perceived air quality or thermal comfort. They should also be user friendly (if
people are to operate them), with low noise emission, energy efficient, highly ergonomic and
aesthetic. [Bol’09]
3.6
Survival of pathogens in air
The survival of pathogens in air is dependent on:
3.7
•
Ventilation (rate, speed, airflow pattern, system, etc.)
•
Humidity & Temperature
•
Air disinfection techniques, e.g. UV-radiation
•
Single Occupancy Rooms
•
Natural Ventilation
Ventilation Rate & Speed vs. survival of pathogens in air
Ventilation Rate & Speed
The probability of transmission from one person to another depends upon the number
of infectious droplets expelled by a carrier, the effectiveness of ventilation, the
duration of exposure, and the virulence of the M. tuberculosis strain.[CDC’00] [wiki]
A simple way to limit the spread of pathogens is by supplying clean outdoor air, reducing the
harmful concentrations indoors. Recirculated ventilation air dilutes viral and bacterial
contamination within a hospital, therefore, it is preferable to ventilate with 100% outside air.
[LiY’07] considered 40 studies between 1960 and 2005 most related to pathogens and
ventilation, and found that 10 studies supported a direct contributory role of
ventilation rate/airflow pattern to the airborne spread of infectious agents. Among
these three were on TB outbreaks [Cal’91] [Edl’92] [Ehr’72], and four studies were on MRSA
and others. [LiY’07] The authors conclude that there is insufficient data on the minimum
ventilation requirement for ventilating public premises such as hospital infectious wards,
to minimize the spread of airborne infections. Among the 10 studies considered to be
conclusive, five specifically examined the role of ventilation rates, i.e. [Hog’94] [Men’00]
[Mos’79] [Ril’62] [Sch’62]. In [Ril’62], air from a TB ward delivered to an exposure
chamber caused 63 infections, while no infection was observed in a different control
chamber with UV-irradiated air delivery. This study also proved the infectivity of
exhaust air from a TB ward.
[Men’00] presented one of the rare detailed population-based studies of the role of
ventilation in hospitals. It showed a higher TB infection risk for healthcare workers
working in non-isolation rooms with ventilation rates of less than two air changes per
hour. [LiY’07] Using natural ventilation, usually a ventilation rate of only 0.5-1 1/h can be
reached.
On ventilation rate, the topic of overcrowding should be mentioned, although it may be
arguable to justify that overcrowding is equivalent to ventilation and airflows. For example,
the studies by [Ele’98] [Leu’04] [Rei’97] on the socioeconomic factors of TB, suggested that
the risk of transmission of TB is not associated with overcrowding at the district level, but
associated with overcrowding at the housing units level. This suggests the importance of
indoor air environments, as the transmission of TB is known to be airborne. [LiY’07]
3.8
Ventilation System, Airflow Pattern, Aerosol Distance Travelled
vs. survival of pathogens in air
An investigation of over 440 buildings conducted by the US National Institute of
Occupational Safety and Health (NIOSH) also suggested that inadequate ventilation was a
key cause of building occupant complaints [Sei’93]. Ventilation, with appropriate air-handling
processes, is used to create an indoor environment with acceptable air temperature,
humidity, air velocity and to remove pollutants for better indoor air quality (IAQ). Dilution of
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room air with clean disinfected air is one of the easiest and best known methods to remove
pathogens and to decrease the risk of infections in rooms. Natural, mechanical and hybrid
ventilation are often used to supply clean air in rooms. However, this method has its
limitations, related to air distribution pattern, occupants’ thermal comfort, etc. Selection and
design of appropriate ventilation systems require detailed knowledge of contaminant
dispersion in buildings to avoid inadequate ventilation as a consequence. [Bol’09]
Natural Ventilation
A multizone airflow simulation helped [Li’05] to find that natural ventilation may have
helped circulate SARS viruses at a building complex in Hong Kong. Natural ventilation
does not have a pre-defined pattern of airflow distribution, so it is more challenging
to calculate contaminant dispersion in the building. The study of [Wan’08], calculating
the airflow and contaminant dispersion in a three-story, naturally ventilated building with
a large atrium, assuming that a contaminant was released in the atrium, indicates that
the contaminant could disperse very far in the atrium from the source (as indicated by
the following figure number d), that the contaminant concentration was mostly more
than 0.1ppm, and that the closer the neighbouring zone was to the source, the higher
the contaminant concentration of the neighbouring zone. [Wan’08] Dispersion of
pollutant in indoor environments may largely depend on the type and location of pollutant
sources. Prior work in this area is mainly focused on active point pollutant sources that are
associated with heat release or an initial momentum. [Yan’04]
Figure: Contamination of naturally ventilated atrium with contaminant source at the right
bottom [Wan’08]
PV Personalized Mechanical Ventilation
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1
The efficiency of PV as compared to other ventilation methods is indicated in the following
figure.
Figure: Reproductive number for influenza, for different ventilation systems and outdoor air
supply rates. The normalized concentration was 1, 0.2, and 0.05 in the cases shown from left to
right [Mor’01].
Mechanical Ventilation – Pressure; Airflow Direction
Influence of Airflow Patterns
Airflow patterns are of great importance indoors, because they determine the path of the
droplet distribution generated from the occupants’ respiratory activities. [Bol’09] Among
the 10 studies considered to be conclusive, five (all occurring in hospitals or pediatric
offices) showed an association between airflow patterns and the spread of diseases,
i.e. [Blo’85] [Gus’82] [Hut’90] [Weh’70], and the study of a SARS outbreak by [Li’05a]
[Won’04] and [Yu’05]. In all five studies, a few secondary cases or even a large number of
cases at a considerable distance away from the index patient were shown to be
infected via an airborne transmission route. As the first conclusive study, [Weh’70] used
smoke tests in a hospital to show the airflow pattern and dispersion of virus-laden aerosols
from the index patient’s room in a three-storey hospital. The smallpox outbreak occurred
in mid- January in Meschede in the former Federal Republic of Germany. The heat emitted
from the radiators used for space heating introduced the upward flows through the
stairwell, as well as above the semi-open windows (for ventilation). Such air currents
carried virus-laden aerosols into other rooms in the upper floors and subsequently
caused infection and disease [Lan’80]. [LiY’07] Eight of the partly conclusive studies also
revealed the probable impact of airflow direction on disease transmission, i.e. [Edl’92]
[Kum’98] [Lec’80] [Li’05b] [Mes’94] [Ols’03] [Rem’85] and [Yu’04]. [LiY’07]
Mechanical Ventilation – Pressure; Airflow Direction
Air Distribution Systems
Two main principles of room air distribution are commonly used in practice: mixing and
displacement ventilation.
Mixing ventilation aims to create a homogeneous environment in the occupied zone.
The clean air is supplied at high velocity to promote mixing with the room air and thus
with the pathogens generated by a sick occupant. In rooms with mixing air distribution the
level of exposure to infected air exhaled from another person is independent of the location
of the person. If one assumes perfect mixing, a reduction of contaminants’ concentration by
a factor requires an increase of the air change rate by the same factor.
Displacement ventilation introduces the clean air at a slightly lower temperature (3–6
0
C lower than room temperature), through floor or wall mounted diffusers. The cold
air, supplied at relatively low velocity, spreads over the floor and moves upwards,
entrained by flows generated from heat sources (people, equipment etc.), and then it is
exhausted close to the ceiling from the better-mixed upper region of the ventilated space.
Under these conditions airborne cross-infection between occupants (who are not too
1
More information upon PV can be found in [Bol’09].
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close to each other) will be low since the warm exhaled air which may carry viruses will rise
upward to the ceiling.
The problem arises in a dynamic environment, i.e. when people move and cough and
the boundary layer around their bodies is disturbed. The airflow pattern is much
dependent on local disturbances because air velocity is quite low (except near the
floor and in thermal plumes generated by people, office equipment etc.). [Den’06] showed
that with mixing ventilation the inlet and outlet positions influence particle deposition, and
have an accumulative effect with that of increased airflow velocity.
Performance of Mixing vs. Displacement Ventilation
[Yan’04] modelled and evaluated the performance of several ventilation methods in pollutant
removal from indoor environments, using experimental data of velocity, temperature, and
tracer gas concentration distributions. Pollutant sources were assumed to be at the floor
level, one with a constant emission rate and the other a fast decaying source (volatile
organic compound emissions from a wood stain). Three ventilation methods, namely
displacement ventilation and two mixing systems using a side grille and ceiling square
diffuser respectively were studied. The mixing ventilation diffusers issue a strong jet that is
able to ‘steer’ air in the entire room, while the displacement diffuser has a weak jet that
produces stratified airflow. When the pollutant sources are distributed on the floor and
not associated with a heat source or initial momentum, displacement ventilation
behaves no worse than perfect mixing ventilation at the breathing zone. Conventional
“mixing” diffusers, on the other hand, could perform better or worse than a perfect
mixing system. [Yan’04]
Comparison of Supply-exhaust Positions vs. Dispersion of Droplet Aerosols
[Wan’05] compared four different types of supply-exhaust positions in regard to
dispersion of droplet aerosols indoors: ceiling (supply and exhaust located in the
ceiling), floor-return (both supply and exhaust placed in the floor), upward (supply in floor,
exhaust in ceiling) and downward (supply in ceiling, exhaust in floor). It was found that the
downward system performed best in controlling the transmission of infection by
exhaled droplets by achieving the best dilution and reducing lateral dispersion
indoors. However, no heat sources were present in the room. The convection flow above
heat sources would definitely influence the airflow interaction in the room and the dispersal
of droplets indoors. A comparison of the performance of three ventilation supply systems
(mixing, displacement and downward air distribution) was carried out in a hospital
environment, to determine which was most capable of protecting patients and health care
workers from cross-infection due to the inhalation of droplet nuclei [Qia’06]. The downward
ventilation performed like the mixing ventilation, due to the counter flow from the free
convection around the human body. So although it is recommended for clean rooms,
infectious wards and operating theatres, downward air distribution may not always
protect people from cross-infection. Displacement ventilation performed worse when the
patient was lying face sideways, because the exhalation jet persisted over a very long
distance, assisted by the thermal stratification. Underfloor ventilation has been shown to
provide air quality similar to that achieved by displacement ventilation when supplied air was
discharged vertically upwards and not horizontally [Cer’06]. The inhaled air quality was
found to deteriorate when increasing the throw of the supply jet from the floor diffuser. The
supply jet promotes mixing close to the floor, which can promote resuspension of particles
(including particles carrying pathogens of respiratory origin) from the floor into the air and up
into the breathing zone.
Dilution could solve to some extend the problem of controlling the level of pathogens
in rooms with total volume ventilation but the limiting factor here would be local
thermal discomfort: both mixing and displacement ventilation can cause draught
problems. Another issue could be the low cost effectiveness of this approach, due to
increased energy use and increased initial costs (bigger ducts, more powerful fans,
over-sizing of the HVAC unit etc.). In densely occupied spaces, like theatres, aircraft or
vehicle cabins, etc., dilution does help but the risk of transmission of diseases by contact
and by droplet transmission, remains high due to proximity of people. [Bol’09]
Mechanical Ventilation – Distance of Aerosols Travelled
In all five studies analyzed by [LiY’07], the considerable distance travelled by the virus- or
bacteria-laden aerosols seemed to be related to building design. In the Meschede smallpox
outbreak [Weh’70], the heating radiator in the index patient’s room introduced the upward
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plume flow through its semi-open window. For the TB outbreak from a draining abscess
[Hut’90], the measles outbreak in a pediatric office [Blo’85] and the nosocomial varicella
outbreak [Gus’82], the index patients rooms were all in positive pressure, which
caused the virus to spread into either corridors or other rooms. It is also noted that in
the nosocomial SARS outbreak [Li’05a], the index patient’s cubicle had an
inoperative return air outlet, which enhanced the spread of aerosols into three other
cubicles in the same hospital ward. [LiY’07] The studies by [Mes’94] and [Yu’04] are
striking, as they showed how the virus-laden aerosols could spread a few kilometres
in a city or between buildings that are 60m apart, due to wind flows. [LiY’07]
3.9
RH and temperature vs. survival of pathogens in air
The conditions of temperature and humidity can inhibit or promote the growth of
bacteria and activate or deactivate viruses. Some bacteria such as Legionella
pneumophila are basically waterborne and survive more readily in a humid environment.
Codes and guidelines specify temperature and humidity range criteria in some hospital
areas as a measure for infection control as well as comfort. [ASH’07]
The chance of mice acquiring airborne influenza infection was found to be inversely related
to ventilation rate. High relative humidity was also shown to be effective in decreasing
the infection rate [Sch’62]. [LiY’07]
So far, knowledge on the influence of relative humidity on pathogenic bacteria is scarce and
the little data available is for opportunistic representatives. In general, mid-range humidity
conditions (40–60%) have been shown to be more lethal to non-pathogenic bacteria
[Hat’69]. Viruses with more lipids tend to be more persistent at lower relative humidity,
while viruses with less or no lipid content are more stable at higher relative humidity
[Ass’00]. [Loo’43] showed that humidity levels of 80–90% for 30 min could render the
influenza virus non infectious to mice, while exposure to lower humidity levels (17–
24%) provided the greatest infectivity. The transmission route was airborne and highly
efficient at low RH (20% or 35%), and less effective at 65%. At low RH droplets
evaporate faster, shrink and change their size, increasing the possibility of being inhaled
if their diameter is less than 10 mm. In other studies the survival of some viruses has been
shown to be independent of relative humidity [Ela’79]. [Har’61] and [Mil’67] showed that
picorna viruses and adenoviruses, respiratory disease causatives and members of non
enveloped virus groups, survive better at high relative humidity. Measles and influenza,
both enveloped viruses, survive best in aerosols at low relative humidity [Jon’64]
[Hem’60]. Studies also report that the effects of relative humidity on virus survival can
0
be influenced either positively or negatively by temperature. At 20 C human corona
virus (upper respiratory tract diseases) was reported to be most stable at intermediate
humidity, but was also relatively stable at low humidity [Ija’85]. The same study also
0
found that virus survival at 6 C and 80% humidity was very similar to the best survival
at intermediate humidity. Lower temperatures have also been shown to enhance
rhinovirus survival at high relative humidities [Kar’85]. [Low’07] reported that influenza
o
virus transmission is inversely proportional to the temperature. At 5 C, the
o
o
transmission of influenza A virus was more effective compared to 20 C or 30 C.
[Bol’09]
3.10
Air Disinfection Techniques vs. survival of pathogens in air
Great effort has been made to find engineering techniques to keep airborne pathogens
away from occupants in buildings, or at levels low enough to be unable to cause a disease:
dilution, filtration, Ultra Violet Germicidal Irradiation (UVGI), etc. The airborne pathogens
might originate from a sick person, from the building itself (infected/polluted HVAC system,
infected building materials etc.) or from an intentional release, i.e. a terrorist attack [LaF’84]
[Kow’03]. [Bol’09] There are 3 basic engineering control measures which may be
employed to reduce the risk of transmission of M. tuberculosis and other airborne
nosocomial pathogens in health care facilities:
1. the use of HEPA filters which are 99.9% efficient for particles 0.3 micrometer
in diameter, which may be mounted either in ductwork systems or within room
spaces, to prevent ingress of airborne pathogens;
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2. and the use of WGI lamps which emit short-wave W radiation in the W-C
range (i.e., 253.7 mn), and which may be mounted either in ductwork systems or
within room spaces, to disinfect airborne pathogens;
3
3. the use of mechanical ventilation techniques to dilute or remove pathogenic
microorganisms present in room air.
In the developed world, health care authorities have tended to focus on the use of advanced
mechanical ventilation systems and HEPA filters as the best means of preventing airborne
nosocomial infections. By comparison the use of WGI has been neglected, primarily
because of the lack of fundamental research that exists relating to disinfection rates and the
practical application of WGI [Nar’97]. However, neither improved mechanical ventilation
techniques, nor the use of HEPA filters, are always effective at controlling airborne
pathogens. These devices can also be expensive to install, difficult to retrofit to
existing installations, and can result in greatly increased running costs [Nar’95]
[Nar’97]. Conversely, through using WGI lamps it is possible to provide a similar
degree of pathogen disinfection in hospital buildings as that achieved by high
ventilation rates, but at a fraction of the capital and operating costs [Nar’97]. In the
developing world where the TB problem is the greatest, health care authorities often do not
have the financial and human resources to construct, operate and maintain expensive
mechanical ventilation systems. In these countries WGI offers the greatest potential, since
large ‘equivalent ventilation rates’ can be easily achieved through the strategic use of fairly
modest W lamp fittings [Ril’76].
Filtration
A method widely used today is the filtration of air in HVAC systems. Classifications and
guidelines exist for applying filtration as part of the ventilation system. They are widely used
by designers [ASH’99] [ISO-14644-1]. Studies show that filtration is a good method to
prevent outside pathogens from penetrating the building envelope through the mechanical
ventilation. [Kow’98] [Kow’02] showed that 80% and 90% filters can produce air quality
improvements that approach those achieved with HEPA filters, but at much lower
cost. Another finding is that microorganisms capable of penetrating HEPA filters are
predominantly nosocomial infections (HEPA filters remove 99.97% of all particles 0.3
mm or larger in diameter). Enzyme filters eradicate microbes by attacking the microbial
cell membrane, but this assumes that they come into close contact with the microbes.
[Yam’06] studied the performance of such an enzyme filter. They used two filters: with and
without enzymes, and found out that the performance of the enzyme filter did not differ
much from that of a control filter, due to adhesion of particles over time on the filter
surface, preventing close contact between the enzymes and any microbes retained by the
filter. [Bol’09]
UltraViolet Germicidal Irradiation (UVGI)
To avoid some of the associated problems of increased dilution, UVGI technology could be
used instead. UVGI light is emitted at wavelength of 253.7 nm by low-pressure
mercury vapour arc lamps. UVGI damages the DNA/RNA of pathogens and makes
them harmless: they cannot reproduce once they have entered their host. Laboratory
research has shown that the germicidal effect of UVGI is primarily a function of two factors:
the intensity of the UVGI energy and the duration of exposure [Luc’46] [Ril’76] [Cha’85]
[KoG’02]. There are two ways to use UVGI application in practice: ceiling/wall mounted or
in-duct application. Disinfection of air by ceiling/wall mounted UVGI started in the 30 s in
USA [Wel’36] [Wel’55]. The inactivation process occurs when the pathogens enter the UVGI
zone: 1.8 m above the floor (the height above which UVGI systems should be installed to
avoid any health risks for occupants). The inactivation rate of UVGI in rooms could be
enhanced by increasing the intensity of light, by promoting better mixing in rooms, or by
generating an upward flow to facilitate the upward transport of pathogens [Ril’55] [Ril’71]
[Ril’71]. Another important factor for UVGI efficiency is the level of relative humidity.
Studies [Pec’01] [XuP’05] show that with increased humidity in the environment the
pathogens are more likely to survive the germicidal effect of the UVGI lamp. [XuP’05]
evaluated the impact of room ventilation rates, UV effluence rates and distribution, airflow
patterns, relative humidity, and photo reactivation on the effectiveness of UVGI systems.
They suggested that in order to obtain maximum benefit from a ceiling/wall mounted UVGI
2
3
For more information on this subject, see [Beg’99]
Explained further in the following section
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3
system, an adequate level of UV radiation of at least 6W of UV-C per m in the upper
zone should be provided. Moreover, the UV radiation should be evenly distributed and
good room air mixing should be provided. Room relative humidity should be kept
around 50%. Values above 75% significantly reduce UVGI performance: the
effectiveness is reduced by more than 40%. UVGI lights are therefore mounted in deep
louver enclosures to prevent overexposure at eye level or excessive reflection from ceilings,
but such casings absorb a large amount of the useful UV energy, making the unit less
efficient. Guidelines for upper-room UVGI application are available [Fir’99a] [Fir’99b].
[Bol’09]
Mounted at the ceiling level, a UVGI unit with louvers would work quite well with
mixing ventilation. The enhanced air mixing would transport any pathogens more rapidly
to the upper part of the room, where they would be inactivated, but this approach would
clearly be less effective when applied to displacement ventilation. Once pathogens had
been transported by the warm convection flow around humans, they would be exhausted
close to the ceiling. This would be the case when the gravity forces acting on the droplets
are small compared to the velocity of the free convection flow, or they would leave the jet
and be deposited in the room. The appropriate UVGI technology here is in-duct
installation, provided recirculation is available. This approach is therefore useful for
large halls with displacement ventilation, where people spent most of the time seated:
theatres, concert halls, offices, etc. [But’48] [Men’03]. Filtration could also be used to control
the pathogen levels in such buildings. However filters are not efficient in protecting
occupants if pathogens are generated inside the occupied space. In duct installation they
are effective at removing the microorganisms or toxins present in the outside air.
Sometimes filters themselves can become a source of bacterial growth and thus contribute
to high pathogen levels in the respirable range: less than 1.1 mm, especially at elevated
humidity, higher than 80% RH [Mor’01]. PCO may generate by-products which can reduce
perceived indoor air quality or in themselves are hazardous. In rooms with mixing ventilation
an alternative solution can be the usage of chilled-beams or convectors, recirculating part of
the room air through a heat exchanger and a local HEPA filter or a UVGI unit. [Bol’09]
Use of UV-light to prevent TB
The prevalence of tuberculosis (TB) worldwide is very high and in many parts of the world
has reached epidemic proportions. About one-third of the global population is estimated to
be infected with Mycobacterium tuberculosis [Mil’96], and in countries such as India this
figure rises to 50% of the adult population [WHO’97].
In addition, the efficacy of the only currently available TB vaccine, BCG, remains the subject
of debate but is accepted to have no protective effects in adults [Chi’99] and is of only
limited use in preventing extrapulmonary forms of TB (e.g., meningitis) in children [Por’94].
This suggests that the use of drug therapies and vaccination alone is not enough to solve
the global TB problem. Prevention using public health engineering techniques may provide
a complementary solution. There are a number of engineering control strategies, such as
the use of ultraviolet germicidal irradiation (UVGI) and advanced ventilation techniques,
which can be used to combat the spread of M. tuberculosis and other airborne pathogens.
Droplet nuclei are formed by the evaporation of droplets produced when an infected patient
coughs. The droplet nuclei are typically 1- 5 lt.rn in size, settle slowly and remain suspended
in air for long periods. These droplet nuclei are so small that they by-pass the innate host
defense mechanisms of the upper respiratory tract and are deposited in the alveoli in the
lungs.
Individuals who become infected with M. tuberculosis have an approximate 10% lifetime
risk of developing post-primary infection [Mil’96]. Because droplet nuclei can remain
suspended in air for several hours, they can travel over long distances and thus can
be distributed widely throughout hospital buildings. The chain of infection is therefore
very much influenced by the ventilation conditions that are experienced in any particular
clinical setting. In addition to TB, many nosocomial infections of a bacterial, fungal or viral
aetiology are transmitted via an airborne route. These include pathogens such as
Acinetobacter spp., Aspergius spp. and varicella-zoster virus. The airborne ‘link’ in the
‘chain of infection’ associated with these diseases and infections is the weakest link, and the
one which gives health care authorities the best opportunity to break the chain. It has been
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demonstrated [Ril’57] [Mil’96] that through the use of engineering measures including
increased mechanical ventilation-rates, negatively pressurized rooms, high-efficiency
particulate air (HEPA) filters, and UVGi lamps, it is possible to control airborne pathogen
levels in hospital buildings. [Beg’99]
Photocatalytic oxidation
Photocatalytic oxidation (PCO) could be achieved by either using fluorescent or UV light.
PCO is an emerging technology in the HVAC industry, especially in purging airborne
bacteria, which is performed by utilizing short-wave ultraviolet light (UVC). The results are
somewhat encouraging, since some pathogens are readily destroyed after treatment with a
TiO2 coated PCO unit [Kri’05] [Pal’07]. However only small portion of the pathogens will be
absorbed on the catalyst and chemically attacked from a single pass system. More info
[Bol’09].
Other cleaning methods like Desiccant rotor, Plasmacluster ions, essential oils and
nanotechnology are described in [Bol’09].
Prevention
The chain of transmission can be broken by isolating patients with active disease and
starting effective anti-tuberculous therapy. After two weeks of such treatment, people
with non-resistant active TB generally cease to be contagious. If someone does become
infected, then it will take at least 21 days, or three to four weeks, before the newly infected
person can transmit the disease to others [wiki TB]
Procedure
Contact Precautions which include:
1.Single Rooms
Monitor alarms are very difficult to hear through
these doors. Therefore:
•
Ensure close supervision of patients at all
times
•
Use remote watch facilities on monitors if
one to one nursing is not required.
•
Open blinds on the windows for easier
viewing, when possible.
Rationale
MRSA positive patients should be nursed in
Rooms 5,6,8, or 9 in ICU 1 only. These rooms
have negative pressure ventilation, thus
reducing the spread to other patients. No MRSA
patients are to be nursed in ICU 2. This allows
the care of vascular patients away from the
MRSA patients.
2.Plastic Aprons
These are to be worn by anyone entering the
room, with the exception of the patient’s visitors.,
and disposed of prior to leaving. These visitors
are, however, not permitted to visit any other
patients in the unit.
This prevents the transmission of MRSA on the
health care workers clothing to other areas of
the unit. In emergency situations, when staff
members clothing may have become
contaminated, the staff member is required to
wear a clean white gown over their
uniform/clothing for the remainder of the shift,
plus the plastic apron.
3. Gloves and Masks
These need to only be worn when in contact with
blood, body substances or mucous membranes.
Staff who are assisting with a MRSA patient then
leaving to care for other patients
(eg.Wardspersons), are required to wear gloves.
Gloves will provide a barrier to the transmission
of MRSA to other patients.
4. Strict Handwashing
Before and after ALL contact.
Tricolsan skin cleanser (Green) before entering
and upon leaving an MRSA room.
Chlorhexidine hand lotion (pink) in-between
interventions on the same patient to prevent
systemic spread from relatively benign nose,
throat or groin colonies.
The main mode of transmission of MRSA is via
health care workers.
Linen skips and rubbish bins are to be kept
within the room, but disposed of as normal.
Charts are often taken around the unit to the
medication room, pharmacy, and staff work
station. So it is important they are contaminated
with MRSA.
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Movement by staff in and out of MRSA rooms
should be kept to a minimum.
To aid this:
• Schedule multiple cares to be
delivered at one time.
• Assemble equipment carefully before
entering rooms.
This is also to reduce the transmission of MRSA
to other areas in the unit.
Items taken into the MRSA room are, wherever
practical, are to remain within the room for the
duration of the patients stay.
• Therefore, Stock in the room must be
kept to an absolute minimum.
• Stock within the room should be
checked at the commencement of each shift to
prevent doubling up.
• Bowls for these patients should be
kept in their rooms and washed with triclosan
between uses.
Medications, dressings and other medical
supplies are very expensive, so it is important to
limit the amount of stock in the room as it will all
be disposed of when the patient is transferred
from Intensive Care.
Should it be necessary for MRSA patients to use
a bathroom/toilet other than their own ensuites,
the area needs to be terminally cleaned.
These are bathrooms are used by other
patients which are not MRSA positive.
All departments that may be involved with the
care of the patient, such as X-ray, endoscopy,
and dietetics need to be made aware of their
status so that appropriate precautions can be
taken.
These health care workers also have contact
with many patients throughout the hospital.
Precautions need to be taken to also reduce
transmission of MRSA.
Cleaning of surfaces within the rooms should be
done daily by the additional cleaning teams.
Additional cleaners maintain curtains and
surfaces in the room to minimize build up of
dust and MRSA.
Screening for MRSA in patients already declared
positive is not necessary, as the patient will be
treated as being MRSA positive for the whole of
their admission regardless of subsequent
negative swabs.
MRSA can remain present for many years in
patients. The Infection Control CNC is to be
contacted re clearance of MRSA.
Psychological impact of these precautions on
patients should be minimized.
• Encourage visitors by not overstating
the risks to them.
• Although contact precautions are to be
used, ensure that quality interaction with the
patient occurs.
• Provide diversions, such as TV or
radio (with personal earphones) where
appropriate.
Some patients may become very distressed
with the door closed in a
isolation room. It is necessary for the door to
remain closed as much as possible to maintain
the negative pressure ventilation.
MRSA positive patients from ICU will
need a single room on the ward to facilitate the
ongoing application of contact precautions.
All stock that remains in the room
after the patient has been discharged is to be
discarded. This includes medications, rolls of
tape, dressing requirements, ECG dots, alcho
wipes. This means that stock in the rooms is to
be kept to an absolute minimum.
Laerdal bags and anything else that
can be re-sterilised should be sent to CSSD
Contact the Additional Cleaning
Team to terminally clean the room. Terminal
cleaning covers the bed, walls floor and curtains.
The same precautions apply on the wards as in
Intensive Care.
Medications and dressings can be very
expensive. So if stock is kept at a minimum,
then wastage costs are also minimized.
Re-sterilising removes the MRSA for future use.
The nursing staff is required to clean the
equipment in the room, including the ventilator,
monitor leads, pumps..
[McL’05]
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3.11
Single Occupancy Rooms vs. survival of pathogens in air
On-site testing in hospitals of UV devices which aim to deactivate airborne pathogens has
provided evidence on the importance of single occupancy rooms. Single occupancy rooms
can create physical barriers to reduce the airborne transmission of infections. Research into
the transport, removal, and deactivation of airborne pathogens in hospitals complements the
design of healthcare facilities by accommodating engineering interventions such as UV,
ventilation design, and single occupancy rooms. [Rob]
[Ned]
Reducing Multiroute Transmission by Means of Single-Bed Rooms and Increased
Isolation
Thus far the three routes of infection transmission have been examined and discussed
separately. In reality, these three routes often intertwine, and environmental approaches
may influence more than one transmission route. This research team has found credible
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evidence for the multi-route impact of single-bed rooms and increased isolation in infection
control. Therefore, we have opted to present this information in a separate section instead
of within the previous sections addressing individual transmission routes. Several literature
review articles have supported the association between single-bed rooms and reduced
infection rates, including [Det’04] review on the relationship between architectural design
and nosocomial infections and [Cha’05] on the advantages and disadvantages of singleversus multi-bed accommodations. Also, [Cal’07] surveyed research on nosocomial
infections in nursing homes and similarly concluded that private bedrooms reduce the risk of
infection as compared to shared bedrooms. The present review conducted a broader,
updated survey and analysis, and evaluated not only environment-infection associations,
but also the underlying mechanisms that could plausibly account for these associations.
Effect of single-bed rooms in reducing airborne infection. Because infected patients
carry airborne pathogens into patient rooms and nursing units, it is important to ensure
sufficient isolation capacity for such patients to prevent the spread of pathogens. Providing
single-bed rooms increases isolation capacity; facilitates filtration, ventilation, and airflow
control (e.g., negative room pressurization); and by these well-established measures or
mechanisms, it plays a key role in preventing a patient with an aerial spread infection from
infecting others and protects immune-compromised patients in nearby rooms from airborne
pathogens. As might be expected, studies of cross infection for contagious airborne
diseases (such as influenza, TB, measles, and chickenpox) have revealed that placing
patients in single rooms [Ben’02], single-bed cubicles with partitions [Gar’73], isolation
rooms [Mul’97], or rooms with fewer beds and more space between patients [McK’76] is
safer than housing them in multi-bed spaces with more patients. [Von’05] reviewed literature
on the isolation of cystic fibrosis patients, for whom respiratory tract infections contributed
markedly to morbidity and mortality. They found in 31 out of 39 studies that cross-infection
of Pseudomonas aeruginosa had been halted by isolating patients. Research on burn
patients and other vulnerable or immune-suppressed patient groups provides strong
evidence that single rooms in combination with air filtration substantially reduce the
incidence of infection and mortality [McM’94] [Pas’98] [Shi’86]. In a study of nursing homes,
[Dri’03] found that roommates of persons infected with influenza had a 3.07 higher relative
risk of acquiring the illness than did individuals assigned to single-bed rooms. Although
MRSA is spread mainly by contact, it has been known for decades that patients with
Staphylococcus aureus infections shed skin scales contaminated with the pathogen, which
become suspended throughout the air in rooms and which can spread the infection to other
patients sharing that space. [Lid’70] documented a significantly reduced rate of nasal
acquisition of Staphylococcus aureus for patients in single-bed rooms than for those in
multi-bed rooms. [Shi’02] found that in rooms with a MRSA patient, the air concentration of
MRSA-contaminated skin scales reached 116 per cubic foot, representing an added risk of
airborne transmission to uninfected patients. The SARS outbreaks in Asia and Canada
highlighted dramatically the failings of multi-bed rooms for controlling or preventing
infections among both patients and healthcare workers. SARS is transmitted by droplets
that can be airborne over a limited area. The point should be emphasized that SARS in
Canada was predominantly a hospital-acquired—not a community-acquired—infection,
because approximately 75% of SARS cases resulted from exposure in hospital settings
[Far’03]. In Canadian and Asian hospitals, the pervasiveness of multi-bed spaces in
emergency departments (EDs) and ICUs worsened SARS cross-infection. Furthermore, the
scarcity of isolation rooms with negative pressure was a serious obstacle to implementing
effective treatment and control measures. Toronto hospitals were forced, on a crisis basis,
to construct hard wall partitions with doors to replace curtain partitions between beds in
multi-bed spaces, and to implement airflow and pressure adaptations in EDs and ICUs to
create many additional negative-pressure isolation rooms with HEPA filtration [Far’03].
[Zim’08]
Effect of single-bed rooms in reducing contact transmission. The use of single-bed
rooms instead of multi-bed rooms also helps to control infections spread by contact. Singlebed rooms can facilitate cleaning and decontamination. As discussed earlier, many surfaces
and features near infected patients quickly become contaminated, creating numerous
reservoirs that can transfer pathogens to patients and staff. Given the vital importance of
cleaning for the removal of contamination, one advantage of single-bed rooms compared to
multi-bed rooms is that they are easier to clean and decontaminate thoroughly after a
patient is discharged. In certain countries, when a patient has been discharged from a multibed room, cleaning staff are not permitted to clean electrical equipment or anything
attached to other patients remaining in the space, thus increasing the risk of cross-infection
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[Ulr’06]. Scrupulous cleaning of double rooms, or the four-bed and six-bed spaces prevalent
in many countries, often entails the disruptive and costly temporary removal of all patients
from these rooms. In addition, as mentioned in an earlier section, even when conventional
cleaning methods are used according to prescribed protocols or the manufacturers'
instructions, extensive contamination by pathogens such as MRSA still remains on surfaces
[Fre’04] [Jea’05]. If more effective cleaning techniques such as HPV are used, multi-bed
rooms present additional challenges because all patients in the room must be transferred to
other spaces during the vaporization treatment. Single-patient rooms may also help to
improve hand-washing compliance and thereby contribute to infection control. Some studies
offer evidence that when all single-bed rooms are furnished with a conveniently located sink
in each, the nosocomial infection rates in ICUs and burn units diminish, as compared to
when the same staff and comparable patients are in multi-bed open units with few sinks
[Gol’81] [McM’94] [McM’85] [Mul’97]. Although these studies did not measure hand-washing
frequency, the investigators posited that increased hand washing was an important factor in
reducing infections in the units with single-patient rooms and more sinks. In several studies
documenting the positive association between single-bed rooms and reduced infection
rates, the reduction in contact transmission (such as via reduced contamination of surfaces)
was not directly measured, but it might have played an important role, based on previous
knowledge. For example, MRSA is spread mainly by contact. Single-bed rooms appeared to
reduce or prevent MRSA infections compared to multi-bed rooms in various healthcare
settings, including 212 ICUs across Germany [Gas’04], 173 hospitals across Europe
[Mac’07], a U.K. hospital with 1,100 beds [Wig’06], and a NICU in the United States [Jer’96].
Also, having a roommate has been identified as a risk factor for nosocomial diarrhea and
gastroenteritis [Cha’00] [Peg’93]. [Ben’02] found that nosocomial infection frequency was
much Health Environments Research & Design, 1(3), 2008 lower in a single-bed pediatric
intensive care unit (PICU) than in a unit with multi-bed rooms and comparable patients, and
they tentatively concluded that single-bed rooms helped to limit the person-to-person spread
of pathogens among patients. Although the pattern of results across studies on balance
strongly suggests that single rooms reduce infection, [Pre’81] finding is anomalous in that it
found single-bed ICU isolation rooms were associated with only a slight, insignificant
reduction in infection rates compared to multi-bed rooms. Several deadly outbreaks of C.
difficile in North American and European hospitals and thorough published investigations
have underscored powerfully the threat to patient safety posed by multi-bed rooms. A highly
virulent infection characterized by diarrhea and colitis, in several countries C. difficile causes
more deaths than MRSA. The infection is spread mainly by contact, and C. difficile spores
can be viable for months on environmental surfaces [Kra’06]. Two outbreaks in the United
Kingdom at two National Health Service hospitals have caused approximately 40 deaths
(Healthcare Commission, 2006) and 90 deaths (Healthcare Commission, 2007),
respectively. The investigations in these hospitals identified a predominance of multibed
rooms with shared toilets, and a scarcity of single rooms with private toilets as key factors
that prevented the timely isolation of patients and contributed to the spread of C. difficile and
the duration and high mortality of these outbreaks (Healthcare Commission, 2006, 2007).
Another study has also reported that single-bed isolation helped prevent the spread of C.
difficile [Mal’83]. [Zim’08]
Single rooms, admission, and proactive separation of patients. Providing a high
proportion of single rooms in hospitals conveys a major safety advantage, because it
enables separation of patients upon admission and makes it possible to prevent cross
infection from unrecognized carriers of pathogens [Ulr’06]. Even if patients are screened for
MRSA, C. difficile, or other pathogens immediately upon admission, processing test results
often requires two or three days, during which time environmental surfaces in the rooms of
infected patients quickly become extensively contaminated, creating pathogen reservoirs
that will be touched by staff and possibly by patients (e.g. [Fre’04]). Accordingly, assigning
an unidentified carrier initially to a multi-bed room heightens the risk of cross-infection. By
the time test results revealing that the patient is colonized or infected are available, it may
be too late to isolate the individual, because transmission to one or more roommates may
already have occurred. A prospective study by [Cep’05] screened patients for MRSA when
they were admitted and placed in multi-bed rooms in the ICUs of two London hospitals.
Patients who proved to be MRSA-positive (after a 3-day delay for testing) were assigned
either to be moved into isolation or to remain in their multi-bed rooms. Findings indicated
that moving patients to single-bed rooms after testing positive for MRSA did not reduce
cross-infection to other patients [Cep’05], supporting the interpretation that the
contamination of surfaces and/or the spread of the infection to roommates occurred in the
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period prior to isolation. Single-bed rooms may also help manage the growing problem of
community-acquired infection. MRSA and other serious multidrug resistant infections are no
longer confined to healthcare settings, but are increasingly widespread and endemic in
communities internationally. According to a study by the U.S. CDC, 13.7% of MRSA
infections in 2005 originated in the community [Kle’07b]. Another 58.4% of MRSA infections
in the United States were community-onset, or manifested themselves outside the hospital,
but had a healthcare link, such as a patient history of surgery, hospitalization, or residence
in a long-term care facility. Hospital-onset MRSA infections accounted for only 26.6% of the
cases. These findings imply that mounting numbers of people admitted to the hospital as
inpatients, or who visit EDs or ambulatory clinics for care, will be carriers of serious
community-acquired or community-onset infections. The difficult and escalating infection
control challenge for hospitals that is posed by community-acquired and community-onset
infections is reflected, for example, in the fact that MRSA has become the most common
cause of skin and soft-tissue infections among patients presenting to EDs in U.S. cities
[Mor’06]. Furthermore, the growing trend toward the spread of antibiotic-resistant pathogens
in communities will inevitably continue as sicker, more vulnerable patients are cared for at
home or in longterm care facilities, and as they receive frequent and prolonged courses of
antibiotics [Ulr’06]. Against this background, in the future hospitals may need to screen and
assign all inpatients to single rooms upon admission to prevent infections from spreading to
other patients. Apart from MRSA, the spread of infections such as C. difficile in communities
implies that single rooms with toilets and good air quality will increasingly be needed in EDs
and outpatient surgery clinics as well as in inpatient units. [Zim’08]
3.12
Materials vs. survival of pathogens in air
Another factor that could play a key role in degrading indoor environments is that many
buildings contain synthetic interior materials and furnishings from walls to carpets to air
conditioning systems, which all can emit a wide variety of pollutants such as the volatile
organic compounds (VOCs) [Bro’94].
3.13
Natural Ventilation vs. survival of pathogens in air
3.13.1 Advantages of Natural Ventilation
Ventilation is a central component of good hospital design. The Victorians knew this and
placed great importance on generous ventilation provision as the basis of a beneficial
therapeutic environment. Modern designers also use ventilation to control the spread of
infection by ‘‘negatively pressurizing’’ high risk zones. Ventilation can be provided by
mechanical systems (fans and ducts) and/or by natural ventilation (using wind and
buoyancy forces to drive air through windows or ventilation ‘‘chimneys’’). Mechanical
ventilation has become popular, as it enables ventilation rates to be closely controlled and
makes deeper floor plates and ‘‘sealed façades’’ viable. It does this however at the expense
of increased carbon emissions. Natural ventilation avoids these ‘‘needless’’ carbon
emissions and has a number of other benefits, including:
• Reduced likelihood mechanical cooling will be needed, because higher ventilation
rates are typically achievable and ‘‘heat pick up’’ in ducts is avoided, to reduce
carbon emissions further
• Research has found that the higher air-change rates provided by natural ventilation
also reduce the buildup of pathogens that cause hospital acquired infections
• Operable windows enhance the amenity of spaces and create a less ‘‘institutional’’
feel
• Capital and maintenance costs are reduced and less space is required for ductwork
and air handling and cooling plant In order to promote the use of natural ventilation
in hospitals and clinics and exploit these benefits, we have carried out extensive
research into the feasibility of natural ventilation as an alternative to mechanical
systems in a variety of settings. Arup studies have explored the synergies between
natural ventilation and building form and daylight, our particular focus is on
exploring the limits of natural ventilation to provide passive cooling in different
climates around the world, when used in conjunction with shade and thermal mass.
On the basis of these studies we believe natural ventilation provides a viable and
beneficial approach in all areas where close control of ventilation and temperature
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are not essential for clinical reasons; this includes the majority of in-patient are
areas and out-patient clinics.
[Cap]
Natural ventilation – The cost benefit
• Reduction in height of building hence structural frame and façade saving.
• Reduction in quantity of suspended ceilings
• Reduced mechanical and electrical systems
• Reduction in installation time on site
• Reduction in commissioning time required
• Reduction in energy use
• Reduction in carbon emissions
• Reduced engineering and ceiling system replacement costs
[Arup, Innovative Design in Healthcare.ppt]
3.13.2 HTM 2025 – Ventilation in Healthcare Premises Design Considerations
The following are textual extracts from HTM 2025 that refer to the requirement for
ventilation, with a statement on the ability of Natural ventilation added by Arup (Barry
Walker).
HTM 2025 – Design Considerations
Para 2.1 Ventilation is essential in all occupied premises. This may be provided
by either natural or mechanical means. The following factors determine the
ventilation requirements of a department or area:
•
human habitation (fresh air requirements);
Statement : Taken from the CIBSE guidance 8-15 litres/person/second. Agreed Value 8
litres/second/person
•
•
•
the activities of the department, that is, extraction of odours, aerosols, gases,
vapours, fumes and dust — some of which may be toxic, infectious, corrosive,
flammable, or otherwise hazardous (see Control of Substances Hazardous to
Health (COSHH) regulations);
dilute and control airborne pathogenic material;
thermal comfort; -
Statement : - calculation of Summertime Temperatures agreed as being one of the criteria
by which the effectiveness of the ventilation system should be measured.
•
•
the removal of heat generated by equipment (for example in catering. wash-up and
sterilizing areas and in some laboratory areas);
the reduction of the effects of solar heat gains;
Statement :- This is related to the calculation of the internal temperature and is intrinsic to
the calculation. Capita have confirmed that they have not allowed for this in their initial
calculations.
•
•
•
the reduction of excessive moisture levels to prevent condensation (for example
Hydrotherapy pools);
combustion requirements for fuel burning appliances (see BS5376, BS5410 and
BS5440);
"make-up supply air" where local exhaust ventilation (LEV) etc is installed.
Para 2.2 Mechanical ventilation systems are expensive in terms of capital and running
costs, and planning solutions should be sought which take advantage of natural ventilation.
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Para 2.3 It is acknowledged that planning constraints imposed by the building shape and/or
functional relationships of specific areas will invariably result in some measure of deep
planning thus minimising the opportunity for natural ventilation.
However, ventilation costs can be minimised by ensuring that wherever practicable, core
areas are reserved for rooms that require mechanical ventilation irrespective of their internal
or peripheral location. Examples are sanitary facilities, dirty utilities and those rooms where
clinical or functional requirements have specific environmental needs; and where for
reasons of privacy, absence of solar gain etc, windowless accommodation is acceptable.
Other spaces appropriate to core areas are those which have only transient occupation and
therefore require little or no mechanical ventilation, for example circulation and storage
areas.
Natural ventilation
Para 2.4 Natural ventilation is usually created by the effects of wind pressure. It will also
occur to some extent if there is a temperature difference between the inside and the
outside of the building. The thermo-convective effect frequently predominates when the
wind speed is low and will be enhanced if there is a difference in height between inlet and
outlet openings. Ventilation induced by wind pressures can induce high air change rates
through a building, provided air is allowed to move freely within the space from the
windward to the leeward side.
Statement :- Capita have single sided ventilation but do not have high level and low level
openings as part of their ventilation strategy.
Para 2.5 As the motivating influences of natural ventilation are variable, it is almost
impossible to maintain consistent flow rates and thereby ensure that minimum
ventilation rates will be achieved at all times. This variability normally is acceptable for
general areas including office accommodation, general wards, staff rooms,
library/seminar rooms, dining rooms and similar areas, which should be naturally
ventilated, that is, provided with opening windows.
2.6 In all cases, however, heat gain or external noise may preclude natural ventilation.
Summertime Temperature Calculations
Para 2.13 Summertime temperature calculations using the method mentioned in paragraph
3.40, should be completed for all areas where there is a risk of excessive temperatures.
“3.40 The calculation method for determining the summertime temperature is described in
section A8 of the CIBSE guide; however, it is very important to select the time of day and
time of year of peak loadings for the calculations, which is dependent upon the orientation
and proportion of solar to total heat gain.”
3.41 Where calculations indicate that internal temperatures frequently exceed external
shade temperatures by more than 3 K, methods of reducing temperature rise should be
investigated. Options include increasing ventilation rates, reducing gains, or providing
mechanical cooling.
Generally, air cooling should be provided where these calculations show that, without
excessive levels of ventilation, internal temperatures are likely to rise more than about 3 K
above external shade temperatures. In these circumstances, cooling should commence
when the space temperature reaches 25°C.
Statement: There is no reference to Maximum external shade temperatures in the statement
above. Arup’s understanding of this statement is that it is best to use natural ventilation first,
but due to the internal temperatures when compared with the external shaded temperatures
are in excess of 3K then recommend use of mechanical ventilation. If this results in high air
flows being required then use cooling but arrange the setpoint for the start of cooling
when the room temperature is above 25°C.
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2.14 Refrigeration plant should be of sufficient capacity to offset heat gains and maintain
areas at a temperature that does not exceed external shade temperatures by more than
about 3 K.
Arups Statement on the use of Natural Ventilation
Although the effects of natural ventilation are not consistent it is possible to limit the affect of
this fluctuation through the careful design of natural ventilation systems and in particular the
design of the windows and their method of opening in order to provide the best possible
opportunity for the natural ventilation system to work.
These factors include (amongst others):
• Cross flow ventilation used where possible to take advantage of both wind and
stack effects
• Where only single sided ventilation is possible then using a single opening at low
level may not provide the required number of air changes for dealing with heat
gains, fresh air requirements and dilution of odours etc.
• For single sided ventilation then there should be a low level opening and a high
level opening ideally approx 1 metre apart. This is achieved in its simplest form by a
centre pivoted window which is restricted to an opening of 100 mm. The windows at
QEH are top hung and provide one opening at low level. Studies have shown (and
can be demonstrated in the empirical evidence we have) this severely reduces the
effectiveness of natural ventilation. This has been modelled by Arup.
• Arup have designed natural, single sided ventilation systems which have
demonstrated compliance with the 3K temperature difference of internal
temperature and coincident external shaded temperature and can be proven
through computer modelling Thermal and CFD. The designs are not revolutionary
and incorporate the same basic design considerations as is well understood when
designing systems of this type.
The measurement system of coincident internal and external temperatures that was
proposed and has been subsequently withdrawn can be achieved by the correct design of
natural ventilation systems. In the case of the design at QEH we do not believe that Capita
considered the influence the design of the opening windows will have on performance, even
though it is an essential part of the ventilation system. The restrictions applied to the
opening of the windows above 100mm for safety purposes is well known and accepted
and this restriction should have been taken into consideration during the design.
The decision to use mechanical ventilation (from the HTM) is based upon the fact that
calculations of heat gain show that natural ventilation will not contain the internal and
external temperatures within 3K. There does not seem to have been any significant attempt
to reduce heat gains in the rooms through the use of external solar shading to at least
provide the opportunity for the natural ventilation system to work more effectively. [Wal’06]
3.13.3 Natural ventilation in healthcare facilities – the designers dilemma
The design of healthcare facilities in the UK as in most other countries in the world is
extremely prescriptive. There is a significant amount of design guidance provided by
the by NHS Estates that clearly states that the majority of spaces in healthcare
facilities should be naturally ventilated whenever possible. The alternative as any design
engineer will know is the introduction of fresh air using a fan driven mechanical ventilation
systems. When comparing the two systems we see that there are some fundamental
reasons, both micro and macro, why the natural ventilation alternative is more
attractive.
1. Capital cost: The capital cost difference for a low temperature hot water heating system
vs. a mechanical ventilation system taken from SPONs 2004 is £xxxxx vs £yyyyyy. We can
quickly and sensibly deduce that the basic cost difference between the two will be that
which is attributed to the air side mechanical system and hence there is a capital cost
increase when using that system.
2. Revenue cost: The revenue cost difference between a mechanical ventilation system and
a low temperature hot water heating system involves a number of factors:
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a). Maintenance cost – when carried out correctly, the maintenance cost of a mechanical
ventilation system can be in the order of 35% more than that of a LTHW heating system.
b). Energy cost – In simple terms there are two major energy cost differences between the
LTHW heating system a mechanical ventilation system. The first is the gas required (if gas
is used) to heat a quantity of air from cold to a temperature that satisfies the needs of the
occupants (re-circulated air should never be an option). The second is the energy
(electrical) that is used to power the fan.
3. Plant and riser space: There is a significant increase in the amount of plant space
required when substituting LTHW heating for mechanical ventilation within a project. The
same applies to the amount of riser space required. This can be easily illustrated by
considering the difference between the specific heat capacity (SHC – 4.2kj/kg.k) of water
and that of air (SHC - 1.02kj/kg.k). There is a factor of 4 difference which means that water
has 4 times the thermal carrying capacity that air has. Therefore, there is a significantly
greater vertical and/or horizontal space to accommodate one the thermal transport systems
as opposed to the other i.e. pipes in the case of water, ducts in the case of air. A simple
calculation based on a 10kw heating load shows that 2*20mm diameter steel pipes will be
required. Add to that the insulation then we have a pipework “corridor” of approximately
160mm * 80mm. A similar ductwork calculation reveals a ductwork “corridor” dimension of
765mm*370mm. The difference becomes even greater when access for cleaning is taken
into account.
Figure: Distribution space: Fresh air ductwork & chilled water pipework in air conditioned hospital.
4. CO2 generation: Global warming is a high environmental and political agenda item and
hence it is the responsibility of all designers to recommend low CO2 emitting systems at
every opportunity. We are extremely fortunate in the UK that we have a climate that allows
us to adopt natural ventilation as our basic means of environmental freshness. It is therefore
not only unnecessary but also irresponsible to design mechanical ventilation systems for a
large proportion of our healthcare facilities.
There are published energy targets for healthcare buildings in the UK of 35 – 55
Gj/100m3/annum. When these figures are looked at in detail we can hypothesise that we
can only realistically meet the targets when natural ventilation solutions are employed.
5. Environmental control: A time clock with internal and external compensation and
thermostatic radiator valves to trim the internal gain is used in the control of the vast
majority of naturally ventilated buildings in the UK. It is a tried and tested system and
providing the TRV’s are of a high quality it works very well. The fall back of course is that in
the event of an individual or group within a room finding the space to warm they can
physically intervene in the control loop and turn the TRV off.
The control of a mechanical ventilation system is a different proposition. The time clock is
still a trustworthy feature however it is the changes in the internal environment that causes
the main control problems. The only sensible way to control a multi-zone mechanical
ventilation system that requires a constant volume flow rate is by terminal reheat. That is the
air supplied from the main air handling unit is heated up to a condition that reflects the
lowest supply air temperature required in the particular zone being served. Prior to the
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supply air outlet terminal in each room there is a re-heat battery fitted which uses either
water or electricity as the heat source. A thermostatic sensor in each room manages the
heat output of the terminal battery to respond to changes in the room condition. Occupants
may be able to change the set point of thermostat by control intervention but they will not be
allowed to turn the air system off completely. In conclusion to provide effective
environmental control of a multi zone mechanical ventilation system we need to spend a
significant amount of money.
6. Infection control: Although the major transmission vehicle of infection within a hospital
environment is considered to be via contact. Airborne transmission (whether primary or
secondary) is being given more attention. The installation of mechanical ventilation
systems can only cause more concern for a number of reasons. Firstly, the complex
networks of ductwork systems are prime routes for pathogens to accumulate as
bacteria or as fungus: Secondly the pressure gradients created by mechanical
ventilation systems could drive the pathogens along corridors and into sensitive and
unconnected departments: Thirdly, the thermodynamic condition of the air,
particularly humidity is not controlled and in winter can reach low levels. A particular
airborne transmission route (droplet nuclei) is susceptible to low humidity levels.
Conversely, in summer if a high humidity level is encouraged within the spaces due to the
increased number of air changes but then fungus such as Aspergilli’s will generate more
readily.
Figure: Relative size of airborne respiratory pathogens.
7. Mechanical ventilation as a means of cooling spaces: Sometimes the installation of
mechanical ventilation systems is justified on the grounds of providing a degree of cooling to
the space. There is reasonable justification but only for the winter months, often during
spring, autumn and certainly always during the summer months a mechanical ventilation
system actually increases the space temperature faster than natural ventilation. The reason
is due to the increased number of air changes introduced into the space. When we couple
this input with the high internal heat gains and the highly efficient fabric which tends to lock
the heat into the space we can appreciate that the internal temperature will rise
considerably and quickly.
8. User control and comfort relationship: Natural ventilation relies on openable windows.
As such the solution is of domestic scale, is familiar to patients and staff, offers staff the
opportunity to control their own environment and also connects staff and patients with
the outside world and offers them welcome daylight. When occupants have control of
their environment they are usually willing to accept a wider thermal band of comfort.
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Figure: Acceptable comfort band when occupants have control of their environment.
From the above points it is clear that there are a significant number of reasons why we
should be promoting the use of naturally ventilated environments within the temperate UK
climate. There are of course specialist environments, specific processes, high-rise towers
with harsh environmental exposure and noisy roadside elevations to deal with. However,
with the exception of the first two we should look to develop a strategy whereby natural
ventilation is our first choice utilising low rise, intelligent windows, sensible orientation
and acoustic barriers, all proven solutions in other design sectors that should be adopted
in healthcare design.
Designers are continually confronted by conflicts during the design process non-more so
than the issues relating to the adoption of natural ventilation solutions. Unfortunately, the
compromise is often made on an unreasonably weighted analysis. For example, one current
healthcare design model relates to deep plan floor-plate. The logic is that the deeper plan
will create close-coupled departmental adjacencies that will offer clinical efficiencies.
Unfortunately, this compromise is based on the hypothesis that on a life cycle
analysis, clinical efficiency is more important than the competing elements in 1 to 8
above. There are a number of reasons why over the course of a 5 year period clinical
efficiencies may not be as expected, one reason is the spread of infection. If clinical
efficiency can be based on proximity then so can spread of infection by contact. If we
agree with that then equally we can agree that the closure of departments and
sickness of staff is driven by spread of infection and that the occurrence of staff
sickness and ward closures will increase the more connected the departments are.
If we add on the increased risk of airborne transmission of infection because of an
increase in the use of mechanical ventilation systems, we have an even greater
reason to use natural ventilation techniques.
A second compromise is made on the basis of what I believe to be an unreasonable design
standard. This is to do with the dimension a window can open before it becomes a danger
to people and items falling out of the windows. HTM 55 “Windows” has a table of 10 items
that represents the main design criteria that we need to comply with:
1. Natural lighting
2. Natural ventilation
3. View
4. Weather tightness
5. Energy conservation
6. Sound insulation
7. Security
8. Safety
9. Fire spread
10.
Cleaning
Unfortunately, under the section on safety there is a paragraph that states “a restricted
opening of not more than 100mm is recommended for use within reach of patients”. This
recommendation has the effect of negating any reasonable design strategy to introduce
natural ventilation as well as the sensible approach to give patients and staff control of their
environment. Designers need to look at the restricted window opening dimension as
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an opportunity to develop more intelligent window designs and not as an excuse to
default to mechanical ventilation solutions.
Complex natural ventilation strategy
Simple natural ventilation strategy
A further restriction for the designer in their quest to create naturally ventilated spaces is the
clients’ brief. However, simple and innocent a statement such as “the space to be designed
to 22°C ±1.5°C” appears, from that point on the natural ventilation strategy cannot be
implemented as the risks of over heating and the subsequent penalties are to great. It
would be far better to state “the designers as part of the natural ventilation strategy are to
develop window details that maintains summertime temperatures of 3°C below the
outside dry bulb temperatures for >95% of the time. This is a far more responsible
approach in our journey towards a sustainable ventilation solution particularly during the
summer period.
Figure: Comparison of energy targets and actual usage in hospitals.
The current energy targets are causing serious concern, with designers spending large
amounts of time trying to provide solutions that satisfy the 35 – 55Gj/100m³ per annum.
Detailed investigation of spatial solutions clearly shows that the recorded figures are more
easily attained when natural ventilation is achieved. This is probably an obvious comment
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for those involved in the healthcare design process. However, there is a danger that in our
quest to achieve a low energy calculation we reduce the volume of the spaces. The
floor area is part of the functional requirement of the brief and hence cannot be
touched. However the floor to ceiling height can be reduced with the result that the
energy usage becomes nearer to the target value and an additional associated saving in
fabric costs. The negative effect is one of patients and staff feeling enclosed within their
environment and natural ventilation solutions again being stifled due to the reduction in the
space to generate convective air movement and reduce the effect of warm stratified layers
within the spaces. Indeed this raises another question we need to address as healthcare
designers and that is why we do not use exposed fabric with night cooling to create
more comfortable environments.
In conclusion, all responsible designers should want to create a naturally ventilated
environment. However, for various reasons we are forced to create mechanically ventilated
spaces. These spaces will eventually need cooling due to the high internal gains and the
increasing fabric thermal efficiency.
We should look at providing a natural ventilation strategy on all healthcare buildings
and we should not stray away from that strategy until we have exhausted all avenues
i.e. life cycle costs of increased capital expenditure, interrogation of the client’s brief
and non-compliant approval of guidance notes etc. We must remember that in many
countries in the world natural ventilation is not an option, we therefore need to ensure that
we take our low energy design solutions as far as we can – helping ourselves and indirectly
helping others. [Ned’05]
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Hospital Guidelines - Electronic Systems Group

Transcription

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