New CSA Noise Standards and Noise Control

Transcription

New CSA Noise Standards
and Noise Control
CAN/CSA Z107.56
Measurement of Occupational Noise Exposure
OHAO, Fall PDC
Christian Giguère & Flora Nassrallah
Toronto - October 23rd, 2013
Hearing Research Laboratory
Table of Contents
•
•
•
•
Noise and Hearing Loss
Standard CAN/CSA Z107.56
Communication Headsets
New Procedures in CAN/CSA Z107.56
 Specialized Methods
 Calculation Method
 Exposure to Music, Radios
• Summary of CAN/CSA Z107.56
• Questionnaire
• Conclusions
• Second most prevalent self-reported work-related injury.
• 22 million American workers are exposed to hazardous
noise (Tak et al., 2009) and 10 million suffer from hearing
loss as a result (NIOSH, 2009).
http://www.dangerousdecibels.org/ with permission
Industrial workplace:
• In a sample of over 1.1 million US workers, about 18%
had hearing loss (Masterson et al., 2012).
 Adjusted Prevalence Ratios:
» Mining: 1.65
» Wood product manufacturing: 1.65
» Construction of buildings: 1.52
Military environment:
• By midlife, 42% of Canadian Force service members
show at least a mild hearing loss (>25 dB), and 26% a
moderate to severe hearing loss (>40 dB) (Abel, 2005).
 Twice more affected than by aging alone.
• Some military trades more at risk: Infantry, artillery,
flight engineers.
Short-term effects of noise exposure:
 Temporary hearing loss (TTS)
 Interference with important hearing tasks
 Stress, fatigue
Long-term effects of noise exposure:
 Permanent hearing loss (PTS)
» Hearing sensitivity (audibility)
» Supra-threshold deficits (distortion)
 Tinnitus
 Cardiovascular and other diseases
Frequency (Hz)
125
250
500
1000
2000
4000
30
60 yrs
40
50
60
80 yrs
Age
70
125
250
500
1000
2000
0
4000
2 yrs
10
8 yrs
20
30
18 yrs
40
28
50
60
70
80
250
500
1000
2000
4000
8000
40 yrs
20
80
Hearing Level (dB HL)
125
20 yrs
10
8000
Hearing Level (dB HL)
Hearing Loss (dB HL)
0
Frequency (Hz)
8000
0
20 yrs
normal
10
20
slight
30
30
mild
40
40
50
50
60
70
Age + Noise
moderate
60 yrs
severe
35 yrs
Noise
80
Pure-tone audiogram
Speech in noise
(Vaillancourt et al., 2011)
Localization in quiet
(Vaillancourt et al., 2011)
Hearing thresholds are poorly related to speech
perception in noise and sound localization.
Effects:
• Individual
 Quality of life (before and after retirement).
• Employer
 High cost of rehabilitation services and compensation
claims.
 WSIB estimated cost of equipment (e.g., hearing aids)
can reach 11000$ every four years in Ontario (Ministry
of Labour, 2007).
• Workplace
 Affects speech communication, warning signal
perception, detection and localisation of critical sounds.
 Decrease in situational awareness, safety, and work
efficiency.
• Canada has been the first country to
issue an occupational noise
measurement standard (1986).
• Updated or reaffirmed in 1994, R1999,
R2004, 2006, R2011.
• The standards specify methods valid
for sources “far” from the ears of
workers using:
 Dosimeter
 Sound level meter (SLM)
 Integrated sound level meter
• Since 2007, the exposure limit for 8
hours is 85 dBA in Ontario and 87 dBA
for federal employees (CCOHS, 2011).
CSA Group with permission
• Revised version of Z107.56
(Publiched in August 2013).
• Sections 4-6 specifies
instrumentation and procedures
based on sound level meter and
noise dosimeters.
• NEW! Section 7 specifies
instrumentation and procedures
for noise sources “close” to the
ears such as headsets.
• NEW! Section 8 specifies
procedures to account for use of
music players, radios, and other
sound reproduction devices.
CSA Group with permission
• Exposing 3 million American workers to high levels of noise
(OSHA, 1999).
• Increased use of wired and wireless communication headsets
in many occupational settings in the past decade.
• Typical uses: call centers, airport ground and control,
construction sites, military sites, industrial sites, etc.
Circum-aural
Intra-concha
http://www.davidclark.com/
Supra-aural
http://www.sennheiser.ca/live/
http://www.plantronics.com/ca/
Inserts
http://www.sensear.com/
Double Protection Muffs
http://www.sensear.com/
Monophonic
Stereophonic
http://www.solutions.3mcanada.ca
1) The measurement problem:
• Noise exposure arises from two sources:
 External noise passing through headset
 Internal audio signal (i.e. speech) from headset
External Noise
Residual Noise
Signal Source
• User adjusts volume setting to ensure the proper reception
of speech/audio signal above the noise entering the device.
1) The measurement problem (cont.):
• Which equipment should be used to measure sound in the
ears?
• Challenges:
 Sound is produced at or in the ears.
» SLM or noise dosimeter not suitable for in-ear
measurements
 Measurements must be carried out while the worker is
conducting his/her normal duties.
 Safety must be maintained.
Noise Dosimeter
(B & K)
Sound Level Meter
(B & K)
2) The assessment problem:
• How to relate in-ear sound measurements to occupational
noise limits?
Frequency Response of External Ear
25
20
Gain (dB)
15
10
5
0
-5
Speaker
-10
0.1
1
10
Frequence
Frequency(kHz)
(kHz)
External
Sound Field
At Eardrum
2) The assessment problem (cont.):
• Sound level is measured at the ear but regulatory limit
(e.g., 85 dBA) is defined in the sound field.
Correction Factor for Diffuse-Field Equivalency
(ISO 11904-2:2004)
Examples of diffuse-field and atear measurements
Diffuse-Field
Level (dBA)
At-Ear Level
(dBA)
Speech
85
89.4
Airplane
85
86.6
Crowd
85
91.3
Riveter
85
93.6
14
12
10
8
6
4
2
0
12,5
16
20
25
31,5
40
50
63
80
100
125
160
200
250
315
400
500
630
800
1000
1250
1600
2000
2500
3150
4000
5000
6300
8000
10000
12500
16000
20000
Correction Factor (dB)
16
1/3 Octave Band (Hertz)
New Procedures in CAN/CSA Z107.56
• Australian/New Zealand Standard (AS/NZS
1269.1:2005).
• From 2007-2011 a Working Group of Technical
Committee s304 of the CSA surveyed suitable methods to
conduct measurements under communication headsets.
• Version 2013 of the standard offers the use of either:
 Specialized methods and equipment (Section 7.3.17.3.3) and
 A simplified calculation method (Section 7.3.4).
• New methods extended to music exposure in workplace
(Section 8).
Specialized Methods:
Section 7.3.1-7.3.3
Based on ISO 11904-1
1) Miniature/probe microphone in Real-ear
(MIRE):
 Method is invasive (comfort, movement)
 Requires trained specialists to ensure safe
and consistent placement (e.g., audiologist)
 Can be resisted by workers
http://www.etymotic.com/
http://www.svantek.com/
(CSA Group with permission)
Section 7.3.1-7.3.3
2) Manikin/artificial ears:
 Complicated logistics
 Need additional electronics and a
pair of matched headsets
 Worker free to move but device
must remain at close proximity
Acoustic Manikin (G.R.A.S.)
Artificial Ears
www.gras.dk/
(CSA Group with permission)
Based on
ISO 11904-2
Type 3.3
(G.R.A.S.)
Type 2
(G.R.A.S.)
Type 1
(B & K)
www.gras.dk/
www.gras.dk/
www.bksv.com/
Field Use
Section 7.3.1-7.3.3
Transforming At-Ear to Sound Field
Long method (preferred):
1) Measure 1/3 octave band levels at the ear.
2) Convert to sound-field levels using conversion table.
3) Apply A-weighting and sum-up 1/3 octave bands.
Short method:
 Use single number to correct from at-ear to sound field
dBA levels (corrections based on AS/NZS standard).
 Manikin, Type 3.3, & Type 2: subtract 5 dB.
 Type 1: subtract 8 dB.
WARNING
Recent research indicates that single number corrections are not always in good
agreement with 1/3 octave band conversions because of factors such as the
frequency response of the headset and the spectrum of the audio signal
(Nassrallah et al., 2013).
Example
Measurements of speech transmission in plane noise from David Clark headset using Type 3.3 artificial ear Long method: 1/3 Octave Band Conversion
1/3 Octave
Artificial Ear
Z107.56 – Table 1
Z107.56 – Table 1
A-Weighted, DiffuseFrequency Band (Hz) Measurements (dB) Diffuse-Field Correction (dB) A-Weighting Factors (dB) Field Equivalent (dBA)
100
125
160
200
250
315
400
500
630
800
1000
1250
1600
2000
2500
3150
4000
5000
6300
8000
10000
83.4
87.5
92.5
86.9
87.6
83.3
81.2
81.6
78.1
76.3
79.1
74.4
76.4
74.2
72.4
64.5
61.7
66.4
72.2
68.0
52.7
0.0
0.3
0.6
0.9
1.2
1.4
1.8
2.3
3.2
4.0
4.6
6.0
8.1
11.4
15.0
14.2
11.9
9.8
8.5
11.0
7.1
-19.1
-16.1
-13.4
-10.9
-8.6
-6.6
-4.8
-3.2
-1.9
-0.8
0.0
0.6
1.0
1.2
1.3
1.2
1.0
0.5
-0.1
-1.1
-2.5
64.3
71.1
78.5
75.1
77.8
75.3
74.6
76.1
73.0
71.5
74.5
69.0
69.3
64.0
58.7
51.5
50.8
57.1
63.6
55.9
43.1
TOTAL = 85.7
Short method: Single Number Correction
(A-weighted artificial ear measurement) – 5 dB
88.7 dBA – 5dB = 83.7 dBA
Calculation Method:
Section 7.3.4
• Simple tool to estimate (predict) noise exposure under
communication headsets based on the relationship between
the noise and signal sources:
Noise Reduction
NR
External Noise
BN
Residual Noise
BN – NR
Signal Source
S = BN – NR + SNR
• Recent analysis of the field data indicates a mean effective
A-weighting listening signal/noise ratio (SNR) of 13.7 dB
with a standard deviation 5.9 dB (Giguère et al., 2012).
• CAN/CSA Z107.56 specifies a SNR of 15 dB.
• Research is being carried out to further validate the use of a
single number SNR.
Calculation Method:
Section 7.3.4
Examples of noise exposure estimation under
non-attenuating and attenuating headsets
Example 1
Non-attenuating
Headset
Example 2
Attenuating
Headset
Background Noise
BN
75 dBA
92 dBA
Noise Reduction
NR
0 dBA
25 dBA
Residual Noise
BN - NR
75 dBA
67 dBA
Signal Source
S = BN - NR + SNR
90 dBA
82 dBA
90.1 dBA
82.1 dBA
Leq,t
Calculation Method:
Section 7.3.4
• Equivalent sound level arising from all work activities
involving headsets (Leq,t,headset) is given by:
Leq ,t ,headset
  BN  NR /10 ton  BN  NR  SNR /10 
 10 log10
 10

t


Residual Noise
BN - NR
Signal Source
BN – NR + SNR
t = duration that the headset is worn during the work shift
ton = duration that the headset signal in on during the work shift
BN = measured A-weighted external background noise level
NR = A-weighted noise reduction of headset (if any), according to CAN/CSA Z94.2
SNR = effective listening signal to noise ratio = 15 dB
• The 8-hr noise exposure level, Lex,8, is calculated by
combining headset (Leq,t,headset) and non-headset (Leq,t,non-headset)
work activities.
Calculation Method:
Case Example
Exposure Estimation
A headset with an effective noise reduction (NR) of 8 dBA is used in a background
noise BN of 84 dBA. The audio signal is present for ton of 4 hr out of a total headset
usage t of 6 hr in a typical 8-hr work shift.
External background noise level (BN)
84.0 dBA
Noise Reduction of Headset (NR)
8.0
Effective background noise level when headset is worn (BN-NR)
76.0 dBA
t = 6 hr
Effective headset communication signal level when present (BNNR+SNR)
91.0 dBA
ton = 4 hr
Equivalent sound level when headset is worn (Leq,6,headset)
89.4 dBA
(headset usage 6 hr)
Equivalent sound level when headset is not worn (Leq,2,non-headset)
84.0 dBA
(no protection 2 hr)
Total noise exposure level (Lex,8 )
88.6 dBA
T =8 hr
dBA
Calculation Method:
Case Example
Noise Mitigation
Assessment
Option 1 Option 2 Option 3 Option 4
Background Noise
BN
84 dBA
76 dBA
-
Headset Noise Reduction
NR
8 dBA
-
18 dBA
-
-
SNR
15 dBA
-
-
-
-
ton
4 hr
-
-
0.25 hr
1.5 hr
Duration of Headset Use
t
6 hr
-
-
-
-
Work shift
T
8 hr
-
-
-
-
Leq,t,headset (dBA)
89.4
81.4
79.4
79.9
81.5
Leq,t,non-headset (dBA)
84.0
76.0
84.0
84.0
80.0
Lex,8 (dBA)
88.6
80.6
81.1
81.2
81.2
Signal to Noise Ratio
Duration of Signal
-
80 dBA
Exposure to Music, Radios:
Section 8
• Music players, radios and other sound reproduction
devices, used for leisure and/or work-related
communications, must be operated normally when
estimating noise exposure.
 For sources “far” from the ears (e.g. truck cab
radio), use SLM or noise dosimeter
 For sources “close” to the ears (e.g. headphone), use
specialized measurement methods specified in
Section 7.3.1-7.3.3
• If it is not possible to operate the sound reproduction
device at the time of measurements, when it is known
to be used in the workplace, the calculation procedure
in Section 7.3.4 shall be used with a SNR of 15 dB.
Exposure to Music, Radios:
Example
Truck Cab Noise Exposure Assessment
Assessment
Background Noise
BN
80 dBA
Fraction of Time Sound Device is Operating
ton/t
0.5
Signal to Noise Ratio
SNR
15 dBA
Leq,t,device operating
BN + SNR + 10log(ton/t)
92.0 dBA
Leq,t,device non-operating
BN
80.0 dBA
Leq,t (dBA)
92.3
Summary of CAN/CSA Z107.56-13
• Z107.56 proposes 2 types of methods to assess noise exposure
from communication headsets:
 Specialized direct measurements (MIRE, manikin, etc.)
 Calculation method requiring only a SLM or noise dosimeter
and information on the noise reduction rating of headset.
• WARNING : The calculation method provides only an indirect
estimate. If results are close to or above the criterion level
(e.g., 85 dBA), noise control measures are needed, e.g.:
 reducing the external background noise,
 using headsets with a higher noise reduction rating, and/or
 limiting the output level and/or duration of headset use.
• If noise control measures are not sufficient to reduce calculated
exposure below the criteron level, measurements with
specialized methods are warranted.
Questionnaire - Survey
• Questionnaire to document:
 Use of communication headsets in the workplace
 Awareness of noise exposure under headsets
 Use and access to noise measurement equipment
• Distributed electronically to researchers, audiologists,
occupational hygienists, acoustical consultants, health
and safety workers in Canada.
• 75 respondents
 11 in occupational hygiene
Questionnaire – Results
Awareness on the problem of noise exposure from
communication headsets
Percentage
70
60
50
40
30
20
10
0
Excellent
Good
Little
No
No answer
knowledge; knowledge knowledge knowledge
expert
Occupational Hygienists
Total Respondents
70
60
50
40
30
20
10
0
Excellent
Good
Little
No
No answer
expert
Total Respondents
Awareness on the techniques of noise
measurement under communication headsets
Percentage
Percentage
Awareness on noise measurement and hearing
loss prevention
70
60
50
40
30
20
10
0
Excellent
Good
Little
No
No answer
expert
Total Respondents
Questionnaire - Results
Access to basic and specialized equipment
to measure noise levels in the workplace
Basic equipment:
E.g., Sound level meter,
Noise dosimeter
Specialized
Equipment:
E.g., Manikin, MIRE
Yes
No
Yes
No
100%
0%
0%
100%
Total Respondents
53.3%
46.7%
32.4%
67.6%
Most have access
to a sound level
meter and/or noise
dosimeter
Most have access to a
MIRE, followed by an
artificial ear, and/or a
manikin
Questionnaire - Results
Interventions with regard to the use of communication headsets
70
60
Percentage
50
40
30
Total Respondents
20
10
0
Never
Once
2-5 times
5-10 times
10 times or more
• From these individuals, only four respondents (no occupational
hygienists), had taken noise measurements under communication
headsets in the workplace during their career.
Conclusions
• CAN/CSA Z107.56 proposes 2 types of methods to
assess noise exposure from communication headsets
 Specialized direct measurements
 Calculation method
• Calculation method is especially suitable for
occupational hygienists given:
 Access to sound level meter or dosimeter is very
high (100%) while access to specialized equipment is
very limited (0%)
 Good overall knowledge of issues pertaining to noise
measurements and hearing loss prevention
 Allow to take concrete actions and assess impact
based on relatively simple calculations
References
Abel, S.M. (2005). Hearing loss in military aviation and other trades: Investigation of prevalence and risk factors. Aviation, Space, and
Environmental Medicine, 76(12), 1128-1135.
Australian/New Zealand Standard. (2013). AS/NZS 1269-1:2005-13. Occupational Noise Management Part 1: Measurement and
Assessment of Noise Immission and Exposure.
Canadian Centre for Occupational Health and Safety. (2011). Noise - Occupational Exposure Limits in Canada. Retrieved from
http://www.ccohs.ca/oshanswers/phys_agents/exposure_can.html?print.
Canadian Standards Association. (2013). Measurement of Noise Exposure, Canadian Standards Association CAN/CSA Z107.56-13,
Mississauga: Canadian Standards Association.
Giguère, C., Behar, A., Dajani, H. D., Kelsall, T., and Keith, S. E. (2012). “Direct and indirect methods for measurement of occupational
sound exposure from communication headsets,” Noise Control Engineering Journal, 60(6), 630-644.
International Organization for Standardization (2002). ISO 11904-1: 2002. Acoustics - Determination of Sound Immission from Sound
Sources Placed Close to the Ear: Part 1: Technique Using a Microphone in a Real Ear (MIRE Technique).
International Organization for Standardization (2004). ISO 11904-2: 2004. Acoustics – Determination of Sound Immission from Sound
Sources Placed Close to the Ear: Part 2: Technique Using a Manikin (Manikin Technique).
Masterson, E. A., Tak, S., Themann, C. L., Wall, D. K., Groenewold, M. R., Deddens, J. A., & Calvert, G. M. (2012). Prevalence of hearing
loss in the United States by industry. American Journal of Industrial Medicine, 56(6), 670-681.
Ministry of Labour. (2007). Amendments to Noise Requirements in the Regulations for Industrial Establishments & Oil and Gas-Offshore.
Queen’s Printer for Ontario.
Nassrallah, F., Giguère, C., & Dajani, H. (June 2nd to 7th, 2013). Comparison of direct measurement methods for headset noise exposure
in the workplace. International Congress on Acoustics, Montréal, Canada.
National Institute for Occupational Safety and Health (2009).
http://www.cdc.gov/niosh/topics/noise/abouthlp/soundadvice.html.
Noise
and
Hearing
Loss
Prevention.
Retrieved
from
Occupational Safety and Health Administration (1999). “Evaluating noise exposure of employees wearing sound-generating headsets,”
Report No.: TED 01-00-015.
Tak, S., Davis, R., & Calvert, G. (2009). Exposure to hazardous workplace noise and use of hearing protection devices among US workers
- NHANES, 1999-2004. American Journal of Industrial Medicine, 52(5), 358-371.
Vaillancourt, V., Laroche, C., Giguère, C., Beaulieu, M.-A., & Legault, J.-P. (2011). Evaluation of auditory functions for Royal Canadian
Mounted Police officers. Journal of American Academy of Audiology, 22, 313-331.

New CSA Noise Standards and Noise Control

Transcription

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