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Hearing Research Laboratory
OHAO, Fall PDCChristian Giguère & Flora Nassrallah
Toronto - October 23rd, 2013
New CSA Noise Standardsand Noise Control
CAN/CSA Z107.56Measurement of Occupational Noise Exposure
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
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Noise and Hearing Loss
• 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 hearingloss as a result (NIOSH, 2009).
http://www.dangerousdecibels.org/ with permission
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Noise and Hearing Loss
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
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Noise and Hearing Loss
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.
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Noise and Hearing Loss
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
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slight
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severe
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Frequency (Hz)
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Age + Noise
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Frequency (Hz)
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80 yrs
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Age
NoisePure-tone audiogram
Noise and Hearing Loss
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Noise and Hearing Loss
Speech in noise
(Vaillancourt et al., 2011) (Vaillancourt et al., 2011)
Hearing thresholds are poorly related to speech perception in noise and sound localization.
Localization in quiet
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Noise and Hearing LossEffects:• 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.
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Standard CAN/CSA Z107.56
• 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 dBAfor federal employees (CCOHS, 2011).
CSA Group with permission
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Standard CAN/CSA Z107.56
• 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
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Communication Headsets
• 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.
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Communication Headsets
Circum-aural
Supra-aural
Intra-concha
Inserts
Monophonic StereophonicDouble Protection Muffs
http://www.davidclark.com/
http://www.plantronics.com/ca/
http://www.sennheiser.ca/live/
http://www.sensear.com/
http://www.sensear.com/
http://www.solutions.3mcanada.ca
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Communication Headsets
1) The measurement problem:
• Noise exposure arises from two sources: External noise passing through headset Internal audio signal (i.e. speech) from headset
• User adjusts volume setting to ensure the proper reception of speech/audio signal above the noise entering the device.
External Noise
Signal Source
Residual Noise
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Communication Headsets
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)
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Communication Headsets
2) The assessment problem:
• How to relate in-ear sound measurements to occupational noise limits?
Speaker
ExternalSound Field
At Eardrum
-10
-5
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0.1 1 10Frequence (kHz)
Gai
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B)
Frequency Response of External Ear
Frequency (kHz)
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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.
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31,5 40 50 63 80 10
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Cor
rect
ion
Fact
or (d
B)
1/3 Octave Band (Hertz)
Correction Factor for Diffuse-Field Equivalency(ISO 11904-2:2004)
Communication Headsets
Diffuse-Field Level (dBA)
At-Ear Level(dBA)
Speech 85 89.4
Airplane 85 86.6
Crowd 85 91.3
Riveter 85 93.6
Examples of diffuse-field and at-ear measurements
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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 7.3.1-
7.3.3) and A simplified calculation method (Section 7.3.4).
• New methods extended to music exposure in workplace (Section 8).
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Specialized Methods: Section 7.3.1-7.3.3
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.svantek.com/
Based on ISO 11904-1
(CSA Group with permission)
http://www.etymotic.com/
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Specialized Methods: 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
Type 3.3 Type 2 Type 1 (G.R.A.S.) (G.R.A.S.) (B & K)
Artificial Ears
Based onISO 11904-2(CSA Group with permission)
Acoustic Manikin (G.R.A.S.)
www.gras.dk/ www.bksv.com/www.gras.dk/
www.gras.dk/
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Specialized Methods: Field Use
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Specialized Methods: 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.
WARNINGRecent 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).
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Specialized Methods: Example
Measurements of speech transmission in plane noise from David Clark headset using Type 3.3 artificial ear
Short method: Single Number Correction(A-weighted artificial ear measurement) – 5 dB
88.7 dBA – 5dB = 83.7 dBA
Long method: 1/3 Octave Band Conversion1/3 Octave
Frequency Band (Hz)Artificial Ear
Measurements (dB)Z107.56 – Table 1
Diffuse-Field Correction (dB)Z107.56 – Table 1
A-Weighting Factors (dB)A-Weighted, Diffuse-
Field Equivalent (dBA)100 83.4 0.0 -19.1 64.3125 87.5 0.3 -16.1 71.1160 92.5 0.6 -13.4 78.5200 86.9 0.9 -10.9 75.1250 87.6 1.2 -8.6 77.8315 83.3 1.4 -6.6 75.3400 81.2 1.8 -4.8 74.6500 81.6 2.3 -3.2 76.1630 78.1 3.2 -1.9 73.0800 76.3 4.0 -0.8 71.51000 79.1 4.6 0.0 74.51250 74.4 6.0 0.6 69.01600 76.4 8.1 1.0 69.32000 74.2 11.4 1.2 64.02500 72.4 15.0 1.3 58.73150 64.5 14.2 1.2 51.54000 61.7 11.9 1.0 50.85000 66.4 9.8 0.5 57.16300 72.2 8.5 -0.1 63.68000 68.0 11.0 -1.1 55.910000 52.7 7.1 -2.5 43.1
TOTAL = 85.7
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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:
• 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.
External NoiseBN
Signal SourceS = BN – NR + SNR
Residual NoiseBN – NR
Noise ReductionNR
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Calculation Method: Section 7.3.4
Example 1Non-attenuating
Headset
Example 2Attenuating
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
Leq,t 90.1 dBA 82.1 dBA
Examples of noise exposure estimation under non-attenuating and attenuating headsets
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Calculation Method: Section 7.3.4
• Equivalent sound level arising from all work activities involving headsets (Leq,t,headset) is given by:
t = duration that the headset is worn during the work shiftton = duration that the headset signal in on during the work shift
BN = measured A-weighted external background noise levelNR = A-weighted noise reduction of headset (if any), according to CAN/CSA Z94.2
SNR = effective listening signal to noise ratio = 15 dB
10/10/
,, 1010log10 SNRNRBNonNRBNheadsetteq t
tL
Residual NoiseBN - NR
Signal SourceBN – NR + SNR
• 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.
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Calculation Method: Case Example
External background noise level (BN) 84.0 dBA
Noise Reduction of Headset (NR) 8.0 dBA
Effective background noise level when headset is worn (BN-NR) 76.0 dBA t = 6 hr
Effective headset communication signal level when present (BN-NR+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
Exposure EstimationA 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.
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Calculation Method: Case Example
Assessment Option 1 Option 2 Option 3 Option 4
Background Noise BN 84 dBA 76 dBA - - 80 dBA
Headset Noise Reduction NR 8 dBA - 18 dBA - -
Signal to Noise Ratio SNR 15 dBA - - - -
Duration of Signal 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
Noise Mitigation
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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.
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Exposure to Music, Radios: Example
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
Truck Cab Noise Exposure Assessment
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Summary of CAN/CSA Z107.56-13
• Z107.56 proposes 2 types of methods to assess noise exposurefrom 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 calculatedexposure below the criteron level, measurements withspecialized methods are warranted.
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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
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Questionnaire – Results
010203040506070
Excellentknowledge;
expert
Goodknowledge
Littleknowledge
Noknowledge
No answer
Perc
enta
ge
Awareness on noise measurement and hearing loss prevention
Occupational Hygienists Total Respondents
010203040506070
Excellentknowledge;
expert
Goodknowledge
Littleknowledge
Noknowledge
No answer
Perc
enta
ge
Awareness on the problem of noise exposure from communication headsets
Occupational Hygienists Total Respondents
010203040506070
Excellentknowledge;
expert
Goodknowledge
Littleknowledge
Noknowledge
No answer
Perc
enta
ge
Awareness on the techniques of noise measurement under communication headsets
Occupational Hygienists Total Respondents
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Questionnaire - Results
Basic equipment:E.g., Sound level meter,
Noise dosimeter
Specialized Equipment:
E.g., Manikin, MIRE
Yes No Yes No
Occupational Hygienists 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
Access to basic and specialized equipment to measure noise levels in the workplace
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Questionnaire - Results
• From these individuals, only four respondents (no occupational hygienists), had taken noise measurements under communication headsets in the workplace during their career.
0
10
20
30
40
50
60
70
Never Once 2-5 times 5-10 times 10 times or more
Perc
enta
geInterventions with regard to the use of communication headsets
Occupational Hygienists
Total Respondents
Hearing Research Laboratory
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 isvery 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
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ReferencesAbel, 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 andAssessment of Noise Immission and Exposure.
Canadian Centre for Occupational Health and Safety. (2011). Noise - Occupational Exposure Limits in Canada. Retrieved fromhttp://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 occupationalsound 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 SoundSources 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 SoundSources 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 hearingloss 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 exposurein the workplace. International Congress on Acoustics, Montréal, Canada.
National Institute for Occupational Safety and Health (2009). Noise and Hearing Loss Prevention. Retrieved fromhttp://www.cdc.gov/niosh/topics/noise/abouthlp/soundadvice.html.
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 CanadianMounted Police officers. Journal of American Academy of Audiology, 22, 313-331.