Hearing Conservation

10/1/99 Created By: C. Miterko 1

29 CFR 1910.95

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ObjectivesObjectivesWhat is sound?What is sound?How the ear worksHow the ear worksHow to measure noiseHow to measure noiseWhat does OSHA says about noise?What does OSHA says about noise?Hearing Conservation ProgramHearing Conservation ProgramReading hearing testsReading hearing testsHearing ProtectionHearing Protection

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What is Noise?What is Noise?Noise is generally Noise is generally defined as unwanted defined as unwanted sound, we are all sound, we are all exposed to noise every exposed to noise every day at home at work day at home at work and in traffic.and in traffic.Hertz (Hz)Hertz (Hz)

– Frequency a high or Frequency a high or low pitchlow pitch

Decibels (dB)Decibels (dB)– The loudness of the The loudness of the

sound sound

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FrequencyFrequencyHumans can typically hear Humans can typically hear

between 20 - 20,000 Hzbetween 20 - 20,000 HzYou can hear different You can hear different

frequencies better than frequencies better than othersothers

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Decibels Decibels

Sound pressure are measured Sound pressure are measured in Decibels (dB) which is a in Decibels (dB) which is a logarithmic measure of sound logarithmic measure of sound pressure levels.pressure levels.

The quietest sound most The quietest sound most humans can detect is 0 dBhumans can detect is 0 dB

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Common SoundsCommon Sounds0 dB Threshold of Hearing 30 dB Soft Whisper

40 dB Quiet Office

60 dB Conversational Speech

80 dB Very noisy restaurant

90 dB Subway

110 dB Woodworking

120 dB Hydraulic press

140 dB Threshold of Pain – Jet plane

180 dB Rocket

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Anatomy of the EarAnatomy of the EarCochlea

Ear Drum

Ear Bones

Semi-Circular Canals

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How do we Hear?How do we Hear?The outer ear collects the soundwavesThe outer ear collects the soundwavesThe waves hit the eardrum, and cause it to The waves hit the eardrum, and cause it to vibratevibrateThe vibrations are sent through the ear bones The vibrations are sent through the ear bones to the cochleato the cochlea

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Inside the Cochlea (snail Inside the Cochlea (snail shell)shell)

Delicate hair cells vibrate to different Delicate hair cells vibrate to different frequenciesfrequencies

Hair cells detect the vibration, and send a Hair cells detect the vibration, and send a signal to the brainsignal to the brain

Loud sounds destroy the hair cells, and Loud sounds destroy the hair cells, and they stop functioning they stop functioning FOREVER!FOREVER!

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The Ear does something The Ear does something else too!else too!

The Semi-circular canalsThe Semi-circular canals– Three tubes laying perpendicular Three tubes laying perpendicular

to one anotherto one another– Filled with fluid and tiny hair cellsFilled with fluid and tiny hair cells– Depending on which way your Depending on which way your

head is tilted, the fluid moves the head is tilted, the fluid moves the hair cells, and they send a signal hair cells, and they send a signal to your brainto your brain

Responsible for balanceResponsible for balance

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How to measure noiseHow to measure noiseDecibels are measured on a Decibels are measured on a

logarithmiclogarithmic scale scale

Every time you add Every time you add 6 dB6 dB, , you you doubledouble the sound the sound pressure of the noisepressure of the noise

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ExampleExampleIn the field, we determined the loudness of In the field, we determined the loudness of

two compressors right next to each othertwo compressors right next to each other

How loud is this area?How loud is this area?– Do we add?Do we add?– Do we add and take the average?Do we add and take the average?

89 dB 87 dB

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Neither, because it is a log scaleNeither, because it is a log scaleWe use the following chartWe use the following chart

82 dB + 83 dB = 86 dB82 dB + 83 dB = 86 dB87 dB + 89 dB = 91 dB87 dB + 89 dB = 91 dB

Difference in dB values

Add to Higher Value

0 or 1 dB 2 or 3 dB 4 or 10 dB 10 or more dB

3 dB 2 dB 1 dB 0 dB

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How does the Safety How does the Safety Person determine noise Person determine noise levelslevelsSound level meterSound level meter

– Determine the Determine the loudness (dB) of loudness (dB) of noise at any given noise at any given momentmoment

Personal DosimetersPersonal Dosimeters– Worn by employeesWorn by employees– Measures the average Measures the average

loudness in an 8 hour loudness in an 8 hour work shift work shift ““8hr. TWA”8hr. TWA” (Time (Time Weighted Average)Weighted Average)

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What does OSHA say?What does OSHA say?At 85 dB (8hr. TWA) (Action At 85 dB (8hr. TWA) (Action level)level)

– Train employeesTrain employees– Make hearing protection Make hearing protection

availableavailable– Sample for noise levelsSample for noise levels– Do hearing testsDo hearing tests– Notify employees of resultsNotify employees of results

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What does OSHA say?What does OSHA say?At 90 dB or moreAt 90 dB or more

(100% Dose)(100% Dose)– We must keep levels at or We must keep levels at or

below 90 dBbelow 90 dB– Or require hearing protection Or require hearing protection

that will lower noise levels to that will lower noise levels to to 90 dBto 90 dB

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What are Our Noise What are Our Noise Levels?Levels?Duration Per Day, Hours Sound Level dBA

8 90

6 92

4 95

3 97

2 100

1½ 102

1 105

¾ 107

½ 110

¼ 115

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Hearing Conservation Hearing Conservation ProgramProgram

Monitoring:Monitoring:Employers should monitor noise exposure Employers should monitor noise exposure

levels to identify employees who are levels to identify employees who are exposed to noise levels at or above 85 exposed to noise levels at or above 85 dBA averaged over 8 working hours, or dBA averaged over 8 working hours, or an 8-hour time-weighted average (TWA).an 8-hour time-weighted average (TWA).

Noise level meters & Noise Dosemeter are Noise level meters & Noise Dosemeter are used after being calibrated.used after being calibrated.

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When the daily noise exposure has two or more When the daily noise exposure has two or more noise exposures at different levels, their noise exposures at different levels, their combined values should be considered. (Use the combined values should be considered. (Use the following formula)following formula)

F(e) = (T(1) divided by L(1) + (T(2) divided by F(e) = (T(1) divided by L(1) + (T(2) divided by L(2)) + ……… (T(n) divided by L(n))L(2)) + ……… (T(n) divided by L(n))

F(e)= The equivalent noise exposure factorF(e)= The equivalent noise exposure factorT= The period of noise exposure at any essentially T= The period of noise exposure at any essentially

constant level.constant level.L= The duration of the permissible noise L= The duration of the permissible noise

exposure at the constant level.exposure at the constant level.If the value of F(e) exceeds unity (the value 1), the If the value of F(e) exceeds unity (the value 1), the

exposure exceeds PEL.exposure exceeds PEL.

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Example:Example:110 dbA 0.25 hours110 dbA 0.25 hours100 dbA 0.5 hours100 dbA 0.5 hours9090 dbA 1.5 HoursdbA 1.5 HoursF(e) = (0.25/0.5) + F(e) = (0.25/0.5) +

(0.5/2)+(1.5/8)(0.5/2)+(1.5/8)F(e)=0.5+0.25+0.1888F(e)=0.5+0.25+0.1888F(e) = 0.938F(e) = 0.938Since F(e) does not exceed Since F(e) does not exceed

unity (1), the exposure unity (1), the exposure limit is within limit is within permissible limitspermissible limits

Duration Per Day, Hours

Sound Level dBA

8 90

6 92

4 95

3 97

2 100

1½ 102

1 105

¾ 107

½ 110

¼ 115

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Audiometric TestingAudiometric Testing• Should the noise level monitoring determine Should the noise level monitoring determine

that employees are being subjected to levels that employees are being subjected to levels equaling or exceeding a TWA of 85 dBA, the equaling or exceeding a TWA of 85 dBA, the next step is to establish an audiometric testing next step is to establish an audiometric testing program for those exposed at no cost to the program for those exposed at no cost to the employee.employee.

• The important elements of an audiometric The important elements of an audiometric program include: Baseline audiograms, Annual program include: Baseline audiograms, Annual audiograms, Control measures, Training, and audiograms, Control measures, Training, and follow-up procedures.follow-up procedures.

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Baseline AudiogramsBaseline Audiograms•It is the reference audiogram It is the reference audiogram against which future audiograms against which future audiograms are are compared.compared.•Must be provided within 6 Must be provided within 6 months of an employee’s first months of an employee’s first exposure at or above 8-hour TWA exposure at or above 8-hour TWA of 85 dBA. (Control measures of 85 dBA. (Control measures should be taken)should be taken)•Baseline Audiogram must be Baseline Audiogram must be preceded by 14 hours without preceded by 14 hours without exposure to workplace noise.exposure to workplace noise.

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Annual AudiogramsAnnual Audiograms• After baseline audiogram has been taken, After baseline audiogram has been taken,

each employee exposed to noise levels at each employee exposed to noise levels at the 85 dBA or above shall have annual the 85 dBA or above shall have annual examination.examination.

• Annual audiogram must be conducted Annual audiogram must be conducted within 1 year of the baseline.within 1 year of the baseline.

• Compared with baseline audiograms Compared with baseline audiograms results.results.

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ContinuedContinued• To determine whether an employee has To determine whether an employee has

experienced any recordable hearing loss.experienced any recordable hearing loss.• The hearing loss is reffered to in the The hearing loss is reffered to in the

OSHA standard as :OSHA standard as :Standard Threshold Standard Threshold Shift (STS).Shift (STS).

• OSHA defines STS as “a change in OSHA defines STS as “a change in hearing threshold relative to the baseline hearing threshold relative to the baseline audiogram of an average of 10 dB or audiogram of an average of 10 dB or more at 2000, 3000, and 4000, Hz in more at 2000, 3000, and 4000, Hz in either ear.either ear.

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AudiogramAudiogram 200

Hz 1000 Hz

2000 Hz

3000 Hz

4000 Hz

6000 Hz

Baseline 5 dB 5 dB 0 dB 5 dB 10 dB 10 dB

Annual 5 dB 5 dB 10 dB 20 dB 35 dB 15 dB

Difference 0 0 10 15 25 5

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ControlControl• The standard states that if the 90 dB PEL The standard states that if the 90 dB PEL

is being exceeded, “feasible is being exceeded, “feasible administrative or engineering controls administrative or engineering controls shall be utilized.shall be utilized.

• If fails, PPE shall be provided and used If fails, PPE shall be provided and used to reduce sound levels.to reduce sound levels.

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Administrative ControlsAdministrative Controls

* Are defined as, “Methods of controlling * Are defined as, “Methods of controlling employee exposures by job rotation, employee exposures by job rotation, work assignment, or time periods away work assignment, or time periods away from the hazards.from the hazards.

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Engineering ControlEngineering Control• Are defined as “ Methods of controlling Are defined as “ Methods of controlling

employee exposures by modifying the employee exposures by modifying the source or reducing the quantity of source or reducing the quantity of contaminants released into the workroom contaminants released into the workroom environment.environment.

• Example: installing noise – absorbing Example: installing noise – absorbing acoustical foam or baffles to capture and acoustical foam or baffles to capture and deaden reverberating noise.deaden reverberating noise.

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Hearing ProtectorsHearing Protectors• Hearing protectors shall be made Hearing protectors shall be made

available and shall be worn by all available and shall be worn by all employees exposed to an 8-hour TWA of employees exposed to an 8-hour TWA of 85 dBA or greaters.85 dBA or greaters.

• Types of hearing protectors:Types of hearing protectors:• Ear muffsEar muffs• Ear plugsEar plugs• Ear canalEar canal

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Hearing ProtectionHearing ProtectionNRRNRR - Noise reduction rating- Noise reduction rating

– Express - 25 NRRExpress - 25 NRR– Classic - 29 NRRClassic - 29 NRR– Max Lite - 30 NRRMax Lite - 30 NRR

DO NOT DO NOT Subtract the NRR from the Subtract the NRR from the noise levelnoise level– WRONG WRONG (109 dB - 25 NRR = 84 dB) (109 dB - 25 NRR = 84 dB)

You must use the You must use the “Safety Factor”“Safety Factor”

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Safety FactorSafety FactorOSHA says the hearing protection is OSHA says the hearing protection is

designed to reduce the noise by the designed to reduce the noise by the NRR, but that is unlikely to happen NRR, but that is unlikely to happen due to :due to :– Leaks in the sealLeaks in the seal– VibrationVibration– Improper insertionImproper insertion

(NRR - 7) / 2(NRR - 7) / 2

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Example of NRR Example of NRR ProtectionProtectionThe noise at a large compressor is The noise at a large compressor is

109 dB109 dBYou are wearing the Express plugs with You are wearing the Express plugs with

an an NRR of 25NRR of 25

Do you have enough protection to place Do you have enough protection to place you below 90 dB level?you below 90 dB level?

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Hearing ProtectorsHearing Protectors

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Ear PlugsEar Plugs

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Ear muffsEar muffs

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Training - RecordkeepingTraining - Recordkeeping• Employees training is very important. All Employees training is very important. All

employees exposed to noise at a TWA of employees exposed to noise at a TWA of 85 dBA or greater shall participate in a 85 dBA or greater shall participate in a hearing conservation training program.hearing conservation training program.

• An accurate records shall maintained of An accurate records shall maintained of all employee exposure measurements.all employee exposure measurements.

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A Final NoteA Final NoteHearing is importantHearing is important

In time, noise levels at 85 dB can In time, noise levels at 85 dB can permanently damage your hearingpermanently damage your hearing

Wear your hearing protection both at Wear your hearing protection both at work and at homework and at home

Choose hearing protection with a high Choose hearing protection with a high NRR, and wear it properlyNRR, and wear it properly

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