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Hearing Conservation & Noise Hearing Conservation & Noise ExposureExposure

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ObjectivesObjectives

What is sound?What is sound? How the ear worksHow the ear works How to measure noiseHow to measure noise What does OSHA says about noise?What does OSHA says about noise? Reading hearing testsReading hearing tests Hearing ProtectionHearing Protection

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What is Sound?What is Sound?

Hertz (Hz)Hertz (Hz)– Frequency a high or Frequency a high or

low pitchlow pitch

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

the sound the sound

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FrequencyFrequency

Humans can typically hear Humans can typically hear between 20 - 20,000 Hzbetween 20 - 20,000 Hz

You can hear different You can hear different frequencies better than othersfrequencies better than others

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Decibels Decibels

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

Some humans can even Some humans can even hear sounds as quiet as -5 hear sounds as quiet as -5 dBdB

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The Loudness of Common The Loudness of Common SoundsSounds

0 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

Noise Thermometer

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Anatomy of the EarAnatomy of the Ear

Cochlea

Ear Drum

Ear Bones

Semi-Circular Canals

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How do we Hear?How do we Hear?

The outer ear collects the The outer ear collects the sound wavessound waves

The waves hit the eardrum, The waves hit the eardrum, and cause it to vibrateand cause it to vibrate

The vibrations are sent through The vibrations are sent through the ear bones to the cochleathe ear bones to 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 they Loud sounds destroy the hair cells, and they stop functioning stop functioning FOREVER!FOREVER!

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The Ear does something else too!The Ear does something else too! The Semi-circular canalsThe Semi-circular canals

– Three tubes laying perpendicular to one Three tubes laying perpendicular to one anotheranother

– Filled with fluid and tiny hair cellsFilled with fluid and tiny hair cells– When your head is tilted, the fluid moves When your head is tilted, the fluid moves

the hair cells, and they send a signal to the hair cells, and they send a signal to your brainyour brain

Responsible for balanceResponsible for balance

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

logarithmiclogarithmic scale scale Every time you Every time you add add 5 dB5 dB, you , you doubledouble

the sound. the sound.

80 dB80 dB 85 dB85 dB

An addition or reduction of 5dB causes either an addition or reduction of 100% in noise according to OSHA.

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ExampleExample In the field, we determined the loudness In the field, we determined the loudness

of two compressors right next to each of two compressors right next to each otherother

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 Neither, because it is a log scalelog scale We use the following chartWe use the following chart

82 dB + 83 dB = 86 dB82 dB + 83 dB = 86 dB 87 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 Person How does the Safety Person determine noise levelsdetermine noise levels

Sound 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. TWA8hr. TWA”” (Time (Time Weighted Average)Weighted Average)

– Can also measure Can also measure noise noise dosedose

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What does BLS say?What does BLS say? At 85 dB (8hr. TWA) At 85 dB (8hr. TWA)

(50% Dose)(50% Dose)– 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 Notify employees of

resultsresults

At 90 dB or moreAt 90 dB or more(100% Dose)(100% Dose)– We must keep levels We must keep levels

at or below 90 dBat or below 90 dB– Or require hearing Or require hearing

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

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Hearing TestsHearing Tests

Determine a baseline audiogramDetermine a baseline audiogram Hearing test every year to determine if you Hearing test every year to determine if you

have experienced a hearing loss have experienced a hearing loss ((Standard Standard Threshold ShiftThreshold Shift))

Standard Threshold ShiftStandard Threshold Shift - A loss of 10 dB - A loss of 10 dB or more at 2000, 3000, or 4000 Hz.or more at 2000, 3000, or 4000 Hz.

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Hearing LossHearing Loss

Impact - One loud bangImpact - One loud bang Cumulative - Years of a noisy environmentCumulative - Years of a noisy environment Tinnitus - Ringing in the earsTinnitus - Ringing in the ears Presbycusis - Hearing loss due to agingPresbycusis - Hearing loss due to aging

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Hearing ProtectionHearing Protection

NRR NRR - Noise reduction rating- Noise reduction rating– Ear Plug - 25 NRREar Plug - 25 NRR– Ear Plug - 29 NRREar Plug - 29 NRR– Ear Plug - 30 NRREar Plug - 30 NRR

DO NOTDO NOT Subtract the NRR from the noise Subtract the NRR from the noise levellevel– 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.” explained explained on separate slideon separate slide

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Safety FactorSafety Factor

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

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Example of NRR Example of NRR ProtectionProtection

The noise from an average chainsaw is The noise from an average chainsaw is 110 dB110 dB You are wearing the foam plugs with an You are wearing the foam plugs with an NRR ofNRR of

2525

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

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(NRR(NRR 25 -25 - 7) = 18 7) = 18

18 / 2 = 918 / 2 = 9

- 9 = - 9 =

YOU ARE ABOVE OSHA LIMITS OF 90 dBYOU ARE ABOVE OSHA LIMITS OF 90 dB

101110 dB

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Final ThoughtsFinal Thoughts

Hearing 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 Choose hearing protection with a proper proper

NRRNRR, and wear it properly, and wear it properly

ResourcesResources

SafetyWorks! 1-877-723-3345SafetyWorks! 1-877-723-3345 OSHA-OSHA- NIOSH –NIOSH – CDC - CDC -