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

10/1/99 2

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

10/1/99 3

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 The loudness of the

sound sound

10/1/99 4

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 frequencies better than othersothers

10/1/99 5

Decibels Decibels

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

Some humans can even hear Some humans can even hear sounds as quiet as -5 dBsounds as quiet as -5 dB

10/1/99 6

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

10/1/99 7

Anatomy of the EarAnatomy of the Ear

CochleaEar Drum

Ear Bones

Semi-Circular Canals

10/1/99 8

How do we Hear?How do we Hear?

The outer ear collects the soundwavesThe outer ear collects the soundwaves

The waves hit the eardrum, and cause it to The waves hit the eardrum, and cause it to vibratevibrate

The vibrations are sent through the ear The vibrations are sent through the ear bones to the cochleabones to the cochlea

10/1/99 9

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!

10/1/99 10

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, an they send a signal to hair cells, an they send a signal to your brainyour brain

Responsible for balanceResponsible for balance

10/1/99 11

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

10/1/99 12

ExampleExample

In 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

10/1/99 13

Neither, because it is a log scaleNeither, because it is a log 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

10/1/99 14

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)

– Can also measure Can also measure noise noise dosedose

10/1/99 15

What does OSHA say?What does OSHA say?At 85 dB (8hr. TWA) (50% At 85 dB (8hr. TWA) (50%

Dose)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 resultsNotify employees of results

10/1/99 16

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

10/1/99 17

What are Our Noise What are Our Noise Levels?Levels?

10/1/99 18

Hearing TestsHearing TestsWe must determine a baseline audiogramWe must determine a baseline audiogram

We test your hearing every year to We test your hearing every year to determine if you have experienced a determine if you have experienced a hearing loss hearing loss (Standard Threshold Shift)(Standard Threshold Shift)

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

10/1/99 19

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

10/1/99 20

Hearing LossHearing Loss

Impact - One loud bangImpact - One loud bang

Cumulative - Years of a noisy Cumulative - Years of a noisy environmentenvironment

Tinnitus - Ringing in the earsTinnitus - Ringing in the ears

Presbycusis - Hearing loss due to agingPresbycusis - Hearing loss due to aging

10/1/99 21

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”

10/1/99 22

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

10/1/99 23

Example of NRR Example of NRR ProtectionProtection

The noise at a large compressor is The noise at a large compressor is 109 dB109 dB

You 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?

10/1/99 24

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