10/1/99Created By: C. Miterko1 10/1/992 Objectives What is sound? How the ear works How to measure...
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Transcript of 10/1/99Created By: C. Miterko1 10/1/992 Objectives What is sound? How the ear works How to measure...
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
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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 The loudness of the
sound 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 frequencies better than othersothers
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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
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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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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
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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, an they send a signal to hair cells, an they send a signal to your brainyour 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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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
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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
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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)
– Can also measure Can also measure noise noise dosedose
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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
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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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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.
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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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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
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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 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?
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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