2 Objectives What is sound? How the ear works How to measure noise What does OSHA says about noise?Reading hearing testsHearing Protection
3 What is Sound? Hertz (Hz) Decibels (dB) Frequency a high or low pitch The loudness of the sound
4 Frequency Humans can typically hear between 20 - 20,000 Hz You can hear different frequencies better than others
5 Decibels The quietest sound most humans can detect is 0 dB Some humans can even hear sounds as quiet as -5 dB
6 The Loudness of Common Sounds Noise Thermometer Click Here
7 Anatomy of the EarEar DrumSemi-Circular CanalsCochleaEar Bones
8 How do we Hear? The outer ear collects the sound waves The waves hit the eardrum, and cause it to vibrateThe vibrations are sent through the ear bones to the cochlea
9 Inside the Cochlea (snail shell) Delicate hair cells vibrate to different frequenciesHair cells detect the vibration, and send a signal to the brainLoud sounds destroy the hair cells, and they stop functioning FOREVER!
10 The Ear does something else too! The Semi-circular canalsThree tubes laying perpendicular to one anotherFilled with fluid and tiny hair cellsWhen your head is tilted, the fluid moves the hair cells, and they send a signal to your brainResponsible for balance
11 How to measure noise Decibels are measured on a logarithmic scale Every time you add 5 dB, you double the sound.80 dB dBAn addition or reduction of 5dB causes either an addition or reduction of 100% in noise according to OSHA.
12 ExampleIn the field, we determined the loudness of two compressors right next to each otherHow loud is this area?Do we add?Do we add and take the average?89 dB?87 dB
13 Neither, because it is a log scale We use the following chart82 dB + 83 dB = 86 dB87 dB + 89 dB = 91 dB
14 How does the Safety Person determine noise levels Sound level meterDetermine the loudness (dB) of noise at any given momentPersonal DosimetersWorn by employeesMeasures the average loudness in an 8 hour work shift“8hr. TWA” (Time Weighted Average)Can also measure noise dose
15 What does BLS say? At 85 dB (8hr. TWA) (50% Dose) At 90 dB or more Train employeesMake hearing protection availableSample for noise levelsDo hearing testsNotify employees of resultsAt 90 dB or more(100% Dose)We must keep levels at or below 90 dBOr require hearing protection that will lower noise levels to to 90 dB
16 Hearing Tests Determine a baseline audiogram Hearing test every year to determine if you have experienced a hearing loss (Standard Threshold Shift)Standard Threshold Shift - A loss of 10 dB or more at 2000, 3000, or 4000 Hz.
17 Hearing Loss Impact - One loud bang Cumulative - Years of a noisy environmentTinnitus - Ringing in the earsPresbycusis - Hearing loss due to aging
18 Hearing Protection NRR - Noise reduction rating Ear Plug - 25 NRREar Plug - 29 NRREar Plug - 30 NRRDO NOT Subtract the NRR from the noise levelWRONG (109 dB - 25 NRR = 84 dB)You must use the “Safety Factor.” explained on separate slide
19 Safety FactorOSHA says the hearing protection is designed to reduce the noise by the NRR, but that is unlikely to happen due to :Leaks in the sealVibrationImproper insertion
20 Example of NRR Protection The noise from an average chainsaw is dBYou are wearing the foam plugs with an NRR of 25Do you have enough protection to place you below 90 dB level?
21 (NRR ) = 1818 / 2 = 9- 9 =YOU ARE ABOVE OSHA LIMITS OF 90 dB110 dB101
22 Final Thoughts Hearing is important In time, noise levels at 85 dB can permanently damage your hearingWear your hearing protection both at work and at homeChoose hearing protection with a proper NRR, and wear it properly
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