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Hearing Conservation. Presented by QBE Loss Control Services. External Ear. Pinna- Cartilaginous sound wave collector External Auditory Canal- Leads to ear drum. Middle Ear. Eardrum Ossicular Chain- 3 bones that transmit sound
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Hearing Conservation Presented by QBE Loss Control Services
External Ear • Pinna- Cartilaginous sound wave collector • External Auditory Canal- Leads to ear drum
Middle Ear • Eardrum • Ossicular Chain- 3 bones that transmit sound • Oval and Round Windows- membranes separating middle & inner ear • Eustachian Tube- connected to throat equalizes air pressure in out and inner ear
Inner Ear • Vestibular System- fluid filled canals • Cochlea- tubular structure filled with fluid and lined with hair cells and nerve endings
Sound • Changes in air pressure • Weakest sound heard is a few millionths of a lb/in2 • Pain threshold 10 million times higher
Decibels • dB- Logarithm of the ratio of a sound pressure level to a reference pressure level • dB = 20 log P/P0 P0 is 20µPA (micopascals) at 1000 Hz (0 dB) • Increase of 3 dB doubles sound energy • dBA- Decibels using “A” scale weighting which reflects how the ear responds to speech frequencies
Sound Levels Pressure PadBA LevelSource 100,000 194 Rocket 200 140 Pain Threshold 6.3 110 Punch Press 2 100 Passing Truck 0.2 80 Noisy Office 0.02 60 Normal Speech 0.006 50 Private Office 0.0002 20 Whisper 0.00006 10 Good Hearing 0.00002 0 Excellent Hearing
Sound Frequency • Frequency- number of times per second air molecules are displaced by sound wave • Hertz (Hz)- cycles per second • Human audible range- 20- 20,000 Hz • Speech frequency 500- 2,000 Hz
Noise • Sound that bears no information • Unwanted by listener • Continual- constant level and frequency • Impact- sharp outbursts less than 0.5 seconds in duration • Intermittent- Wide frequency range several times per day
Noise Effects • Masks wanted sounds • Interferes with speech • Causes auditory fatigue • Damages hearing • Annoyance/stress
Non-Noise Induced Impairments • Physical blockage • Traumatic damage • Disease- infections, tumors, degenerative • Heredity damage • Drugs- streptomycin, quinine • Presbycusis- loss due to aging • Tinnitus- head noises
Types of Hearing Loss • Conductive- external and middle ear - mechanical • Sensorineural- inner ear- nerves and hair cells • Mixed- conductive and sensorineural
Effects of Noise • Temporary Threshold Shift • Permanent Threshold Shift
Threshold Shift Variables • dBA level • Frequency • Duration of exposure • Number and length of rest periods • Type of sound- continuous or impact • Individual differences
Purpose of Audiometric Testing • Test hearing acuity before exposure to noise (baseline) • Annually check hearing acuity against baseline • Check effectiveness of Hearing Conservation Program • Record significant threshold shifts
Audiometric Testing • Measure hearing ability at 500, 1000, 2000, 3000, 4000 and 6000 Hz • Standard Threshold Shift- average change in hearing threshold greater than 10 dB at 2000, 3000 and 4000 Hz in either ear
Noise-Induced Hearing Loss • Higher frequency loss usually first • Permanent damage to cochlea • Insidious- gradual with no pain effect
OSHA Noise Standard • OSHA Action Level- 85 dBA average noise level for an eight hour shift or 50% dose • OSHA Permissible Exposure Limit- 90 dBA average noise level for an eight hour shift or 100% dose
Noise Dose • A measure of noise as a percentage of the permissible limit. • Dose=100 C1+ C2+ C3+... Cn T1 T2 T3 Tn Where Cn is the duration of exposure to a noise level and Tn is the allowable time for exposure to that noise level. (See Tables in OSHA Noise Standard).
Other Shift Lengths Shift Length50% Dose100% Dose 14 hr 81.0 86.0 12 hr 82.1 87.1 11 hr 82.7 87.7 10 hr 83.4 88.4 9 hr 84.2 89.2 8 hr 85 90 7 hr 86 91 6 hr 87.1 92.1
Action Level Exceeded Implement Hearing Conservation Program • Noise monitoring • Provide hearing protectors • Audiometric testing • Training • Recordkeeping
Permissible Exposure Level Exceeded • Implement Hearing Conservation Program • Use engineering and administrative controls to reduce noise levels • Require use of hearing protectors
Choosing Hearing Protection • Ease of use • Fit and comfort • Hygienic considerations • Retainability within ear canal or over ears • Heat/cold/moisture
Noise Reduction Rating (NRR) • EPA required noise attenuation factor for all hearing protection devices • Maximum noise attenuation of hearing protectors about 35 dBA • Optimal attenuation under laboratory conditions
OSHA NRR Determination • Subtract 7 dB from NRR • Take %50 for a safety factor Example: 100 dBA noise exposure NRR for ear Muff= 19 dBA 1. 19 dBA - 7 dBA = 12 dBA 2. 12 dBA x 0.50 = 6 dBA 100 dBA- 6 dBA = 94 dBA. This is above 90 dBA limit so pick more protective protection.
Ear Plugs • Formable • Custom-molded • Must fit tightly in ear canal • Hands must be clean • Must be checked and readjusted
Ear Muffs • Must seal around ear • Hair must be pushed aside • Glasses may interfere • Use with plugs if over 105 dBA
Use of Protectors • Inspect before use • Worn, loose, stiff or deformed protectors should be discarded • Do not use soiled plugs • Make sure fit is snug • Wash and clean frequently according to manufacturer’s requirements • Wash hands before inserting plugs • Don’t use “homemade” protectors
Employee Training • Effects of noise on hearing • Company Hearing Protection Program and policies • Specific noise hazards in the workplace • Purpose of hearing protectors • Proper use of hearing protectors • Audiometric testing • Individual employee responsibilities
Noise Controls • Engineering controls • Administrative controls
Engineering Controls • Enclosures • Control booths • Shields • Sound absorbing materials and coatings • Reduce vibrations • Change noise frequency • Reduce speeds • Reduce air pressures • Install mufflers on air devices • Increase distances • Provide proper maintenance of equipment • Reduce part dropping distances
Administrative Controls • Change way work is performed • Reduce number of workers in noisy areas • Minimize duration of exposure • Rotate between noisy and quiet areas • Provide quiet lunch/break areas