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 LevelsPressure Pa dBA Level Source

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

Audiogram

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 Monitoring

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 Length 50% Dose 100% 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

Noise Controls

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