Hearing Conservation TDIBrooks International Hearing Conservation n Ear

Hearing Conservation TDI-Brooks International

Hearing Conservation n Ear Anatomy n n n Outer Ear Middle Ear Inner Ear

Hearing Conservation n Parts of the Ear n External ear n n n Pinna or auricle- portion attached to the outer surface of the head External ear canal Middle ear n n n Eustachian tube Ear drum Ossicular chain (hammer, anvil, stirrup)

Hearing Conservation Oval window and round window n Mastoid air cell system n n Inner ear Cochlea n Organ of Corti n Vestibular system (semi-circular canals) n

Hearing Conservation n External ear n n Pinna-visible part of the ear, functions as a funnel to collect sound External ear canal-separates the external ear from the middle ear, tube through which sound travels to the eardrum.

Hearing Conservation n Middle ear is between the ear drum and the bony wall of the inner ear. The ossicles (bones) are located here. n Eustachian tube-connects middle ear to the back of the nose. equalizes the pressure in the middle ear with atmospheric pressure (opens during yawning and swallowing).

Hearing Conservation n Ear drum-separates external ear canal from the middle ear and is connected to the oval window by the ossicles (conduct sound). This is a thin membrane that vibrates when sound waves hit it.

Hearing Conservation n Ossicular chain-hammer, anvil and stirrup. These are three small bones. Sound is transferred from the eardrum to the oval window. The hammer is set into motion by movement of the eardrum which then causes the anvil and stirrup to move and vibrate the oval window.

Hearing Conservation n Oval window and round window-located on the inner wall of the middle ear. Move in response to sound and transmit mechanical motion into the fluid of the inner ear.

Hearing Conservation n Inner ear-contains the receptors for hearing and position sense (balance). n n Vestibular receptive system-organ of equilibrium. Three semi-circular canals filled with fluid that respond to motion. Nerves then conduct this information to the brain about position. Cochlea-looks like a snail shell, also house the organ of corti (center of sense of hearing).

Hearing Conservation n Vibrations of the stirrup set the fluid of the cochlea into motion which then stimulates hair cells attached to nerve endings that sets up electrical impulses that are transmitted to the brain and interpreted as sound.

Hearing Conservation n Basically, outer ear collects sound waves from the air and funnels them into the ear canal where they are transported to the ear drum. The collected sound waves cause the eardrum to move back and forth in a vibrating mechanical motion that is passed on to the bones of the middle ear. The stirrup is embedded in the oval

Hearing Conservation n window. As the stirrup rocks back and forth it passes vibrations on to the inner ear through the oval window and into the fluid of the inner ear (cochlea). The movement of the fluid interacts with the hair cells in the cochlea which are connected to nerves that transmit the sound signals to the brain.

Hearing Conservation n As we age we steadily loose hearing acuity, particularly high frequencies. n n A young ear can hear sounds from 20 Hz to 20, 000 Hz. A person in their 60’s may be able to hear up to 12, 000 Hz. Human speech ranges from 300 to 4000 Hz.

Hearing Conservation n Types of hearing loss n n n Conductive-somehow the conductive processes are damaged, the inner ear is intact (damage to outer or middle ear) Sensorineural-hearing loss due to damage to the deep ear structures or auditory nerve. (Sensori-organs of the inner ear, neural-nerve fibers) Mixed hearing loss-some combination of both

Hearing Conservation n n Occupational hearing loss is defined as a hearing impairment of one or both ears, partial or complete that results form ones employment. Two categories of hearing loss n n Acoustic trauma Noise-induced hearing loss

Hearing Conservation n Acoustic trauma is the injury to the sensorineural elements of the inner ear. Acoustic trauma is produced by one or a few exposures to sudden, intense noise from blasts, explosions or by direct trauma to the ear.

Hearing Conservation n Noise induced hearing loss is the cumulative, permanent of the sensorineural type that develops over month or years of hazardous noise exposure.

Hearing Conservation n n Sound is any pressure variation that the ear can hear. The number of pressure variations over time is frequency (Hz). Noise-unwanted sound. Measure sound in d. B (decibels) Loudness depends upon sound pressure and impacted by frequency (pitch).

Hearing Conservation n Hearing loss risk factors n n n n Intensity of the noise (sound pressure level) Type of noise (frequency) Period of daily exposure Total duration of exposure Individual susceptibility Age Coexisting hearing loss and ear damage

Hearing Conservation n First 4 are most important and are called noise exposure factors.

Hearing Conservation Sound Pressure (u. Pa) 20 Sound Pressure Level (d. B) Example 0 Threshold of hearing 2, 000 40 Quiet office 200, 000 80 Very noisy restaurant 2, 000 100 Loom in textile mill, electric furnace

Hearing Conservation Sound Pressure (u. Pa) Sound Pressure Level (d. B) Example 20, 000 120 Hydraulic press 200, 000 140 Threshold of pain, jet plane

Hearing Conservation n Examples: n n 20% of the population between 50 and 59 experience a hearing loss of 20% without any industrial noise exposure. . However, this increases to 27% if exposed to steady state noise at 90 d. B, and is 36% if exposed to 95 d. B

Hearing Conservation n Current beliefs are that exposure of the unprotected ear to sound levels about 115 d. B is hazardous. Exposure to sound levels below 70 d. B is safe and does not produce any permanent hearing loss. The majority of industrial noise exposure fall within this range.

Hearing Conservation n n Frequency also factors into hearing loss. Noise about 500 Hz has a greater potential for causing hearing loss. The incidence of noise-induced hearing loss is directly related to total exposure time. Intermittent exposures are less damaging to the ear.

Hearing Conservation n Classes of Noise Exposure n n n Continuous (broadband) Intermittent Impact-sharp burst of sound

Permissible Noise Exposure (OSHA) Duration per Day (h) 8 6 4 Sound level (d. B) 90 92 95 3 2 1. 5 1 0. 5 0. 25 97 100 102 105 110 115

Hearing Conservation n Controls n n n Engineering-add sound controls Administrative-alter work schedules to reduce worker exposure, alter machine operation times to expose fewer workers. PPE-hearing protection devices-acoustic barriers that reduce the amount of sound energy transmitted through the ear canal to the inner ear.

Hearing Conservation n Classes of hearing protection n n Enclosures (entire head)-helmets worn by astronautsoffers protection of 35 d. B at 250 Hz to about 50 d. B at higher frequencies. Aural inserts (ear plugs) n n n Formable Custom molded premolded

Hearing Conservation n Superaural protectors (canal caps)-seal external openings of the ear. Soft material held in place by a light weight headband. Circumaural protectors (earmuffs)-consist of two cup shaped devices that fit over the entire external ear held in place by headband. According to OHSA standard, hearing protection should be worn in when exposed to 85 d. B for a 8 hour time weight average.

Hearing Conservation n n What type of PPE to use depends upon work location, sound frequency and fit to individual, how often exposed to noise. Check the noise reduction rating of hearing protection device.