The Health and Safety Executive notes that there were 74,000 reported cases of work-related hearing loss in 2004 to 2005. In 1997 to 1998, those figures were closer to half a million. Both education and regulations have likely decreased these numbers of preventable hearing loss, but it’s important that hearing is protected where possible. What is noise-induced hearing loss and how can NIHL be prevented? Here’s our guide for site managers.
What is NIHL?
Noise-induced hearing loss or NIHL is a permanent hearing impairment from exposure to high levels of noise. It may cause a person to hear only a narrow range of frequencies, impaired perception of sound, or another impairment like sound-sensitivity, ringing in the ears, or the inability to understand normal speech.
The most common cause of hearing loss is excessive noise exposure. Because noise exposure can happen at work, there are regulations in place. The daily average exposure should be no more than 87 dB with hearing protection in place. The regulations mandate that hearing should be protected from excessive noise at work that may cause hearing loss or tinnitus.
How Does Hearing Work and How Can It Be Damaged?
Hearing works when sound waves enter the ear canal and vibrate the eardrum. The vibrations are sent to the tiny bones in the middle ear: the malleus, incus, and stapes. The bones couple the air vibrations to the fluid vibrations in the snail-shaped fluid-filled cochlea of the inner ear. The fluid in the cochlea ripple and a wave forms along the basilar membrane (the partition between the upper and lower parts in the cochlea). Sensory hair cells, which sit on top of the basilar membrane ride on the wave, and as they move up and down the microscopic an overlying structure, bending which causes the pores of the stereocilia to open. Hair cells at one end perceive low frequencies and the other end perceives high frequencies. This action sends chemicals rushing in the cells, which causes an electrical signal. The electrical signal is sent to the brain and is translated into recognisable sound.
When noises are too loud, the sound kills the hair cells in the inner ear. After prolonged exposure, more hair cells are destroyed, and, as hair cells diminish, hearing decreases. Dead hair cells cannot be restored at present.
Noise level and the length of exposure can put someone at risk for NIHR. Sounds over 85 dB can cause permanent hearing loss. Loud bursts of sound such as from gunshots or explosions can rupture the eardrum or damage the three small bones in the middle ear, resulting in immediate and permanent loss of hearing, or tinnitus, which is a ringing, buzzing, or roaring in the ears or head.
Common Sounds and Their Intensity
Here’s a (modified) chart from the American Hearing Research Foundation about common sounds, and exposure levels:
Approximate Decibel Level Examples
the quietest sound you can hear.
whisper, quiet library.
normal conversation, sewing machine, typewriter.
noise from heavy city traffic, electric motors, heavy machinery, construction, factory, highway work sites
lawnmower, shop tools, truck traffic; 8 hours per day is the maximum exposure (protects 90% of people).
movie, chainsaw, pneumatic drill, snowmobile, mp3 player at max volume; 2 hours per day is the maximum exposure without protection.
sandblasting, loud rock concert, jackhammer, power saw, carpentry, construction, auto horn, sirens, motorboats, health club, video arcade,; 15 minutes per day is the maximum exposure without protection.
gun muzzle blast, jet engine, airport industry, police work; noise causes pain and even brief exposure injures unprotected ears; maximum allowed noise with hearing protector.
firecrackers and firearms
Can NIHL Be Reversed?
There’s no cure or ability to reverse NIHL. Once the inner ear’s hair cells have been damaged, then they cannot be restored. NIHL can be treated with hearing aids, but hearing aids only amplify sounds (like a microphone) and cannot restore normal hearing - there need to be some hair cells left intact for them even to work.
There is a chance that noise can cause reversible hearing loss, which is called a temporary threshold shift. Sometimes that occurs when people are exposed to gunfire or firecrackers; the person temporarily loses hearing, hears a ringing in the ears and tinnitus.
However, any exposure can cause permanent, irreversible hearing loss or damage.
Can NIHL Be Prevented?
Yes, hearing loss can be prevented. Here are four steps to prevent NIHL.
Conduct a risk assessment on site to understand the surrounding environment in the workplace. On site, you may have the buzz of nearby traffic, and you may have equipment that will run most of the day. Will there be any machinery that will make sounds that are at an uncomfortable level? How long will these sounds go on for? Is there risk of hearing loss from these sounds? Figure out the risk of exposure to these loud sounds, and plan accordingly.
Reduce Length of Exposure
Since people can stand loud noises for short periods of time, but not for extended periods of time, then reducing the exposure time to that sound is key. When conducting your on-site risk assessment, consider how long your workers will be exposed to each sound, and the number of dB the worker will be exposed to. Anything reaching unsafe levels requires appropriate hearing protection. However, when in doubt, use hearing protection and make sure that workers are not exposed to sounds for longer than recommended. Some sounds can cause damage after fifteen minutes, and others cause damage after a few hours. Assess which sounds can cause what type of damage, and after how long to understand what measures need to be put in place.
Wear Hearing Protection
When your workers will be exposed to loud noises above 85 dB, then they will need to be issued hearing protection. When operating machinery, power tools, outdoor equipment, and so on, provide hearing protection in the form of earplugs or earmuffs to decrease the intensity of the sound.
Earplugs fit in the outer ear canal and block the ear with an airtight seal. Improperly fitted, dirty, or worn earplugs will not work properly. Foam earplugs are inexpensive. They can be banded if the employee has trouble keeping them in his or her ears or simply standard earplugs.
Earmuffs and ear defenders fit over the outer ear, and form an air seal to block the ear canal. They are held in place with an adjustable band. Earmuffs won’t seal around glasses or long hair. The headband tension must hold the earmuffs securely around the ear.
The correct hearing protection can reduce the noise by 15-30 dB. Better quality earplugs and earmuffs have an equal sound reduction. Earplugs are often better for low-frequency noise, and earmuffs work best for high-frequency noise. If combined, the double protection adds 10-15 dB of further protection than when used alone. If noise exceeds 105 dB, then hearing protection should be combined.
For very loud noises - like those over 105 dB - no type of hearing protection will stop very loud noises causing some level of damage.
Allow Some Noise
Check that normal conversation can be heard when using hearing protection. If the hearing protection reduces all noises then there may be other dangers outside of hearing problems since your workers may not be able to hear shouts of danger. All noise should not be entirely eliminated.
For added protection, all workers should avoid noise that is too loud, too close, or goes on for too long. The distance from the sound and length of exposure are factors in protecting hearing. Hearing is a precious thing to lose, and, since it’s so easy to damage hearing irreversibly, it should be protected.
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