Work-related hearing loss threatens hundreds of thousands of workers. In addition to hearing impairment, noise can cause other effects—it can startle, irritate, disrupt concentration and sleep, and increase stress. By increasing stress, noise can contribute to circulatory problems and heart attacks. Noise interferes with communication and can mask warning sounds like back-up alarms on a construction site or an evacuation signal in a factory.
Exposure to sudden and intense noise, like an explosion or nearby siren, can cause immediate damage and pain ranging from a ringing in the ears to hearing loss. Hearing loss depends on the duration of noise exposure, the level of noise and the susceptibility of the individual. Several studies show that exposure to certain chemicals may increase noise-induced hearing loss. Age, disease, some drugs and previous exposures also affect hearing. A person can experience permanent hearing loss without ever suffering pain in the ears. Permanent hearing loss caused by excessive exposure to noise cannot be repaired.
While the permissible exposure limit is 90 decibels (dBA) averaged over an 8-hour time period (TWA) NIOSH has recommended an 8-hour exposure limit of 85 dBA-TWA.
Noise can be controlled three ways:
- Reduce the amount of noise released at the source. Most noise problems have several practical and efficient engineering control options. Reducing force, speed, vibration and friction reduces noise. For example: mount stationary machinery on vibration-absorbing pads, maintain belts and fans so they function properly, and enclose sources with sound-absorbing material. Processes may be substituted.
- Reduce noise by changing the path between the source and the ear. For example, increase the distance from the source and decrease noise reflection from the walls and ceilings.
- Reduce noise at the ear. This can be done with personal protection (earplugs or muffs), or by isolating the worker in an enclosure lined with sound-absorbing material. Job rotation to reduce exposure time can also contribute to noise control.
An effective hearing conservation program includes noise monitoring, worker training, and signs posted to indicate high noise areas.
Earmuffs or plugs should be available to all workers exposed above 85 dBATWA. Hearing protectors must be properly fitted to work.
Earmuffs and plugs are labeled with a Noise Reduction Rating (NRR) that states how many decibels the muff or plug absorbs. A poorly understood fact is that NRRs are established in a laboratory environment and not in a real workplace, where fit is less than perfect. It has been found that actual worker fit affects the listed NRR so much that it recommends subtracting 25% from the NRR for earmuffs, 50% for formable earplugs, and 70% for all other earplugs. The NRR should not be relied upon as listed on the ear protector unless they are adjusted and properly fit the wearer.