According to the National Institute for Occupational Safety and Health (NIOSH), four million people go to work each day exposed to damaging noise, 10 million people in the U.S. have noise-related hearing loss, and 22 million workers are exposed to potentially damaging noise each year.
With this in mind, employers have the responsibility to create hearing conservation programs should their employees be exposed to harmful noise levels and durations. The following excerpt is taken directly from OSHA's Occupational Noise Exposure page:
|How loud is too loud?
Noise is measured in units of sound pressure levels called decibels, named after Alexander Graham Bell, using A-weighted sound levels (dBA). The A-weighted sound levels closely match the perception of loudness by the human ear. Decibels are measured on a logarithmic scale which means that a small change in the number of decibels results in a huge change in the amount of noise and the potential damage to a person's hearing.
OSHA sets legal limits on noise exposure in the workplace. These limits are based on a worker's time weighted average over an 8 hour day. With noise, OSHA's permissible exposure limit (PEL) is 90 dBA for all workers for an 8 hour day. The OSHA standard uses a 5 dBA exchange rate. This means that when the noise level is increased by 5 dBA, the amount of time a person can be exposed to a certain noise level to receive the same dose is cut in half.
The National Institute for Occupational Safety and Health (NIOSH) has recommended that all worker exposures to noise should be controlled below a level equivalent to 85 dBA for eight hours to minimize occupational noise induced hearing loss. NIOSH has found that significant noise-induced hearing loss occurs at the exposure levels equivalent to the OSHA PEL based on updated information obtained from literature reviews. NIOSH also recommends a 3 dBA exchange rate so that every increase by 3 dBA doubles the amount of the noise and halves the recommended amount of exposure time.
Here's an example: OSHA allows 8 hours of exposure to 90 dBA but only 2 hours of exposure to 100 dBA sound levels. NIOSH would recommend limiting the 8 hour exposure to less than 85 dBA. At 100 dBA, NIOSH recommends less than 15 minutes of exposure per day.
As you can see, the NIOSH recommendation is more conservative than the OSHA standard requires. This may be confusing to employers, but the good news is that this exposure can be largely eliminated by putting the proper controls in place. Noise induced hearing loss is permanent, so the risks are significant.
The first choice is the elimination of the loud noise. Although this may be infeasible it should be considered. Replacing loud equipment with quieter models to decrease the exposure is a possible method. Secondly, consider an engineering control to limit the exposure. Installing insulation or acoustic tiles, or isolating machine components might be options to reduce the sound levels.
Administrative controls would be the next choice. This could include the rotation of employees to reduce each person’s exposure, training employees as to the hazards of excessive noise, and creating policies/procedures such as a formal Hearing Conservation Program.
Last, we are left with personal protective equipment (PPE). If all methods to reduce the noise to safe levels have been exhausted, then the only remaining choice is to protect employees with PPE. The choices are vast, but the imperative is that the PPE fit properly, be worn correctly, and cleaned/maintained appropriately. There are protectors available that are designed for specific tasks, those which protect under various conditions (such as electric arc flash), that have varying protection levels, and that are worn over the ears, block the ear canal opening, or that are inserted into the ear canal. Regardless of the choice, keep these things in mind regarding hearing protection devices:
- The noise reduction rating (NRR) on the packaging is only valid if worn perfectly at all times the worker is exposed. With the vagaries of fit, installation, condition of the PPE, and inconsistent use, OSHA takes this a step further to say that the NRR should be reduced by this method: NRR – 7dB, then divide by 2. So an NRR of 20 would actually be only 6.5dB.
- Hearing protectors reduce the dB level entering the ear canal. This protects the delicate inner ear components from harmful sound levels, but does not diminish the worker’s ability to hear important ambient noise such as malfunctioning equipment or aural alarms. Workers who already have hearing damage might find it more difficult to understand voices; however, these workers must be protected in order to prevent further damage!
For more information regarding hearing conservation, ear and hearing damage, or hearing protection check out the resources from It’s a Noisy Planet, OSHA’s Noise in Construction Pocket Guide, and NIOSH.