How loud is loud? And why should it matter? You've heard it all before, right? Well, let's check your know-how with this quick test of fact and fiction about noise exposure.
In the United States, the Permissible Exposure Limit (PEL) for noise-exposed workers on a 12-hour workshift is lower than for workers on an 8-hour workshift. TRUE!
OSHA's 90 dBA exposure limit is based upon an 8-hour time-weighted average (TWA). A worker on a 12-hour workshift should use an exposure limit of 87 dBA. Longer exposure times require lower exposure limits to be safe. For this reason, workers on extended workshifts also require hearing protectors with greater attenuation.
Any worker exposed to noise under the OSHA limit of 90 dBA TWA is safe. FALSE!
While OSHA does indeed define its PEL at 90 dBA TWA, it clearly states that this level is intended only to protect most workers—not all. A significant number of workers will still suffer permanent hearing loss at exposure levels of 85-90 dB TWA. This prompted Europe to lower its permissible exposure limit to 85 dB in 2006. In fact, the U.S. is one of the few countries still using the less protective 90 dB limit—a condition which many concerned safety professionals, including the American Industrial Hygiene Association [AIHA], are trying to change.
Noise is typically measured in A-weighted decibels (dBA). A-weighting is a correction added to noise measurement equipment to mimic the human ear. TRUE!
Most sound level meters and personal noise dosimeters have an optional A-weighting switch, allowing the user to apply an internal filter that corrects the measurements. These A-weighting corrections mimic the frequency sensitivity of the human ear, which is not as sensitive to low and high-frequency sounds as it is to mid-frequency speech sounds. OSHA advises taking your noise measurements in A-weighted decibels in Hearing Conservation Programs.
Removing an earplug for just a few minutes during the workday will not affect overall protection. FALSE!
The math seems skewed, but because the decibel scale is logarithmic (not linear), small intervals of no protection quickly cancel long intervals of adequate protection. If a worker wears a well-fit earplug with an NRR of 30 dB, but removes that earplug for just 15 minutes (cumulative) while working in noise throughout the 8-hour workday, it is as though an earplug with NRR of 15 dB was worn for the entire workday. Noise-exposed workers need to be reminded to wear hearing protection properly 100% of the time during exposures.