NIOSH Uses Newer Method to Measure Impulsive Noise Exposures at Firing Ranges

A NIOSH health hazard evaluation (HHE) report published in August (see found that firearms instructors’ exposures to high-intensity impulsive noise during tactical training exercises were significantly higher than the NIOSH ceiling limit of 140 decibels (dB). A federal agency had requested that NIOSH measure the instructors’ impulsive noise exposures when training with firearms and weapons systems and calculate how much weapons fire the instructors could be exposed to per day without incurring a significant risk of hearing loss.

“The instructors were exposed to impulsive noise levels between 150 and 175 dB for most of the firearms used,” says Chuck A. Kardous, MS, PE, a research engineer in the NIOSH Division of Applied Research and Technology. “They were much higher than what you’d see at an industrial operation, where the impulsive noise is typically less than 140 dB.”
Kardous explains that the measurements were performed using the NIOSH Impulsive-Noise Measurement System (NIMS). NIOSH began developing NIMS in the early 2000s after a similar investigation showed that instruments typically used to measure impulsive noise levels, such as noise dosimeters and sound level meters, were not equipped to measure high levels of impulsive noise. 
"This was the first time we’ve used the NIMS for measuring impulsive noise at a firing range on an HHE,” said Scott E. Brueck, MS, CIH, a senior industrial hygienist at NIOSH. 
Impulsive noise is characterized by a sharp rise and rapid decay in sound levels that is less than one second in duration, and is considered to be more damaging to hearing than continuous noise. High peak levels of impulsive noise can result in instantaneous mechanical damage to the inner ear, unlike continuous noise, which tends to cause hearing damage over time.