NIOSH Uses Newer Method to Measure Impulsive Noise Exposures at Firing Ranges
A NIOSH health hazard evaluation (HHE) report published in August (see http://bit.ly/hheimpulsivenoise) 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.
"IHs have to ensure that firearms instructors are using proper hearing protection and are getting their initial and annual audiograms."
Brueck and Kardous recommend that firearms instructors minimize exposures by wearing dual hearing protection and that all employees be fit-tested for the insert-type hearing protectors they use. They also recommend the use of noise suppressors, if legally permissible, to reduce peak sound pressure levels and the installation of other noise controls such as acoustical materials and panels at firing ranges.
“Some firing ranges have operator booths where the instructors will stand during tactical exercises to minimize exposures,” Brueck states. “Administrative controls can also be implemented. When we know the allowable number of rounds that a person can be exposed to, instructors can use that information to limit their number of rounds per day.” The Bureau of Justice Statistics estimates that 1.2 million law enforcement officers are employed by federal, state, and local police departments and they all must participate in annual firearms qualification exercises. Brueck believes that the role of IHs in investigating noise exposures at firing ranges will continue to grow. “IHs have to ensure that firearms instructors are using proper hearing protection and are getting their initial and annual audiograms,” he says. “We have to get the word out that the methodology used in the past has not been adequate and make sure that people are using the right tools and methods to assess impulsive noise.”
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