For typical small arms weapons, ANOR values have permitted many thousands of rounds to be fired per day with hearing protection. Even though the assessment methodology has changed, the goal has always been to protect all but the most susceptible 5% of the exposed population from having their hearing permanently impaired ( Patterson, 1985). Newer ANOR assessment methods are part of MIL-STD 1474E ( U.S. Department of Defense, 1997) for many years to determine how many rounds per day (Allowable Number of Rounds, or ANOR) could be fired when either single (ear plugs or ear muffs) or double (both ear plugs and ear muffs) hearing protection were worn. These characterizations of the impulse sound were used in the Department of Defense (DOD) Design Criteria Standard for Noise Limits (MIL-STD 1474 D) ( U.S.

The risk of hearing loss associated with intense impulse noise has long been thought to be correlated to the number of rounds to which an individual may be exposed, the peak level of the noise, and to the B-duration of the impulse (a measure of the time it takes for the impulse noise to decay to levels 20 dB lower than the peak level Garinther, 1975). Several shipboard, ground, and air transportation and weapon platforms create interior 110 dBA environments during operation ( James and McKinley, 2004 Tufts, 2009). An 8-h average level of 85 dBA triggers the need for Hearing Conservation Programs (Occupational Health and Safety Administration, or OSHA) and any exposure in the Army and Air Force to levels of 85 dBA (regardless of average levels) mandates hearing protection be worn ( OSHA, 1983 U.S.

Almost all of the ground and air transportation platforms expose crew and passengers to steady-state noise higher than 85 dBA while operating. Several classes of weapon systems expose crew to impulse noise levels that exceed 180 dBP. Department of Defense, 2010) at the operator's ears. For example, with the exception of the bayonet and the crossbow (which are used today by Special Forces), every Military weapon system makes more than 140 dB peak sound pressure level (dBP), a level generally considered the maximum for a single safe unprotected exposure for impulse noise ( OSHA, 1983 U.S. In fact, they are likely to have exposure to some of the most intense sounds that can be found in any occupation. All Military personnel are going to be exposed to loud sounds.

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