![]() Atherly and Martin (1971) first proposed using an integrated A-weighted equivalent energy as a damage risk criterion. In reference to this standard, some suppressors are labeled as Hearing Safe if they are not expected to produce sound levels in excess of 140 dB SPL. The MIL-STD-1474D (1997) included no limits for impulsive sounds with peaks below 140 dB SPL, and it assumed that all exposed listeners would use hearing protectors above 140 dB SPL. The peak sound pressure level of the weapon, the B-duration (the time for the envelope of the gunshot to decay by 20 dB from the peak impulse level) and the number of shots that were expected to be fired were used to estimate the allowable number of rounds that a person could “safely” fire. Department of Defense used the MIL-STD 1474D as a de facto DRC. The simplest of these criteria is based on the peak level, wherein peak levels over 140 dB SPL are considered hazardous to adults and peak levels over 120 dB SPL are considered hazardous to children ( WHO 1997). Several noise exposure damage risk criteria (DRCs) for small caliber firearms exist to protect persons from hearing hazards. This component of firearm noise associated with the projectile is not expected to be altered by the use of a suppressor. Therefore, if the propellant charge is capable of accelerating the projectile to a supersonic speed, an N-wave will still be produced. Under ideal conditions, the suppressor does not alter the velocity of the projectile. ![]() Thus, the effectiveness of the suppressor will depend upon the length of the suppressor, the number of baffles and orifice dimensions within the suppressor. The peak energy escaping the muzzle is diminished by allowing the expanding gasses to pass through small orifices separating the baffle sections. The shock front can be disrupted by passing through a series of baffles in the suppressor. ![]() As an engineering noise control, the firearm suppressor minimizes the muzzle blast by breaking up the initial wavefront. The muzzle blast is characterized by a sharp pressure rise that generally follows an exponentially decaying oscillation as the gases condense at the shock wave and then return to their quiescent state. Figure adapted from Rasmussen et al 2009, Figure 9. The peak levels of the N-wave and shock wave are indicated with inverted triangles. The N-wave will start at the trajectory of the bullet and radiate cylindrically outwards from that line (See Figure 1).Īn example of an N-wave preceding the blast wave. If the bullet is accelerated to supersonic speed, the waveform observed down range will include a ballistic N-shaped wave (N-wave) in addition to the muzzle blast. Depending upon the ammunition characteristics, the projectile may be accelerated beyond the speed of sound in air thus breaking the sound barrier. After the projectile exits the barrel, the gases and unburnt propellant follow and produce what is called the muzzle blast. The primer ignites and combusts the powder, producing a larger volume of gas that forces the projectile out of the barrel. The trigger releases a firing pin that strikes a cartridge containing a primer, powder, and the projectile. ![]() The pull of a gun trigger initiates a chain reaction of events that result in one or more projectiles being fired down range. Limiting the time or number of rounds or the type of ammunition that a person may fire in a given training session is an administrative control. Firearm suppressors are an engineering noise control. However, the standard for industrial hygiene practice has been to follow a hierarchy of controls, beginning with eliminating or replacing the process that produces the exposure, then moving to engineering or administrative solutions to minimize the exposure, and then finally relying on personal protective equipment as a last resort. The most common approach to protecting the shooter and bystanders from the high-level impulse exposures has been to provide personal protective equipment - hearing protection devices (HPDs). The impulses from gunfire present a significant hazard to the hearing of the shooter and nearby shooters or bystanders. 30 caliber rifle with a muzzle brake ( Murphy et al 2012). ![]() 22 caliber rifle to well above 175 dB peak SPL for a. Peak sound pressure levels have been reported for small caliber rifles, pistols and shotguns ranging between 140 decibels peak sound pressure level (dB peak SPL) for a. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |