Sound Attenuation from Earmuffs and Earplugs in Combination: Maximum Benefits vs. Missed Information
Abstract
High noise levels from aircraft, small and large caliber weapons, land vehicles, ships, or submarines are characteristic of military operational environments. Continuous levels in the interior of fixed or rotary wing aircraft or in the vicinity of jet engines range from 100 - 130 dBA (15,18). Peak sound pressure levels from impulse noise produced by a howitzer may be as high as 180 dB SPL (28). Small caliber weapons such as assault rifles generate peak levels of about 150 - 165 dB SPL (15). Studies have shown that long-term exposure to unprotected 8-h A-weighted equivalent levels exceeding 85 dBA or instantaneous sound pressure levels of 140 dB will result in high-tone hearing loss (21,23). The 8-h A-weighted equivalent for a single round fired from a howitzer is 96 dB; a series of 20 rounds generates 109 dB (16). While the reduction of noise at the source through engineering controls may not be feasible in these situations, the use of personal hearing protection devices provides an easily implemented and low-cost method of hearing conservation (11). The sound attenuation provided by hearing protection devices varies widely across makes and models, particularly for earplugs. For earmuffs, attenuation increases from about 15 dB at 0.125 Hz to about 35 dB at 1 kHz and then remains fairly stable. In general, earplugs provide relatively more attenuation (15 - 40 dB) below 1 kHz, but are about the same above 1 kHz for highly rated devices (11). The attenuation realized by the individual user may fall short of expectation due to problems with fitting of the device, inadequate maintenance, incorrect sizing, slack headband tension, or incompatibility with other protective gear (2,6,11). Studies of measurements made inside earmuffs with probe microphones have shown that the attenuation may be sufficient to protect against a pistol or rifle shot, but will not reduce the level of blasts from a bazooka or canon to safe levels.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 2006
- Accession Number
- ADA507742
Entities
People
- Patricia Odell
- Sharon M. Abel
Organizations
- DRDC Toronto