Measurement of impulse peak insertion loss for four hearing protection devices in field conditions

Abstract

Objective-In 2009, the U.S. Environmental Protection Agency (EPA) proposed an impulse noise reduction rating (NRR) for hearing protection devices based upon the impulse peak insertion loss (IPIL) methods in the ANSI S12.42-2010 standard. This study tests the ANSI S12.42 methods with a range of hearing protection devices measured in field conditions. Design-The method utilizes an acoustic test fixture and three ranges for impulse levels: 130-134, 148-152, and 166-170 dB peak SPL. For this study, four different models of hearing protectors were tested: Bilsom 707 Impact II electronic earmuff, E·A·R Pod Express, E·A·R Combat Arms version 4, and the Etymotic Research, Inc. Electronic BlastPLG™ EB1.Study sample-Five samples of each protector were fitted on the fixture or inserted in the fixture's ear canal five times for each impulse level. Impulses were generated by a 0.223 caliber rifle.

In-depth survey report: comparison of the performances of three acoustic test fixtures using impulse peak insertion loss measurements, Rudyard, Michigan.

“…During testing, care was exercised to avoid having visible wrinkles of the flanges, which could introduce an acoustic leak. Flanged earplugs fitted into the shortest ear canal of the single-ear ISL ATF may not have had a good seal with the ear canal extension (Murphy, 2003;Murphy et al, 2012). In two other unpublished studies conducted at Fort Rucker (2011) and at EARCAL (2014), the IPIL observed for flanged earplugs exhibited slightly less attenuation for the longer ear canals of the 18 mm GRAS 45 CB and the 16 mm ISL-2 ATFs than for the 13-mm ISL-2 ATF.…”

“…The three fixtures were chosen to compare results with previously published data collected with the ISL fixtures (Murphy and Tubbs, 2007;Berger and Hamery, 2008;Murphy et al, 2012). The single-ear ISL ATF had an IEC 60711 ear simulator (B&K 4157 with a B&K 4398 quarter-inch microphone) with ear canal length of 10 mm and an inner diameter of 7.5 mm (Buck and DeMezzo, 2008).…”

“…These protectors are illustrated in Figure 1. These protectors were selected to compare the attenuation results with an earlier study that was conducted with different acoustic noise sources (Murphy et al, 2012). The ETYPlugs are now manufactured with two different sized ear tips.…”

“…The third (original NIOSH) fixture was a single-eared fixture and was built by ISL in 2001 according to their original designs (Parmentier et al, 2000). The purpose of including the third fixture in this study was to compare the performance with previously published data collected with the original ISL fixture (Murphy and Tubbs 2007;Murphy et al, 2012).…”

“…The NRR for a typical passive hearing protector seems to provide a lower bound for the attenuation of a protector when used in impulse noise (Murphy and Tubbs, 2007;Murphy et al, 2012;Khan et al, 2013). The upper bound of attenuation appears to be the bone conduction limit (Berger et al, 2003;Khan et al, 2013).…”