NIOSH and 3M E-A-RCAL both purchased acoustic test fixtures from the French-German Research Institute of Saint-Louis (ISL) built following the publication of the ANSI/ASA S12.42-2010 standard. In the Discussion section, the effects of the fixture position, ear canal length, and the performance of double protection are discussed. In the Results section, the impulse waveforms are described and the results for each of the hearing protector conditions and the statistical analyses are presented. The Methods section describes the construction of the test fixtures, the acoustic impulse source, the hearing protectors used as well as the data acquisition system and analysis methods. This paper reports and compares the measurements obtained with both fixtures. This study utilized two models of the same ATF to measure the impulsive response of four hearing protector conditions. Comparative measurements of the performance of hearing protectors with an ATF are useful for the development of national and international standards also, the methods in the American National Standards Institute/Acoustical Society of America (ANSI/ASA) S12.42 standard are still being refined to understand the assessment of hearing protection when exposed to high-level impulse noise. The purpose of this study that was carried out at the 3M E-A-RCAL Laboratory (Indianapolis, IN, USA) was to utilize a more controlled laboratory environment to investigate the impulse peak insertion loss (IPIL) performance of a variety of protectors. In previous field studies, NIOSH personnel evaluated different ATFs, hearing protectors, and impulse noise sources. The American National Standards Institute Subcommittee 12 (Noise) Working Group 11 subsequently revised the ANSI S12.42 standard using the EPA methods. The peak levels are allowed to vary from target levels within a range of ☒ dB, and the initial overpressure (A-duration) can vary between 0.5 and 2.0 milliseconds (ms). The EPA's methods evaluate a protector's performance at nominal impulse levels of 132, 150, and 168 dB peak SPL. The US Environmental Protection Agency (EPA) recently proposed a new metric to characterize the performance of hearing protection devices in high-level impulse noise. Acoustic test fixtures (ATFs) have been used to measure insertion loss of hearing protection devices over a wide range of impulse levels, 110-190 decibel peak sound pressure level (dB peak SPL). Human subjects cannot ethically be used to assess HPD performance with high-level impulse noise due to the risk of inducing a threshold shift in the event that the protection fails to work as expected. Hearing protection devices (HPDs) attenuate and filter an impulse and are integral to damage risk criteria and occupational safety and health standards. High-level, short-duration impulses present a greater risk of noise-induced hearing loss than continuous noise of similar and equivalent energy levels. For the NIOSH ATF, the right ear IPIL was 0.3 dB greater than the left ear IPIL. For the E-A-RCAL ISL ATF, the left ear IPIL was 2.0 dB greater than the right ear IPIL. The IPILs measured for the E-A-RCAL fixture were 1.4 dB greater than the National Institute for Occupational Safety and Health (NIOSH) ISL ATF. Four hearing protection conditions were tested: Combat Arms earplug with the valve open, ETYPlugs ® earplug, TacticalPro headset, and a dual-protector ETYPlugs earplug with TacticalPro earmuff. The fixtures were identical except that the E-A-RCAL ISL fixture had ear canals that were 3 mm longer than the National Institute for Occupational Safety and Health (NIOSH) ISL fixture. Two models of an ATF manufactured by the French-German Research Institute of Saint-Louis (ISL) were evaluated with high-level acoustic impulses created by an acoustic shock tube at levels of 134 decibels (dB), 150 dB, and 168 dB. IPIL is the difference between the maximum estimated pressure for the open-ear condition and the maximum pressure measured when a hearing protector is placed on an acoustic test fixture (ATF). Impulse peak insertion loss (IPIL) was studied with two acoustic test fixtures and four hearing protector conditions at the E-A-RCAL Laboratory.