Calculation of laboratory spectrum uncertainty for various categories of hearing protectors

Hearing protection devices (HPD) are commonly used to protect workers exposed to dangerous levels of noise, and their effective attenuation can now be routinely assessed using fit testing system, also known as Field Attenuation Estimation Systems (FAES). FAES typically rely on the use of the Noise Level Reduction Statistics (NRSA), a single number factoring in the attenuation obtained at the seven octave band frequencies from 125 to 8000 Hz, and accounting for the spectrum uncertainty component resulting from different slopes in the HPD attenuation across these frequencies. In the current study, this spectrum uncertainty has been computed from the NIOSH 2004 Compendium, a large database of typical laboratory attenuation, for a large number of HPDs (n=340). It has been found to be ranging from 0.4 dB to 4.8 dB. The study also includes a detailed spectrum uncertainty budget for the various categories of earplugs (roll-down foam , premolded), semi-inserts and earmuffs. These values could be used as reference values in the upcoming ANSI S12.71 standard on FAES.