THE ANSI STANDARD S12.68-2007 METHOD OF ESTIMATING EFFECTIVE A-WEIGHTED SOUND PRESSURE LEVELS WHEN HEARING PROTECTORS ARE WORN: A CANADIAN PERSPECTIVE

摘要

The most serious and difficult issue with hearing protection devices (HPD) is to estimate the protected noise level at the wearer's ear Such estimation is difficult for two reasons. First, the effective field attenuation of an HPD on a given user is rarely known. Instead, the Noise Reduction Rating (NRR), specified in the USA by Code of Federal Regulations CFR 40 Part 211, that represents the 98th percentile of the group attenuation of test-subjects tested in a laboratory, is currently used. Such use of the NRR provides a highly unrealistic assessment, not only because the NRR value dramatically overestimates the attenuation with respect to real-life situations, but also because the NRR does not reflect the inter-subject variability in terms of attenuation for a given HPD Second, is the issue associated with the practical use of the NRR is that it requires the C-weighted exposure level, which is rarely available in practice, and assumes that the noise spectrum is flat per octave-band (pink noise).