Mining Publication: Current State of Insert-Type Hearing Protector Fit-Testing: Follow-On Measurements in the Steel Industry and Fit-Testing in a Mobile Environment
In a previous issue of Spectrum (October 1999, 16/4), a system of measuring the attenuation provided by insert-type hearing protectors was described. That report described experiences using the FitCheck (Michael & Associates, Inc.) System in a pilot project involving the steel industry during 1998. The FitCheck system utilizes a set of large custom-designed headphones that stand off of the ears and do not affect hearing protector fit. These headphones are used to conduct audiograms on individuals who wear insert-type hearing protectors, both with the hearing protection device (HPDs) fitted and with the ears open. The attenuation provided at each test frequency is calculated by first subtracting the cars open threshold from the cars occluded threshold. This value is then adjusted by applying a regressions equation correction that allows direct comparison to laboratory data. This small correction factor is applied to account for the difference between headphone and sound field audiometric procedures.