Computing cochlear pressure exposures from weapon systems using free-field to cochlea transfer functions

Overpressures generated by weapon systems can induce cochlear damage. Historically, the risk of injury has been assessed using free-field pressure waveforms. However, this approach fails to consider the modifying effects of human tissue and bone. To address this limitation, we developed transfer functions that convert free-field pressure signatures into approximations of the exposures that reach the cochlea. These transfer functions were derived from simultaneous free-field and cochlear pressure data recorded during shock tube exposures at varying peak pressures (1, 4, 8, and 12 psi) with and without hearing protection devices (HPDs). Our findings indicate that high frequencies (> ∼1000 Hz) are amplified by the human skull. Weapon system pressure signatures are processed using the transfer functions to approximate the intracochlear pressure differential between the scala vestibuli and scala tympani. The pressure-dependent transfer function is interpolated between the collected data based on the peak pressure of the incident waveform. The transformed data shows that the protective effects of HPDs vary based on the incident waveform. Protection tends to be effective at high frequencies, while low frequency pressures often exceed a 140 dB limit. Future studies may identify optimal HPDs for weapon operators that mitigate the harmful effects of blast exposures.