AUDIBILITY OF REVERSE ALARMS UNDER HEARING PROTECTORS FOR NORMAL AND HEARING-IMPAIRED LISTENERS

The question of whether or not an individual suffering from a hearing loss is capable of hearing an auditory alarm or warning is an extremel y important industrial safety issue. The ISO Standard that addresses a uditory warnings for workplaces requires that any auditory alarm or wa rning be audible to all individuals in the workplace including those s uffering from a hearing loss and/or wearing hearing protection devices (HPDs). Research was undertaken to determine how the ability to detec t an alarm or warning signal changed for individuals with normal heari ng and two levels of hearing loss as the levels of masking noise and a larm were manipulated. Pink noise was used as the masker and a heavy-e quipment reverse alarm was used as the signal. The rating method parad igm of signal detection theory was used as the experimental procedure to separate the subjects' absolute sensitivities to the alarm from the ir individual criteria for deciding to respond in an affirmative manne r. Results indicated that even at a fairly low signal-to-noise ratio ( 0 dB), subjects with a substantial hearing loss [a pure-tone average ( PTA) hearing level of 45-50 dBHL in both ears] were capable of hearing the reverse alarm while wearing a high-attenuation earmuff in the pin k noise used in the study.