The question of whether or not an individual suffering from a hearing loss is capable of hearing an auditory alarm or warning is an extremely important industrial safety issue. International standard ISO 773 1—1986(E), Danger Signals for Work Places — Auditory Danger Signals, requires that any auditory alarm or warning be audible to all individuals in the workplace, including those suffering from a hearing loss and/or wearing hearing protection devices (HPDs). Very little research has been conducted to determine how an individual's hearing level affects his/her ability to detect an auditory alarm or warning in a high-noise environment while wearing an HPD.

The research effort described herein was undertaken to determine how the ability to detect an alarm or warning signal changed for individuals with normal hearing and two levels of hearing loss as the levels of masking noise and alarm were manipulated. Pink noise was used as the masker since it is a generally-accepted, generic substitute for industrial noise. A heavy-equipment reverse alarm was used as the signal since it is a common alarm in industrial facilities and construction sites. The rating method paradigm of signal detection theory was used as the experimental procedure in order to separate the subjects’ absolute sensitivities to the alarm from their individual criteria for deciding to respond in an affirmative manner.

Results indicated that even at a fairly low signal-to-noise ratio (0 dB), individuals with a substantial hearing loss [a pure-tone average (PTA) hearing level on the order of 45-50 dBHL in both ears] are capable of hearing the alarm while wearing a high-attenuation earmuff. Predictive models were developed using nonlinear regression techniques. These models may be used to predict whether or not individuals with known hearing levels will be capable of hearing the alarm under known conditions or to determine the level of alarm presentation in order to be heard reliably by individuals with a specified range of hearing for given noise levels