Fire Alarms

Audible alarm signals for people who are deaf or hard of hearing

by Peter Mapp, Ph.D., FASA, FAES

Impairment of hearing may not mean that a person is completely insensitive to sound. Many people with severe impairment have sufficiently clear perception of some types of conventional audible alarm signals (particularly those in the 500 Hz to 1,000 Hz band and rich in harmonics) and so may not need special provision, but high-frequency tones, for example, above 2 or 3 kHz may not be audible. Other venue or site occupants may be able to warn people with hearing loss (PWHL) of the initiation of alarms and, where necessary, procedures should be put in place to provide this contact facility.

In addition, visual alarms can be provided at strategic locations. The use of portable (radio based) alarms may also provide a solution. These may be visual and/or tactile and need to be able to provide notification at the portable alarm of the loss of radio signal/ interconnection with the main ESS control equipment and also, ideally, at the ESS central fault monitoring facility. (NFPA 72 requires a specific alarm signal for sleeping rooms where people may have Mild to Severe hearing loss, which comprises a signal with a fundamental frequency of 520Hz ± 10 % producing 75 dBA at the pillow). Figure 1 illustrates the harmonic structure and SPLs of a 66 dBA 500Hz square wave based warning tone.