Smoke Alarms and Hearing Loss - What Works Best?

A new study published in the February 2009 edition of the journal Ear and Hearing (Volume 30, No. 1, pp 73 - 80) investigated the effectiveness of various smoke alarms in waking people with hearing loss, and concluded that those utilizing a low frequency square wave signal were more effective than others tested. According to the study's lead author, there are currently two brands of smoke alarms utilizing a 520 Hz square wave available in the United States.

The study's abstract is provided here;for a copy of the full article or a subscription to the journal, visit: www.ear-hearing.com

Title: Smoke Alarms for Sleeping Adults Who are Hard-of-Hearing: Comparison of Auditory, Visual, and Tactile Signals

Authors: Bruck, Dorothy, School of Psychology, Victoria University, Australia

Thomas, Ian, Centre for Environmental Safety and Risk Engineering, Victoria University, Australia

Address for correspondence: Dorothy Bruck, School of Psychology, Victoria University, PO Box 14428, MCMC Melbourne 8001, Australia. E-mail: dorothy.bruck@vu.edu.au.

Objectives: People who are hard-of-hearing may rely on auditory, visual, or tactile alarms in a fire emergency, and US standards require strobe lights in hotel bedrooms to provide emergency notification for people with hearing loss. This is the first study to compare the waking effectiveness of a variety of auditory (beeps), tactile (bed and pillow shakers), and visual (strobe lights) signals at a range of intensities.

Design: Three auditory signals, a bed shaker, a pillow shaker, and strobe lights were presented to 38 adults (aged 18 to 80 yr) with mild to moderately severe hearing loss of 25 to 70 dB (in both ears), during slow-wave sleep (deep sleep). Two of the auditory signals were selected on the basis that they had the lowest auditory thresholds when awake (from a range of eight signals). The third auditory signal was the current 3100-Hz smoke alarm. All auditory signals were tested below, at, and above the decibel level prescribed by the applicable standard for bedrooms (75 dBA). In the case of bed and pillow shakers intensities below, at, and above the level as purchased were tested. For strobe lights three levels were used, all of which were above the applicable standard. The intensity level at which participants awoke was identified by electroencephalograph monitoring.

Results: The most effective signal was a 520-Hz square wave auditory signal, waking 92% at 75 dBA, compared with 56% waking to the 75 dBA high-pitched alarm. Bed and pillow shakers awoke 80 to 84% at the intensity level as purchased. The strobe lights awoke only 27% at an intensity above the US standard. Nonparametric analyses confirmed that the 520-Hz square wave signal was significantly more effective than the current smoke alarm and the strobe lights in waking this population.

Conclusions: A low-frequency square wave signal has now been found to be significantly more effective than all tested alternatives in a number of populations (hard-of-hearing, children, older adults, young adults, alcohol impaired) and should be adopted across the whole population as the normal smoke alarm signal. Strobe lights, even at high intensities, are ineffective in reliably waking people with mild to moderate hearing loss.