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Low Frequency Alarms are more likely to wake Inebriated People, People with Impaired Hearing and Older Folks

By Mark K. Goldstein, Ph.D., May 15th, 2012

According to the Research study by Bruck and Thomas of Victoria University in Australia we need to change the alarm signal for most life safety alarms.  The study entitled "Waking Effectiveness of Alarms for Adults who are Hard of Hearing," most audible signals used by life safety products such as carbon monoxide and smoke alarms did not wake up 43 percent of tested subjects.  These subjects have only mild to moderate hearing loss. Today alarms use about 3000 Hz to 4000 Hz.

Many of these subjects were unable to hear the 3100 Hz tone when awake.  By adding a strobe light to the alarm in the test an additional 27 percent of the hard of hearing subjects were awakened.

In another test using a different frequency (520 Hz) and using a square wave output signal from the alarm, 92 percent were awakened.  Other frequencies were tested but 520 Hz was the most successful at just a sound level of 75 dBA and alerted 100 percent at 95 dBA.

The study, authored by Dorothy Bruck and Ian Thomas of Victoria University, Australia, estimated at least 34.5 million people in the United States have partial hearing loss and projected that this number would increase due to the aging of the baby boomer generation.

The NFPA 720 Committee accepted a proposal to require a 520 Hz low-frequency tone to awaken people with hearing loss.  This means that sleeping areas required to have CO alarms will need to use 520 HZ.  The 520 Hz CO alarm signal will be required after January 1, 2015 in locations where the hearing impaired might be in commercial sleeping areas.   In CO detection systems, the 520 Hz tone shall be provided voluntarily for those with hearing loss or if the law or code requires them. These new requirements are based on several studies but the first I know of was done in Australia.  They have been a leader in hearing loss alert and hearing loss for alcohol-impaired adults.  On the lighter side, I know of several people lining up to take part in some future studies of hearing loss for alcohol-impaired adults because they suspected that the beer will be provided by the researchers.

Bruck, D., Ball, M., & Thomas, I. R. (September 2011). Fire fatality and alcohol intake: Analysis of key risk factors. Journal of Studies on Alcohol and Drugs, 72(5), 731-736.

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