August 2, 2007- According to the July 2007 study, "Waking Effectiveness of Alarms for Adults who are Hard of Hearing," the typical audible signal used by smoke alarms failed to wake up 43 percent of tested subjects with mild to moderately severe hearing loss despite the fact that all were able to hear the 3100 Hz tone when awake. Strobe lights woke up only 27 percent of the hard of hearing subjects. In contrast, a specific audible multiple frequency signal consisting of a 520 Hz square wave [1]successfully alerted 92 percent of the subjects at the benchmark 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 Hearing Loss Association of America (HLAA) has long suspected that people have died in fires because they could not hear or wake up to high-frequency smoke alarms, but government investigations of fire fatalities have not inquired into whether the victims had hearing loss. Neither audible smoke alarms nor strobe lights were specifically tested with hard of hearing people during stages of deep sleep until the twenty-first century. The findings of this study indicate that millions of people with hearing loss will not be wakened from deep sleep by audible alerts which use only one tone in the high frequencies rather than a range of frequencies beginning at approximately 500 Hz.
"This study shows there is a critical need for emergency warning systems to be redesigned or supplemented as soon as technically feasible, said Terry Portis, executive director of the Hearing Loss Association of America. "Millions of people do not and will not know that they will not wake up to the high-pitched tones used by most emergency alerts. We call upon manufacturers of emergency alerting equipment, such as smoke alarms, carbon monoxide alarms, and weather radios, to provide solutions that recognize this reality as soon as possible."
The study evaluated the performance of six different signals for waking up hard of hearing people from deep sleep and found the 520 Hz square wave to be the most effective of all the signals. Bed and pillow shakers awoke 80 percent of the subjects at benchmark levels, awaking the majority very quickly, but did not wake up 100 percent of the subjects even at higher levels of intensity.
For people with more severe hearing loss, the authors recommended studying the effectiveness of two or more different signals, such as a 520 Hz square wave audible signal with a tactile alert and/or a strobe light.
"Even though strobe lights may not be effective by themselves at waking up hard of hearing people from deep sleep, it's important to remember that strobe lights are still needed for alerting deaf people when they are awake and are not in contact with a tactile alerting device," said Dana Mulvany, member of the Technical Panel for the research project.
"Presently, there are no known emergency alerting products on the market incorporating a range of tones and also including a low frequency near 500 Hz," Mulvany said. "Other research has already shown that the 520 Hz square wave is superior to the 3100 Hz tone for waking up other vulnerable populations, such as elderly people and people under the influence of alcohol. All manufacturers of emergency warning devices, including smoke alarms, carbon monoxide alarms and weather radios, should explore methods of providing variations of the 520 Hz square wave as an audible alert so that people with unknown, temporary or permanent partial hearing loss can be awoken quickly from deep sleep. Manufacturers also need to specify the frequency response of their audible alerts so that customers of all kinds can make informed decisions about their purchases."
Brenda Battat, associate executive director of HLAA, said: "Operators of hotels, motels, college dormitories and many other facilities with sleeping areas must ensure that they provide equally effective communication access for people with hearing loss to the building alarm system, which is required by Title II and III of the Americans with Disabilities Act (ADA). Many deaf or hard of hearing guests have been provided portable alerting systems with a bed shaker, but these systems have typically not provided effective alerting when the building alarm system is triggered and have only been activated by smoke within the guest's own room, which is too late for optimal notification. We urge people with hearing loss to file complaints under the Americans with Disabilities Act if they are not provided effective alerts to the building alarm system by ADA-covered entities."
Hearing Loss Association of America thanks the Fire Protection Research Foundation for commissioning this research study, and Drs. Bruck and Thomas for their intensive work on this study. The study is available online at: www.nfpa.org/assets/files//PDF/Research/hardofhearing&alarms.pdf
[1] A 520 Hz square wave signal contains multiple harmonics of the fundamental 520 Hz frequency, becoming a multiple-frequency signal which is thus more likely to be heard by people with sufficient hearing at one or more of the frequencies in the signal.
About Hearing Loss Association of America
The Hearing Loss Association of America (HLAA), founded in 1979 under the name of Self Help for Hard of Hearing People, opens the world of communication to people with hearing loss through information, education, advocacy and support. HLAA publishes the bimonthly Hearing Loss Magazine, holds annual conventions, Walk4Hearing, and more. Information can be found at www.hearingloss.org. The national headquarters is located at 7910 Woodmont Avenue, Suite 1200, Bethesda, MD 20184. HLAA has chapters and state organizations across the country.
