Optimizing Fire Alarm Notification for High-Risk Groups
NFPA Journal®, November/December 2007
Smoke alarms in homes have contributed to a 50 percent decrease in fire deaths in the United States since the late 1970s. Despite this success, the NFPA’s Fire Protection Research Foundation continually strives to improve this number. Several research studies conducted by the Foundation over the past two years have focused on understanding the factors that impact the effectiveness of smoke alarms and how this changes for certain parts of the population.
The objective of the most recent study, sponsored by the U.S. Department of Homeland Security, was to study the optimization of fire alarm systems for three population groups deemed to be at high risk. The groups (selected through the development and application of a unique vulnerability assessment model) were the hard of hearing, the alcohol impaired and adults in a large group setting.
To study the effectiveness of alarms in waking the hard of hearing and the alcohol impaired, two comprehensive sleep studies with a total of 80 subjects were carried out at Victoria University of Technology. The range of impairments of both groups was in the moderate (not severe) range. In the first study, several auditory signals and a variety of alternative alarms that employ methods other than sound, such as bed shakers, pillow shakers and strobe lights, were studied for their effectiveness in alerting hard-of-hearing individuals of an emergency when they were asleep.
Results showed that the standard audible emergency evacuation signal (a repeating pattern of three tones and a pause) with a lower pitch tone (520 Hz square wave) awakened 92 percent of the hard-of-hearing participants when used at or below the code-minimum sound level of 75 decibels for 30 seconds.
The same device awakened 100 percent of the participants when raised to 95 decibels at the pillow. Researchers also noted that participants that awoke to signals were most likely to do so within the first 10 seconds of the signal’s inception. The lower pitch tone was found to be significantly more effective than the higher pitch tone (typically 3150 Hz) commonly used in today’s smoke alarms.
Based on the study, the overall single best option for alerting people with mild to moderately severe hearing loss is the use of low-frequency square wave auditory signaling devices. These devices surpass bed shakers, pillow shakers and strobe lights when presented alone. Ideally this square wave signal should be as loud as possible. The study that used moderately alcohol-impaired individuals found similar results.
Overall, the results were consistent and verifiable that the use of low-frequency square wave auditory signaling devices are the most effective for the aged, the young, the alcohol impaired, and the hard of hearing in a range of studies sponsored by the Foundation and others.
In a related discovery, the study that focused on moderately hard-of-hearing individuals found that many people are not aware of their hearing impairment. This finding, together with the findings related to alcohol impairment, suggest that any standard audible smoke alarm for the general population should emit a signal that maximises the chances hard-of-hearing people will have to awaken (provided such a signal presents no increased risk to other sections of the population).
Reports of these studies are available on the Foundation’s website. The results are under consideration for implementation in the next edition of NFPA 72®, The National Fire Alarm Code®.
Kathleen H. Almand, P.E., FSFPE, is the executive director of the Fire Protection Research Foundation.