Fire and Life-Safety Innovations in Audio

By Consulting Specifying Engineer Staff November 2, 2004

Two new innovations in audio technology that are applicable to fire-protection and security systems in buildings have been announced recently—directional sound technology and smart audio surveillance.

Directional sound technology works in conjunction with smoke detectors and audible/visible notification devices to expedite occupant evacuation from burning buildings. Device manufacturers that are using this technology claim that it provides significant improvement over using only visual-based emergency egress aids, such as emergency lighting and photoluminescent guidance strips and standard sound alarms.

Directional sound systems deploy a series of evacuation beacons throughout a facility that offer easy-to-understand, nonverbal cues to draw people through the building and out to safety.

“Sound beacons are not intended to replace traditional fire-alarm sounders,” says Professor D. Withington of the University of Leeds School of Biomedical Sciences and lead researcher on the directional sound studies. He explains that the fire alarm plays an important role in alerting people to potential threats, but that their sound does not help people find their way out.

“The fire alarm sound itself would be unsuitable for use over an exit. It is a narrowband sound and thus not possible to localize,” says Withington.

Neurophysiologists and psychoacousticians have studied how the brain processes sounds and what types of sound prompt accurate responses. Test subjects reported that the melodies, denoting “up” or “down” information, informed them not only of the presence of a staircase but also of the intended direction of travel. They intuitively understood the associative meaning of the sound. Overall evacuation time in tests using the beacons was reduced substantially—by more than two-thirds in many cases. In fact, evacuation times were close to what would have been expected under ideal visual conditions with prior building knowledge.

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In the world of security, a new audio surveillance system may be used to fight crime. Software developed by Ted Berger, director of the University of Southern California Center for Neural Engineering, can be trained to recognize and distinguish sounds that are indicators of a security breach or a safety hazard, such as a gunshot or the rattle of someone climbing a chain-link fence. The software is based on mathematical models that mimic the way the brain interprets sound, but it can distinguish between two similar sounds far more precisely than the human ear.

Oak Brook, Ill.-based Safety Dynamics plans to implement the software in surveillance devices that monitor urban activity . Mounted on streetlight poles, the devices will listen for gunshots, then guide surveillance cameras toward the source of the sounds. Berger says the technology can also be used for large-scale security; an array of detectors placed along a deserted border, for example, could listen for footfalls or whispers, painting a scene solely on the basis of acoustic information. The detectors could then notify a central location of any suspicious activity.

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