fire alarm

Fire alarm notification appliance

A fire alarm notification appliance is an active fire protection component. A notification appliance may use audible, visible, or other stimuli to alert the occupants of a fire or other emergency condition requiring action.

Audible appliances have been in use longer than other methods. Today's appliances produce sound pressure levels between 45 and 120 decibels at ten feet.

The majority of audible notification appliances installed prior to 1996 produced a steady sound for evacuation. In general, no common standard at that time mandated any particular tone, or pattern for audible fire alarm evacuation signals. While less common than a steady sound, differing signalling methods were used for the same purpose. These are named with respect to their distinctive structure and include, March Time (usually 120 pulses per minute but sometimes at 90 pulses or 20 pulses per minute, depending on the panel), Hi-Lo (repeatedly changing tone), Slow-Whoop (slow rising sweep upwards in tone) among others. Today these methods are confined to applications intended to trigger a response other than evacuation alone.

In 1973, the Autocall fire alarm company manufactured the first voice-evacuation fire alarm system , and starting in the 1980s many other companies began producing voice-evacuation fire alarm systems, which have become popular for high-rises, schools, hospitals among other large facilities. Voice-evacuation alarms typically are not as loud as horns or bells, and usually sound an alarm tone (typically either Slow Whoop or a Code-3 tone) and a voice message warning that an emergency has been reported and to evacuate the building (often also mentioning not to use elevators). Voice-evacuation systems can also be used by personnel to give specific information and/or instructions over the alarm system. Usually they are either tied into the building's public address system or are outfitted with their own speakers (usually also equipped with strobe lights).

In 1996, the ANSI and the NFPA recommended a standard evacuation pattern to eliminate confusion. The pattern is uniform without regard to the sound used. This pattern for smoke alarms is named the Code-3 temporal pattern (often referred to as T3) and produces an interrupted four count (three half second pulses, followed by a one and one half second pause). CO (carbon monoxide) detectors are specified to use a similar pattern using four pulses of tone (often referred to as T4).

In the United States, the 1990 Americans with Disabilities Act (ADA) triggered changes in evacuation signaling methods to include the hearing impaired. Audible fire alarm, would now include strobe lights to alert the hearing impaired. The 1996 ADA also required that the strobe to be at least 15 candelas and have a flash rate of at least 60 flashes a minute. Strobes are often required to have translucent or clear lenses (in recent years, very few fire alarm companies manufacture translucent-lens strobes) More recent research suggests that strobe lights are not effective at waking sleeping adults with hearing loss and suggest that a different alarm tone is much more effective. Individuals in the hearing loss community are seeking changes to improved awakening methods.

Older fire alarm notification appliances may have included incandescent lights as part of the audible appliance. Today, these are considered inadequate for the purposes of the ADA. These have been replaced by high intensity white strobe lights flashing at a uniform rate of between 1 and 2 flashes per second. In some cases this requires electronic synchronization of appliances supplied from different sources. Bells are often mounted onto plates that include a strobe unit on them. These are called retrofits. Although they are often used for bells, they are sometimes used for horns as well, sometimes used to upgrade old fire alarm systems in an instance where replacing the old horn (and light plate) is unnecessary.

Alarms and alerts

The primary function of the notification appliance is to alert persons at risk. Several methods are used and documented in industry specifications published by UL.

Alerting methods include:

  • Sound (audible signals)
    • usually around 3200 Hz due to component constraints
    • 45dB to 120dB A weighted for human hearing
  • Light (visible signals)
    • 15cd to 1000cd candela output
    • 1 to 2 flashes per second

While current technology is very effective at detecting smoke and fire conditions, there have been concerns about the effectiveness of the alerting function in awakening sleeping individuals in certain high risk groups of people.

Initial research into the effectiveness of the various alerting methods is sparse. Recently (2005-2007), research sponsored by the NFPA has focused on understanding the cause of a higher number of deaths seen in high risk groups such as the elderly, those with hearing loss, and those who are intoxicated.

Research findings suggest that a low frequency (520 Hz) square wave output is significantly more effective in the high risk individuals at awakening. It is expected that products using the new alerting technology will be available in the future.


See also

Alarm manufacturers

References

  • National Fire Protection Code, Article 72
  • Underwriters Laboratories UL 217: Single and Multiple Station Smoke Alarms
  • Underwriters Laboratories UL 1971: Signaling Devices for the Hearing Impaired

External links

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