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 any other method of notification. Most of today's appliances produce sound pressure levels between 45 and 120 decibels at ten feet.
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
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 signaling 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 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 1971, Space Age Electronics introduced the first
combined audio/visual notification appliance. Visual signals
throughout the 1970s and 1980s were usually white or red
incandescent lights. In the 1980s, most new installations began to
include visual signals. In the United States, the 1990 Americans
with Disabilities Act (ADA) triggered changes in evacuation
signaling methods to include the hearing impaired. Audible
notification appliances would now include strobe lights to alert the
hearing impaired. This made incandescent lights inadequate for the
purposes of the ADA. Many existing installations that did not
include visual signals were retrofitted with strobe plates. These
retrofit plates would allow for the easy installation of a strobe
without replacing the audible signal. 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. Companies such as Wheelock and Simplex
discontinued their translucent strobes, and replaced them with new,
clear, high-intensity strobes. Today, strobe synchronization is
often used to synchronize all strobes in a uniform flash pattern.
This is to prevent individuals with photosensitive epilepsy from
potentially experiencing seizures due to unsynchronized strobes.
Voice evacuation systems have become popular for
high-rises, schools, hospitals, and 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 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. In the 1990s, voice
evacuation started to become the standard for large facilities, and
is still growing in popularity.
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. 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. It is expected that products using the new alerting technology will be available in the future.