Introduction
P/N 151204
1-3
Limitations of Fire Alarm Systems
Manufacturer recommends that smoke and/or heat detectors be located throughout a protected premise following the
recommendations of the current edition of the National Fire Protection Association Standard 72 (NFPA 72), manufacturer’s
recommendations, State and local codes, and the recommendations contained in Guide for the Proper Use of System Smoke
Detectors, which is made available at no charge to all installing dealers. A study by the Federal Emergency Management
Agency (an agency of the United States government) indicated that smoke detectors may not go off or give early warning in as
many as 35% of all fires. While fire alarm systems are designed to provide warning against fire, they do not guarantee warning
or protection against fire. A fire alarm system may not provide timely or adequate warning, or simply may not function, for a
variety of reasons. For example:
•
Particles of combustion or smoke from a developing fire may not reach the sensing chambers of smoke detectors because:
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Barriers such as closed or partially closed doors, walls, or chimneys may inhibit particle or smoke flow.
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Smoke particles may become cold, stratify, and not reach the ceiling or upper walls where detectors are located.
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Smoke particles may be blown away from detectors by air outlets
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Smoke particles may be drawn into air returns before reaching the detector.
In general, smoke detectors on one level of a structure cannot be expected to sense fires developing on another level.
•
The amount of smoke
present may be insufficient to alarm smoke detectors. Smoke detectors are designed to alarm at
various levels of smoke density. If such density levels are not created by a developing fire at the location of detectors, the
detectors will not go into alarm.
•
Smoke detectors, even when working properly, have sensing limitations. Detectors that have photoelectronic sensing
chambers tend to detect smoldering fires better than flaming fires, which have little visible smoke. Detectors that have
ionizing-type sensing chambers tend to detect fast flaming fires better than smoldering fires. Because fires develop in
different ways and are often unpredictable in their growth, neither type of detector is necessarily best and a given type of
detector may not provide adequate warning of a fire.
•
Smoke detectors are subject to false alarms and nuisance alarms and may have been disconnected by users. For example,
a smoke detector located in or near a kitchen may go into nuisance alarm during normal operation of kitchen appliances.
In addition, dusty or steamy environments may cause a smoke detector to falsely alarm. If the location of a smoke
detector causes an abundance of false alarms or nuisance alarms, do not disconnect the smoke detector; call a professional
to analyze the situation and recommend a solution.
•
Smoke detectors cannot be expected to provide adequate warning of fires caused by arson, children playing with matches
(especially within bedrooms), smoking in bed, violent explosions (caused by escaping gas, improper storage of flammable
materials, etc.).
•
Heat detectors do not sense particles of combustion and are designed to alarm only when heat on their sensors increases at
a predetermined rate or reaches a predetermined level. Heat detectors are designed to protect property, not life.
•
Warning devices (including horns, sirens, and bells) may not alert people or wake up sleepers who are located on the other
side of closed or partially open doors. A warning device that activates on a different floor or level of a dwelling or
structure is less likely to awaken or alert people. Even persons who are awake may not notice the warning if the alarm is
muffled by noise from a stereo, radio, air conditioner or other appliance, or by passing traffic. Audible warning devices
may not alert the hearing-impaired (strobes or other devices should be provided to warn these people). Any warning
device may fail to alert people with a disability, deep sleepers, people who have recently used alcohol or drugs, or people
on medication or sleeping pills.
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Please note that:
i)
Strobes can, under certain circumstances, cause seizures in people with conditions such as epilepsy.
ii)
Studies have shown that certain people, even when they hear a fire alarm signal, do not respond or comprehend
the meaning of the signal. It is the property owner’s responsibility to conduct fire drills and other training exer-
cises to make people aware of fire alarm signals and instruct on the proper reaction to alarm signals.
iii) In rare instances, the sounding of a warning device can cause temporary or permanent hearing loss.
•
Telephone lines needed to transmit alarm signals from a premises to a central station may be out of service or temporarily
out of service. For added protection against telephone line failure, backup radio transmission systems are recommended.
•
System components, though designed to last many years, can fail at any time. As a precautionary measure, it is
recommended that smoke detectors be checked, maintained, and replaced per manufacturer's recommendations.
•
System components will not work without electrical power. If system batteries are not serviced or replaced regularly, they
may not provide battery backup when AC power fails.
•
Environments with high air velocity or that are dusty or dirty require more frequent maintenance.
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Summary of Contents for SILENT KNIGHT SK-5208
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