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Fire Alarm System Limitations
An automatic fire alarm system–typically made up of
smoke detectors, heat detectors, manual pull stations,
audible warning devices, and a fire alarm control panel
with remote notification capability–can provide early
warning of a developing fire. Such a system, how-
ever, does not assure protection against property dam-
age or loss of life resulting from a fire.
The 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
the Guide for Proper Use of System Smoke Detectors,
which is made available at no charge to all installing
dealers. A study by the Federal Emergency Manage-
ment Agency (an agency of the United States govern-
ment) indicated that smoke detectors may not go off
in as many as 35% of all fires. While fire alarm sys-
tems are designed to provide early 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 func-
tion, for a variety of reasons:
Smoke detectors may not sense fire where smoke
cannot reach the detectors such as in chimneys, in or
behind walls, on roofs, or on the other side of closed
doors. Smoke detectors also may not sense a fire on
another level or floor of a building. A second-floor
detector, for example, may not sense a first-floor or
basement fire.
Particles of combustion or "smoke" from a develop-
ing fire may not reach the sensing chambers of smoke
detectors because:
• Barriers such as closed or partially closed doors,
walls, or chimneys may inhibit particle or smoke
flow.
• Smoke particles may become "cold," stratify, and
not reach the ceiling or upper walls where detectors
are located.
• Smoke particles may be blown away from detectors
by air outlets.
• Smoke detectors may be drawn into air returns be-
fore reaching the detector.
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 photoelec-
tronic 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 detec-
tor may not provide adequate warning of a fire.
Smoke detectors cannot be expected to provide
adequate warning of fires caused by arson, children
playing with matches (especially in bedrooms), smok-
ing in bed, and violent explosions (caused by escaping
gas, improper storage of flammable materials, etc.).
PrecauSmall.PMD
01/10/2005
While a fire alarm system may lower insurance
rates, it is not a substitute for fire insurance!
Heat detectors do not sense particles of combustion
and alarm only when heat on their sensors increases at
a predetermined rate or reaches a predetermined level.
Rate-of-rise heat detectors may be subject to reduced
sensitivity over time. For this reason, the rate-of-rise
feature of each detector should be tested at least once
per year by a qualified fire protection specialist. Heat
detectors are designed to protect property, not life.
IMPORTANT! Smoke detectors must be installed in
the same room as the control panel and in rooms used
by the system for the connection of alarm transmission
wiring, communications, signaling, and/or power. If
detectors are not so located, a developing fire may
damage the alarm system, crippling its ability to report
a fire.
Audible warning devices such as bells may not alert
people if these devices are located on the other side of
closed or partly open doors or are located on another
floor of a building. Any warning device may fail to
alert people with a disability or those who have re-
cently consumed drugs, alcohol or medication. Please
note that:
• Strobes can, under certain circumstances, cause
seizures in people with conditions such as epilepsy.
• 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 exercise to make people aware of
fire alarm signals and instruct them on the proper
reaction to alarm signals.
• In rare instances, the sounding of a warning device
can cause temporary or permanent hearing loss.
A fire alarm system will not operate without any
electrical power. If AC power fails, the system will
operate from standby batteries only for a specified
time and only if the batteries have been properly main-
tained and replaced regularly.
Equipment used in the system may not be techni-
cally compatible with the control. It is essential to use
only equipment listed for service with your control
panel.
Telephone lines needed to transmit alarm signals
from a premise to a central monitoring station may be
out of service or temporarily disabled. For added
protection against telephone line failure, backup radio
transmission systems are recommended.
The most common cause of fire alarm malfunction is
inadequate maintenance. To keep the entire fire alarm
system in excellent working order, ongoing mainte-
nance is required per the manufacturer's recommenda-
tions, and UL and NFPA standards. At a minimum, the
requirements of NFPA 72 shall be followed. Environ-
ments with large amounts of dust, dirt or high air ve-
locity require more frequent maintenance. A mainte-
nance agreement should be arranged through the local
manufacturer's representative. Maintenance should be
scheduled monthly or as required by National and/or
local fire codes and should be performed by authorized
professional fire alarm installers only. Adequate writ-
ten records of all inspections should be kept.
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