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2 PN 15037:D2 9/9/02
Fire Alarm System Limitations
While a fire alarm system may lower insurance rates, it is not a substitute for fire insurance!
An automatic fire alarm system —typically made up of
smoke detectors, heat detectors, manual pull stations,
audible warning devices, and a fire alarm control with
remote notification capability—can provide early warn-
ing of a developing fire. Such a system, however, does
not assure protection against property damage or loss
of life resulting from a fire.
The Manufacturer recommends that smoke and/or heat
detectors be located throughout a protected premise fol-
lowing 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 systems
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 function, for a variety of rea-
sons:
Smoke detectors may not sense fire where smoke can-
not 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 detec-
tor, 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 particles may be drawn into air returns before
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 den-
sity 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 cannot be expected to provide ade-
quate warning of fires caused by arson, children playing
with matches (especially in bedrooms), smoking in bed,
and violent explosions (caused by escaping gas,
improper storage of flammable materials, etc.).
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 dam-
age 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 recently con-
sumed drugs, alcohol or medication. Please note that:
• Strobes can, under certain circumstances, cause sei-
zures 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 com-
prehend 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 electri-
cal 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 maintained and
replaced regularly.
Equipment used in the system may not be technically
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 transmis-
sion 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 maintenance
is required per the manufacturer's recommendations,
and UL and NFPA standards. At a minimum, the
requirements of Chapter 7 of NFPA 72 shall be followed.
Environments with large amounts of dust, dirt or high air
velocity 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 written
records of all inspections should be kept.
Precau-S-4-2002.fm