D200-33-00 11 I56-1944-07
©
2003 System Sensor
Limitations of Fire Alarm Systems
Manufacturer recommends that smoke and/or heat detectors be locat-
ed throughout a protected premise following the recommendations of
the current edition of the National Fire Protection Association Standard
72, National Fire Alarm Code (NFPA 72), manufacturer’s recommenda-
tions, 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 gov-
ernment) 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 warn-
ing or protection against fire. Any alarm system is subject to compro-
mise or failure to warn for a variety of reasons. For example:
• Particles of combustion or “smoke” from a developing fire may
not reach the sensing chambers of the smoke detector because:
- Barriers such as closed or partially closed doors, walls, or
chimneys may inhibit flow.
- Smoke particles may become “cold” and stratify, and may
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 reach-
ing 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 cham-
bers 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.
For example, a smoke detector located in or near a kitchen may
go into nuisance alarm during normal operation of kitchen appli-
ances. In addition, dusty or steamy environments may cause a
smoke detector to falsely alarm. If the location of a smoke detec-
tor 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 warn-
ing of fires caused by arson, children playing with matches
(especially within bedrooms), smoking in bed, violent explo-
sions (caused by escaping gas, improper storage of flammable
materials, etc.).
• Heat detectors do not sense particles of combustion and are de-
signed to alarm only when heat on their sensors increase at a
predetermined rate or reaches a predetermined level. Heat detec-
tors 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.
- 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 re-
sponsibility to conduct fire drills and other training exer-
cises to make people aware of fire alarm signals and in-
struct 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 premis-
es 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.
• To keep your fire alarm system in excellent working order, on-
going maintenance is required per the manufacturer’s recom-
mendations and UL and NFPA standards. At a minimum the
requirements of Chapter 7 of NFPA 72 shall be followed. A main-
tenance agreement should be arranged through the local manu-
facturer’s representative. Maintenance should be performed
annually by authorized personnel only.
• The most common cause of an alarm system not functioning
when a fire occurs is inadequate maintenance. As such, the
alarm system should be tested weekly to make sure all sensors
and transmitters are working properly.
• Although designed for long life, fire alarm devices including
smoke detectors may fail at any time. It is recommended that
smoke detectors shall be replaced every 10 years.
• Any smoke detector, fire alarm system or any component of that
system which fails shall be repaired or replaced immediately.
In general, fire alarm systems and devices will not work without
power and will not function properly unless they are maintained
and tested regularly.
While installing a fire alarm system may make the owner eligible
for a lower insurance rate, an alarm system is not a substitute for
insurance. Property owners should continue to act prudently in
protecting the premises and the people in the premises and should
properly insure life and property and buy sufficient amounts of
liability insurance to meet their needs.
