FireNET FNP-1127-SLC Manual v1.0 UL
4
xNo Detection: Particles of combustion or smoke from a developing fire may not reach the
sensing chambers of smoke detectors because:
1. Barriers (such as closed or partially closed doors, walls, or chimneys) may inhibit
particle or smoke flow.
2. Smoke particles may become cold, stratify, or not reach the ceiling or upper walls
where detectors are located.
3. Smoke particles may be blown away from detectors by air outlets.
4. Smoke particles may be drawn into air returns before reaching the detector.
xNo Multi-Floor Detection: In general, smoke detectors on one level of a structure cannot be
expected to sense fires developing on another level.
xInsufficient Smoke: 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 the detector, the detector
will not go into alarm.
xSmoldering vs. Flaming Fires: Smoke detectors, even when working properly, have sensing
limitations. Detectors that have photoelectric 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.
xFalse Alarms and Pre-Fire Disconnection: 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.
xFast Fires and Explosions: Smoke detectors cannot be expected to provide adequate
warning of fires caused by arson and children playing with matches (especially within
bedrooms), smoking in bed, violent explosions (caused by escaping gas, improper storage of
flammable materials, etc.).
xHeat Detectors: 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.
xUnheeded Warning: 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 aware 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.
xStrobes: Strobes can under certain circumstances, cause seizures in people
with conditions such as epilepsy.
xDrills: 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 exercises
to make people aware of fire alarm signals and instruct on the proper reaction
to alarm signals.
xHearing Loss: In rare instances, the sounding of a warning device can cause
temporary or permanent hearing loss.
