Fire Alarm System Limitations
An automatic fire alarm system–typically made up of smoke detectors, heat detectors, manual pull stations, audible warn- ing devices, and a fire alarm control with remote notification capability–can provide early warning 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 detec- tors 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 Emer- gency Management Agency (an agency of the United States government) indicated that smoke detectors may not go off in as many as 35% of all fires. While fire alarm systems are de- signed to provide early warning against fire, they do not guar- antee 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:
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 build- ing. A second-floor detector, for example, may not sense a first-floor or basement fire.
Particles of combustion or "smoke" from a developing fire may not reach the sensing chambers of smoke detectors be- cause:
•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 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 ion- izing-type sensing chambers tend to detect fast-flaming fires better than smoldering fires. Because fires develop in differ- ent 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), smoking in bed, and violent explosions (caused by escaping gas, improper storage of flammable materials, etc.).
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 detec- tors 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, com- munications, 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 recently consumed drugs, alcohol or medi- cation. 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 responsi- bility 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 maintained and replaced regularly.
Equipment used in the system may not be technically com- patible 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 tele- phone line failure, backup radio transmission systems are rec- ommended.
The most common cause of fire alarm malfunction is inade- quate 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 stan- dards. At a minimum, the requirements of NFPA 72 shall be followed. Environments with large amounts of dust, dirt or high air velocity require more frequent maintenance. A main- tenance 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 profes- sional fire alarm installers only. Adequate written records of all inspections should be kept.