This document provides minimum design regulations to safeguard life, limb, health, property, and public welfare. It provides information for regulating and controlling the permitting, design, construction, quality of materials, use and occupancy, location, and maintenance of all buildings and structures within the authority of jurisdiction (AHJ). It also regulates certain specific equipment within all buildings and structures.
Fire Alarm Control Unit
In most cases, the fire alarm control unit, not the device, performs the actual determination of the alarm state.
Line detectors- Detection is continuous along the entire length of the detector in these detection devices. Typical examples may include certain older pneumatic rate-of-rise tubing detectors, projected beam-smoke detectors, and heat-sensitive cable.
Bimetallic- In a bimetallic detector two metals with different rates of thermal expansion are bonded together. Heat causes the two metals to expand at different rates, which causes the bonded strip to bend. This action closes a normally open circuit, which signals an alarm. Detectors with bimetallic elements automatically self-restore when the temperature returns to normal.
An electronic circuit sends a signal to the FACU when the rate of temperature rise that is sensed exceeds 15°F per minute and when a specific temperature is sensed.
A non restorable fusible line-type heat detector uses a pair of steel wires in a normally open circuit.
Light scattering detectors use the reflective properties of smoke particles to detect the smoke. The light scattering principle is used for the most common single-housing spot-type detectors. Beam detectors rely upon smoke to block enough light to cause an alarm (obscuration principle).
Secondary Power and Notification Devices
As defined by NFPA 72, standby time for operation of the system of secondary power must be no less than 24 hours central, local, proprietary, voice communications, household, auxiliary, and remote systems.
Any batteries used for secondary power must be able to be recharged 48 hours.
Because ADA requirements dictate clear or white xenon (or equivalent) strobe lights, most interior visual notification devices are furnished with clear strobe lights.
When more than two strobes are visible from any location, the strobes must be synchronized to avoid random flashing which can be disorienting and may actually cause seizures in certain individuals.
Fire Alarm Signals and Announcements
Audible signals used for fire alarms in a facility that contains other sound-producing devices must produce a unique sound pattern so that a fire alarm can be recognized.
Voice announcements can be made to inform occupants what the problem is or how to evaluate. In most cases, the voice announcements are pre-recorded and selected as required by the system. Live announcements can also be made from a microphone located at the FACU or at the remote panel.