Traditionally, fire alarm systems involved only audible notification appliances. Recently, the codes have changed, requiring audible and visible…
minimum of 7 5 wo rd
minimum of 7 5 wo rds.
Unit Lesson Early detection and notification of a fire or other emergency is critical in ensuring life safety for occupants. A person’s chance of surviving a structure fire is dependent upon the amount of time that passes between the start of the fire, the person’s realization that there is a fire, and the time it takes for the person to evacuate the area or building (Jones, 2015). In most cases, there is very little time to evacuate before the area becomes dangerous. Fire alarm systems provide early notification in a fire emergency. Such early notification is critical to a person’s chance for survival. For this reason, the model codes require the installation of some type of fire alarm system in many types of occupancies. In addition to causing the evacuation of occupants, fire alarm UNIT VI STUDY GUIDE Fire Alarm and Detection Systems FIR 3305, Fire Protection Structure and Systems 2 UNIT x STUDY GUIDE Title systems can also provide notification and alerts to the local fire department or emergency response agency. In this unit, we discuss types of fire alarm systems and their components and functions. Fire Alarm Systems A fire alarm system is a group of interconnected components and devices that are designed to cause a response by building occupants. Components of the modern fire alarm system can range from very basic to extremely complex, based on the hazard to be protected. Components of fire alarm systems should be tested by a nationally recognized testing laboratory, and each system should be installed in accordance with the National Fire Protection Association (NFPA) 72: National Fire Alarm and Signaling Code. The basic components of a fire alarm system are the fire alarm control panel (FACP), initiating devices, and notification appliances. The FACP is a system component that receives input from automatic and manual fire alarm devices and may provide power to detection devices or communication devices. The FACP is considered the brain of the fire alarm system. All components of the fire alarm system are generally tied into the FACP, including notification appliances, emergency voice communications systems, elevator recall, and signaling. Alarm signals can be confirmed at the FACP, and the system can also be reset at the FACP. The fire alarm and detection system is also required to have a primary power supply as well as a backup power supply to ensure that the system will operate even if the main power supply fails. Many older FACPs used conventional technology to link to manual fire alarm boxes and bells to provide for evacuation. This technology provides for limited communication between the FACP and system devices. Upon activation of an alarm, only general information is provided at the panel concerning the device and its location. Today’s FACPs utilize addressable technology, involving state-of-the-art electronics, microprocessors, and intelligent software that provide specific information concerning device identification, alarm location, and type. The location of a fire condition is detected and recorded at each individual device, identifying exactly where the fire is occurring. This improves response time for emergency responders (Jones, 2015). Initiating Devices Initiating devices interface with the FACP to provide manual or automatic means of activating the fire alarm and supervisory signals. Initiating devices essentially sense the presence of fire, smoke, heat, or other hazardous conditions. These devices then send a signal to the FACP. Examples include manual pull stations, heat detectors, smoke detectors, flame detectors, water-flow devices, or tamper switches. These devices are essentially telling the fire alarm system that it sees a problem and notifies the system. Manual pull stations allow occupants within a location to activate the fire alarm system. These pull stations generally send a signal, activate the fire alarm system, provide occupant notification, and may notify a monitoring company, which in turn notifies the fire department. After operation, some pull stations required a special tool or key to deactivate the alarm and return them to the normal position. Older pull stations that require a single action or hand motion to activate are subject to accidental activation by jarring or accidental contact. Pull stations that require two actions, such as a lift up and pull down, or push in and pull down have replaced many single action stations. Heat detectors are temperature-sensitive devices that sense temperature changes and cause an alarm to sound at a specific point. There are two types of heat detectors: rate-of-rise and fixed temperature. Rate-ofrise detectors operate on a rapid increase in element temperature—generally, a 12-15 degree increase per minute. Rate-of-rise detectors may not respond to slowly developing fires. Fixed temperature heat detectors are designed to activate the alarm system when the surrounding temperature exceeds its operating temperature, causing a reaction in a heat-sensitive element within the detector. FIR 3305, Fire Protection Structure and Systems 3 UNIT x STUDY GUIDE Title Smoke detectors are devices that sense smoke, generally as an indicator of a fire. Commercial smoke detectors send a signal to the alarm panel, which, in turn, activates the fire alarm. Household smoke detectors, sometimes called smoke alarms, emit an audible or visual alarm from the detector itself. Smoke detectors detect smoke either through photoelectric operation or ionization operation. A photoelectric detector contains a source of infrared or ultraviolet light. When smoke enters the optical chamber it disrupts the transmission of light which causes activation of the alarm. Photoelectric detectors are believed to be more responsive to smoldering fires. Ionization detectors contain a radioactive material in a chamber. When smoke enters the chamber it disrupts the electrical activity within the chamber, causing the alarm to activate. Ionization detectors are believed to be more sensitive to flaming fires. Flame detectors operate by detecting the light in the ultraviolet (UV) wave spectrum or the infrared (IR) wave spectrum. UV detectors detect the UV radiation emitted from a fire during the ignition stage. IR detectors detect sudden changes or increases in radiation emitted from fire gases. Water-flow devices are mechanical or electrical devices installed in the fire sprinkler system that acts as an interface between the fire sprinkler and fire alarm systems. Water-flow devices detect water flowing through the sprinkler system, as in the case of a sprinkler head activation, causing the evacuation signal to sound. Most firefighters consider the activation of a flow alarm to be a greater indicator of a fire than an alarm system activation. This is primarily due to the number of false fire alarms to which they have responded. Tamper switches are mechanical or electrical devices connected to fire sprinkler control valves. Tamper switches detect when a sprinkler control valve has been partially or fully closed (tampered with). Tamper switches generally result in a supervisor signal activation at the fire alarm control panel. Notification Appliances Notification appliances provide notification to building occupants that action may need to be taken. Notification may be audible, visual, textual, or tactile. Notification devices include bells, horns, chimes, buzzers, sirens, speakers, strobe lights, and lamps. Older notification devices, those installed prior to 1996, provide a steady alarm signal for evacuation. Notification appliances installed since 1996 utilize a three-pulse temporal pattern alarm signal. This pattern is characterized by three half-second pulses followed by a 1.5-second pause. This pattern is repeated for a minimum of 180 seconds. There are three general types of signals provided by the fire alarm and detection system. They include the alarm, supervisory signal, and trouble signal. Alarm signals are activated through the presence of fire, smoke, or heat. The alarm signal indicates a need to evacuate. Activation of fire alarm signal may also perform secondary functions such as the closing of fire doors, pressurization stairwells, or recall elevators. Supervisory signals indicate an off-normal condition of the complete fire alarm system. Trouble signals indicate a problem with a monitored circuit or component of the fire alarm system or power system. When a fire alarm system activates, certain operational events take place. Fire alarm systems are classified based on which operational events take place, how they take place, and if the system serves more than one purpose. The major types of fire alarm systems are protected premises, supervising stations, and emergency communications systems. Local or protected premises systems provide notification to the building occupants at the premises. No signal is sent off-site. Supervising station alarm systems include auxiliary alarm systems, proprietary alarm systems, central station systems, and remote receiving systems. Each of these systems is continuously monitored at a remote location for the purpose of receiving alarm, taking action, and notifying the appropriate authority. Emergency communications systems provide audible notification of an emergency (Jones, 2015). As with any fire protection system, it is important that the systems are reviewed, installed, and tested to ensure effective operation. Fire detection and alarm systems are no exception. Generally, there is a review of Residential smoke detector (Alexandrov, 2009) FIR 3305, Fire Protection Structure and Systems 4 UNIT x STUDY GUIDE Title the proposed installation of the fire protection system (fire alarm system), given shop drawings and system specifications, to ensure the system is evaluated for code compliance and installed in accordance with the approved drawings. Deficiencies are identified, documented, and reported in accordance with the applicable codes and standards in the policies of the jurisdiction. The review of these construction documents may be done by a fire inspector, plan reviewer, fire protection engineer, or a fire code enforcement officer. In many cases, fire alarm and detection systems are considered the first line of defense against fire. When properly installed and inspected, they can provide occupants with the warning needed to survive and evacuate. References Alexandrov, O. (2009). Residential smoke detector [Photograph]. Retrieved from https://commons.wikimedia.org/wiki/File:Residential_smoke_detector.jpg Jones, A. M., Jr. (2015). Fire protection systems (2nd ed.). Burlington, MA: Jones & Bartlett Learning.