A fire alarm system is an active fire protection system that detects fire or the effects of fire. In so doing, it provides one or more of the following services: it notifies the occupants, notifies persons in the surrounding area, summons the fire service, and controls all the fire alarm components in a building.
Fire alarm systems can include alarm initiating devices, alarm notification appliances, control units, fire safety control devices, annunciators, power supplies, and wiring. These systems have helped save millions of lives. One drawback, however, is that such a system can be disrupted by deliberate false alarms.A Siemens MXL fire alarm control panel (top) and graphic annunciator (bottom).
Types of components
A fire alarm system is composed of components which can be classified into the following categories.
- Fire alarm control panel (FACP; or fire alarm panel) - this is a central control device involved in detecting, reporting, and acting on occurrences of fires within a building.
- Initiating devices - these devices either sense the effects of a fire, or are manually activated by personnel, resulting in a signal to the fire alarm panel. Examples are heat detectors, smoke detectors, manual pull stations, and sprinkler pressure or flow switches.
- Power supply - because one of the fire alarm system objectives is life safety, fire alarm system power supplies are redundant, and relatively very reliable as compared to electronic or electrical systems of similar complexities (for example, HVAC control systems). Primary supply is typically commercial light and power. A back-up/secondary supply is provided by sealed, lead-acid batteries. NAC power supplies for additional notification appliances beyond the original capability of the FACP. Generators are permitted under strict rules.
- Notification appliances - these devices provide stimuli for initiating emergency action and provide information to users, emergency response personnel, and occupants. Examples are bell, horn, speaker, light, or text display that provides audible, tactile, or visible outputs.
- Signaling line circuits (SLC) - the wiring which carries data information.
- Supervisory signals - detecting devices and signaling to indicate a condition in fire protection systems which is not normal and could prevent the fire protection system from functioning as intended in the event of a fire. An example is a closed valve which controls the water supply to a fire sprinkler system. This does not indicate the failure of a component or subsystem of the fire alarm system.
- Trouble signal - signaling to indicate a wiring fault. Sometimes specific components or features of the fire alarm system, of which could prevent the fire alarm or fire suppression system from functioning as intended. An example is a disconnected wire at a heat detector.
- Remote annunciation - A usually alpha-numeric display (may be graphic) that indicates where in the building the alarm originated. It may also indicate the type of device. Used by emergency personnel for locating the fire quickly. Sometimes these will contain some control functions such as alarm silence and alarm reset. Must be key or keypad controlled.
Fire alarm systems have devices connected to them to detect the fire/smoke or to alert the occupants of an emergency. Below is a list of common devices found on a fire alarm.
- Manual pull stations/manual call points - Devices to allow people to manually activate the fire alarm. Usually located near exits. Also called "manual pull boxes."
- Smoke detectors - Spot type: photoelectric and ionization; Line type: Projected beam smoke detector; Air-Sampling type: cloud chamber
- Water flow switches - Detect when water is flowing through the fire sprinkler system
- Rate-of-Rise and thermostat (heat) detectors - Detect heat changes
- Valve supervisory switch - Indicates that a fire sprinkler system valve that is required to be open, is now closed (off-normal).
- Carbon monoxide detector - Detects poisonous carbon monoxide gas and usually only connected to household fire alarm systems. Very rarely, commercial systems.
- Notification appliances - Visual and audible devices to alert people of system activation.
- Magnetic door holder - Doors are allowed to close when the fire alarm is activated.
The design of the overall goals, general system type, and integration into the other facility systems (active fire suppression, HVAC, lighting, electrical power, fire barriers, etc.) is performed by competent engineers with experience in fire protection, who are licensed within the geographical area of practice, such as a U.S. state or a Canadian province. This is done in conjunction with the architect's design team during the design phase of the building project. The detailed component selection and layout is provided by a technician as hired by the contractor during the construction phase. In the United States, that person is usually certified for fire alarm design by the National Institute for Certification of Engineering Technologies (NICET).
The design is typically provided in compliance with the model building codes having jurisdiction in that area. In the United States, NFPA 72, The National Fire Alarm Code, is usually used for the installation methods, testing and maintenance. Property insurance company recommendations are also sometimes incorporated.
Extensions of existing systems is done considering the original system, and more than likely will be proprietary to match the existing equipment.
Audio evacuation systems
An audio evacuation system or voice evacuation system is a type of fire alarm notification system. In addition to, or in place of, sirens, horns, bells, and alarm tones, an audio evacuation system plays a voice message with evacuation instructions. These messages can be customized for various types of installations, and multi-lingual capabilities are usually available.
The rationale behind audio evacuation systems is, though conventional fire alarm notification devices alert occupants of a building of the presence of an emergency, they do not provide detailed information to the occupants, such evacuation routes or instructions. The problem lies in buildings where there are large amounts of frequently changing occupants who are not necessarily familiar with the locations of emergency exits or stairwells. These types of buildings are designated in model building codes as "areas of assembly," such as buildings with a capacity of three hundred or more people, but voice evacuation rules usually only apply when the occupant load exceeds one thousand persons. Areas of assembly include churches, movie theaters, auditoriums, department stores, restaurants, shopping malls, airports and museums. Additionally, such a system is usually intergrated with a fire telephone or paging system, which permits the fire department or building manager to give specific evacuation instructions pertinent to current conditions in real time.
Many audio evacuation systems permit multiple messages. For instance, "non fire" messages can be programmed for situations such as a hazardous material spill, gas leaks, security breaches, severe weather, and so forth.
In the United States, audio evacuation is now required in many jurisdictions for new structures that are classified as an area of assembly, as well as in new high rise buildings and skyscrapers. Retrofitting older structures is not required, although new fire alarm installations can be required to have audio capabilities. Similar trends are occurring in other countries as well.
- Traister, John E. 1995. Security/Fire Alarm Systems: Design, Installation, and Maintenance 2nd edition. Columbus, OH: McGraw-Hill. ISBN 0070652961
- Bunker, Merton W. 2007. NFPA's Pocket Guide to Fire Alarm System Installation 2nd edition. Sudbury, MA: Jones and Bartlett Publishers, Inc. ISBN 0763746053
- Gagnon, Robert. 1997. Design of Special Hazard & Fire Alarm Systems. Florence, KY: Thomson Delmar Learning. ISBN 0827382936