Returning to the Foundations: fire alarm systems

CarolinaFireJournal - By Mike Coffey
By Mike Coffey
10/05/2012 -

Fire alarm systems have become commonplace responses in today’s fire service. Between carbon monoxide alarms, general fire alarm activations, smoke detectors, other detection devices and pull stations — we stay busy answering these calls for service. Understanding what the system and devices attached to them are telling us can help identify problems and keep properties from becoming even more of a statistic than they already are.


The primary purpose of a detection system is to alert people in a building to respond to a possible fire situation through a visual and audible signal, and alert the fire department for response. Systems are designed to respond and transmit signals through electrical impulses, pneumatic pressure changes, hydraulic changes or mechanical activation. These detections cannot define the cause or intensity, but only respond to the stimuli and activate the visual and audible warning devices. False alarms cannot be attributed to occupants or the system itself. Some of the reasons for false alarms may be improper system selection, random detector placement or other ways to circumvent the system.

Occupant alerting is more sophisticated as well. Audible Claxton horns, sirens, computerized announcements, white strobe lights, vibration equipment and changes in the air movement system are used. All work well for all groups of people with the traditional means of notification (horns, bells, whistles, sirens) supplemented for the disabled population — visual = white strobes/lights and vibration for both hearing and visual impairments.

The computerized message directs occupants to take certain actions and gives instructions on those actions. This may interfere with directions given to occupants by firefighters. Uses of prerecorded messages for actions to take are still in use for manual or automatic activation of the fire alarm system. Even manual announcements over the building’s intercom system are still used in some buildings and override the automated message. Some studies from the 1990s and earlier show that alarm devices located in apartments have better chances of awakening occupants than traditional hall-mounted warning devices.

The sooner a fire alarm detection system picks up a fire situation with smoke, heat or flame detection, the more time occupants have to evacuate the building — more lives saved — the more time fire control teams or firefighters have to extinguish a fire before the building construction becomes weakened (depending on response capabilities). The longer a fire continues to develop equals the more time — and resources — needed for extinguishment. Detection devices not only activate the alarm system, they can activate built-in suppression systems, close fire doors to isolate areas, turn off sections of the heating/ventilation/air conditioning system (HVAC) and activate smoke dampers within them, and give approximate locations in which to find the fire problem and initiate a wide variety of auxiliary functions involving environmental, utility and process controls — including elevator control. They may also deactivate magnetic locking security systems to allow firefighter entry to the property.

The detection system must be considered from an analysis approach — what does the occupant want the system to do? In order to get the maximum from the system, four items must be considered: sensitivity, reliability, maintainability and stability. Sensitivity is established by system design with an exception to products-of-combustion units that adjust themselves. Thermal sensing units have fixed spacing ratings based and testing approved by Underwriters Laboratories or Factory Mutual testing labs. Reliability relates to the ability of the system and the components to be in proper working order at all times and work as they are supposed to.

The highest reliable components are fixed temperature or rate compensated heat detectors. Rate-of-rise detectors are slightly lower in reliability along with all products of combustion and flame detection relying on electric components having higher failure rates. Maintainability varies to the complexity of the system’s design. Detection units requiring higher periodic maintenance have a direct influence to keeping the system online. Stability related to the system’s ability to sense fires over extended periods without changing sensitivity. Actual detector performance varies to design, which company makes the unit, the company’s quality control methods and the training and supervision of the people installing the system.

Notification of the fire department is the next step alarm systems perform. This may be the weakest link involving most communities’ fire protection system. Studies performed by the National Fire Protection Agency from the late 1980s and into the 1990s indicated a national average of nuisance alarms to real alarms was between 17 and 27 to one — 17 to 27 nuisance alarms to one real alarm — with 1987 data indicating a total of fire department responses to false alarms being at 10 percent. Since more systems have come online in the last 25 years, that number has gone up as well. Systems that do fail are attributed to technical malfunctions, transfer or telephone defects, smoke from welding and cutting, smoke from vehicles or tobacco use and construction dusts from wood or sheetrock sanding and cutting.

The basic components of a detection system involve the detectors themselves, initiating devices and a receiving element. The detectors involve sensing either smoke, by ionization or photoelectric smoke detectors; heat, using fixed temperature, rate-of-rise or rate-compensated detectors; or flame detection, using infrared, ultraviolet or combination units — with the newest addition being the fire gas detector. Carbon monoxide detectors are by far the most popular for residential use.

Although there are still some pneumatic temperature devices in service, most of the detection devices use microprocessors to monitor the detector’s condition and location upon activation. This act makes them addressable to indicate where the problem is to fine-tuning the detector’s sensitivity. Unfortunately, to the owner or occupant, this also requires more maintenance to keep the detector reliable. Detectors must be tested and should reset once testing is done (another cost). Some detectors do degrade and must be replaced when testing is complete. Other disadvantages are overall cost of the system, problems between detectors and control panel signals and servicing of the system.

Initiating devices are the sensing parts of the detection system and are connected by an electrical initiating circuit. They can be manual or automatic. These circuits, when split up inside buildings become zones corresponding to certain physical features of the building — area, floors sections — to indicate where a problem lies. The circuits end up at a control point — main fire alarm panel — that serves several functions. The panel may have near it the emergency backup power system for automatic switchover, supervisory capability to notify people of trouble within the system and other notification and shutdown switches for the various building utilities. Annunciator panels at various entry points can help identify problem zones, provided a map of the zone system is close by, without having to go to the main alarm panel. Some of these devices can be pneumatic or hydraulic by design as well.

The receiving element either retransmits signals from detection devices or converts the alarm signal to audible and visual alarms for occupants to leave the premise and can make the call to the fire department, loss prevention office or alarm monitoring company. Depending on the system, if monitored by a loss prevention officer or security officer or alarm monitoring company, a manual telephone call is made to supplement the automatic alarm notification. The thing to remember here is do not reset/turn off the alarm until firefighters determine cause of alarm activation. They — property occupants or owners or the Incident Commander — can silence an alarm, just not reset the panel alarm to normal operations. Once source of alarm is determined/neutralized/determined to be a malfunction — system can be reset with damaged systems deactivated until repairs are made.

All systems must meet local building codes and requirements. The NFPA issues an alarm standard called “NFPA 72 – The National Fire Alarm Code” that dictates requirements for all types of systems. These are adopted by the code making authorities and legislated into law by lawmakers.

From a safety standpoint: firefighters need to understand operations and limitations of detection systems. From a customer service standpoint: firefighters who know how systems work can help dispel myths about systems and can advise building owners/occupants on appropriate actions to take when an alarm sounds. Most people have no idea how fire prevention/detection systems work. There are often more false alarms in buildings with systems than actual fires. Firefighters can help owners/occupants determine what caused system activation and prevent future false alarms, along with restoring system to normal operations. A major problem with false alarms — people become used to hearing them and then do not respond appropriately. This action cost three students their lives in 2000 at Seton Hall University. An actual fire was detected, but the students were used to hearing the alarm and stayed in place.

These are some of the basics on alarm systems with some more information on how these systems work. As time marches on, we will be dealing more with alarm systems than we are now. Being familiar with systems in your area and educating the public on correct actions to take puts us all on the same level.

Captain Coffey currently serves as one of the training officers of the High Point Fire Department. He has been an instructor with the NC Community College system and the Office of the State Fire Marshal since 1990. He can be reached at [email protected].
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