What is a fire alarm system?

A fire alarm system is designed to detect a fire early enough for people to get out and for damage to be limited. In a commercial building it is an integrated system of detectors, a control panel and notification appliances, often connected to a central station, and something entirely different from a standalone smoke alarm.

How the system must be designed is governed by national codes and standards and by requirements from insurers and local authorities. The choice of detectors, the extent of coverage and the level of maintenance determine both how quickly the alarm gets ahead of the fire and how often it goes off unnecessarily.

Fire alarm systems and smoke alarms are not the same thing

The terms are often confused, but the difference is significant. A smoke alarm is a single, battery-powered unit mounted on the ceiling in a home. It only sounds locally, in the room where it is installed.

An automatic fire alarm system is a supervised installation. Detectors, control panel and notification appliances are linked together, the system sounds the alarm throughout the entire building at once, and it monitors itself. If a wire is cut or a detector fails, the control panel signals a trouble condition instead of silently ceasing to work. This is the level required in offices, industrial facilities, hotels, healthcare facilities and other larger buildings.

How the system works

A fire alarm system works as a chain, from detection to notifying the right people.

The detectors sense smoke, heat or flames and send a signal to the fire alarm control panel. The panel is the brain of the system: it interprets the signal, sounds the alarm through horns and strobes, and can control other systems in the building. When needed, the alarm is passed on to a central station, which in turn contacts the fire department. This ensures that no alarm is missed just because nobody happens to be on site.

Different types of detectors

Which detector is the right fit depends on the space and on what could catch fire. Detectors are usually divided into a few basic types:

• Photoelectric smoke detectors, which sense smoke and are the most common choice in offices and general areas.
• Heat detectors, which respond to temperature and suit kitchens, garages and dusty environments where smoke detectors cause nuisance alarms.
• Flame detectors, which detect the radiation from open flames and are used in industrial facilities and large open spaces.
• Air-sampling smoke detectors, which draw in air through a network of pipes and detect smoke at a very early stage, for example in data centers.

Most systems combine several types, so that each part of the building gets the detector best suited to that particular area.

Manual pull stations

Not everything should depend on technology. A system is supplemented with manual pull stations, the red boxes found near exits and in stairwells.

They allow anyone who discovers a fire to trigger the alarm immediately, without waiting for smoke to reach a detector. In high-occupancy buildings they speed up evacuation.

Codes and requirements for the system

Automatic fire alarm systems are designed, installed and maintained in accordance with national fire alarm codes and standards. These describe how the system should be designed, installed and maintained.

The requirements rarely come out of nowhere. An insurer may require a code-compliant system in order to issue or renew a policy, and some facilities face requirements through building codes or inspections by the authority having jurisdiction. A key element is having a designated person responsible for the system, who regularly tests it and documents that the alarm is working.

When the fire alarm controls other systems

A fire alarm often does more than sound. In a modern building it is integrated with other systems, so that the right things happen automatically when the alarm is triggered.

Fire doors held open by magnetic door holders are released so that they close and contain the smoke, HVAC systems can be shut down or redirected, and elevators are recalled to the main floor. The alarm can also unlock doors on egress routes that are otherwise controlled by a digital locking system. Many systems are also connected online, which means status and faults can be monitored remotely, part of the broader IoT field.

False alarms and maintenance

The biggest practical challenge is false alarms. Dust, cooking fumes, steam and construction dust can fool a smoke detector, and every nuisance alarm erodes trust and can cost money if the fire department responds unnecessarily.

The solution is the right detector in the right place and regular maintenance. The person responsible for the system tests the alarm, cleans detectors and keeps a logbook, and at regular intervals a third-party inspection is carried out. A fire alarm system that is not maintained loses both sensitivity and credibility.

Before an installation

Start with what actually needs to be protected, whether people, facilities or sensitive equipment, and what insurers and codes require. That determines the scope of the system and which detectors are needed.

Then have a qualified fire alarm contractor design the system in accordance with the applicable codes, and make sure a responsible person is designated from day one. A fire alarm system is not a product you install and forget, but a system that must evolve with the building.