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 business or public building it is an integrated system of detectors, a control panel and sounders, often connected onwards to an alarm receiving centre (ARC), and something entirely different from a standalone smoke alarm.

How the system must be designed is governed by national standards and by requirements from insurers and the relevant 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 fitted to the ceiling in a home. It only sounds locally, in the room where it is installed.

An automatic fire alarm system is a monitored installation. Detectors, control panel and sounders are linked together, the system raises the alarm throughout the whole building at once and it monitors itself. If a cable is cut or a detector fails, the control panel reports a fault instead of silently ceasing to work. This is the level required in offices, industrial premises, hotels, healthcare facilities and other larger buildings.

How the system works

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

The detectors sense smoke, heat or flames and send a signal to the control panel. The panel is the brain of the system: it interprets the signal, raises the alarm through sounders and visual beacons, and can control other systems in the building. Where required, the alarm is passed on to an alarm receiving centre, which in turn contacts the fire and rescue service. This ensures that no alarm is missed simply because nobody happens to be on site.

Different types of detector

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

• Optical 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 false alarms.
• Flame detectors, which detect the radiation from open flames and are used in industrial settings and large halls.
• Aspirating smoke detectors, which draw in air through a network of pipes and detect smoke at a very early stage, for example in data centres.

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

Manual call points

Not everything should depend on technology. A system is supplemented with manual call points, the red boxes found by exits and in staircases.

They allow anyone who discovers a fire to raise the alarm immediately, without waiting for smoke to reach a detector. In busy premises they speed up evacuation.

Standards and requirements for the system

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

The requirements rarely come out of nowhere. An insurer may require a system that meets the relevant standard in order to provide or renew cover, and some organisations face requirements through building regulations or inspections by the authorities. A key element is having a designated person responsible for the system, who regularly tests it and records 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 linked to 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, ventilation can be shut down or redirected, and lifts are sent to the ground floor. The alarm can also unlock doors on escape 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 wider 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 unwanted alarm erodes confidence and can cost money if the fire and rescue service attends 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 log book, and at regular intervals an independent inspection is carried out by a third party. A fire alarm system that is not maintained loses both sensitivity and credibility.

Before an installation

Start with what actually needs protecting, whether people, premises or sensitive equipment, and what insurers and regulations require. That determines the scope of the system and which detectors are needed.

Then have a competent fire alarm contractor design the system in accordance with the applicable standards, 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.