Fire Secure UK
Fire Alarms: Plain English Guide
What is a fire alarm system?
A fire alarm system is used to raise the alarm when there is, or may be, a fire.
In simple terms, it is made up of:
- Devices that detect or report a fire
- A control panel that processes the information
- Warning devices that alert people in the building
- Power supplies, cabling and interfaces that allow the system to operate reliably
A fire alarm system may be activated manually by a person, automatically by detectors, or by signals from other fire safety systems.
Important note
This page is a simple introduction for non-engineers.
It is not a design guide, installation guide, commissioning procedure or maintenance document. Fire alarm systems should be designed, installed, commissioned, maintained and modified by competent people in accordance with the relevant standards, including BS 5839-1 for non-domestic premises.
For individual definitions, see:
Fire Alarm Terminology: Plain English Guide
What does a fire alarm system do?
A fire alarm system can perform several functions depending on the building and system design.
Common functions include:
- Warning people to evacuate
- Alerting staff to investigate
- Identifying the area where a fire or fault has occurred
- Sending signals to an Alarm Receiving Centre
- Releasing fire doors
- Starting smoke control systems
- Shutting down ventilation or plant
- Recalling lifts or preventing lift use
- Operating other fire protection or safety systems
Not every fire alarm system does all of these things. The exact function depends on the building, fire strategy, risk assessment, system category and agreed design.
Fire alarm system categories
BS 5839-1 uses system categories to describe the purpose and extent of fire alarm protection.
This matters because saying “fire alarm to BS 5839-1” is not enough on its own. The category tells people what the system is intended to achieve.
| Category | Plain English meaning |
|---|---|
| M | Manual system only. People raise the alarm by pressing manual call points. |
| L1 | Automatic detection throughout the building for life safety. |
| L2 | Automatic detection in escape routes and additional higher-risk areas. |
| L3 | Detection in escape routes and rooms opening onto escape routes. |
| L4 | Detection in escape routes only, such as corridors and stairways. |
| L5 | Detection provided for a specific life safety objective. |
| P1 | Automatic detection throughout the building for property protection. |
| P2 | Automatic detection in defined areas for property or business protection. |
A system can have more than one purpose. For example, a system may be described as L2/P2 if it is intended to provide both life safety and property protection.
Main parts of a fire alarm system
Most fire alarm systems are made up of the same broad types of equipment.
The exact equipment used depends on the building, the system category, the evacuation strategy and the fire alarm design.
Fire alarm control panel
The fire alarm control panel is the main control unit for the system.
It receives signals from detectors, manual call points and interfaces. It then displays information, operates alarms, monitors for faults and may send signals to other systems.
The panel may show conditions such as:
- Fire
- Fault
- Disablement
- Test
- Power fault
- System fault
On an addressable system, the panel may show the exact device that has activated. On a conventional system, it may only show the affected zone.
Manual call points
A manual call point is the red break-glass or resettable unit used by a person to manually raise the alarm.
They are normally positioned so that people can raise the alarm while leaving the building.
In plain English:
A manual call point is the “press here if you discover a fire” device.
Manual call points remain important even where automatic detection is installed, because a person may discover a fire before a detector operates.
Automatic fire detectors
Automatic fire detectors monitor for signs of fire.
Different detector types are used for different environments. The correct detector depends on the room, fire risk, likely fire type and false alarm risk.
Common detector types include:
| Detector type | Simple description |
|---|---|
| Smoke detector | Detects smoke particles in the air. |
| Heat detector | Detects heat from a fire. |
| Multi-sensor detector | Uses more than one sensing method, such as smoke and heat. |
| Carbon monoxide fire detector | Detects carbon monoxide produced by fire. |
| Beam detector | Uses a beam of light to detect smoke across a large space. |
| Aspirating smoke detection | Draws air through pipework to sample it for smoke. |
| Flame detector | Detects radiation from flames. |
| Line heat detection | Uses heat-sensitive cable or tubing to detect heat along a route. |
Detector selection and siting should always be carried out by a competent person. A detector that is suitable in one area may be unsuitable in another.
Fire alarm warning devices
Fire alarm warning devices alert people that there is a fire alarm condition.
Common warning devices include:
| Device | Simple description |
|---|---|
| Sounder | Makes the fire alarm noise. |
| Visual alarm device | Flashes to provide a visual warning. |
| Voice sounder | Plays a recorded spoken message. |
The alarm needs to be suitable for the building and the people using it. Some buildings may need visual alarms, voice messages, staged alarms or special arrangements for people who are Deaf or hard of hearing.
Zones
Fire alarm systems use zones to help people understand what is happening.
There are two important types:
| Type | Meaning |
|---|---|
| Fire detection zone | The area where the fire alarm activation or device is located. |
| Alarm zone | The area where the fire alarm warning is given. |
These are not always the same thing.
For example, a detector may activate in one part of a building, but the alarm may sound in a different area depending on the evacuation strategy.
A clear zone plan should normally be provided near the fire alarm panel so staff, engineers and firefighters can quickly understand the building layout.
Addressable and conventional systems
Fire alarm systems are commonly described as either addressable or conventional.
| System type | Plain English meaning |
|---|---|
| Addressable | The panel can identify individual devices, such as a specific detector or call point. |
| Conventional | Devices are grouped into zones, and the panel normally shows the affected zone rather than the exact device. |
Addressable systems are common in medium and large buildings because they provide more detailed information. Conventional systems are often found in smaller or older buildings.
Interfaces to other systems
Fire alarm systems often connect to other building systems.
This may include:
- Door holders
- Access control systems
- Smoke control systems
- Sprinkler systems
- Fire suppression systems
- Lifts
- Ventilation plant
- Building management systems
- Alarm Receiving Centres
These connections are usually made through input and output interfaces.
Interfaces are important because they can affect other life safety systems. They should be clearly designed, tested and documented.
Power supplies and batteries
A fire alarm system normally has:
- A normal supply, usually mains electricity
- A standby supply, usually rechargeable batteries
The standby batteries allow the system to continue operating for a period of time if the mains supply fails.
Battery faults should not be ignored. If the mains fails and the batteries are defective, the system may not continue to operate as intended.
Fire alarm cabling
Fire alarm systems normally use fire-resisting cables so that critical parts of the system can continue operating during a fire for long enough to support evacuation and other required functions.
Cable type, routing, support, segregation and installation quality all matter.
Poor cabling or poor installation can cause:
- Faults
- False alarms
- Earth faults
- Communication problems
- Loss of devices
- Loss of sounders
- Reduced system reliability
Wireless and networked systems
Some fire alarm systems use radio links instead of cables for some or all devices. These are often called wireless, radio-linked or hybrid systems.
Some larger systems have multiple fire alarm panels connected together. These are called networked systems.
Both wireless and networked systems still require proper design, commissioning, testing and maintenance.
Faults, disablements and false alarms
Fire alarm systems monitor themselves for problems.
Common system conditions include:
| Condition | Plain English meaning |
|---|---|
| Fault | The system has detected a problem. |
| Disablement | Part of the system has been deliberately isolated or turned off. |
| False alarm | The alarm has operated due to something other than a real fire. |
| Unwanted fire alarm signal | A false alarm that has been passed to the fire and rescue service. |
A fault does not always mean the whole system has failed, but it should still be investigated.
The urgency depends on what is affected, the building type, occupancy, fire strategy and whether temporary measures are in place.
Fire alarm logbook
The fire alarm logbook records important events relating to the system.
This may include:
- Weekly tests
- Fire alarm activations
- False alarms
- Faults
- Disablements
- Engineer visits
- Maintenance work
- Modifications
- Cause and effect changes
A good logbook helps premises management, engineers and auditors understand the history of the system.
Weekly testing and servicing
Most fire alarm systems require routine user testing and periodic servicing.
Weekly testing is normally a basic user check to confirm that the system can raise an alarm and that occupants are familiar with the alarm signal.
Servicing is a more detailed inspection and test carried out by competent people. It checks the system condition, operation, batteries, devices, interfaces, documentation and fault history.
What information is useful when reporting a fire alarm issue?
When reporting a fire alarm issue, useful information includes:
- Site name and address
- Panel location
- Exact message shown on the panel
- Whether the system is in fire, fault, disablement or normal condition
- Whether the alarm is sounding
- Whether the building is occupied
- Whether any part of the system is disabled
- Whether sounders, detectors, call points, signalling or interfaces are affected
- Whether there have been repeated false alarms
- Any recent works, leaks, power cuts or building changes
- Photos of the panel display, if safe and appropriate
This information helps the service desk, account manager or engineer understand the urgency and likely cause of the issue.
Common misunderstandings
“The panel is beeping, so the fire alarm is going off.”
Not necessarily. A beeping panel may indicate a fault, disablement or warning condition rather than a fire alarm.
“One detector fault means the whole system has failed.”
Not usually. A single detector fault may only affect one device, but it still needs investigation.
“The fire alarm is fine because the green light is on.”
A green power light only shows that the panel has power. It does not prove every detector, sounder, interface or battery is working correctly.
“The system has automatic detection, so manual call points are not needed.”
Manual call points are still normally important because people may discover a fire before automatic detection operates.
“A fire alarm system stops fires.”
A fire alarm system does not stop a fire starting or spreading. It warns people and can trigger other safety actions.
Summary
A fire alarm system is used to detect or report fire, warn people and support the building’s fire strategy.
For non-engineers, the key things to understand are:
- What the system is intended to achieve
- What type of system category has been specified
- Which part of the system is affected
- Whether life safety, evacuation, monitoring or other fire safety systems are affected
- Whether the issue is a fire, fault, disablement or false alarm
For individual terms and definitions, see: