How We Design a Fire Alarm System

A fire alarm is only as good as its design. Here's how we decide what your building needs, what goes into the design and the paperwork that proves it was done properly.

Manual

Call points only. People raise the alarm themselves.

Life, whole building

Detection throughout, for the earliest possible warning.

Life, escape routes plus higher-risk rooms

Escape routes plus rooms where a fire is more likely or more dangerous.

Life, escape routes plus rooms opening onto them

Warns people before smoke blocks their way out.

Life, escape routes only

Detection in corridors and stairways.

Life, a specific risk

Designed around one particular risk identified in the fire risk assessment.

Property, whole building

Detection throughout to protect the building and its contents.

Property, specific areas

Detection in defined high-risk or high-value areas.

Our most-fitted detector

Optical smoke detectors

Detects smoke particles with a light sensor inside the chamber. Responds quickly to the slow, smoky fires most likely in offices and escape routes.

Best for

Offices, corridors, escape routes, bedrooms

Watch out for

Steam, dust and aerosols can cause false alarms

Where smoke would false alarm

Heat detectors

Triggers at a fixed temperature or when the temperature rises quickly. Slower than a smoke detector, so it is used where smoke detection would cause false alarms.

Best for

Kitchens, plant rooms, dusty or steamy areas

Watch out for

Not suitable on escape routes where early warning is needed

Fewer false alarms

Multi-sensor detectors

Combines smoke and heat sensing and compares the two before raising the alarm. Good where a smoke detector alone suffers occasional false alarms.

Best for

Mixed-use areas, staff rooms, receptions

Watch out for

Settings must suit the room; we set them at commissioning

High ceilings

Optical beam detectors

Sends an infrared beam across a large space and alarms when smoke blocks it. One beam can cover an area that would need many point detectors.

Best for

Warehouses, atriums, sports halls

Watch out for

Needs solid mounting and a clear line of sight

Very early warning

Aspirating smoke detection

Draws air through a pipe with small sampling holes to a sensitive detector. Gives very early warning, and the detector can sit somewhere easy to reach.

Best for

Server rooms, cold stores, high or hard-to-reach areas

Watch out for

Pipework design is specialist and must be tested

Anyone can raise the alarm

Manual call points

The red break-glass or push units that let anyone raise the alarm. Fitted on exit routes and at every storey and final exit, usually about 1.4m from the floor.

Best for

Every exit route and final exit

Watch out for

Protective covers help where call points get knocked

Loud enough to wake you?

Sounders must reach at least 65 dB(A) throughout the building, or 5 dB(A) above background noise where that's higher. In sleeping areas the requirement is 75 dB(A) at the bedhead, so people wake up. We plan sounder positions on the drawings and measure the levels at commissioning.

Still working in a power cut

A standard system must run for at least 24 hours on standby batteries and then sound the alarm for 30 minutes. We calculate battery size as part of every design and check it at commissioning and at every service.

Answers come only from our standards library and quote their sources. They are general guidance, not advice for a specific building, and are produced automatically, so check the source before relying on them. Please don't include names or personal details in your question.

What category of fire alarm do I need?

What is the difference between conventional and addressable systems?

How long should the batteries last?

What paperwork should I have?