If you have ever read a fire alarm quote or specification you will have seen codes such as L1, L2 or P1. They are the system categories set out in BS 5839-1, the UK standard for fire detection and alarm systems in non-domestic buildings. They describe how much of the building is protected and why. This guide explains them in plain English.
The three families: M, L and P
- M (manual): no automatic detectors. People raise the alarm by pushing a call point.
- L (life protection): automatic detection to protect people.
- P (property protection): automatic detection to protect the building and its contents, and to limit business disruption.
Life protection categories (L)
L1: detection throughout
Automatic detectors in all areas of the building. This is the highest level of life protection and is typical for places where people sleep, such as care homes and hotels, or where the risk to life is highest.
L2: escape routes plus defined risk areas
Covers everything in L3, plus detectors in specified rooms where a fire is more likely or could be dangerous, for example kitchens, plant rooms and areas of higher fire risk.
L3: escape routes and rooms opening onto them
Detection in the corridors and stairwells people use to escape, and in rooms that open onto those routes, so that people are warned before the escape route becomes unusable.
L4: escape routes only
Detectors in the circulation areas, such as corridors and stairways, and not in the rooms themselves.
L5: tailored to a specific risk
A custom design where the fire risk assessment or fire engineering identifies particular areas that need protection.
Property protection categories (P)
P1: detection throughout
Detectors in every area, so that a fire is found as early as possible. It is often chosen where downtime or loss of equipment would be very costly, or where an insurer asks for it.
P2: defined high-risk areas
Detectors only in the parts of the building where the risk or the value is concentrated, such as server rooms, plant rooms or storage.
How do you pick the right category?
- Start with your fire risk assessment. It identifies where fires could start, who could be at risk and how people escape.
- Consider who uses the building. Sleeping occupants or vulnerable people push you towards a higher category.
- Check what your insurer requires.
- Decide whether property protection is needed on top of life protection, and combine categories if so (for example L2 with P2).
A note on standards
BS 5839-1 is revised from time to time, so a design should always follow the current edition. If your system was designed under an earlier edition, it may be perfectly acceptable, but a competent engineer should confirm that it still suits how your building is used today.
Need help deciding? Our team can review your building and your risk assessment and recommend the right design. See our fire alarm installation service, and read about how often fire alarms must be tested.
Frequently asked questions
Which fire alarm category does my business need?
It depends on your building, how people use it and your fire risk assessment. Many offices and shops use L2 or L3, while sleeping accommodation and high-risk buildings need L1 or similar. A designer should confirm the category against your risk assessment.
What is the difference between conventional and addressable?
Conventional panels show which zone an alarm is in. Addressable panels identify the exact device, which is faster in larger buildings and gives more information for maintenance.
Is category P1 compulsory?
No. P categories protect property and business continuity rather than life. They are often chosen because of insurance requirements or the value of what is inside the building.