Fire Alarm Categories Explained: M, L1-L5, P1 & P2

A plain-English guide to BS 5839-1 fire alarm categories, what each one covers and which one your building is likely to need.

What a fire alarm category means

BS 5839-1 sorts fire alarm systems in non-domestic buildings into categories. The category says what the system is designed to protect and where automatic detection goes. It is the first thing a designer, fire risk assessor or insurer will ask about.

There are three groups: M for manual systems, L for systems that protect life, and P for systems that protect property. A building can have a combined category, such as L2/P2. Since BS 5839-1:2025 the designer must state the category in the system documents and agree it with the user or purchaser.

Category M: manual systems

Category M systems have manual call points and sounders but no automatic detection. They rely on people discovering a fire and raising the alarm. They can suit small, simple buildings that are occupied whenever they are open, but most fire risk assessments now call for some automatic detection.

Category L: life protection

L1: automatic detection throughout the whole building, including roof spaces and voids where needed. Gives the earliest warning, often used in care homes, hospitals and complex buildings.

L2: everything in L3, plus detection in rooms that present a high fire risk or where people are at particular risk, such as kitchens, plant rooms or sleeping areas.

L3: detection on escape routes and in rooms that open onto them, so a fire is detected before it blocks the way out. Common in offices, shops and HMOs.

L4: detection in the escape routes themselves, such as corridors and stairways. A basic level of automatic protection.

L5: a bespoke system designed to meet a specific fire safety objective, for example to protect a particular area or support another fire safety measure. The design must be documented.

BS 5839-1:2025 extends detection for L1, L3 and L4 to main access and egress stairways as well as escape routes. It also recommends smoke or multi-sensor detection in sleeping rooms. See our BS 5839-1:2025 guide.

Category P: property protection

P1: automatic detection throughout the building, to call the fire and rescue service as early as possible and limit damage.

P2: detection only in defined high-risk or high-value areas, such as a server room, archive or stock area.

Property protection is usually driven by an insurer and almost always needs a monitored connection to an alarm receiving centre. Detection that nobody hears at night does not protect much property.

Which category does my building need?

The category should come from your fire risk assessment, and sometimes from your insurer or building control. Typical examples we see:

Small shop or office, occupied when open: often L3 or L4 with manual call points

Multi-storey offices or mixed-use buildings: L2 or L3, depending on layout and risk

Hotels, guest houses and HMOs: L2 or L1, with smoke detection in bedrooms

Care homes and supported housing: usually L1, with remote monitoring

Warehouses and factories: L3 or L2 for life safety, often combined with P2 or P1 for insurers

Schools: commonly L2 or L3, sometimes with P2 for out-of-hours protection

Homes and flats: BS 5839-6

Fire alarms in homes, HMOs and inside individual flats are covered by BS 5839-6, which uses Grades (A, C, D1, D2, F1, F2) for the type of equipment and Categories (LD1, LD2, LD3, PD1, PD2) for coverage. A typical new-build house uses Grade D1, Category LD2. A larger HMO with a panel is often Grade A, Category LD2.

Salts Fire & Security is BAFE SP203-1 registered for fire alarm design, installation, commissioning and maintenance. We will look at your building and fire risk assessment and recommend the right category before we quote. See our fire alarm service, or find us in Bradford, Leeds, Manchester and beyond.

Common questions

What are the fire alarm categories?

BS 5839-1 uses Category M (manual), Categories L1 to L5 (life protection) and Categories P1 and P2 (property protection). Each sets out where automatic detection is needed.

What is the difference between L1 and L2?

L1 has automatic detection throughout the whole building. L2 covers escape routes, rooms opening onto them and specific high-risk rooms, but not every area.

Which fire alarm category does an HMO need?

It depends on the size and layout. Smaller HMOs often use a BS 5839-6 Grade D system. Larger HMOs commonly need a Grade A system with a panel, typically Category LD2. Your local authority and fire risk assessment set the requirement.

Who decides the fire alarm category?

The category normally comes from the fire risk assessment, the insurer or building control. Under BS 5839-1:2025 the designer must state it and agree it with the user or purchaser.

Can a building have more than one category?

Yes. Combined categories such as L2/P2 are common where both life safety and property protection are needed.

Can you tell me what category my existing system is?

Yes. We can survey the system against your fire risk assessment and BS 5839-1 and confirm the category in writing.

Last reviewed 04/11/2026 by the Salts Fire & Security team, Baildon. This is general guidance; your fire risk assessment and the full standard take priority.

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Fire Alarm Categories Explained: M, L1 to L5, P1 and P2