Fire alarm system categories explained (BS 5839-1: L, P and M)

Direct answer

BS 5839-1 classifies non-domestic fire detection and alarm systems into categories that describe what the system is mainly intended to do: M systems are manual (call points only, no automatic detection), L systems are for life protection (with automatic detection, in sub-categories L1 to L5), and P systems are for property protection (sub-categories P1 to P2). This article is an orientation only. The precise definition of each sub-category, and which category your premises needs, must be taken from the current BS 5839-1 and determined by a competent designer through the fire risk assessment — not chosen arbitrarily.

Applies to

• Products / Models: Not applicable (system design concept, not a product feature)
• Firmware / Version: Not applicable
• Region: UK
• Standards: BS 5839-1 (system categories)

Why systems are categorised

• The category records the purpose and extent of the system so that everyone — designer, installer, responsible person and inspector — shares the same expectation of what it covers.
• The required category for a building is an output of the fire risk assessment and the designer's judgement, not a free choice by the occupier.

The three families (general intent only)

• M — manual systems. Provide a means of raising the alarm manually (for example manual call points) without automatic fire detection.
• L — life protection systems. Include automatic fire detection with the primary aim of protecting life. BS 5839-1 defines several sub-categories (commonly written L1 to L5) that describe how much of the building is covered by automatic detection, ranging from comprehensive coverage to detection in defined areas only.
• P — property protection systems. Include automatic fire detection with the primary aim of protecting property, with sub-categories (commonly written P1 to P2) describing the extent of coverage.

The lists L1–L5 and P1–P2 above are named only to show that sub-categories exist. Their exact meanings, the areas each one requires to be covered, and the right choice for your premises must come from the current BS 5839-1 and a competent designer — do not treat this article as the definition.

The category is determined, not chosen

• A competent designer selects the category from the fire risk assessment, the building use, and any requirement of the authority having jurisdiction.
• The chosen category should be recorded in the system documentation and reflected at commissioning and handover — see Fire alarm commissioning and handover: what to expect.
• Changing the building use or layout can change the category required; review it with a competent person rather than assuming the original category still applies.

When to contact technical support

• If you do not know what category your system was designed to, check the system documentation or ask a competent person.
• If you need to confirm the correct category for your premises — this requires a competent designer and the current BS 5839-1, not a general article.

Safety note

This article is general guidance for Hochiki Europe products. Installation, commissioning, maintenance and modification of fire detection and alarm systems must be carried out by a competent person in accordance with the applicable standards (for example BS 5839-1 in the UK) and the requirements of the relevant authority having jurisdiction. Always refer to the current product manual and data sheet for the exact model before carrying out any work.

References

• BS 5839-1 (current edition) — system categories (M, L1–L5, P1–P2) and their definitions
• The system's design documentation (records the designed category)

Last reviewed: 2026-06-16 — Reviewed by: Takashi Ishikawa