Fire Alarm Categories L1 to L5 — Which Do You Need?
BS 5839-1 defines six fire alarm system categories from L1 (maximum life safety) to P2 (limited property protection). Picking the wrong category over-protects, or worse, under-protects. Here is a practical guide.
L and P categories
BS 5839-1 splits fire detection and alarm systems into two purposes:
- L — Life safety
- P — Property protection
Within each, there are categories defining the extent of coverage.
The L categories
| Category | Coverage | Typical use | |---|---|---| | L1 | All areas | Hospitals, care homes, high-risk | | L2 | Escape routes + risk rooms | Hotels, schools | | L3 | Escape routes + rooms opening onto them | Most office buildings | | L4 | Escape routes only | Small premises, low risk | | L5 | Specific risk-driven | Bespoke, derived from FRA |
The P categories
- P1 — Property protection throughout the building
- P2 — Property protection in defined high-value or high-risk areas only
These are typically driven by insurer requirements rather than the Fire Safety Order.
How the category is decided
The category should be derived from the Fire Risk Assessment, not chosen by default. The FRA identifies:
- Who is at risk (sleeping accommodation? mobility impaired? high occupant numbers?)
- The fire load
- The escape strategy (single staircase? compartmented escape? phased evacuation?)
- The required pre-alarm warning time
The assessor then specifies the category that meets the identified risk.
Common over-specification
We frequently see commercial offices specified at L1 when L3 would meet the FRA-derived risk. The cost difference can be 30-50% over the system lifecycle, with no safety benefit.
Common under-specification
Conversely, we see hotels and HMOs specified at L4 when L2 is required. This is a serious life safety risk — the wrong category is treated by enforcement as equivalent to no system.
The mixed-system question
For mixed-use buildings (e.g. retail + residential above), categories may differ by demise:
- Common parts: L2/L3
- Residential demise: BS 5839-6 LD1/LD2/LD3 (the domestic equivalent)
- Commercial demise: L3/L4
A competent designer matches each demise to the appropriate part of BS 5839.
Documenting the choice
The category and its justification must be documented in:
- The system design certificate
- The Fire Risk Assessment
- The commissioning certificate
If you cannot locate this documentation, the system's compliance status is uncertain.
MetroFire delivers L1 to L5 alarm design, install and BS 5839-1 servicing across London and the South East. Book a system review.
