Two standards
Commercial and domestic alarm categories are different
BS 5839-1:2025 is the current code of practice for fire detection and alarm systems in non-domestic premises. BS 5839-6:2019+A1:2020 covers domestic premises. Mixed-use buildings may require both approaches in different areas and careful interface design.
The Fire Safety Order requires appropriate warning arrangements but does not prescribe one BS category for every premises. The FRA and strategy establish the objective; a competent designer turns it into a system specification.
Non-domestic life safety
M and L1 to L5 categories
M is a manual system. L categories add automatic fire detection for life safety. Lower or higher numbers do not represent a simple quality ranking: each category has a defined coverage objective.
| Category | Core objective | Coverage in plain English |
|---|---|---|
| M | Manual warning | Manual call points and alarm devices; no automatic detection objective |
| L1 | Maximum life protection | Automatic detection throughout the premises |
| L2 | Additional life protection | L3 coverage plus automatic detection in specified high-risk or high-hazard areas |
| L3 | Standard life protection | Escape routes and rooms opening onto them, to warn before routes become untenable |
| L4 | Modest life protection | Automatic detection in escape routes |
| L5 | Specific life-safety objective | Automatic detection in expressly defined areas for a stated fire-safety objective |
Non-domestic property protection
P1 and P2 categories
P categories focus on protecting property and business continuity, often through early detection and transmission to an alarm-receiving centre. They can be combined with M or L categories when both life and property objectives apply.
P1
Automatic detection throughout the premises, intended to minimise the time between ignition and detection across the building.
P2
Automatic detection in defined areas where fire risk or business consequences justify property protection.
Combined category
A specification might combine life and property objectives, but should state each category and any variations clearly.
Response matters
Early detection only protects property if notification, investigation and fire-service calling arrangements are reliable.
Domestic premises
LD1, LD2 and LD3 categories
In domestic premises, LD categories describe the extent of automatic detection intended for life safety. The correct category depends on the dwelling, occupants and applicable housing or building guidance.
| Category | Protection objective | Broad coverage |
|---|---|---|
| LD1 | Maximum life protection | Detection throughout areas in which a fire might start, subject to the standard’s normal exclusions |
| LD2 | Additional life protection | LD3 coverage plus detection in specified higher-risk rooms or areas |
| LD3 | Minimum life protection | Detection in circulation spaces forming escape routes |
Specification and verification
Who decides the alarm category?
The category should be derived from the FRA, fire strategy, occupancy, evacuation arrangements and relevant sector guidance. The responsible person, risk assessor, competent alarm designer and other project professionals may need to coordinate; an installer should not silently redefine the objective.
The proposal should state category, coverage, drawings, cause-and-effect, interfaces, monitoring, audibility or visual alarm needs, variations and certification. Commissioning and maintenance then test whether the installed system achieves that specification.
- Confirm whether areas are domestic, non-domestic or mixed
- State the full category and every L2, L5 or P2 area/objective
- Document agreed variations from the code
- Coordinate lifts, doors, smoke control, suppression and remote signalling
- Consider people with hearing or other access needs
- Keep design, installation, commissioning and maintenance evidence