The right fire alarm category depends on whether a building is domestic or non-domestic, what the fire risk assessment says, and whether the aim is to protect life, property or both. BS 5839 is split into Part 1 for non-domestic premises and Part 6 for domestic premises. For most commercial buildings, the category should come out of the fire risk assessment before anyone designs or prices a system.
What is the difference between BS 5839-1 and BS 5839-6?
BS 5839-1 covers fire detection and alarm systems in non-domestic premises. It was revised in 2025 (BS 5839-1:2025), and the IET’s Wiring Matters summary of the key changes is a useful starting point for anyone reviewing an existing system. Part 1 uses life protection categories M and L1 to L5, plus property protection categories P1 and P2.
BS 5839-6 covers domestic premises, including flats and houses in multiple occupation (HMOs). It uses system grades alongside domestic categories LD1, LD2 and LD3. Mixed-use buildings that contain both domestic and non-domestic areas need both parts applied to the relevant areas.
What do the BS 5839-1 categories M, L1 to L5 and P1 to P2 mean?
- Category M – manual only. Someone must operate a manual call point on discovering a fire. There is no automatic detection.
- L1 – automatic detection throughout all areas of the building where a fire could start, including voids and roof spaces.
- L2 – detection on escape routes plus defined high-risk rooms and rooms opening onto escape routes.
- L3 – detection on escape routes and in rooms opening onto them, to give warning before escape routes become unusable.
- L4 – detection only within escape routes such as corridors and stairwells.
- L5 – a bespoke, localised system protecting a specific area or risk identified by the fire risk assessment.
- P1 – property protection detection throughout the building.
- P2 – property protection detection in defined high-risk or high-value areas only.
Categories can be combined. A building might have an L3 system for life safety with P2 coverage in a server room or plant room, for example.
What are the domestic grades and LD categories under BS 5839-6?
BS 5839-6 grades describe how the system is built. Grade A is the most robust, with separate detectors, sounders and control equipment to the BS EN 54 series and standby power. Grade C uses detectors and sounders on a common power supply with standby power and central control. Grades D1 and D2 are mains-powered alarms with standby batteries (tamper-proof in D1, user-replaceable in D2), while Grades F1 and F2 are battery-only alarms.
The LD categories describe coverage. LD1 covers all areas where a fire could start (other than bathrooms, shower rooms and toilets, which generally do not need detection). LD2 covers escape routes plus rooms with a higher fire risk, such as kitchens and principal living rooms. LD3 covers escape routes only.
Which category and grade apply to rented homes and HMOs?
BS 5839-6 includes a table setting out the minimum grade and category for different types of domestic premises. For many rented homes and smaller HMOs it recommends a Grade D1 system with LD2 coverage, but larger HMOs, sheltered housing and premises with communal areas can need higher grades or a BS 5839-1 system in the common parts. The fire risk assessment, and any local housing authority licensing conditions, should settle the specification for each building.
Who decides which fire alarm category a building needs?
In non-domestic premises, the legal duty sits with the Responsible Person under the Regulatory Reform (Fire Safety) Order 2005. They must make sure there is a suitable and sufficient fire risk assessment and that the fire detection and warning arrangements are appropriate for the premises. GOV.UK’s guidance on workplace fire safety sets out those responsibilities.
In practice, the required category should be documented in the fire risk assessment, prepared by a competent fire risk assessor, before a system is designed or priced. Choosing a category on cost alone, or leaving it to whoever quotes the installation, is how buildings end up with systems that do not match the risk.
Can one building have more than one fire alarm category?
Yes. Mixed-use buildings often need BS 5839-1 in commercial or communal areas and BS 5839-6 in individual dwellings. Within non-domestic premises, an L5 or P2 element can be added on top of a broader category to cover a specific risk. Wherever more than one category applies, the split should be clearly recorded so that testing, servicing and logbook records cover each area correctly.
How often should fire alarm systems be tested and serviced?
For BS 5839-1 systems, the usual recommendation is a weekly test, operating a different manual call point each week, and periodic inspection and servicing by a competent person at intervals of no more than six months. Every test, fault and false alarm should be recorded in the system logbook. For domestic systems under BS 5839-6, alarms should be tested regularly, typically monthly, using the test button where fitted.
Categories should also be reviewed whenever a building’s use, layout or occupancy changes, not left until the next service visit. A storage area converted into offices, or an open-plan floor split into cellular rooms, can change what detection is needed.
Delta First can arrange fire alarm servicing through vetted specialist subcontractors and keep it alongside your other statutory duties through our full compliance management service. Our directly employed electrical team also carries out commercial EICR testing in Essex and the planned electrical maintenance that sits alongside a building’s fire safety arrangements.
Is a Category M manual system ever enough on its own?
Sometimes. Category M relies on people discovering a fire and raising the alarm, so it only suits premises where people are present, awake and alert whenever the building is occupied, and where a fire is unlikely to develop unseen. If the fire risk assessment calls for automatic detection – for example in sleeping accommodation, unoccupied areas or rooms where a fire could block escape routes – a manual system alone will not satisfy it. That is a compliance gap, not a cost saving.
Frequently asked questions
Which BS 5839 category do most offices need?
There is no single answer. Many offices have an L-category system, but the fire risk assessment should determine the category based on layout, occupancy and escape routes.
Does BS 5839 apply to HMOs?
Yes. HMOs generally fall under BS 5839-6, although larger HMOs and buildings with communal areas may also need a BS 5839-1 system in the common parts.
How often should a commercial fire alarm be serviced?
BS 5839-1 recommends inspection and servicing by a competent person at intervals not exceeding six months, plus weekly user testing.
Key takeaways
- BS 5839-1 (revised in 2025) covers non-domestic premises and uses categories M, L1 to L5, P1 and P2.
- BS 5839-6 covers domestic premises and uses grades (A, C, D1, D2, F1, F2) with categories LD1 to LD3.
- Category M is manual only; L1 gives automatic detection wherever a fire could start.
- The Responsible Person is accountable, and the category should be set out in the fire risk assessment.
- Mixed-use buildings often need both parts of BS 5839 applied to different areas.
- Commercial systems need weekly testing and servicing at least every six months, with a logbook kept up to date.
Talk to Delta First
Delta First Building Services is a Colchester-based M&E contractor working across Essex, Suffolk and London, with commercial work in Norfolk. Our directly employed electrical team is supported by vetted specialist subcontractors where extra certification is needed, and we offer genuine 24/7 emergency cover. Get in touch to arrange a survey or quote.