A plain-English guide to BS 5839-1:2025, the current UK code of practice for commercial fire detection and alarm systems. It covers the L, P and M categories, what changed from the 2017 edition on 30 April 2025, and what a compliant system looks like once it is installed. Written and reviewed by the fire and security engineering team at Hawthorne in Norwich.
Last updated 9 September 2026. Reflects BS 5839-1:2025, in force since 30 April 2025.
Quick answer
BS 5839-1:2025 is the British Standard code of practice for the design, installation, commissioning and maintenance of fire detection and fire alarm systems in non-domestic premises. It came into effect on 30 April 2025 and replaced BS 5839-1:2017, which was withdrawn on the same date. It is not law in itself, but it is the benchmark that fire risk assessors, insurers, building control and the fire and rescue service use to judge whether a commercial fire alarm system is adequate under the Regulatory Reform (Fire Safety) Order 2005.
Within BS 5839-1, the system you need is described by a category. L1 to L5 are for life safety, P1 and P2 are for property protection, and M is for manual call points only. The category is set by your fire risk assessment, your insurer and, in some premises, the enforcing authority. Most commercial buildings end up with L1, L2 or L3.
The 2025 edition does not require existing systems to be ripped out. It does change what a new, extended or modified system should look like, what documentation you should hold, and what a servicing visit should cover. The changes are summarised in the table below and explained in the rest of this guide.
Contents
- What BS 5839 actually is
- What changed in BS 5839-1:2025
- The L categories: life safety
- P1 and P2: property protection
- M: manual only
- How you decide which category you need
- What compliance looks like once installed
- What the 2025 edition means for an existing system
- Common mistakes we see
- Frequently asked questions
What BS 5839 actually is
BS 5839 is a British Standard published by BSI, not a piece of legislation. Fire safety law in England and Wales (the Regulatory Reform (Fire Safety) Order 2005) places a duty on the "responsible person" to make sure fire detection and warning arrangements are appropriate for the building. BS 5839 is the standard that fire risk assessors, designers, installers and insurers use to interpret that duty, and Approved Document B of the Building Regulations references it directly.
The standard has several parts. BS 5839-1 covers fire detection and fire alarm systems in non-domestic premises, which is where almost all commercial property sits. BS 5839-6 (currently BS 5839-6:2019+A1:2020) covers domestic premises and houses in multiple occupation. This guide is about BS 5839-1.
BS 5839-1 is a code of practice. That means it gives recommendations to competent people rather than absolute pass or fail requirements. A designer can depart from a recommendation where there is a justified reason, but under the 2025 edition every departure (a "variation") must be agreed, documented and recorded in the system logbook, and a small number of departures are now classed as unacceptable.
What changed in BS 5839-1:2025
BS 5839-1:2025 was a full revision, developed by BSI technical committee FSH/12/1, and it superseded BS 5839-1:2017 on 30 April 2025. The headline changes, drawn from the standard itself and from the Fire Industry Association and IET guidance on it, are set out below.
| Area | BS 5839-1:2017 | BS 5839-1:2025 |
|---|---|---|
| Detectors in sleeping rooms | Heat detectors commonly accepted in bedrooms of hotels, care homes and student accommodation | Smoke, multi-sensor or carbon monoxide fire detectors recommended in any room where people sleep, unless the fire risk assessment justifies heat detection. Not retrospective for existing bedrooms |
| Zone plans | Recommended | Omitting a zone plan at the control panel is now an unacceptable variation. Responsibility for producing it must be agreed and documented |
| Remote monitoring in residential care premises | Recommended | Absence of remote monitoring where it is needed to meet the standard is an unacceptable variation |
| Variations from the standard | Only "major" variations had to be recorded | All variations recorded in the logbook and on the certificates |
| Manual call points | 25 m and 16 m travel distance references | Simplified: no call point should be more than 45 m along the route a person would walk. Not on stair landings in phased-evacuation buildings. Mounting height tolerance of +200 mm / -300 mm |
| Signal transmission to an alarm receiving centre | General guidance | Defined limits: Category L systems 90 seconds for a fire signal and 3 minutes for a transmission fault; Category P systems 120 seconds and 31 minutes |
| False alarms | Guidance on reduction | New "False Alarm Notice" to be fixed at the control panel of any system with an automatic connection to the fire and rescue service. All false alarms logged, investigated and reviewed |
| Cables | Red fire alarm cable common; mains supply colour varied | Fire alarm and low-voltage mains supply cables should be a single common colour. Functional earth identified pink (FE) per BS 7671 Table 51 |
| Interfaces and ancillaries (door holders, smoke vents, lift returns) | No explicit accessibility recommendation | Must be accessible for maintenance and testing |
| Ceiling obstructions | Beam and duct rules without a clear cut-off | Closely spaced beams defined as less than 1 m apart. A gap of more than 300 mm above a feature means it is not an obstruction to smoke flow |
| Extensions and modifications | Covered within general clauses | New dedicated section. Any addition or alteration should carry a modification certificate and updated records |
| Certificates | 2017 model forms | All design, installation, commissioning, verification and modification certificates on the 2025 model forms with the new clause numbering |
| Terminology | "Care homes", "fire service", "acceptance", "engineer" | "Residential care premises", "fire and rescue service", "handover", "technician", aligned with BS 4422:2024 |
| Competence | Competent person defined | Competent persons expected to maintain competence through continuing professional development |
| Other detection types | Point detectors | Linear heat detection cable formally recognised (BS EN 54-22 and BS EN 54-28) |
| Standby batteries | Capacity formula divided by 2 | Formula amended to use the total alarm period (T2). Battery fitted date may be written on the battery |
The numbering of the standard also changed throughout. Clause 4 of the 2017 edition moved into the introduction and sub-clause lettering was dropped, so any certificate, specification or maintenance checklist that quotes 2017 clause numbers is now out of date even where the technical content is the same.
Sources: IET Wiring Matters, Key changes to BS 5839-1:2025 (September 2025); Fire Industry Association, Guide to the changes in BS 5839-1:2025; BSI, BS 5839-1:2025.
The L categories: life safety
L1: full coverage for life safety
Smoke detection in all rooms, voids, ceiling cavities and roof spaces, except where it would be impractical (a sealed plant room, for example). Used where the priority is to evacuate everyone safely from a fire wherever it starts. Common in residential care premises, hospitals, hotels and other sleeping-risk premises, and large multi-storey buildings. Under the 2025 edition, sleeping rooms in an L1 system should have smoke, multi-sensor or carbon monoxide fire detection rather than heat detection.
L2: escape routes plus high-risk areas
Detection on every escape route and every room opening onto one, plus any specific high-risk area identified in the fire risk assessment. Used where the building has a known higher-risk zone (a kitchen, a workshop with flammable materials, a battery storage area, or rooms where people sleep) but does not need full coverage everywhere.
L3: escape routes plus adjoining rooms
Detection on escape routes, plus the rooms that open onto them. The aim is to give people enough warning to get out before smoke reaches the corridor or stairs. Common in offices, retail units and smaller commercial buildings. The 2025 edition adds main access and egress stairways to the areas that L1, L3 and L4 systems should cover.
L4: escape routes only
Detection in circulation areas, corridors and stairwells, usually combined with manual call points on each floor. Used in lower-risk premises where the route out is well separated from the rooms.
L5: localised
Detection only in a specified part of the building to meet a specific fire safety objective. Use is limited and is decided by the fire risk assessor or fire engineer rather than chosen as a default.
P1 and P2: property protection
P1 is full property protection: detection in all areas to protect the building and its contents. Used where the building or what it holds is high-value (a data centre, a warehouse with sensitive stock, a heritage building). Insurers often specify P1 directly.
P2 is localised property protection. The same idea as P1 but only for defined parts of the building: a loading bay, a server room, a specific high-value area.
M: manual only
M is the category for buildings that rely on manual call points and sounders alone, with no automatic detection. Permitted in some lower-risk situations but increasingly rare for new commercial work. Most commercial buildings will need at least L4 or L5 in addition.
How you decide which category you need
Under clause 4 of BS 5839-1:2025, where a category is stipulated by an enforcing authority, a property insurer or the purchaser, that category should be used. Where nobody has stipulated one, the designer must state clearly which category the design meets so the purchaser can check it against the building's fire strategy. Three documents drive the choice in practice.
The fire risk assessment is the starting point. The category is an output of the assessment, not an input to it.
Your insurer's policy schedule may add requirements on top. Some insurers specify P1 detection regardless of what the fire risk assessment recommends, because their concern is property loss rather than life safety. If your policy mandates a category, that is the floor.
Local fire authority guidance can raise the bar in specific premises types. Residential care premises and licensed premises are common examples. The fire and rescue service does not normally specify a category by default, but can do so during inspection or licensing.
What compliance looks like once installed
Compliance with BS 5839-1 is not a one-off event. The standard covers four phases and you need evidence at each, on the 2025 model forms.
Design. The designer provides drawings, a zone plan (or documented agreement on who produces it) and a design certificate confirming the system meets the specified category, with any variations listed. Keep the certificate.
Installation. The installer provides an installation certificate at the end of the work. Keep this too.
Commissioning and handover. A commissioning technician tests every device, sounder, visual alarm device and interface, confirms signal transmission times where the system is monitored, fixes the False Alarm Notice to the panel where there is an automatic connection to the fire and rescue service, and signs the commissioning certificate. Handover should include as-fitted drawings, all certificates, the logbook, the user instructions and the cause-and-effect matrix where one exists.
Maintenance. BS 5839-1 sets minimum service intervals: a competent person should inspect and test the system at least every six months, and the user should carry out a weekly test, operating a different manual call point each week so every call point is tested in rotation. Every false alarm should be logged and investigated. Any change, any device added or removed, and any variation should be recorded in the system logbook.
If any one of these is missing, you have a system installed to BS 5839 but not necessarily a compliant one.
What the 2025 edition means for an existing system
The standard is not retrospective. A system designed and commissioned to BS 5839-1:2017 does not have to be replaced because the standard has been revised. What changes is the frame of reference for everything that happens to it from now on.
Servicing. Six-monthly service visits carried out after 30 April 2025 should be recorded on 2025 forms and checked against the 2025 recommendations. Expect your servicing provider to check the zone plan is present and accurate, confirm interfaces are accessible, and review the false alarm log.
Extensions and modifications. Adding detectors, moving a call point, changing the cause-and-effect or connecting to an alarm receiving centre now falls under the new modification section. The work should meet the 2025 edition and be covered by a modification certificate.
Sleeping accommodation. Hotels, residential care premises and student accommodation with heat detectors in bedrooms do not have to change them immediately. The 2025 edition expects the upgrade to smoke or multi-sensor detection when the system is substantially replaced or extended, or sooner if the fire risk assessment calls for it.
Monitored systems. If your panel has an automatic link to the fire and rescue service via an alarm receiving centre, a False Alarm Notice should now be displayed at the panel, and the transmission path should meet the 90-second (Category L) or 120-second (Category P) fire-signal limit. With the UK switch to all-IP telephone lines, older signalling equipment on analogue lines needs checking.
Documentation. If your only certificates are 2017 forms, they remain valid records of the original work. Any new certificate issued for the same system should be on a 2025 form.
Common mistakes we see
Specifying a category without a fire risk assessment. The category is the output of the assessment, not an input to it. Designing a system before the assessment is done usually means redoing it later.
Skipping commissioning. Some installers will do design and installation but leave commissioning to "another time". The installation is not compliant until commissioning is signed off.
Maintenance gaps. A six-month service that has been missed for a year. A weekly user test that no one is doing. These are the most common audit failures because they are easy to forget and easy to evidence (or not).
Undocumented additions. Adding a sounder, moving a detector or extending the loop without going back to the original designer. Under the 2025 edition any change should be documented, certificated and re-commissioned.
Missing or out-of-date zone plans. The 2025 edition treats the absence of a zone plan as an unacceptable variation, and FIA guidance treats an outdated or inaccurate one as a major non-conformity.
Mixing categories. A building that is L3 in one zone and L4 in another with no documented reason. This usually happens when extensions or refurbishments are added without updating the design certificate.
Frequently asked questions
Is BS 5839-1:2025 a legal requirement?
No. BS 5839-1 is a code of practice, not legislation. The legal duty comes from the Regulatory Reform (Fire Safety) Order 2005 in England and Wales and its equivalents in Scotland and Northern Ireland. BS 5839-1 is the accepted way of showing that duty has been met, and Approved Document B references it directly, so a system that falls short of it is very hard to defend.
When did BS 5839-1:2025 come into force?
30 April 2025. BS 5839-1:2017 was withdrawn on the same date.
Do I have to upgrade my existing fire alarm to the 2025 edition?
Not automatically. The standard is not retrospective. Your fire risk assessment decides whether the existing system still meets the building's needs. Any extension, modification or substantial replacement should be carried out to the 2025 edition.
What is the difference between BS 5839-1 and BS 5839-6?
BS 5839-1 covers non-domestic premises. BS 5839-6 covers domestic and small residential premises. Most commercial buildings use BS 5839-1. Houses in multiple occupation can fall under BS 5839-6 depending on size and layout, and the common parts of blocks of flats often sit under BS 5839-1.
How often should a commercial fire alarm be tested and serviced?
A weekly user test, operating a different manual call point each week, and a full inspection and test by a competent person at least every six months. Both should be recorded in the logbook.
What is the False Alarm Notice?
A notice introduced by BS 5839-1:2025 that must be displayed at the control panel of any system with an automatic connection to the fire and rescue service. It reminds staff that an activation will call the fire and rescue service and that false alarms must be investigated and logged.
How long does a BS 5839 system last?
The standard does not set a fixed lifespan. Detectors typically have a manufacturer-specified life of around ten years. Control panels can last longer with regular service. Follow the manufacturer's guidance and replace components when they reach end of life or fail commissioning checks.
Do I need a connection to the fire and rescue service?
Not by default. BS 5839-1:2025 does expect remote monitoring in residential care premises where it is needed to meet the standard. For most other commercial buildings, connection to an alarm receiving centre is a separate decision, often driven by insurance.
How much does a BS 5839 compliant system cost?
It depends on the building, the category and the number of devices. For an indicative range without entering your details, use the Hawthorne pricing calculator, or see our guide to commercial fire alarm systems.
Need a BS 5839-1:2025 compliant system designed, installed or serviced?
Hawthorne designs, installs, commissions and maintains BS 5839-1 fire detection and alarm systems for commercial buildings across Norfolk, Suffolk, Cambridgeshire, Essex and the rest of the UK, from our base in Norwich. We are SSAIB registered (NORF034) and Cyber Essentials certified. Call 01603 425100, use the pricing calculator for an indicative range, or contact us for a site survey and quote.
About the author
Dr Andrew Threadgold is Co-Owner of Hawthorne. Hawthorne acquired Security Solutions Yes Limited in December 2024 and rebranded as Hawthorne in January 2026. The technical content of this guide was reviewed by Hawthorne's fire and security engineering team against BS 5839-1:2025 and the FIA and IET guidance on it.
Last updated: 9 September 2026 (revised for BS 5839-1:2025). First published May 2026.