BS 5839-1:2025: what changed, and what it means for your building

Source: this page follows the Fire Industry Association’s Guide to the changes in BS 5839-1:2025 (Version 1, June 2025, PDF on the FIA website).

A new structure

BS 5839-1 was first published in 1980 and the 2025 edition followed a full review. It has a new introduction, built mostly from clause 4 of the 2017 edition, and new BSI-style numbering throughout: for example, the old 22.3 e) on detector distances below ceilings is now 21.2.4. Where only the numbering changed, the recommendations are the same.

The introduction explains that the system should be designed to support the building’s evacuation procedures, not the other way round, and that whether a building needs a fire alarm at all is decided by the fire risk assessment or the enforcing authority, not by the standard. It notes that systems are appropriate for virtually all buildings except very small, open-plan premises, and aren’t normally needed in the communal areas of purpose-built blocks of flats.

Terms and definitions now match BS 4422:2024, the fire vocabulary standard, with new or updated definitions including access room, inner room, area of low fire risk, competent person (with a note that keeping competence up is likely to need continuing professional development), fire detection zone, storey and storey exit. New normative references include product standards for line-type heat detectors (BS EN 54-22 and BS EN 54-28) and alarm receiving centres (BS EN 50518).

Categories of system

• L2 now includes rooms where people sleep, which count as high-risk rooms needing protection, so heat detectors are no longer permitted in them.
• Stairway lobbies now need automatic detection. Before, they could be left out as areas of low risk.
• L3 and ceiling voids: the separation between a room’s void and the escape route no longer has to be “fire-resisting construction”, which was hard to define. It should be solid construction with no holes in it, to keep smoke out of the escape route.
• L4 and flue-like structures: a detector is now recommended at the top. Unlike L1, L2, L3 and P1, L4 doesn’t call for a detector near the penetration on every floor.

Heat detectors and detector choice

Heat detectors shouldn’t be used in rooms where people sleep in L2 systems, nor in L3 systems. This isn’t retrospective: existing systems don’t need changing unless they’re having new work, such as an upgrade.

Detector selection (now Annex D) has more emphasis. Where detectors can be set to different modes, as multi-sensors can, the designer should record the type and configuration chosen, give it to the commissioning technician and include it in the operation and maintenance manual. Where point smoke detectors could cause false alarms, multi-sensors are recommended instead. A multi-sensor set to respond to heat and smoke takes the lower ceiling height limit, the one for heat. Sprinkler heads can still act as heat detectors, but their indication mustn’t be confused with the fire detection zones, and a sprinkler zone shouldn’t overlap more than one detection zone.

Variations: some are no longer acceptable

BS 5839-1 is still a code of practice that allows variations, but these are now considered too detrimental to life safety to be acceptable:

• No zone plan in premises with more than one zone on any storey, particularly premises where people sleep
• No facility to send fire alarm signals to an alarm receiving centre in a residential care home, or in supported housing where a BS 5839-6 Grade A system would be needed

All variations need justifying, especially if proposed at installation or commissioning, and every agreed variation should be recorded in the logbook, not just the “major” ones as in 2017.

Siting and installation

• Interfaces should be accessible for maintenance, in line with the CDM Regulations 2015. That might rule out putting one inside another system’s enclosure.
• Obstructions: ducting near the ceiling should be treated as a wall if the gap above it is under 300 mm and it’s deeper than 10% of the ceiling height. Detectors shouldn’t be closer to beams, ducts or light fittings up to 250 mm deep than twice their depth; anything with a gap of more than 300 mm above it isn’t an obstacle. Closely spaced beams are now defined as about 1 m or less, centre to centre.
• Voids: a new figure shows where, and at what depth, detectors go in voids.
• Linear heat detection is recognised under BS EN 54-22 (resettable) and BS EN 54-28 (non-resettable).

Manual call points

Siting is simplified to a maximum of 30 m in a straight line and 45 m of actual travel to reach a call point; designers can make them shorter. The mounting height is 1.4 m, up to 200 mm higher or 300 mm lower. Protective covers, recommended since 2017, should now be transparent. The confusing reference to “enclosed stairways” has gone: a call point on a stairway landing belongs to the zone serving the accommodation on that level, except at the final exit level.

Sounders, tones and remote indicators

• The same sounder can now give different warnings, using different tones or messages.
• In schools, the fire alarm can signal the start and end of lessons, with each class change signal now up to 10 seconds (it was 5), to allow for delays in addressable systems. The standard notes the FIA’s guidance on using fire alarms for lockdown.
• Remote indicators should show red, and be checked at the annual service to make sure they haven’t been blocked or painted over.

Signalling to alarm receiving centres

With the analogue phone network switching off in 2027, the standard now sets maximum times for alarm transmission:

• A separate power supply for the transmission equipment should conform to BS EN 54-4 or BS EN 50131-6 Grade 4.
• A new label on or next to the control panel reminds the building’s management that the system is connected to the fire service through an ARC, so it’s told before tests.
• The ARC should be given relevant information about the premises, such as whether people sleep there, to pass to the fire service.
• Where practicable, the signal should show the type of device that triggered it and whether coincidence filtering is in use.

Cables, labelling and power

• All fire alarm cables and the low-voltage mains supply to the system should be one common colour, red preferred. The mains supply should be in fire-resisting cable of the same grade.
• A functional earth conductor should be pink or marked “FE”, in line with BS 7671 Amendment 2 (it used to be cream).
• Batteries should be labelled with their installation date; permanent marker is acknowledged as acceptable.
• The recommendations on isolating the mains supply are now in one clause.

False alarms

Guidance on limiting false alarms is now one section (clauses 29 to 33). The user should arrange for every false alarm to be investigated, and the commissioning organisation should explain how, and explain the categories of false alarm so each is recorded correctly. The trigger points haven’t changed, but are now expressed as rates:

• Preliminary investigation when false alarms over the previous 12 months exceed four per 100 detectors per year
• In-depth investigation for systems with more than 40 automatic detectors when the rate exceeds five per 100 per year

A new Annex F gives the calculation: false alarm rate = 100 × (number of false alarms ÷ number of automatic detectors), with worked examples.

Documentation and handover

The handover documents should now include a cause and effect matrix, or a written description of how the cause and effect works. That can be as simple as “this system operates as a simultaneous evacuation”. The user should be told to keep the documentation up to date and available.

Servicing

• About every six months, with any visit between five and seven months after the previous one acceptable, measured from the date of acceptance. In 2017, going over six months meant the system was no longer compliant.
• The panel’s clock should be checked at every visit, especially where there are day and night settings.
• Where signals go to an ARC, every type of signal (for example fire and fault) should be checked at every visit.
• Disabling parts of the system during servicing should be kept to a minimum, and the building’s management told which areas are affected.
• At the 12-monthly visit: functional tests of smoke detectors in ventilation ducts, and a check that the zone shown on the panel matches the zone tested and the zone plan.
• Keeping addressable text descriptions correct is the building management’s responsibility; checking them every five years or so may be prudent.
• A new clause on remote services and cyber security: protecting access points and network paths, authenticating remote connections, and a risk assessment before any remote service.
• If a reported fault can’t be repaired, its indication shouldn’t be hidden.

Extensions and modifications

A new Section 7 covers extensions and modifications. New work should follow the current edition, though the system as a whole might not. The certificate is now an extension or modification certificate, updating a control panel’s firmware counts as a modification that needs one, and redundant devices should be removed or clearly marked as no longer in use.

Logbook and annexes

The logbook should record all variations, and the model logbook is now Annex H. The annexes have been reordered. The battery calculation (now Annex E) uses a total battery alarm period, T2, in line with the rest of the BS 5839 series; the result doesn’t change. Try it with our fire alarm battery size calculator.

What it means for existing systems

• You don’t have to replace a compliant system because the standard changed
• Extensions and modifications, including firmware updates, should follow the 2025 edition and be certified
• Servicing should follow the current edition, including checking every ARC signal type at every visit
• Your fire risk assessment may recommend improvements, such as replacing heat detectors in bedrooms, at its next review

A quick checklist for responsible persons

• Is there a zone plan by the panel, and does it match the building?
• Are all agreed variations written in the logbook?
• Is every false alarm investigated and recorded?
• Are signals to your alarm receiving centre tested at each service?
• Has anyone updated the panel’s firmware? If so, is there a modification certificate?
• Are your services between five and seven months apart?

Not sure how your system measures up against BS 5839-1:2025? Site surveys and advice are free: we’ll look at it and tell you honestly what it needs.

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