Specifying Fire Detection and Alarm Systems to BS 5839-1:2025

What changed between BS 5839-1:2017 and BS 5839-1:2025?

BS 5839-1:2025 took effect on 30 April 2025 and withdrew the 2017 edition. It renumbers the whole standard and adds recommendations on variations, cause and effect, sleeping room detection and alarm transmission that change what a specification must say.

BS 5839-1:2025 took effect on 30 April 2025, and the 2017 edition was withdrawn on the same date (IET Wiring Matters). It is still a code of practice, so its recommendations can be varied, but the 2025 edition narrows what may be varied and moves several decisions from the installer to the designer. A specification that still cites the 2017 edition, or that copies 2017 clause references into certificates and schedules, is out of date.

The 2025 revision was a full review. The numbering is new throughout: the lettered sub-clauses of 2017 have gone, and BSI numbering applies, so clause references in certificates and checklists need re-keying (FIA, Guide to the changes in BS 5839-1:2025). The text of the need for a system has moved into the introduction, because a standard for how to design a system should not decide whether one is needed. That decision still belongs to the fire strategy, the fire risk assessment, the enforcing authority or the insurer.

Several terms changed to align with BS 4422:2024. Care homes are now residential care premises, the fire service is the fire and rescue service, the engineer is a technician and acceptance is now handover (IET). Specifications and certificates that use the old words will not match the standard the contractor is working to.

Other changes a specifier will notice

Smoke detection obstruction rules were tightened. Ductwork and similar obstructions close to the ceiling are treated as a wall where the gap above is under 300 mm and the obstruction is deeper than 10% of the ceiling height, and isolated beams or fittings up to 250 mm deep keep detectors at least twice that depth away (FIA). Call points are now measured to a 45 m travel distance, with a mounting height tolerance of 200 mm above and 300 mm below 1.4 m. Cables and the low voltage mains supply should be a single, common colour, with red preferred, and the functional earth is identified pink or marked FE.

Maintenance wording changed too. A six-monthly service is now acceptable between five and seven months after the previous one, with the date of handover or acceptance as the datum. A new clause covers remote services and cyber security, and updating CIE firmware counts as a modification that needs a certificate. These are the maintainer's duties, but a specification that requires a maintenance contract or a first-year service should quote them correctly.

Domestic premises are covered by BS 5839-6:2019+A1:2020 rather than by this part, although BS 5839-1 does cover the design, installation and commissioning of Grade A systems conforming to BS 5839-6, with a few exceptions (IET). The standard's introduction also records that systems are not normally required in communal areas of purpose-built blocks of flats (FIA). That is a statement about the standard, not a substitute for the fire strategy of any one building.

How do the categories M, L1 to L5, P1 and P2 work, and who chooses?

The category sets the extent of automatic detection and its purpose. It is chosen from the fire strategy, an enforcing authority, an insurer or the purchaser, and the specification should state it with its source rather than leave it to the installer.

BS 5839-1 sets out categories, but the choice is not the installer's. Where an enforcing authority, an insurer or the purchaser stipulates a category, that category should be used. If the designer has not been told which, the designer must make clear to the purchaser or their agent which category the design conforms to, so that it can be checked against the fire strategy (IET, clauses 4.1 and 4.2). The specifier's job is to close that loop before the tender, not to leave it for the installer to discover.

The categories divide into manual systems, life protection systems and property protection systems. The extent of automatic detection is the thing each category sets. The wording below is a summary of the standard's intent, not a quotation.

What 2025 changed for the main life categories

Category L2 now includes rooms in which people sleep, because they are treated as high-risk rooms, so heat detectors are no longer used in them under L2 and L3 unless a fire risk assessment justifies it. The recommendation is not retrospective, and existing systems need not be changed until they are extended or substantially replaced (FIA, IET). Stairway lobbies now require detection. For category L4, a detector is now recommended at the top of flue-like structures, and clause 7.5 now includes main access and egress stairways (FIA).

Guidance on whether a system is needed, and at what category, sits in the building and fire safety guidance, including BS 9991, BS 9999 and, in England, Approved Document B, Volume 2 of which references BS 5839-1 (IET). The fire strategy is the owner of the category; see the Avoice guide to fire strategy reports. The specification should quote the fire strategy reference and revision, so that a later change to the strategy flags the clause for review.

What does the designer specify and what is left to the installer?

The designer specifies the category, zoning, detector selection rules, interfaces, cause and effect, signalling and certification. The installer completes device positions, cable routes and power supply calculations, and certifies them.

The designer fixes the category, the zoning, the detector selection logic, the interfaces, the cause and effect, the signalling arrangement and the certification route. The installer completes the detailed device positions, cable routes, power supply calculations and loop layout, and proves them. Where that split is not written down, both sides assume the other owns it.

BS 5839-1 itself expects an exchange of information and a definition of responsibilities. Where the designer proposes the category, it should be discussed and agreed with the user or purchaser. The designer and purchaser should agree whether visual alarm devices are included. The responsibility for creating the zone plan should be clearly defined, agreed and documented (IET, clauses 5.4, 5.5 and 5.7). Each of those is a line in a design responsibility matrix, and the specification should reflect the matrix rather than repeat it. See the M&E design responsibility matrix guide, and the architect version.

Variations

The 2025 edition changes the status of variations. All agreed variations should be recorded in the logbook, and all need justification, particularly when proposed at installation or commissioning stage (FIA). Two variations are no longer acceptable at all: no zone plan where a storey has more than one zone, and no facility to transmit fire alarm signals to an ARC in a residential care home, or in supported housing where a Grade A system to BS 5839-6 is necessary. The specification should say that no variation is accepted without the written approval of a named person, and that the variations schedule is a handover deliverable.

Competence is a procurement question as well as a technical one. Third-party certification of a fire detection and alarm contractor, for example to BAFE SP203-1 as the FIA notes, is a common way to evidence it. Whether the project requires it is a client decision, and it should appear in the preliminaries or the specification rather than being assumed.

How should cause and effect and interfaces be specified?

Write a cause and effect matrix that connects every input to every output, name an owner for each end of every interface, and issue it with the tender. The 2025 edition recommends a matrix or description in the handover documents.

Write the cause and effect as a table that connects every input to every output, and issue it with the tender. The 2025 edition recommends that a cause and effect matrix, or a text description where the strategy is simple, is included in the documentation given to the purchaser or user (FIA). In practice it is the document the commissioning engineer tests against, so it is better written by the designer than reconstructed by the installer.

Start from the evacuation strategy. A simultaneous evacuation can be described in a sentence. A phased evacuation, an alert and evacuate arrangement, or a building with a smoke control system needs a matrix. The standard's introduction makes the same point from the other direction: the system should support the evacuation procedure, not the other way round.

Every row is an interface, and every interface has two ends. The fire alarm contractor supplies the signal. Another trade supplies and owns the device that acts on it. The specification should state who supplies the interface unit, who wires each side, who programs it, and who attends the joint test.

Smoke control

The fire alarm gives the input and the smoke control package gives the output. Specify which party issues the control signal, the fail-safe state, and the joint test of the strategy as a whole. The smoke control design standard is stated in the fire strategy and should be quoted in the clause.

Sprinklers

Where sprinkler heads act as heat detectors, the sprinkler operation indication should leave no doubt which area has operated, and a sprinkler zone should not overlap more than one fire detection zone (FIA). Specify flow switch and valve monitoring outputs and the fire detection zone each belongs to.

Lifts

Specify the lift recall or homing requirement, who supplies the signal, who tests it with the lift contractor, and the evacuation or firefighting lift arrangements in the fire strategy.

Access control

BS 7273-4 covers the control arrangements for mechanisms that unlock, release or open doors in a fire. The FIA notes it can take precedence over BS 5839-1 for category L4 and L5 systems. Specify which doors release, on which signal, the fail-safe behaviour, and who tests.

The 2025 edition adds two points that affect interface specifications. Interfaces and ancillary devices, such as fire door magnets and smoke vents, should be accessible for maintenance. That rules out burying an interface unit in an enclosure that belongs to another trade, where reaching it would mean isolating that trade's equipment (FIA, IET). Where the system is also used for school class change signals, the 2025 edition allows it up to 10 seconds, and FIA publishes separate guidance on lockdown.

What must the specification clause contain, and how is the system certified?

The clause must name the standard and edition, category, responsibilities, interfaces, signalling, variations, competence, certificates and handover documents. Certification runs in four steps: design, installation, commissioning and handover.

The clause must state the standard and edition, the category and its source, the protected spaces, who designs what, the interface and cause and effect arrangements, signalling, variations, competence, certificates and handover deliverables. Anything left out is something the installer prices without being asked.

Certification follows the project in four steps, with model certificates in the standard. The designer issues a design certificate. The installer certifies installation. The commissioning technician certifies commissioning. The system is then handed over, which is the 2025 term for what the 2017 edition called acceptance (IET). Verification and extension or modification certificates are also provided for. Check the standard itself for the complete list of model certificates. Because certificate clause references changed with the new numbering, forms based on 2017 need re-keying (IET).

Statutory handover runs alongside the BS 5839-1 documents. Regulation 38 of the Building Regulations 2010 requires the person carrying out the work to give fire safety information to the responsible person at completion or occupation, and to notify the building control authority once the responsible person has acknowledged receipt. The fire alarm file is part of that information. For higher-risk buildings the same information feeds the golden thread: see the golden thread guide for building services and the guide to commissioning, soft landings and O&M clauses.

Questions engineers ask about BS 5839-1

When did BS 5839-1:2025 come into effect?

BS 5839-1:2025 came into effect on 30 April 2025, and BS 5839-1:2017 was withdrawn on the same date. The 2025 edition is the current code of practice for fire detection and alarm systems in non-domestic premises.

Can heat detectors still be used in bedrooms?

The 2025 edition recommends smoke, multi-sensor or carbon monoxide detection in rooms where people sleep, unless a fire risk assessment justifies heat detection. The recommendation is not retrospective, so existing systems need not change until they are substantially replaced or extended.

Does BS 5839-1 apply to dwellings?

Domestic premises are covered by BS 5839-6:2019+A1:2020. BS 5839-1 does cover the design, installation and commissioning of Grade A systems that conform to BS 5839-6, with a few exceptions.

Is a cause and effect matrix required?

The 2025 edition recommends that a cause and effect matrix, or a text description of how cause and effect operates, is included in the documentation provided to the purchaser or user. Simple strategies can be described in a sentence, while complex ones need a matrix.

Can a variation from the standard be agreed at commissioning?

All variations now need justification, especially if proposed at installation or commissioning, and all agreed variations are recorded in the logbook. Omitting a zone plan where a storey has more than one zone is not an acceptable variation.

Who chooses the system category?

The category comes from the enforcing authority, the insurer, the purchaser or the fire strategy. If the designer is not told the category, the designer should make clear which category the design conforms to, so that the purchaser or their agent can check it against the fire strategy.

Where Avoice fits

A fire alarm clause fails at the joins: the category in the clause that no longer matches the fire strategy, the standard cited at the wrong edition, the cause and effect that disagrees with the smoke control section.

Avoice writes building services specifications alongside architectural ones, so the fire alarm section can sit in the same workspace as the fire strategy summary, the door schedule and the smoke control package. The office master holds the practice's fire alarm clause as a governed library entry. Practice rules can enforce the words and standards the practice requires, for example that a standard is cited with its current edition. Avoice MEP and structural specifications are structured to CAWS or Uniclass 2015, the same as architectural specifications.

The pre-issue Technical Review compares the specification against schedules and drawings, which is where a door release interface that appears in one place and not another, or a category that differs between documents, shows up before tender. The Compliance module holds the building regulations tracker and, for higher-risk buildings, golden thread and Gateway 2 support, so regulation 38 fire safety information and handover documents can be tracked as project record. Software retrieves, compares and flags. The fire engineer and the services engineer still decide the category, the strategy and the cause and effect.