Sleeping rooms: L2 now includes them, and heat detection is out of favour
The Category L2 definition has grown. L2 has always been the L3 objective plus named high-hazard or high-risk areas; the 2025 edition writes sleeping rooms into the definition itself — warning people asleep in their own rooms is now part of what L2 means (Clause 4). A specification that says "L2" now carries sleeping-room detection by default — worth re-reading tender documents written against 2017 assumptions, because detector counts rise on L2 jobs.
Alongside that, the edition turns away from heat detection where people sleep. Heat detectors are now listed among the types not to use in sleeping accommodation; the stated preference on new and substantially refurbished work is smoke, multi-sensor or carbon monoxide detection (Clause 20), and the hotel/HMO variation wording that used to soften this in the category-selection table has gone. A fire-risk-assessment justification can still support heat detection in a particular room — but a bedroom heat detector is now something a new servicing contractor flags as a non-conformity on takeover (Clause 44). For the category framework itself — what L1 to L5, P and M actually cover — see our BS 5839 categories guide; the same shift shows up domestically in BS 5839-6's grading, which that guide also covers. And in taller residential blocks, sleeping-risk provision increasingly pairs with a separate BS 8629 evacuation alert system — a different system, outside BS 5839-1's scope.
In practice — the multi-sensor detector is the natural beneficiary. Where a 2017-era L2 or L3 design put a heat detector in a bedroom to hold down false alarms, the 2025 answer is usually a multi-sensor — the Gent S-Quad range combines smoke, heat and (in some variants) CO sensing in one addressable head.
Stairway lobbies: the low-fire-risk exemption is gone
The one design change most likely to be walked past, and it moves detector counts. The 2017 edition gave stairway lobbies two ways out of detection: its L1/P1 exclusion list named them beside toilet lobbies as skippable at low fire risk, and its L3 provision for lobbied stairway approaches sat in a note, again qualified by low fire risk. The 2025 edition closes both. Only toilet lobbies remain excluded, so in L1 and P1 systems the lobby itself now gets a detector; and for L3 — and L2, which builds on it — the note is now body text with the qualifier gone: where a stairway is reached through a lobby, detection goes on the room side of each door opening onto that lobby (Clause 7).
In practice — re-survey before re-quoting. A job priced against a 2017-era layout will not have counted heads at lobbied stairway approaches; on L1 and P1 work the lobby itself needs covering too.
Detector siting: distances unchanged, obstructions redefined
The spacing numbers all survive — what changed is what counts as a wall or an obstacle, in three refinements within Clause 21. A new rule first: an obstruction running close under the ceiling — ductwork is the obvious case — is treated as a wall where the clear gap above it is under 300 mm and its depth exceeds 10% of ceiling height (21.2.12); 2017 ran those two tests separately, never in combination. A new note works the other way: an isolated attachment no deeper than 250 mm with over 300 mm clear above it is no obstacle to smoke flow, so the twice-its-depth offset does not apply. And "closely spaced" beams now have a number — roughly 1 m or less between centres (21.2.14) — where 2017 left the phrase undefined. The 500 mm keep-clear and the radial distances are untouched.
Manual call points: the 25 m/16 m rule is gone; covers and height are explicit
The 2017 edition cut its 45 m and 30 m call-point travel-distance recommendations down to 25 m and 16 m where many occupants had limited mobility, or where processes made rapid fire development likely. That reduced figure has disappeared from the 2025 edition (Clause 19): the general distances remain, and in high-hazard areas the designer is now asked to shorten the distance commensurately with the risk — a judgement, not a number. Templates that hard-code 25 m/16 m need editing. For the full call-point picture — siting, covers, height and the folklore around them — see our call points guide.
Two things that were loose are now explicit. Mounting height is 1.4 m above finished floor level, measured to the centre of the operating face, with a stated tolerance of +0.2 m/−0.3 m — so 1.1 m to 1.6 m is in tolerance, and the old habit of treating 1.4 m as absolute (or quietly ignoring it) is replaced by a real band. And the protective cover every call point should now carry is specifically a transparent one — the device still sited conspicuously against a contrasting background, as before, so it reads as a call point at a glance (Clause 19).
Standby batteries: Annex D is now Annex E, and the formula gains T2
The normative method for sizing standby batteries moved from Annex D to Annex E (Clause 24, Annex E). The method itself is the familiar one — a 25% ageing margin over the standby load plus a de-rated alarm load — but the alarm period is now an explicit variable, T2, in the formula rather than an assumption folded into it. If your battery-sizing spreadsheet cites "Annex D" or hides the alarm period, it needs a revision pass; any calculation carried forward from a 2017-era design is worth re-running.
Our fire alarm battery calculator already works to the 2025 Annex E method, including the conditional de-rating factor, and rounds up to the stocked 12 V flame-retardant battery sizes.
Alarm transmission to an ARC: the timings now have numbers
Where a system signals to an alarm receiving centre, Clause 14 now states how fast. Category L: a fire signal should register at the ARC within 90 s, and a catastrophic transmission failure — no alarm signal able to get through at all — should be flagged at both the ARC and the panel within 3 min. Category P: 120 s and 31 min (that last value is as printed in the published edition). The 2017 text set no such timings. Three riders sit alongside: where fire signalling shares an intruder and hold-up alarm system's routing equipment, that equipment's power supply should meet BS EN 54-4 or BS EN 50131-6 grade 4; a notice at the panel should warn of the live link to the fire and rescue service; and the ARC should hold the premises facts that matter — sleeping accommodation above all — with the signal, where practicable, identifying the device type and any coincidence operation (Clause 14).
New: remote services and cybersecurity
The 2025 edition adds a maintenance recommendation with no 2017 equivalent: remote services and cybersecurity (Clause 43.4, with reference to BS EN 50710 on secure remote services). Where a panel can be reached remotely — by the manufacturer, the service provider or a cloud gateway — the edition asks for physical prevention of unauthorised access to the connection, authentication before any remote session, and a risk assessment before remote reading, control or writing, with a check of full operation afterwards.
It pairs with a rule in the new extensions-and-modifications section: if the software, firmware or cause-and-effect programming changes, someone still has to prove the change on site — typically within one to seven days — and making the change remotely does not waive that check (Clause 46). Remote diagnostics earn their keep; the edition simply keeps the on-site confirmation attached. Systems with cloud connectivity — Gent's CLSS platform among them — now sit squarely inside these provisions; our CLSS guide covers what that connectivity involves.
Servicing: a real window, and a relaxed voltage test
The service interval loosened its collar without changing its intent. The 2017 wording capped the gap between service visits at six months; 2025 says approximately six months, and states plainly that five to seven months between visits is acceptable, with the date of acceptance as the datum for the sequence (Clause 43). Contract schedules gain honest breathing room — this is a window, not an invitation to drift.
Within the service visit itself, the expectation for the power-supply check moved: with the standby battery disconnected and the alarms activated — or the full alarm load simulated — the power supply output should sit close to nominal voltage, with at least 85% considered reasonable, where 2017 looked for 95%. The batteries themselves are examined separately and momentarily load-tested with the mains disconnected. The edition also adds annual checks that were not itemised before: that the zone indication at the panel actually matches the zone plan on the wall, and that indications agree across multiple or repeat panels (Clause 43). One 2017 allowance appears to have gone: there is no longer wording that lets routine functional detector tests be omitted where automatic self-monitoring is judged to prove the detector — the 2025 text asks for a functional test on every detector. The wider testing routine — the weekly test, the logbook, who does what — is covered in our fire alarm testing guide; the change here is the edition delta, not the routine.
The definitions layer and the renumber map
The quietest change ripples furthest. The 2025 edition sources its vocabulary from BS 4422:2024, and several everyday terms were renamed on the way through: a fire signal is now a fire alarm signal, a detection zone is a fire detection zone, a detector is a fire detector. The competent-person definition is stronger, with continuing professional development now in the picture. And the dual-path alarm-transmission definition dropped its "diverse technology" wording — resilience is now handled in the body of the standard instead, which advises different technologies for the two paths where automatic calling of the fire service is critical to life safety (Clauses 3 and 14).
Then there is the renumber. The 2017 edition's Clause 4 was absorbed into the Introduction, shifting the design clauses from Categories onwards down by one; further back, two clauses merged and extensions-and-modifications became its own section, moving the commissioning and maintenance clauses down again. A single offset will mislead you — use the map. Our summary of the numbers practitioners cite most:
Clause renumbering, 2017 → 2025 (our summary — verify against the standard)
| Topic | 2017 clause | 2025 clause |
|---|
| Categories of system | 5 | 4 |
| Variations | 7 | 6 |
| Fire detection zones | 13 | 12 |
| ARC alarm transmission (communication with the fire & rescue service) | 15 | 14 |
| Audible alarm signals | 16 | 15 |
| Manual call points | 20 | 19 |
| Detector types & selection | 21 | 20 |
| Detector siting & spacing | 22 | 21 |
| Control & indicating equipment | 23 | 22 |
| Power supplies | 25 | 24 |
| Cables & wiring | 26 | 25 |
| Commissioning | 39 | 37 |
| Acceptance → Handover | 42 | 40 |
| Routine testing | 44 | 42 |
| Inspection & servicing | 45 | 43 |
| Modifications | 46.4 | 46 |
The annexes reshuffled too:
Annex reshuffle, 2017 → 2025 (our summary)
| Content | 2017 | 2025 |
|---|
| Standby battery capacity method (normative) | D | E |
| Detector selection & application (informative, reorganised) | E | D |
| Typical noise levels | B | C |
| Control/transmission for portable tactile devices | C | B |
| False-alarm rate calculation (new) | — | F |
| Model logbook format | F | H |
The practical consequence: every "see clause X.Y" citation in a specification, O&M manual, certificate template or service contract is now edition-specific. Purge 2017 numbers from live templates, and where a document must serve both editions, cite the edition with the number.
Smaller changes worth knowing
- Unacceptable variations are now named (Clause 6). Some departures cannot be signed off as agreed variations: the absence of a zone plan where any storey has more than one zone (above all where people sleep), and the absence of alarm transmission to an alarm receiving centre in a residential care home or in supported housing needing a BS 5839-6 Grade A system.
- Temporary systems are out of scope (Clause 1). Waking-watch and interim alarm schemes — cladding-remediation buildings, construction sites — are now explicitly outside BS 5839-1.
- CO fire detectors gained ground (Clause 20). Carbon monoxide fire detectors, used alongside smoke detection, are now permitted on escape routes across Category L systems rather than the narrower 2017 cases.
- Detector siting carries over (Clause 21). The 500 mm keep-clear, its 250 mm depth threshold and the twice-their-depth offset for shallow ceiling attachments all continue from 2017; where detectors also actuate other fire-protection measures, spacing takes the lower of the BS 5839-1 and BS 7273-4 values — as before.
- Sounder and signal tweaks (Clause 15). The core sound-level figures are unchanged, but the cap on the school class-change signal doubles from 5 s to 10 s, and a new rule protects speech on emergency voice communication systems from being drowned by the alarm.
- Warnings for people who are Deaf or have a hearing impairment (Clause 17). There is now a cited product standard, BS 5446-3:2015, and a clear split: fault-monitored devices can form the primary warning; unmonitored ones only supplement it.
- Extensions and modifications get their own section (Clauses 45–46). Extensions now carry their own clause and share a renamed model certificate (G.7); kit stranded by a modification should come out where practicable — or be labelled clearly, so nobody mistakes a dead device for a live one.
- Functional-earth conductors are identified pink (Clause 28), or marked "FE", per BS 7671:2018+A3.
- False-alarm rates get a worked method (new Annex F). The calculation of false alarms per hundred detectors per year is now formalised in an annex with worked examples, feeding the investigation tiers in the body of the standard.
- Handover tightened (Clauses 38–40). The handover check now includes the correct count of call-point replaceable elements and tools, and the cause-and-effect matrix travels with the system documentation.
- User duties eased slightly (Clause 47). The daily panel check is now asked for "where practicable" with a weekly fallback, and spare call-point "frangible elements" became "replaceable elements" — plastic resettable elements count.
- Category L4: flues and shafts (Clause 21). Where a flue-like structure, lift shaft or enclosed chute penetrates ceilings, an L4 system now gets a detector at the head of the shaft — 2017 exempted L4. The per-level detector within roughly 1.5 m of the penetration stays an L1, L2, L3 and P1 matter.
- Multi-sensor configuration is recorded (Clause 20.11). Where detection has selectable operating modes, the designer records the chosen types and configurations; the record passes to the commissioning technician, sits in the O&M manual (Clause 38) and is updated on modification (Clause 46).
- Fault indications stay visible (Clause 44). Where a defect cannot be fixed during the servicing attendance, the fault indication is not to be hidden — suppression is the standard's own example of what not to do.
- New service-visit checks (Clause 43). Every visit: any timeclock checked and adjusted — the attached note points at time-related filtering. Annually: duct-mounted smoke detectors functionally tested to the manufacturer's instructions, and visual fire indicators verified as neither blocked from view nor painted over (the operation check itself dates from 2017).
- Variations tightened (Clause 6). Variations surfacing during installation or commissioning are documented with a justification for approval, and every agreed variation is recorded in the logbook — 2017 asked that only for major non-compliances.
- Interfaces must be reachable (Clause 8). Interfaces to other systems should sit where a technician can maintain them — which can rule out housing them inside the other equipment's enclosure.
- One cable colour, mains included (Clause 25). The single common colour — red preferred — now covers the low-voltage mains supply as well as the fire alarm cables themselves.
- And in one line each: a multi-sensor's ceiling-height limit reads from the lowest Table 3 figure among its detection types (Clause 21); sprinkler-as-heat-detector indication must not confuse sprinkler area with detection zones, one sprinkler zone spanning at most one detection zone (21.2.6); linear heat detecting cable gains product standards, BS EN 54-22 resettable and BS EN 54-28 non-resettable (Clause 10); the L3 void note now turns on whether the room-to-escape-route construction continues through the void, 2017's "fire-resisting" wording having gone (Clause 21); remote fire indicators show red (12.5); the stairway call-point zoning rule drops 2017's "enclosed" (12.1); the non-fire-use restriction now attaches to the evacuation tone, not the device — other messages may share the device on distinct tones — and a note points to FIA lockdown guidance (Clause 15); battery installation dates may be permanent-marker rather than label (Clause 24); multi-sensors are preferred over point smoke detectors where false-alarm risk runs high (Clause 33); the commissioning or handover organisation now advises the user to investigate every false alarm, the investigating duty itself being 2017-era (Clause 29); the commissioning technician now advises the user to keep documentation current and available to all interested parties (Clause 38); servicing disablements are minimised and notified to management (Clause 43.2); and the definitions clause gains BS 4422:2024 entries (access room, inner room, place of ultimate safety, storey exit among them) while the normative-reference list grows (BS 5446-3, BS EN 54-22/-28, BS EN 50518 among the additions) (Clauses 2–3).
What to do now — by role
If you design: update templates to 2025 clause numbers; treat L2 as including sleeping-room detection and price detector counts accordingly; default sleeping-room detection to smoke, multi-sensor or CO; remove hard-coded 25 m/16 m call-point reductions and justify high-hazard spacing on the risk; apply the 250 mm obstruction test and the BS 7273-4 lower-spacing rule in siting calculations.
If you install: mount call points at 1.4 m (+0.2 m/−0.3 m) to the centre of the operating face, with transparent covers, against a contrasting background; identify functional-earth conductors pink or "FE"; expect the commissioning pack to be checked for the cause-and-effect matrix and call-point spares at handover on addressable systems.
If you service: plan visits on the five-to-seven-month window from the acceptance date; apply the 85% standby voltage expectation; add the new annual checks — zone plan against panel indication, consistency across panels, indicator condition — and functionally test every detector; on takeover, report the named non-conformities, bedroom heat detection included; put remote-access arrangements through the Clause 43.4 questions before connecting.
If you manage premises: ask where your zone plan is — in most premises its absence is now treated as an unacceptable variation; check the daily panel look-over is happening where practicable; hold spare replaceable elements for your call points; and record agreed variations in the logbook so the next servicer inherits the truth.
We supply fire detection equipment to the current edition — BAFE SP203-1 registered, UK-wide, quote-only. If a 2025-edition spec has changed your detector schedule or battery sizing, send it over for a quote or call 0844 997 0001.
