Plain-English summaries of the key requirements for fire detection and fire alarm systems in non-domestic buildings — searchable, and including what changed in the 2025 edition.
Based on BS 5839-1:2025 · Last reviewed October 2026
These are plain-English summaries to help you find your way around BS 5839-1:2025. They are not the text of the standard and may not reflect the latest amendments — always refer to the current published standard for definitive requirements.
Automatic detection throughout the building for the earliest possible warning to occupants.
Definition
Automatic fire detection throughout all areas of the building, including voids deeper than 800 mm. Only areas of low fire risk — such as toilets, toilet lobbies, bathrooms and very small cupboards (under about 1 m²) — can be left out. Since 2025, stairway lobbies are no longer on that list.
Where it applies
Buildings where the highest level of life safety is required. Rarely specified in full due to cost; more common to use L2 with specific L1 additions.
L3 coverage plus defined high-risk areas — which, since 2025, include every room where people sleep.
Definition
Automatic fire detection as for Category L3, plus defined areas of high fire risk. BS 5839-1:2025 treats rooms in which people sleep as high-risk, so they need detection in an L2 system.
Sleeping rooms (2025)
Heat detectors should no longer be used in rooms where people sleep — use smoke detectors or suitable multi-sensor detectors instead. The change is not retrospective: existing systems only need to change when new work is carried out, such as an upgrade.
Where it applies
Common in residential care, hotels, HMOs (Houses in Multiple Occupation) and other premises with a sleeping risk where full L1 coverage is not needed.
Detection on escape routes and in the rooms that open onto them, to give warning before escape routes become impassable.
Definition
Automatic fire detection as for Category L4 (circulation areas forming escape routes), plus the rooms that open onto those escape routes. The aim is to detect a fire in a room before smoke makes the escape route unusable.
Room detectors
The usual limits on distance below the ceiling (25–600 mm for smoke detectors, 25–150 mm for heat detectors) do not apply to the detectors in rooms opening onto the escape routes.
Sleeping rooms (2025)
Heat detectors should not be used in rooms where people sleep, even in a Category L3 system.
Where it applies
Offices, shops, factories and other premises where the main aim is to protect the means of escape.
Detection in circulation areas forming escape routes, such as corridors and stairways — plus, since 2025, a detector at the top of lift shafts and other flue-like structures.
Definition
Automatic fire detection within the circulation areas and spaces that form part of escape routes, such as corridors and stairways.
Lift shafts and flues (2025)
A detector should be fitted at the top of any lift shaft or other vertical flue-like structure. Unlike Categories L1, L2, L3 and P1, L4 does not also need detectors within about 1.5 m of the openings on each floor.
Where it applies
Premises where the fire risk assessment calls for early warning on the escape routes only.
Detection throughout the building to provide the earliest warning for property protection.
Definition
Automatic fire detection throughout all areas of the building, including roof voids and ceiling voids, to minimise the time between ignition and the fire being detected.
Where it applies
Heritage buildings, high-value storage, data centres, or where insurance requirements demand comprehensive detection for property protection.
Coverage, spacing and ceiling height limits for point smoke detectors.
Flat ceilings
No point on the ceiling should be more than 7.5 m from the nearest detector. On a square grid that means up to 10.6 m between detectors and 5.3 m to the walls — about 112 m² per detector (often rounded to 100 m²).
Ceiling height
Up to 10.5 m generally, or up to 12.5 m for no more than 10% of the ceiling area. For higher ceilings use optical beam or aspirating detection.
Corridors less than 2 m wide
The areas of coverage need not overlap, so detectors can be up to 15 m apart, with no more than 7.5 m from the end walls.
Pitched ceilings and apexes
If the apex is less than 600 mm higher than the eaves, treat the ceiling as flat. Otherwise fit detection at or near the apex; the coverage of the apex detectors can be increased by 1% for each degree of slope, up to a maximum of 25%. (For heat detectors the apex limit is 150 mm.)
Distance below the ceiling
The sensing element should be between 25 mm and 600 mm below the ceiling.
Coverage and spacing for point heat detectors, and where they should not be used.
Flat ceilings
No point on the ceiling should be more than 5.3 m from the nearest detector — up to 7.5 m between detectors and 3.8 m to the walls on a square grid, about 56 m² per detector (often rounded to 50 m²).
Ceiling height
Class A1 heat detectors: ceilings up to 9.0 m. Other classes: up to 7.5 m. Any class can be used up to 10.5 m over no more than 10% of the ceiling area.
Corridors less than 2 m wide
Detectors can be up to 10.6 m apart, with no more than 5.3 m from the end walls. Note that heat detectors are not normally appropriate in escape routes in Category L systems.
Where not to use them
In escape routes of Category L systems; where smoke could threaten escape before a heat detector would respond; where a small fire could cause serious damage (Category P); and, since 2025, in rooms where people sleep (Categories L2 and L3).
Temperature rating
The static response temperature should be at least 29 °C above the average ambient temperature and at least 4 °C above the highest temperature the detector is expected to experience. Higher-rated (e.g. 90 °C) detectors are commonly used in kitchens.
Distance below the ceiling
The sensing element should be between 25 mm and 150 mm below the ceiling.
Optical beam smoke detectors for large open spaces and high ceilings.
Ceiling height
Normal sensitivity: ceilings up to 25 m (28 m for no more than 10% of the area). Enhanced sensitivity (alarm at 35% attenuation or less): up to 40 m (43 m for 10% of the area), with supplementary detection recommended unless the risk of smoke stratification is minimal.
Mounting position
The beam normally runs parallel to the ceiling and within 600 mm of it. Lower beams are used as supplementary detection (e.g. where smoke could stratify) or where practical constraints require it.
Spacing
Each beam covers up to 7.5 m either side, so parallel beams can be up to 15 m apart, with no more than 7.5 m to a wall parallel to the beam. Beam length (transmitter to receiver or reflector) depends on the product, commonly 10–100 m.
Considerations
Avoid paths subject to steam, fumes, or strong air currents. Ensure stable mounting — structural movement can cause false alarms. Align and test beams at commissioning and after any building work.
Minimum clearances from walls, obstructions, light fittings and ventilation.
Walls and partitions
No detector within 500 mm of a wall, partition or anything treated as a wall. Keep a clear space of 500 mm below every detector.
Air inlets and ventilation
No detector within 1 m of an air inlet or forced-ventilation outlet — including wall-mounted air conditioning units. Where a perforated ceiling is used for air supply, blank off the perforations within 600 mm of each detector.
Light fittings and other attachments
Light fittings, ducts and other ceiling attachments up to 250 mm deep obstruct the flow of smoke: keep detectors at least twice the obstruction's depth away (e.g. 200 mm from a 100 mm deep fitting). For deeper obstructions keep at least 500 mm away.
Heat sources and condensation
Do not mount detectors directly above radiators, cookers, boilers or other heat sources, or in areas subject to condensation.
Obstructions near the ceiling (2025)
Ducting and similar obstructions installed close to the ceiling are treated as walls if the gap above them is less than 300 mm and they are deeper than 10% of the ceiling height. Where there is more than 300 mm clear space above a feature, it is not treated as an obstacle to smoke.
How structural beams, partitions and storage affect detector siting.
Deep beams
Structural beams deeper than 10% of the overall ceiling height are treated as walls, so each bay is protected as a separate room.
Shallower beams and obstructions
Beams and other obstructions up to 250 mm deep that are not treated as walls: keep detectors at least twice the obstruction's depth away from them.
Closely spaced beams (2025)
Beams about 1 m or less apart (centre to centre) are now defined as closely spaced. Closely spaced beams and honeycomb ceilings have their own siting rules: depending on the beam depth and cell width, detectors go either on the underside of the beams or within the cells — check the standard for the exact rule.
Partitions, racking and storage
Partitions, racking or stored goods whose top is within 300 mm of the ceiling are treated as walls.
Quick reference for choosing the right detector type for each environment.
Optical smoke detectors
Best for: clean offices, bedrooms, corridors, hotel rooms, communal areas.
Most common general-purpose detector. Detects visible smoke particles from smouldering fires.
Heat detectors
Fixed-temperature or rate-of-rise detectors for areas where smoke detectors would cause false alarms, such as kitchens or dusty or steamy areas.
Not for escape routes in Category L systems or, since 2025, rooms where people sleep.
Beam and aspirating detectors
Beam detectors: high ceilings, warehouses, atriums.
Aspirating (e.g. VESDA): server rooms, clean rooms, heritage buildings, voids where sampling pipes are easier to route. Highest sensitivity available.
Multi-sensor detectors
Multi-sensor detectors (e.g. smoke and heat, or smoke, heat and CO) can significantly reduce false alarms, and BS 5839-1:2025 recommends them where point smoke detectors would carry a higher false alarm risk.
The designer should record how each multi-sensor is configured (Annex D includes a form).
If the smoke element is switched off at times (e.g. day/night modes), space them as heat detectors; one that needs both heat and smoke to raise an alarm is limited to the ceiling height for heat detectors.
Guidelines for positioning and distributing sounders throughout the building.
Distribution principle
Sounders should be distributed so that the required sound level is achieved at all occupiable points. Fewer, louder sounders are generally less effective than more, distributed sounders.
Doors and partitions
Expect a loss of about 20 dB(A) through a normal door and about 30 dB(A) through a fire door, so sounders are often needed on both sides of doors or within each room.
Tones (2025)
The fire evacuation signal should be the same throughout the building. The same sounders may now also give other signals — such as school class change or lockdown — using a clearly different tone or message. Class change signals should last no more than 10 seconds.
Resilience
Arrange sounder circuits so that a single fault still leaves at least one sounder near the control panel working.
Voice alarm systems
Where voice alarm is used, speech intelligibility needs to be verified — see BS 5839-8. Messages should be clear and agreed with the building operator.
BS EN 54-23 visual alarm devices — when they are needed and how they are rated and installed.
When VADs are required
Where ambient noise exceeds 90 dB(A) and sounders alone cannot achieve required levels.
Where hearing-impaired occupants are present or expected.
In areas where audible warnings may not be perceived (ear protection zones, noisy machinery areas).
Flash rate and colour
Flash rate between 0.5 Hz and 2 Hz.
Red or white light (one colour per product, ideally one colour throughout a building).
VADs are not designed to wake sleeping people.
Coverage categories (BS EN 54-23)
Ceiling (C), wall (W) and open-class (O) devices. Ratings describe the coverage volume — e.g. W-2.4-5 is wall-mounted at up to 2.4 m and covers a 5 m × 5 m area; C-3-7.5 is ceiling-mounted at up to 3 m and covers a circle 7.5 m in diameter.
Installation
Wall-mounted VADs at least 2.1 m above floor level.
Synchronise VADs that can be seen together — unsynchronised flashing can appear faster and risks triggering photosensitive epilepsy.
Allow for their higher current draw in battery calculations and cable sizing.
Mounting height, distances and locations for manual call points (MCPs).
Mounting height (2025)
1.4 m above finished floor level, with a tolerance of +200 mm / −300 mm — so between 1.1 m and 1.6 m. Mounting below 1.1 m (e.g. for wheelchair users) needs to be agreed as a variation.
Distances (2025)
No more than 45 m actual travel distance to the nearest call point, or 30 m in a straight line (useful in open areas, or before the layout is fixed). These are maximums: designers can specify shorter distances, for example where fire could develop rapidly or occupants have limited mobility (the 2017 edition used 25 m in such cases).
Locations
At every storey exit and every final exit to open air, and close to hazardous processes.
A call point on a stairway landing belongs to the zone of the accommodation on that floor, not the stairway zone (except at the final exit level).
Visibility
On a contrasting background and readily visible. Where they need to be seen from the side, such as in corridors, they should project from the wall (about 15 mm) rather than be fully recessed.
Types of manual call points and applicable standards for fire alarm systems.
Type A — direct operation (break glass)
Most common in the UK. Single-action operation: break the frangible element to activate. Conforms to BS EN 54-11 Type A. Resettable units use a replaceable plastic element or key-reset mechanism.
Type B — indirect operation (lift cover)
Two-action operation: lift a hinged cover, then press a button. Conforms to BS EN 54-11 Type B. Less common in UK fire alarm systems but may be specified in environments where accidental activation is a concern.
Addressable vs conventional
Addressable MCPs report their individual address to the panel, allowing exact location identification. Conventional MCPs trigger a zone circuit — the panel identifies the zone but not the individual device.
Response time
The fire alarm signal should be given within 3 seconds of a call point being operated (up to 10 seconds only as an agreed variation).
Applicable standards
BS EN 54-11 covers manual call points; BS 5839-1 covers design, installation, commissioning and maintenance of the system.
Call points should be UKCA or CE marked; third-party certification (e.g. LPCB) is strongly recommended.
Weekly user tests and routine servicing of manual call points.
Weekly test
Operate one call point each week, at about the same time, using a different call point each time so they are all tested in rotation. BS 5839-1 sets no maximum period for completing the rotation, so in large buildings it can take many weeks. Use a test key where available rather than breaking frangible elements.
What to check
Confirm the panel receives the correct zone/address signal.
Confirm sounders operate.
Confirm any ARC (Alarm Receiving Centre) transmission is received — tell the ARC before testing.
Check the call point is undamaged, clearly visible and not obstructed.
Servicing
Call points are also tested by a competent person as part of routine inspection and servicing (clause 43 of BS 5839-1:2025), and any damaged frangible elements or covers are replaced.
Record keeping
Record the date, the call point tested, the result and any action taken in the system logbook, which should be kept on site.
Colour, signage, labelling and protective covers for manual call points.
Colour
Manual call points are red (BS EN 54-11), with an operating element that contrasts clearly with the body of the unit.
Signage
A "FIRE ALARM CALL POINT" or "Break Glass — Press Here" sign should be provided adjacent to or above each MCP where it is not immediately obvious. Signage should comply with BS 5499 / ISO 7010 where applicable.
Location labelling
Each call point should be labelled with its zone number or address to aid identification during testing and fault-finding. Labels should be durable and legible, typically on or immediately adjacent to the device.
Protective covers
BS 5839-1 recommends hinged protective covers on call points to prevent accidental operation; since 2025 these covers should be transparent. Covers that sound a local warning when lifted can deter misuse but must not obstruct genuine operation.
Fire resistance and identification of fire alarm cables.
Which cables need fire resistance
All critical signal paths and the final low-voltage mains supply circuits to fire alarm equipment should use fire-resisting cable. Non-critical circuits that fail safe — for example door holder circuits that release on loss of power — need not.
Standard fire resistance
Classified PH30 when tested to BS EN 50200, including the Annex E water spray test — proven to keep working for at least 30 minutes. Suitable for most buildings.
Enhanced fire resistance
PH120 when tested to BS EN 50200 and 120 minutes when tested to BS 8434-2 (flame, mechanical shock and water spray). Needed, for example, in unsprinklered buildings over 30 m high and in buildings with phased evacuation.
Cable colour (2025)
All fire alarm cables — and, since 2025, the low-voltage mains supply cable to the system — should be one common colour, with red preferred. Black or white cables should not be used.
Other requirements
Conductors at least 1 mm².
Functional earth conductors identified by pink insulation or sleeving, or marked "FE" (2025).
Cables installed in buildings are construction products and must carry CE or UKCA marking with a reaction-to-fire class under BS EN 50575.
Segregation, fixings, routing and loop resistance.
Segregation
Keep fire alarm cables segregated from other circuits so they cannot be affected by interference or damaged by faults in other systems — for example in dedicated containment or a separate compartment of shared trunking.
Fixings and protection
Use non-combustible fixings so cables stay supported in a fire, and protect cables wherever they are vulnerable to mechanical damage.
Routing
Route cables to avoid areas of high fire risk where possible. Cables passing through fire compartment walls/floors must be fire-stopped. Avoid routing near heat sources, steam pipes, or areas subject to mechanical damage.
Maximum loop resistance
Depends on the panel — always check the manufacturer's data. As a guide, a 1.5 mm² copper conductor is about 12.1 Ω per km at 20 °C, so a loop (out and back) is about 24 Ω per km of route.
Electromagnetic door holders and release mechanisms connected to the fire alarm system.
Purpose and operation
Electromagnetic door holders keep fire doors open for convenience and release them automatically on fire alarm activation. Doors close under their own closer force when the electromagnet de-energises (fail-safe).
Connection to fire alarm
Door releases are controlled by the fire alarm through the cause-and-effect arrangements — typically releasing on alarm in the relevant zone(s). BS 7273-4 covers the actuation of door release mechanisms. Door holder circuits that release on loss of power (fail safe) need not be wired in fire-resisting cable.
Rating and positioning
Door holder must have a holding force that exceeds the door closer force.
Position as high as practical on the door or frame for maximum holding leverage.
Swing-free holders allow doors to be moved but return them to the held-open position.
Testing
During routine testing, check that doors release and close fully when the alarm operates, that door closers are correctly adjusted and that doors latch. Record the results in the logbook.
Interfaces between the fire alarm and other building systems — AOVs, dampers, lifts, HVAC.
AOVs (Automatic Opening Vents)
Open on detection in the relevant zone to allow smoke venting.
Typically roof-mounted or high-level window actuators.
Test their operation during routine servicing.
Fire dampers and gas/oil shutoff
Fire dampers: close to prevent smoke spread through ductwork.
Gas/oil shutoff valves: close on alarm to remove fuel sources.
Both must be documented in the cause-and-effect matrix.
Lift recall and stairwell pressurisation
Lifts: recall to ground floor, doors open, then disable for normal use. Fire-fighting lift remains operational.
Stairwell pressurisation: activate on alarm to keep escape stairs clear of smoke.
HVAC: disable on alarm to prevent distributing smoke through the building.
Cause-and-effect (2025)
Document which inputs trigger which outputs. BS 5839-1:2025 recommends handing over a cause-and-effect matrix — or, for simple systems, a description such as "simultaneous evacuation" — with the system documentation, and keeping it up to date.
Location of interfaces (2025)
Interfaces should be located where they can be reached for maintenance — not, for example, inside another system's enclosure that needs other contractors or a power-down to open.
Mains supply, standby battery duration and battery sizing.
Mains supply
A permanent connection (not via a plug and socket) on a dedicated circuit, with the isolating device labelled "FIRE ALARM — DO NOT SWITCH OFF" or similar. BS 5839-1:2025 brings the recommendations on isolating the mains supply together in a single clause (in 2017 they were split between clauses 25 and 29).
Standby duration
Category L and M systems: 24 hours on standby, then 30 minutes in alarm — or 6 hours plus 30 minutes where there is an automatically started standby generator.
Category P systems: 24 hours longer than the longest period the premises are left unoccupied, up to 72 hours — or 24 hours where power supply faults will be noticed within 6 hours, or are signalled to an ARC that alerts a keyholder.
Battery sizing (Annex E)
Cmin = 1.25 × ((T1 × I1) + D × (I2 × T2)), where T1 is the standby period, I1 the standby current, I2 the alarm current and T2 the alarm period (0.5 h). D = 1.75 derates the battery for the high alarm current, and 1.25 allows for ageing. Include the extra current of VADs, door holders and network equipment.
Batteries
Label each battery with its installation date (2025).
Replace at the end of the manufacturer's stated service life, or sooner if they fail a load test.
The charger should recharge a fully discharged battery to 80% of capacity within 24 hours (BS EN 54-4).
When ceiling and floor voids need detection, and where to site it.
When voids need detection
Where the system category calls for protection of an area, voids within it deeper than 800 mm should normally be protected (unless agreed as a variation). Shallower voids should also be protected if the fire risk warrants it — for example where they contain significant combustible materials or could let fire and smoke spread unseen.
Siting in voids (2025)
Voids up to 1.25 m deep: sensing element in the top 125 mm.
Voids from 1.25 m to 1.5 m deep: within the top 10% of the void.
Voids over 1.5 m deep: treat as a normal room (25–600 mm below the ceiling for smoke detectors, 25–150 mm for heat).
Zoning
Voids within the same fire compartment as the area they serve can be included in the same detection zone.
Void barriers and access
Void barriers at compartment walls must maintain fire resistance — fire can spread unseen through voids.
Access panels are required for maintenance of void detectors.
Aspirating detection is often preferred in voids as sampling pipes are easier to route than point detectors.
Operate a manual call point each week, at about the same time, using a different call point each time so they are all tested in rotation. Confirm the fire alarm sounds throughout and that any ARC receives the signal.
Who can do it
A designated responsible person (building manager, caretaker, etc.) can carry out weekly tests. Does not require a specialist fire alarm engineer.
Monitored systems
Tell the ARC before testing so the test is not treated as a real alarm. BS 5839-1:2025 recommends a "false alarm notice" at the panel stating that the system is connected to the fire and rescue service via an ARC, with the ARC's phone number.
Recording
Record the date, time, call point tested (location or address), whether alarm sounded correctly, and any faults. Maintain the log book on site and available for inspection.
BS 5839-1's monthly checks — for standby generators and vented batteries — plus common good practice.
Standby generators
Where an automatically started generator forms part of the standby supply, start it each month by simulating failure of the mains supply, and run it on load for at least an hour.
Vented batteries
Where vented batteries are used, visually inspect the batteries and their connections each month and put right any defects, such as low electrolyte levels.
Good practice
Many premises also do a quick monthly check: the panel shows normal, no faults or disablements are outstanding, detectors and call points are not covered or obstructed, and logbook entries have been followed up.
Routine inspection and servicing by a competent person, about every six months.
Interval (2025)
About every 6 months: any time between 5 and 7 months after the previous visit is acceptable, with the date the system was accepted as the starting point. (The 2017 edition said visits should not be more than 6 months apart.) More frequent visits, such as quarterly, are a contract choice rather than a requirement of the standard.
Detector testing
Every automatic detector should be functionally tested over each 12-month period, usually split across the two visits. Tests should prove that smoke, heat or CO can reach the sensing element — heat detectors are tested with a suitable heat source, not a naked flame.
At every visit
Check the panel's clock (important for day/night modes) and confirm that each type of signal sent to an ARC — such as fire and fault — is received correctly. Keep disablements to a minimum and tell the premises management which areas are affected.
Documentation
Record the devices tested, faults found and actions taken, update the logbook, and issue an inspection and servicing certificate (model certificates are in Annex G).
Checks to complete across each 12 months of servicing.
Devices
Over each 12 months every automatic detector should be functionally tested, and call points, sounders, visual alarms and interfaces checked for correct operation.
Added in 2025
Functional testing of smoke detectors in ventilation ducts.
Confirming that the zone shown at the panel is the zone being tested, and that it matches the zone plan.
Checking remote indicators work and have not been obstructed or painted over (their indication should be red).
Cable and wiring checks
Visual inspection of cable routes for damage. Check fire stopping where cables pass through walls/floors. Verify cable fixings are secure. Insulation resistance testing if problems are suspected.
Batteries and power supplies
Check batteries and chargers, including a load test where appropriate, and replace batteries that have reached the end of their service life.
Text descriptions
Checking addressable text descriptions is not a routine servicing task — the premises management should report any changes — but confirming them every few years (e.g. every 5 years) is prudent.
Fire alarm logbook requirements — what to record and where to find it in the standard.
Requirement
A fire alarm log book must be kept on the premises at all times. It should be stored near the fire alarm panel and be readily available for inspection by the fire authority, insurers, or the responsible person.
What to record
All fire alarm events: genuine alarms, false alarms, faults, pre-alarms.
All tests: weekly call point tests and routine service visits.
All maintenance: repairs, device replacements, software changes.
All modifications and extensions to the system.
For weekly tests: date, time, device tested, result, name of tester.
Variations (2025)
All agreed variations should now be recorded in the logbook — previously only "major" variations had to be.
In the standard
Clause 48 of BS 5839-1:2025 covers the logbook, and Annex H gives a model format (it was Annex F in the 2017 edition).
Electronic log books
Electronic records are acceptable provided they can be accessed on-site, are backed up, and can be printed if required for inspection. Must contain the same information as a paper log book.
Maximum area, storeys and search distance for fire detection zones.
Maximum zone area
No detection zone should exceed 2,000 m² of floor area. Zones containing only manual call points can be up to 10,000 m² in large open-plan areas.
Single storey
A zone should cover only one storey, unless the total floor area of the building is less than 300 m². Stairwells, lift wells and similar vertical structures should be separate zones.
Search distance
Someone searching a zone should not have to travel more than 60 m from where they enter it to find the fire (addressable systems with suitable displays can be an exception).
Fault protection
Short-circuit isolators should limit the loss of detection from a single fault to no more than 2,000 m², and from two faults to no more than 10,000 m².
Zone plan requirements and how zones should be identified at the panel.
Zone plan (2025)
A correctly orientated zone plan should be displayed next to every control panel and repeater, unless the panel has a suitable display (e.g. an illuminated mimic). Not having one where any storey has more than one zone — particularly where people sleep — is no longer acceptable as a variation.
Zone numbering
Zones should be logically numbered (e.g. by floor and area). Numbering should be intuitive for the fire brigade and building occupants. Avoid gaps in numbering sequences.
Zone identification at the panel
The panel must clearly indicate which zone is in alarm or fault. For addressable systems, individual device identification is preferred in addition to zone indication. Zone text descriptions should be meaningful (e.g. "Ground Floor — East Wing" not just "Zone 3").
Addressable vs conventional
Addressable systems identify individual device locations, reducing search time. Conventional systems rely on zone indication only — zone sizing is more critical for rapid fire location in conventional systems.
Where staff help occupants to evacuate (e.g. residential care) and more than 10 people sleep, the system should be addressable.
BS 5839-1:2025 guidance on investigating false alarms and when deeper investigation is needed.
Investigate every false alarm (2025)
The user should arrange for every false alarm to be investigated, and the commissioning or handover organisation should explain how — including the categories of false alarm, so each one is recorded correctly.
Trigger points
Annex F gives the false alarm rate as 100 × number of false alarms ÷ number of automatic detectors (per year).
Over 4 per 100 detectors in the previous 12 months: preliminary investigation.
Systems with more than 40 detectors averaging over 5 per 100: in-depth investigation.
Immediate actions
Identify and address the triggering device. Do NOT simply isolate the device permanently — this reduces protection. If a detector is repeatedly causing false alarms, investigate root cause: contamination, wrong type for environment, positioning, environmental changes.
ARC and fire service
Many fire and rescue services now challenge or do not attend automatic alarms. Give the ARC full information about the premises (e.g. whether people sleep there) and, where practicable, send the type of device that triggered the alarm and whether coincidence filtering is used.
Detector choice
BS 5839-1:2025 recommends multi-sensor detectors where point smoke detectors would carry a higher risk of false alarms (see Annex D).
Frequent causes of unwanted fire alarms and how to address them.
Cooking and steam
Detectors too close to kitchens, kettles, or bathrooms. Solution: relocate the detector or use a more suitable type — such as a multi-sensor, or a heat detector where heat detection is acceptable (not in sleeping rooms or Category L escape routes).
Dust and contamination
Construction work, cleaning, or poor maintenance causing dust ingress into optical detectors. Solution: clean or replace detectors, temporarily cover during planned building work (with formal impairment procedure).
Insects
Small insects entering detector chamber and scattering light (optical detectors). Solution: insect mesh screens, regular cleaning, consider environmental changes.
Aerosols and vapour
Spray deodorants, air fresheners, e-cigarettes near detectors. Solution: relocate the detector away from likely spray use, use signage, or consider a multi-sensor detector.
Environmental changes
Building use changes (new kitchen, partition changes affecting airflow, new HVAC). Solution: review detector type and positioning whenever building modifications occur. The fire alarm system should be reviewed as part of any refurbishment project.
Remote connections to the fire alarm system should be authenticated, and remote work risk-assessed (clause 43.4).
Authentication
Before a remote connection is accepted, the request should be authenticated by the control panel (CIE) or gateway software.
Risk assessment
Before any remote service — especially read, control or write functions — assess the potential effect on the panel's operation. If there is any risk, whoever is responsible must make sure the system is fully operational when the remote work is finished.
Good practice
Change default passwords, give each user only the access they need, and keep a record of remote sessions.
Physical protection for the system's network connections and access points.
Physical protection
Prevent unauthorised access to the system, its access points and network paths — for example by locking communications cabinets and fitting anti-tamper plugs to patch leads.
Identification
Keep a record of every network connection to the system and what it is for, so unauthorised connections can be spotted (good practice).
Inspection
At service visits, check that physical protections are intact and that no unauthorised connections have been made, and report anything found.
Maximum times for fire alarm signals to reach the alarm receiving centre (ARC).
Category L systems
A fire alarm signal should be indicated at the ARC within 90 seconds. Total failure of the transmission system (no path able to carry signals) should be indicated at the ARC and at the panel within 3 minutes (clause 14.17).
Category P systems
A fire alarm signal should be indicated at the ARC within 120 seconds, and total failure of the transmission system at the ARC and panel within 31 minutes (clause 14.18).
Power for transmission equipment
Where alarm transmission equipment has its own power supply unit, it should conform to BS EN 54-4 or BS EN 50131-6 Grade 4.
Testing
At every service visit, check that each type of signal sent to the ARC — such as fire and fault — is received correctly.
Which premises need an ARC connection, and what the ARC should be told.
When an ARC connection is needed
Residential care homes — and supported housing that needs a BS 5839-6 Grade A system — should automatically transmit fire alarms to an ARC. Leaving this out is no longer acceptable as a variation.
Information for the ARC
Give the ARC relevant information about the premises, such as whether people sleep there, so it can pass this to the fire and rescue service. Where practicable, signals should also show the type of device that triggered them and whether coincidence filtering is in use.
False alarm notice
A notice on or next to the panel should state that the system has an active connection to the fire and rescue service via an ARC, with the ARC's phone number — so users remember to contact the ARC before testing.
Calling 999
In occupied premises, automatic transmission does not replace a 999 call — someone should still call the fire and rescue service.
Preparing alarm signalling for the switch-off of the analogue telephone network — an industry change rather than a clause of BS 5839-1.
PSTN switch-off
The UK's analogue telephone network (PSTN) is being switched off, currently due to be completed by the end of January 2027. Signalling that relies on PSTN lines needs to move to IP-based paths before then.
IP signalling options
IP signalling over broadband, cellular (4G/5G), or dual-path communicators that use both. Dual-path signalling keeps working if one path fails.
Migration assessment
During service visits, identify systems still using PSTN-dependent signalling. Advise the responsible person on migration options and timescales. Record the current signalling method and any migration plan in the service report.
Compatibility
Not all existing fire alarm panels support IP signalling natively. An external IP communicator may be needed. Verify compatibility with the ARC provider and ensure the signalling equipment is approved for the purpose.
Clause numbers: 2017 → 2025
Most clause numbers changed in BS 5839-1:2025. Clause 4 of the 2017 edition (the need for a system) moved into a new Introduction, so clauses 5 to 30 each moved down by one. In the false alarm section, 2017 clauses 31 and 33 were merged, so from clause 34 the numbers move down by two. Clauses 1 to 3, 47 and 48 kept their numbers, and a new Section 7 (clauses 45 and 46) covers extensions and modifications.
Enter an old clause number to find the new one. Some subclauses were renumbered within their clause too, so check the subclause in the 2025 edition.
Enter a clause number from the 2017 edition, such as 45.3.
Clauses renumbered between BS 5839-1:2017 and BS 5839-1:2025
2017 clause
2025 clause
Topic (2025 title)
5
4
Categories of system
6
5
Exchange of information and definition of responsibilities
7
6
Variations from the recommendations of this document
8
7
Relationship between system category and protected areas
9
8
Actuation of other fire protection systems or safety facilities
10
9
Systems in explosive gas or dust atmospheres
11
10
System components
12
11
Monitoring, integrity and reliability of circuits external to control equipment
13
12
Fire detection zones
14
13
Alarm zones
15
14
Communication with the fire and rescue service
16
15
Audible alarm signals
17
16
Visual alarm signals
18
17
Fire alarm warnings for people who are Deaf or have a hearing impairment
19
18
Staged fire alarms
20
19
Manual call points
21
20
Types of fire detector and their selection
22
21
Siting and spacing of automatic fire detectors
23
22
Control and indicating equipment
24
23
Networked systems
25
24
Power supplies
26
25
Cables, wiring and other interconnections
27
26
Radio-linked systems
28
27
Electromagnetic compatibility
29
28
Electrical earthing
30
29
Responsibility for limitation of false alarms and unwanted fire alarm signals
31
30
Categories and causes of false alarms
32
31
Investigation of false alarms
33
30
Categories and causes of false alarms
34
32
Design process for limitation of false alarms and unwanted fire alarm signals
35
33
Measures to limit false alarms and prevent unwanted fire alarm signals
36
34
Responsibility of installer
37
35
Installation practices and workmanship
38
36
Inspection and testing of wiring
39
37
Commissioning
40
38
Documentation
41
39
Certification
42
40
Handover
43
41
Verification
44
42
Routine testing
45
43
Inspection and servicing
46
44
Non-routine attention
3.12
3.13
Terms and definitions
13.2.1
12.1
Fire detection zones
22.3
21.2
Siting and spacing of automatic fire detectors
45.3
43.2.1
Inspection and servicing
Annexes
Some annexes changed letter too. Annexes A and G kept their letters, and a new Annex F covers calculating the false alarm rate.
Annexes re-lettered between BS 5839-1:2017 and BS 5839-1:2025
