BS 5839 Fire Alarm Standard: The Complete UK Guide

• BS 5839-1 — Fire detection and fire alarm systems for buildings. Covers non-domestic premises including offices, shops, factories, hospitals, schools, hotels, and other commercial and industrial buildings. This is the comprehensive part of the standard, covering complex multi-zone systems with addressable panels, aspirating detection, voice alarm, and interface with other building systems.
• BS 5839-6 — Fire detection and fire alarm systems for domestic premises. Covers individual dwellings, flats, maisonettes, and sheltered housing. This part is simpler in scope and covers standalone smoke alarms, interlinked mains-powered detectors, and domestic fire alarm panels.

• Design — system category selection based on the fire risk assessment, detector types and siting, sounder coverage, manual call point positioning, zone planning, cable selection and routing, power supply requirements, and panel specification.
• Installation — cable installation methods, fire-resistant cable requirements, segregation from other services, containment systems, connection methods, and labelling requirements.
• Commissioning — full functional testing of every device, cause and effect testing, sounder level measurements, battery drain tests, false alarm management, and handover documentation.
• Maintenance — weekly user tests, monthly checks, quarterly inspections, and annual professional servicing. The standard sets out exactly what must be checked at each interval.

Category L — Life Protection

• L1 — Full coverage. Detectors installed throughout all areas of the building, including roof voids, floor voids, and risers. This provides the earliest possible warning of fire anywhere in the building. Required for sleeping accommodation in high-risk buildings such as care homes and hospitals.
• L2 — Coverage of escape routes plus high-risk areas. Detectors in all corridors, stairways, landings, and rooms that open onto escape routes, plus any rooms identified as high fire risk (for example, plant rooms, kitchens, laundry rooms, electrical intake rooms).
• L3 — Coverage of escape routes only. Detectors in corridors, stairways, landings, and rooms that open onto escape routes. The aim is to warn occupants before the escape route is blocked by fire or smoke. This is the most common category for offices and shops.
• L4 — Coverage of escape routes within circulation areas only. Detectors in corridors, stairways, and landings only — not in rooms. This provides a reduced level of protection compared to L3.
• L5 — Custom coverage. Detectors installed only in specific areas identified in the fire risk assessment. Used where only certain parts of the building require automatic fire detection.

Category P — Property Protection

• P1 — Full coverage for property protection. Detectors throughout the building to give the earliest possible warning of fire for the purpose of minimising property damage. Often required by insurers for warehouses, data centres, and high-value commercial properties.
• P2 — Partial coverage for property protection. Detectors in high-risk areas only, such as plant rooms, server rooms, or areas with flammable materials. Used where the fire risk assessment identifies specific areas with elevated fire risk.

• Grade A — A fire alarm panel with conventional or addressable detection, dedicated fire alarm cabling (typically fire-resistant FP200 or MICC), separate power supply with battery back-up, manual call points, and sounders/visual alarm devices. This is the standard for commercial premises under BS 5839-1 and for large or high-risk HMOs.
• Grade B — Similar to Grade A but uses a fire alarm control panel with a power supply that forms part of the dwelling mains supply, rather than a dedicated supply. Less common in practice.
• Grade C — Detectors and sounders connected to a common central power supply (for example, a mains transformer with battery back-up) but without a fire alarm control panel. The system uses detectors with relay outputs to trigger sounders.
• Grade D1 — Mains-powered detectors with a tamper-proof (non-user-replaceable) integral standby battery, interlinked by hard wiring. This is the most common grade for domestic installations — the standard interlinked smoke alarm system that most electricians install in domestic rewires and new builds. A common mistake is fitting a user-replaceable battery where a tamper-proof battery is required for D1.
• Grade D2 — Mains-powered detectors with a user-replaceable integral standby battery, interlinked by radio (wireless). Used where running new wiring for interlinked alarms is not practicable — for example, in existing properties where chasing walls is undesirable.
• Grade F1 — Battery-only detectors (no mains connection), interlinked by radio. Used in existing dwellings where mains wiring is not available or practicable.
• Grade F2 — Battery-only detectors with no interlinking. These are standalone individual smoke alarms. The lowest grade and the minimum level of protection.

• Detector siting — smoke detectors must be sited on the ceiling, at least 300mm from any wall or light fitting. In corridors, detectors must be spaced at maximum 15m intervals (7.5m from each end wall). In rooms, the maximum coverage area depends on the detector type and ceiling height — typically 100m² for a point-type smoke detector in a room up to 10.5m high. In kitchens, a heat alarm must be used in place of a smoke detector (cooking fumes trigger false alarms from optical or ionisation smoke detectors). The heat alarm must be sited away from extractor fans, cooking appliances, and other heat sources — position it to avoid direct exposure to normal cooking heat while still detecting a developing fire.
• Cable requirements — for Grade A systems, fire-resistant cable must be used (BS 7629 or BS 8434, commonly known as FP200 or MICC). Standard PVC cables (BS 6004) are not acceptable for fire alarm circuit wiring because they will fail in a fire. Cable routes should avoid areas of high fire risk where practicable.
• Manual call points — required at every exit point on every storey in commercial premises (BS 5839-1). They must be mounted at a height of 1.4m from the floor, with the break glass element facing the direction of travel. Not required in domestic dwellings under BS 5839-6.
• Sounder coverage — fire alarm sounders must achieve a minimum sound level of 65dB(A) in all accessible areas, or 75dB(A) at the bedhead in sleeping accommodation. This must be measured with all doors closed. In noisy environments, the sounder level must be at least 5dB(A) above the ambient noise level.

BS 5839-1 Testing Schedule (Commercial)

• Weekly — User test. Activate one manual call point per week (rotating through all call points over the year) to confirm the panel enters fire condition and the sounders operate. Record the test in the fire alarm log book.
• Monthly — Visual inspection. Check the panel for fault indicators, verify battery charging, inspect any accessible wiring for damage, and check that all detectors and call points are unobstructed.
• Quarterly — Professional inspection. A competent fire alarm engineer tests 25% of the detectors (so all detectors are tested over the course of a year), checks sounder operation, and inspects the panel and wiring.
• Annually — Full professional service. Every detector, call point, sounder, and interface device is tested. Battery capacity is tested under load. Cable integrity is verified. The panel firmware is checked. A full test report is issued.