Reducing False Alarms in Fire Alarm Systems: Causes, Standards, and Practical Fixes

Unwanted fire alarm activations are the largest single cause of wasted fire service responses in the UK — and most are preventable. If you're maintaining a system with a recurring false alarm problem, this guide covers how to identify the root cause, what BS 5839-1 says about managing it, and the practical fixes that actually work.

Why False Alarms Matter

The cost of a false alarm goes beyond the inconvenience of an evacuation. Repeated false alarms:

• Erode occupant confidence in the system — people stop evacuating promptly
• Result in the fire service issuing a warning or charging for repeated attendances (under the Fire and Rescue Services Act 2004, fire services can charge for repeated false alarms from certain premises)
• Can lead to building managers disabling or isolating detectors, which creates genuine life safety risk
• Add servicing costs and emergency callout charges

BS 5839-1:2025 addresses the limitation of false alarms in a dedicated section (Section 3, Clauses 29 to 33). It recommends a preliminary investigation when the false alarm rate over the previous 12 months exceeds four false alarms per 100 detectors per annum, and an in-depth investigation for systems with more than 40 automatic fire detectors when the average rate exceeds five per 100 detectors per annum (Fire Industry Association, Guide to the changes in BS 5839-1:2025).

Categories of False Alarm Cause

1. Inappropriate detector type or siting

The most common root cause — and the most fixable. The wrong detector for the environment will alarm repeatedly regardless of how well it's maintained.

Optical smoke detectors in kitchens, canteens, or plant areas — optical detectors respond to airborne particles. Cooking steam, smoke from toasters, or dust from a workshop will trigger them reliably.

Ionisation detectors in smoky environments — ionisation detectors (now largely phased out, but still in service) are highly sensitive to small combustion particles. Any smoking area, kitchen, or area with welding or cutting operations will cause regular false alarms.

Heat detectors in areas with temperature extremes — a heat detector whose EN 54-5 class does not suit the room's normal maximum temperature (plant rooms, kitchens, roof voids in summer) sits close to its operating point and can alarm without a fire. Choose the class from the highest temperature the area normally reaches.

Fix: Specify the correct detector type for the environment. For kitchens: heat detectors (A2R or CS type). For dusty plant areas: multi-sensor detectors with appropriate sensitivity settings or heat detectors. For areas near HVAC discharge points: move detectors or adjust siting.

2. Environmental contamination

Detectors that are correct for the environment but operating in conditions that are degrading their calibration.

Dust accumulation — optical chambers collecting dust over time increase their sensitivity. In dusty areas the reading of an optical detector in clean air can creep up steadily between visits.

Insect ingress — insects entering the detection chamber are the single most common cause of spurious activations on addressable optical detectors. A spider or fly entering an optical chamber will reliably trigger an alarm.

Condensation — temperature cycling in roof spaces or external areas causes condensation to form in the detection chamber, which optical detectors respond to.

Fix: Increase inspection frequency in problem areas. On addressable systems, trend the analogue values at each visit: a detector whose clean-air reading is rising compared with its neighbours of the same type, or with its own earlier readings, is due for cleaning or replacement per the manufacturer's guidance. Consider detectors with enhanced insect ingress protection (most modern multi-sensor units have better-sealed chambers).

3. Accidental activation

Manual call point activation — MCP glasses broken by accident or as a prank. Common in schools, retail, and multi-occupancy buildings.

Steam and aerosol products — cleaning products, deodorants, and hairsprays can trigger optical detectors. Common in hotel rooms and changing areas.

Building works — contractors triggering detectors with welding, cutting, grinding, or dust. Should be managed with hot work permits and appropriate detector isolation — but often isn't.

Fix: MCPs in high-risk areas (schools, public areas) can be replaced with push-button types rather than glass-break, which reduces accidental activation. Confirm the hot work permit process is enforced for all building works. Zone isolation procedures should be documented and followed.

4. System faults presenting as alarms

Some false activations are actually system faults manifesting as alarms:

Wiring degradation — on conventional systems, intermittent wire contacts can cause voltage fluctuations that the panel interprets as an alarm condition.

PSU instability — a failing PSU causing voltage drops can trigger detectors on some panel designs.

Incorrect panel configuration — fault conditions (e.g., earth fault) being incorrectly mapped to trigger alarm outputs.

Fix: Pull the event log and look for patterns. Faults and alarms occurring together, or alarms only at specific times (suggesting electrical transients) point to system issues rather than detector issues.

BS 5839-1 Guidance on Unwanted Alarms

Section 3 of BS 5839-1:2025 (Clauses 29 to 33) sets out a structured approach to investigating and reducing unwanted alarms:

1. Investigate each unwanted alarm — record the cause in the log book
2. Classify the cause — was it avoidable or unavoidable?
3. If avoidable, take action — adjust detector siting, type, sensitivity, or occupant behaviour as appropriate
4. Review after 12 months — if the rate hasn't reduced, a more systematic review is required

The trigger points scale with the number of detectors. For a 500-detector system, four false alarms per 100 detectors per annum is 20 false alarms in a year (500 ÷ 100 × 4), above which a preliminary investigation is recommended; an in-depth investigation is recommended when the average rate exceeds five per 100 detectors per annum, which is 25 a year. See how to calculate the false alarm rate.

Practical Measures

Alarm confirmation / alarm verification

Alarm confirmation introduces a delay before the alarm is transmitted to the ARC or triggers evacuation. The panel waits for a second detector to confirm before treating the activation as a genuine alarm.

This is not appropriate for all system categories — L1 and high-risk L2 systems should not have confirmation delays that compromise escape time. However, for P-category systems or areas where false alarms are frequent and life risk is low, confirmation can significantly reduce unwanted responses.

BS 5839-1 Annex C covers alarm confirmation schemes.

Coincidence detection

Similar to alarm confirmation but requires two detectors in different zones (or a coincidence pattern defined in the panel configuration) before triggering. Commonly used in pre-action suppression systems but can be applied to evacuation systems in appropriate circumstances.

Reduce detector sensitivity

On addressable systems, many panels allow per-device sensitivity adjustment. Reducing sensitivity in problem areas (e.g., an optical detector near a kitchen serving hatch) can prevent false alarms without replacing hardware.

This should be used carefully — sensitivity reduction reduces the system's detection capability. Any sensitivity adjustment must be documented and justified by the risk assessment.

Replace or relocate problem detectors

The most reliable fix for environmentally-caused false alarms is to change the detector type or move it. A heat detector where an optical detector was is often the right answer in environments where steam or dust is present.

Documenting the Investigation

Every unwanted alarm should be recorded in the log book with:

• Date and time
• Zone or device address
• Cause (if identified)
• Action taken

If a pattern of unwanted alarms is developing, a formal investigation report is appropriate — recording the pattern, the investigation steps, and the remediation action. This protects the maintenance contractor and the responsible person if the matter is reviewed by an insurer or enforcing authority.

IFS Pro's digital logbook captures unwanted alarm entries with cause categorisation, and flags sites with elevated false alarm rates for investigation. Available at incognitofiresecurity.com.