What BS 5839-1:2025 means for fire alarm engineers

The long-awaited update to BS 5839-1 has landed – and it’s far more than a tidy-up. The 2025 revision introduces practical, safety-driven changes that will immediately impact how we design, install, commission and maintain fire alarm systems in non-domestic premises. Dr Tom Brookes, Managing Director of ZZEUS Training and Chairman of the BSI Technical Committee FSH12/1, is responsible for BS 5839-1:2025. Here, he looks at some key technical updates you can’t ignore.

Let’s start with a long-overdue clarification: fire alarm mains cables must now be red. Clause 25.9 explicitly recommends that red is the preferred colour. This clears up years of ambiguity and finally aligns legal requirements with what has been best practice for some time.

Maintenance sees a major improvement in clarity too. According to Clause 43.2.1, routine service intervals must fall within a five to seven-month window. Anything longer than seven months is considered non-compliant. And don’t forget the clock: Clause 43.2.10 makes it mandatory to check and adjust the control panel time during each maintenance visit – something that can easily be overlooked after power cuts or daylight saving time (DST) changes.

When ‘Variations’ go too far

Clause 6.5 mandates that all variations from the standard must be documented in the fire alarm logbook, with justification. This is now a clear requirement – no more verbal agreements or undocumented changes.

However, Clause 6.6 outlines two non-permissible variations that are now considered unacceptable under any circumstances:
• No zone chart in multi-zone buildings (especially where people sleep) = non-compliant.
• No ARC connection for systems in supported housing (requiring Grade A under BS 5839-6) or in residential care homes.

These cannot be overridden, even with agreement – the risk to life is too great.

Installers take note

Clause 22.1.2 and 34.9 require that all interfaces and isolators must be accessible – no longer burying them in risers or behind ceilings. Meanwhile, Clause 46.1.7 states that redundant devices must be removed.

A quiet but important change appears in Clause 28.2, requiring that any functional earth (FE) conductor be identified with pink sleeving or marked ‘FE’ as defined in BS 7671 Table 51.

Design and detection updates

Under Clause 20.2(c), the definition of an L2 system now includes sleeping risk areas, in addition to escape routes and high-risk rooms. Clause 4(b)(2) also reinforces that heat detectors are not suitable in sleeping areas, where smoke could pose a threat to life before heat is detected.

Clause 21.1.3(b) introduces a new requirement for smoke detection at the top of lift shafts in L4 systems, recognising the vertical chimney effect of smoke spread.

Minor but meaningful

A minor but helpful tweak in Clause 24.3.3 allows you to write battery replacement dates directly onto the battery with indelible pens, removing the need for separate stickers for anyone who has an aversion to stickers.

Finally, Clause 3.13 strengthens the definition of a ‘competent person’, who must now show evidence of up-to-date training and experience. Ongoing CPD is no longer optional – it’s part of staying compliant.

Final thoughts

BS 5839-1:2025 marks one of the most user-focused and practical rewrites in years. It removes ambiguity, enforces better records, and reminds us that competence – not shortcuts – keeps people safe. These changes deserve to be embraced, not just read.

Let’s raise the bar. Let’s lead.

– Dr Tom Brookes, Managing Director of ZZEUS Training and Lindum Fire Services, and Chairman of the Fire & Security Association (FSA) and BSI Technical Committee FSH12/1

For more information, please visit zzeus.org.uk

This article appeared in Electrotechnical News July/August 2025 edition – read it here