BS 5839-1:2025: Key Changes Explained
The core code of practice for fire detection and alarm systems in UK non-domestic buildings has moved on. BS 5839-1:2017 was withdrawn and replaced by BS 5839-1:2025, and the current edition is now the 2025 one. For engineers, that means "work to the current edition" has a new meaning, and it is worth understanding what has changed and where to look for the detail. This guide gives an orientation to the update, while pointing firmly back to the standard itself as the authoritative source.
The central point is that BS 5839-1:2025 is now the current edition of the code, updating the previous version to improve reliability, reduce false alarms and strengthen early warning — with the standard itself the authoritative source for the detail.
Who this is for
This is for competent fire alarm engineers keeping their practice current with the code of practice. The experience level assumed is competent engineer. Use this as orientation only; the authoritative detail is in BS 5839-1:2025 itself, supported by industry guidance such as the Fire Industry Association's guide to the changes. Nothing here replaces reading the standard, and specific requirements should always be verified against it rather than a summary.
A new edition of the standard
BS 5839-1:2017 was withdrawn and replaced by BS 5839-1:2025, so the 2025 edition is now the current version of the code of practice for fire detection and alarm systems in non-domestic premises. From that point, references to the "current edition" — including those throughout technical guidance and this platform's articles — mean the 2025 version. The change of edition is itself the first thing to absorb: an engineer working to a withdrawn edition is working to superseded guidance. Engineers should work to BS 5839-1:2025 and consult the standard, and industry guidance, for the authoritative detail rather than relying on summaries.
The direction of the changes
Rather than reinventing the approach, the 2025 edition updates and refines the previous one. Broadly, it is aimed at improving system reliability, reducing false alarms, and strengthening early warning and the clarity of the design, installation, commissioning and maintenance recommendations. The overall thrust is evolution towards more reliable systems and fewer unwanted alarms, with clearer responsibilities at each project stage. The precise changes are set out in BS 5839-1:2025 and summarised in industry guidance such as the FIA's guide to the changes. Understanding the direction helps an engineer read the detail with the right expectations, but the direction is not a substitute for the specifics.
Areas the update touches
Industry guidance on the 2025 edition points to a number of areas that have been updated or clarified — among them the management and calculation of false alarms, detector selection in certain premises, detection in particular locations, the identification of fire alarm cabling, and the calculation of standby power. These are the kinds of practical areas where the current edition may differ from the previous one. Because specifics such as figures, categories and methods must come from the standard and not from a summary, this article deliberately does not restate them; the point is to know that these areas have moved and to check them against BS 5839-1:2025 and the FIA guidance. An engineer aware that an area has changed will look it up; one who assumes nothing has changed will not.
What it means for existing systems
A common and reasonable question is what the update means for systems already installed. The standard is guidance for design, installation, commissioning and maintenance, and how a change applies to an existing system is a matter of competent judgement: a compliant existing system does not automatically become non-compliant on the day a new edition is published, but the current edition informs new work, alterations and assessments. From field experience, the sensible approach is neither to panic-retrofit everything nor to ignore the update, but to consider the changes through the fire risk assessment and competent judgement against BS 5839-1:2025. Where an existing system may warrant review in light of the update, that is worth flagging to the responsible person rather than assuming it is either fine or urgent.
What engineers should do
In practice, keeping current is straightforward in principle. Familiarise yourself with BS 5839-1:2025 and the industry guidance on the changes, work to the current edition on new and altered systems, and consider the changes when assessing existing systems, all with competent judgement. Critically, do not rely on secondary summaries — including this one — for specific requirements; verify against the standard itself. Record work against the current edition, and flag where an existing system may warrant review. The professional habit is simple: know the current edition is the 2025 one, and read it.
Common points to check
Recurring issues include work still being carried out to the withdrawn 2017 edition, specific requirements taken from summaries rather than the standard, and existing systems not considered against the current edition where relevant. Confirming practice is aligned to BS 5839-1:2025, verified against the standard, is the essential check.
When not to rely on this alone
When not to use this article: do not use it as a statement of the specific requirements of BS 5839-1:2025. It is orientation only. The authoritative source is the standard itself, supported by industry guidance, applied by competent professionals.
Relevant standards
The current code of practice is BS 5839-1:2025, which replaced the withdrawn BS 5839-1:2017. It is a code of practice, not law; the legal duty for fire precautions in most non-domestic premises sits under the Regulatory Reform (Fire Safety) Order 2005. Separate the legal duty from the recommended methods, always work to the current edition, and verify specific requirements against the standard itself.
Professional disclaimer
This is an educational and workflow resource for competent engineers and does not replace BS 5839-1:2025, the industry guidance, or competent judgement. It is orientation only; verify all specific requirements against the current standard.
Related documentation
Use this with BS 5839-1:2025 itself and the industry guidance on the changes, such as the FIA's guide. Work to the current edition, verify specifics against the standard, and flag existing systems that may warrant review in light of the update.