Key changes to BS 5839-1:2025 – Part 1
The British Standards Institution (BSI) technical committee FSH/12/1 is responsible for developing and maintaining standards for fire detection and fire alarm systems. The latest standard to receive an update is Part 1 of BS 5839, the code of practice for the design, installation, commissioning, and maintenance of fire detection and fire alarm systems in non-domestic premises.
This two-part article reviews the key changes to the standard as well as reviewing questions that arise when the electrical installations of BS 7671:2018+A2:2022+A3:20241 (BS 7671) meet the fire detection and fire alarm systems of BS 5839-1:20252.
Introduction to BS 5839-1:2025
BS 5839-1:2025 is an industry-recognized standard, widely used by fire safety professionals, technicians and building managers, which covers non-domestic premises, including public facilities and commercial buildings. Generally, it does not apply to domestic premises, which are covered by BS 5839-6:2019+A1:20203, although it does cover the design, installation and commissioning of Grade A systems conforming to BS 5839-6 with a few exceptions.
All British standards are subject to regular review, and the BS 5839 series is no different. The updates to the standard reflect changes in technology, fire safety best practices and lessons from real-life fire incidents.
British standards are split into types; see BS 0:20214. BS 5839-1 is deemed a ‘code of practice’, providing guidance and recommendations to competent users on how to conform to the standard.
Users can choose to modify any suggestions with methods that produce results that are comparable to, or exceed, the standard. In contrast, a ‘specification’ provides an objectively verifiable set of absolute requirements for products, materials, services, etc., to achieve a specific outcome.
When did BS 5839-1:2025 come into effect?
BS 5839-1:2025 came into effect on the 30th of April 2025, and BS 5839-1:20175 was withdrawn on the same date.
What are the changes?
It is important to note that the changes to the standard range from the addition of a new section to minor tweaks to a clause. While this article focuses on many changes to BS 5839-1:2025, it does not cover them all, and therefore, it is essential that those using the standard familiarize themselves with all the changes.
Section 1: General
Introduction
Clause 4 of BS 5839-1:2017, which included information on the “Need for a fire detection and fire alarm system", has been relocated to the introduction, while a new BSI numbering format has been applied throughout the standard. The previously used letters for the subclauses are no longer in use, and personnel designing, installing, commissioning and maintaining fire detection and fire alarm systems will need to take account of this; for example, certificate clause references may need to be adjusted as appropriate.
Normative references
Several new normative references have been added to Clause 2 of the standard, including:
- BS 5446-3:2015 Detection and alarm devices for dwellings – Part 3: Specification for fire alarm and carbon monoxide alarm systems for deaf and hard of hearing people
- BS EN 50085-1 Cable trunking systems and cable ducting systems for electrical installations – Part 1: General requirements
- BS EN 50518 Monitoring and alarm receiving centre.
Terms and definitions
To align with BS 4422:2024 Fire. Vocabulary6, several terms and definitions used within the standard have been added or modified. Notable terminology changes include ‘care homes’ now being termed ‘residential care premises’, ‘fire service’ now being known as ‘fire and rescue service’, ‘acceptance’ now being termed ‘handover’, and ‘technician’ formerly being ‘engineer’.
Additionally, the standard now recommends competent persons to engage in and demonstrate continual professional development.
“Competent person. Person, suitably trained and qualified by knowledge and practical experience, and provided with the necessary instructions to enable the required task(s) to be carried out.
NOTE: Maintenance of competence is likely to require continuing professional development (CPD). (Clause 3.13)”
Categories of system
Changes to Clause 4 include:
Where a category of system is stipulated in the requirements imposed by an enforcing authority, by property insurers, or by the purchaser of the system, that category should be used. (Clause 4.1.)
If a designer has not been informed of the category of system, they need to make clear to the purchaser, or their agent, the category of system to which their design would conform. This is so the purchaser or their agent can take further advice as to whether that category would be compatible with any fire strategy for the premises. (Clause 4.2.)
Exchange of information and definition of responsibilities
Changes to Clause 5 include:
Where the designer of the fire detection and fire alarm system has proposed the category of system, this should be discussed and agreed upon with the user or purchaser. (Clause 5.4.)
The designer and user or purchaser should also agree as to whether or not the fire detection and fire alarm system is to incorporate one or more visual alarm devices. (Clause 5.5.)
The responsibility for the creation of the zone plan should be clearly defined, agreed upon and documented. (Clause 5.7.)
Variations
The standard now recommends that all variations be recorded in the system logbook; previously only ‘major variations’ were recommended to be recorded. However, due to no definition of ‘major’ being provided, this caused confusion. Furthermore, due to fatalities from several fires, unacceptable variations are now clarified.
Zone plans provide a clear and accurate layout of a building, identifying the location of fire detection devices and zones. This is particularly essential for the fire and rescue service, where, for example, addressable systems are not in use; therefore, the standard now deems the omission of a zone plan as an unacceptable variation. (Clause 6.6 (a).)
Additionally, the absence of remote monitoring in residential care premises and supported housing, where remote monitoring is considered necessary to meet the recommendations of BS 5839-1 (a Grade A system according to BS 5839-6:2019 is necessary), is also regarded as an unacceptable variation. (Clause 6.6 (b).)
Section 2: Design considerations
Relationship between system category and protected areas
Previously, Category L1, L3, and L4 systems were recommended to have smoke detectors, multi sensor detectors, or a mixture of smoke and combustion gas fire detectors provided in all escape stairways, all corridors and any other areas that form part of the common escape routes. This clause has now been slightly modified to include main access and egress stairways. (Clause 7.5.)
Actuation of other fire protection systems or safety facilities
To assist engineers carrying out maintenance and servicing, the standard makes it clear that interfaces and ancillary devices, such as fire door magnets and smoke vents, should be accessible. (Clause 8.5.)
Fire detection zones
It is now recommended that any visual indication provided by remote fire indicators should be red. (Clause 12.5.1.)
Communication with the fire and rescue service
Alarm Receiving Centres (ARCs) act as a central hub, receiving signals from activated alarms and then verifying the alert before contacting the appropriate emergency service. The standard now recommends the ARCs to have information on the type of premises, such as whether persons sleep at the premises. Additionally, ARCs should ideally receive information about the type of device that triggered the alarm and whether multiple devices activated simultaneously. (Clause 14.10.)
The performance criteria for signal handling of Category L and P systems have been clarified:
- Category L system: 90 seconds for fire signal and 3 minutes for failure of transmission equipment. (Clause 14.17.)
- Category P system: 120 seconds for fire signal and 31 minutes for failure of transmission equipment. (Clause 14.18.)
The rationale behind this is to ensure prompt response and fault awareness while increasing system reliability.
Appropriate information is an essential part of any fire detection and fire alarm system; identifying this, the standard has introduced the ‘False Alarm Notice’ (see Figure 1) to be positioned at the control and indicating equipment with an automatic connection to the fire and rescue service. (Clause 14.22.)
Figure 1 Example ‘False Alarm Notice’
Audible and visual alarm signals
Class change alarms in schools can now be integrated into fire detection and fire alarm systems if they can be easily distinguished from the fire alarm signal. The alarm should not exceed 10 seconds. (Clause 15.1.12 (b).)
In the updated standard, enhanced focus is placed on safeguarding all building occupants, particularly those with hearing impairments or mobility concerns. The commentary to Section 16 points to the need for visual alarm devices to be specific to the premises, for example, in locations where a person who is deaf or has a hearing impairment is likely to be alone, such as toilets or plant rooms.
Manual call points (MCPs)
The siting recommendations for MCPs have been adjusted, with a new note added. MCPs should not be installed in stairway landings in multistorey buildings with phased evacuation, as doing so could result in persons travelling down the stairway operating an MCP several floors below that on which a fire is located, resulting in evacuation of inappropriate areas. Additionally, where persons press an MCP on multiple floors, this can lead to confusion for the fire and rescue service regarding the location of the fire. (Clause 19.4.)
Reference to the 25 m and 16 m travel distances to an MCP has been removed; however, the position of an MCP should not be greater than 45 m along the measured route a person would follow. (Clause 19.5.)
The commentary to Section 6 of the standard puts emphasis on the judgement of experts where rigid adherence to a particular clause might not be appropriate in all cases and minor variations might not have any significant effect. Subsequently, MCPs are now permitted to have a +200 mm / -300 mm tolerance. (Clause 19.8.)
Types of fire detector and their selection
Rapid detection of fire is crucial where occupants are likely to be sleeping, for example, in hotels, student accommodation and residential care premises. Smoke detectors are more sensitive to smoke when compared with heat detectors, which rely on the increase of temperature. Previously, heat detectors were deemed to protect the adjacent escape route as opposed to the bedroom itself.
Section 20 has addressed detector selection, now recommending smoke, multisensory or carbon monoxide fire detectors, unless a fire risk assessment justifies the use of heat detection in sleeping areas. The standard clarifies that the recommendation for smoke detectors, rather than heat detectors, need not be applied retrospectively in existing bedrooms, for example, hotels. Recommendations for upgrades would perhaps be better left until systems incorporating heat detection in these rooms are subject to substantial or complete replacement or extension.
Siting and spacing of automatic fire detectors
Obstructions are often an issue for those installing smoke detectors. Structural beams, ductwork, light fittings or other isolated ceiling attachments not greater than 250 mm in depth, create obstacles to the flow of smoke detectors and should not be mounted closer to the obstruction than twice the depth of the obstruction. The standard has introduced a new note that clarifies that where there is a gap above any of these features greater than 300 mm, the features are not regarded as an obstacle to the flow of smoke. (Clause 21.2.9.)
Power supplies
To align with on-site practice, technicians are now permitted to record the battery-fitted date directly on the battery. (Clause 24.3.3.)
The formula for calculating the minimum capacity of valve-regulated lead-acid batteries has been amended. The previous method of dividing by 2 has been replaced by T2, which is the total battery alarm period in hours (h). (Annex E.1.)
Cables, wiring and other interconnections
While red is the common colour used for fire alarm cables, the colour of the low voltage mains supply cable has sometimes caused confusion. The standard has cleared this up by stating all fire alarm and low voltage mains supply cables should be of a single, common colour. (Clause 25.9.)
Electrical earthing
The functional earthing (FE) conductor of the fire detection and fire alarm system is now required to be identified in accordance with Table 51 of BS 7671; see extract below. (Clause 28.2.)
| Function | Alphanumeric | Colour |
| Functional earthing conductor | FE | Pink (PK) |
Summary
Adhering to the standard assists those designing fire detection and fire alarm systems in providing an early warning to occupants, supports evacuation, and ultimately, reduces the risk of injury or death.
While a code of practice, BS 5839-1 continues to underpin the fire safety recommendations of statutory documents, such as the Building Regulations Approved Document B Volume 2: Buildings other than dwellings7(England), which references the standard directly. This is reflected for all other devolved nations’ versions of the Building Regulations for fire safety. For those responsible for fire detection and fire alarm systems, authorizing systems that do not conform to the standard risks enforcement action, prosecution, delays in project completion, building insurance implications and reputational damage.
Further reading
IET Wiring Matters Issue 92 “Back to the Forum: Withdrawn Standards”
Acknowledgements
- Jon Elliott
- Leon Markwell
- Michael Peace
- Tim Benstead.
References
- BS 7671 Requirements for Electrical Installations, IET Wiring Regulations, Eighteenth Edition
- BS 5839-1:2025 Fire detection and fire alarm systems for buildings - Design installation. commissioning and maintenance of systems in non-domestic premises. Code of practice.
- BS 5839-6:2019+A1:2020 Fire detection and fire alarm systems for buildings – Code of practice for the design, installation, commissioning and maintenance of fire detection and fire alarm systems in domestic premises.
- BS 0:2021 A standard for standards. Principles of standardization.
- BS 5839-1:2017 Fire detection and fire alarm systems for buildings - Code of practice for design, installation, commissioning and maintenance of systems in non-domestic premises.
- BS 4422:2024 Fire. Vocabulary.
- Approved Document B Volume 2: Buildings other than dwellings.