A construction site needs a temporary fire detection and alarm system whenever the permanent building system is not yet installed, not yet commissioned, or not able to cover the areas currently occupied or worked in, which in practice means for most of a project's duration on anything beyond a small refurbishment. Under the Regulatory Reform (Fire Safety) Order 2005, the responsible person (usually the principal or main contractor) has to ensure the site has appropriate fire detection and warning arrangements at every stage, not just once the finished building's own system is live. What to specify depends on site size, layout, occupancy and the work taking place, but the starting reference points are BS 5839-1 for design and EN 54 for the equipment itself.

A construction site needs a temporary fire detection and alarm system whenever the permanent building system is not yet installed, not yet commissioned, or not able to cover the areas currently occupied or worked in, which in practice means for most of a project's duration on anything beyond a small refurbishment. Under the Regulatory Reform (Fire Safety) Order 2005, the responsible person (usually the principal or main contractor) has to ensure the site has appropriate fire detection and warning arrangements at every stage, not just once the finished building's own system is live. What to specify depends on site size, layout, occupancy and the work taking place, but the starting reference points are BS 5839-1 for design and EN 54 for the equipment itself.

Who is responsible, and when the duty applies

The Regulatory Reform (Fire Safety) Order 2005 (the FSO) is the law that governs general fire precautions on non-domestic premises in England and Wales, including construction sites while work is underway. Article 3 defines the "responsible person" as whoever has control of the premises; on a construction site this is normally the principal contractor, or the main contractor where no principal contractor has been appointed under the Construction (Design and Management) Regulations 2015.

Two duties matter most for this topic. Article 9 requires the responsible person to carry out and keep up to date a fire risk assessment. Article 13 requires that, where necessary to safeguard people on the premises, the site is equipped with "appropriate fire-fighting equipment and with fire detectors and alarms," sized and specified against the use of the premises, what is stored or being worked on there, and who is present. Fire detection is therefore not an optional add-on once the client's permanent system goes in: it is a live legal duty for the responsible person throughout construction, and the risk assessment is what determines what "appropriate" means for that site at that stage.

HSE's construction guidance sets out the same expectation in practical terms: a warning system that everyone on site can recognise and hear above other site noise, escape routes that stay available and unobstructed as the layout changes, and an assembly point people can actually reach. HSE's fuller reference guidance, HSG168 *Fire Safety in Construction*, covers this in more depth, including how fire risk should be considered from design stage through to handover.

Why a site's fire strategy cannot stay static

A finished building has one fire strategy. A construction site usually has several, one after another, because the physical layout keeps changing: a groundworks phase becomes a structural frame, then a fit-out with compartment walls going up floor by floor, then a phased handover where some floors are occupied by client staff while others are still under construction. Escape routes that worked in month three may be blocked, relocated or simply gone by month nine. Detection coverage designed for an open shell does not automatically cover the same footprint once partitions, risers and temporary hoardings are in.

This is precisely why the fire risk assessment required under Article 9 is described as something to be kept "up to date," not filed once at the start. In practice that means reviewing detection coverage and evacuation routes at each significant change of layout or occupancy, not on a fixed calendar regardless of what has actually changed on site.

Hot works: the highest-risk activity on most sites

Hot work (welding, cutting, grinding, soldering, and any process generating flame, sparks or significant heat) is consistently one of the largest causes of serious construction fires, which is why it gets dedicated treatment in industry guidance rather than being folded into general precautions. The Joint Code of Practice on the Protection from Fire of Construction Sites and Buildings Undergoing Renovation (JCoP), now in its 10th edition, continues to treat hot work as a long-standing risk requiring specific controls, alongside wider site fire prevention measures. The Code applies as a contractual requirement on projects above £2.5 million in contract value, and is recommended as best practice below that threshold.

Where hot work is planned, a permit-to-work system, a dedicated fire watch during and after the activity, and detection coverage that is not disabled or isolated in the work area for longer than strictly necessary are standard control measures referenced across HSE and industry guidance. If a detection system is temporarily isolated to allow hot work in a dusty or steam-affected area, that isolation should be time-limited, recorded, and reinstated as soon as the work finishes.

Temporary detection and alarm: what "temporary" actually means

A temporary fire alarm system is not a lesser standard of protection: it is a system designed and installed to cover a site during a phase where the permanent system is not yet available, using equipment and a design approach suited to a changing environment. Wireless, radio-linked detectors and sounders are the standard technology choice for this, because they can be relocated as the layout changes without re-cabling, and because they can be commissioned and extended quickly as new areas come into use.

The design reference point for any UK fire detection and alarm system, temporary or permanent, is BS 5839-1, the code of practice for design, installation, commissioning and maintenance of fire detection and alarm systems in non-domestic premises. A revised edition, BS 5839-1:2025, came into effect on 30 April 2025, replacing the 2017 edition. Detection and sounder equipment specified against BS 5839-1 should be EN 54-compliant, meaning it meets the relevant European product standard for fire detection and fire alarm system components.

When a temporary system is the right call

A temporary system is appropriate whenever the permanent system does not yet exist, is not yet commissioned, or does not cover the areas currently in use, which covers most of a build programme on anything beyond the smallest refurbishment. It is also appropriate during phased handovers, where occupied and unoccupied areas sit side by side and need separately zoned coverage.

What changes between a temporary and a permanent specification

The underlying design principles are the same: detection matched to the fire strategy, coverage matched to occupancy and use, a warning that is audible and recognisable throughout the area at risk. What differs is how the system is built and managed: temporary systems are specified for portability and rapid reconfiguration, commissioned and re-tested each time the layout changes materially, and formally handed over or decommissioned once the permanent system takes over that coverage. That handover point, meaning who signs off that the permanent system is live and adequate before the temporary system is removed, should be agreed and documented in advance, not decided informally on the day.

What to specify: a buyer's checklist

When briefing a supplier for a temporary system, useful questions to put in the specification include:

• Coverage area and phasing. Which zones need coverage now, and how will that change as the programme progresses.
• Detection type. Smoke, heat, or multi-sensor detection appropriate to the work being carried out in each zone (heat detection where dust or fumes would cause false alarms from smoke detectors, for example).
• Standard referenced. Confirm the system is designed against BS 5839-1 and built from EN 54-compliant components.
• Interlinking and audibility. How detectors and sounders communicate across the site, and whether the alarm is audible and distinguishable above site noise in every occupied area.
• Isolation procedure for hot works. How and for how long detection can be isolated for hot work, and who authorises and logs it.
• Reconfiguration process. How quickly the system can be extended or relocated as the layout changes, and who re-tests it after each change.
• Maintenance and fault response. Who tests the system on what schedule, and the target response time for a reported fault.
• Handover to the permanent system. The agreed process and sign-off for removing the temporary system once permanent detection is live.

Evacuation planning around a temporary system

A detection and alarm system only does its job if people know what the alarm means and where to go when they hear it. HSE's guidance is explicit that the warning has to be recognisable by everyone on site, that escape routes need to stay available and unobstructed as work progresses, and that assembly points need to be genuinely reachable: on a small site that might be no more than the pavement outside, but on a larger or phased site it needs planning as layouts change. Evacuation plans, like the detection layout itself, should be reviewed at each significant change to the site rather than left as a single document produced at induction and never revisited.

Competent design and installation

Article 13 of the FSO also requires the responsible person to nominate competent people to implement fire-fighting and detection measures. For a temporary system, that means the design and installation should be carried out by people who understand both BS 5839-1 design principles and the practical realities of a live construction site, not just installed to a generic detector count. AOG's DefendX division designs and installs fire detection and alarm systems in accordance with the applicable fire strategy and relevant BS 5839 recommendations, using EN 54-compliant equipment where specified, with commissioning, testing and handover documentation provided on completion. DefendX does not hold BAFE third-party certification; competence and standards compliance are evidenced through the design and commissioning process itself, and buyers who require BAFE-certified installation specifically should confirm that requirement before appointing any supplier.

This guide describes the regulatory framework and the process a responsible person should expect from a competent supplier. It is not a substitute for a site-specific fire risk assessment, and following it does not by itself discharge any legal duty under the FSO: that depends on the actual risk assessment, system design and management arrangements in place for the site in question.