Temporary fire detection and alarm systems for construction sites (TFDAS)
Construction sites change from week to week – layouts, occupancy and fire loads are never the same for long. Existing codes of practice for fire detection, such as BS 5839-1, were written for permanent, finished buildings and have limited application to a live site.
T-Category Fire Alarms are a classification framework developed specifically for temporary systems on construction projects. The categories give contractors, health and safety professionals and fire alarm contractors a shared way of describing what level of fire detection a project needs – from a fully manual system through to automatic detection targeted at a specific risk. Our free best-practice guide sets out the full framework, along with guidance on design, installation, commissioning, and maintenance.
The T-Categories
Which category applies to a project is determined by its site-specific Fire Risk Assessment. The guide includes a full selection table showing how the categories typically apply across different project types.
Category TM
These are manual systems and, therefore, consist of linked Call Points and Sounders only, and incorporate no automatic fire detectors.
Category T2
Systems located in partially occupied buildings where an outbreak of fire in the construction area needs to be communicated to the occupied areas of the building. In such systems automatic detection will be installed on a risk assessed basis to provide early warning before the fire breaks out of the construction area. Automatic detection may also be required for property protection purposes.
Category T3
Systems in which automatic detection is installed in rooms, areas or corridors opening onto an escape staircase. The objective of a Category T3 system is to give a warning of fire at an early enough stage to enable all occupants to escape safely, before the escape staircases are impassable.
Category T4
Systems in which automatic detection is installed on escape staircases only to give a warning of fire at an early enough stage to enable all occupants to escape safely, before the escape routes are impassable.
Category T5
Systems in which automatic detection is added in specific locations to satisfy a specific fire safety objective. Often, the design is based on a localised need for fire detection in only part of a building (e.g. material storage areas). Protection might be provided to compensate for some departure from normal guidance elsewhere, for example extended travel distances. In refurbishment projects automatic detection may be required for property protection purposes.
Frequently asked questions
What is a T-Category fire alarm?
T-Category Fire Alarms are a classification system for temporary fire detection and alarm systems (TFDAS) on construction projects. The categories describe the level and purpose of automatic detection a site needs: Category TM covers manual systems of linked call points and sounders with no automatic detection; T2 to T5 add automatic detection targeted at particular risks - partially occupied buildings, escape staircases, and specific high-risk locations such as material storage areas. The full definition of each category is set out in our best practice guide.
Who decides which T-Category a construction project needs?
The site-specific Fire Risk Assessment determines the category. The T-Category framework provides the language for specifying it, but the assessment of risk on a particular project - its size, structure, occupancy, fire load and escape arrangements - is what drives the decision. The guide includes a selection table showing how the categories typically apply across different project types, which is intended as a starting point for that assessment rather than a prescriptive list.
How do T-Categories relate to BS 5839-1 L-Categories?
They are separate classification systems and should not be treated as interchangeable. BS 5839-1 was written for permanent, finished buildings, while the T-Categories are defined by the circumstances of a construction project. Specifying a T-Category is not the same as specifying the similarly-lettered or numbered L-Category, and one should never be substituted for the other in a design, a specification or a Fire Risk Assessment. Section 1.2 of the guide sets out the relationship in full.
How does this guide relate to the JCoP and HSG168?
It is intended to be read alongside them, not instead of them. The Joint Code of Practice is the overarching code for fire prevention across a construction site as a whole, of which the fire detection and alarm system is one part. This guide provides the detailed technical methodology for that specific part, expanding on what the JCoP references without setting out in full. HSG168 remains the underlying HSE guidance on legal compliance and general fire safety methodology that both are designed to support.
Do site cabins need their own fire alarm system?
It depends on where they sit and what happens in them. Where site cabins are within 10 metres of another building, or are used for cooking or drying clothes, the JCoP requires the alarm system to comply with BS 5839-1: 2025 - so these fall outside the T-Category framework. Other site cabins are likely to form part of the fire alarm system covering the construction area. The guide covers both situations.
Is the T-Category framework an official standard?
It is a best practice framework published by Howler, developed from experience of temporary fire detection on construction projects since 1986. It is not a British Standard or a statutory requirement. It is intended as a common reference point for contractors, health and safety professionals and fire alarm contractors, and we welcome feedback and suggestions for future editions - email [email protected].
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