Construction Site Fire Safety: Extinguisher Types, Hot Works Permits, Site Fire Plan and Part 3 of BS 5839-1

Summary

Fire on a construction site is a serious and regularly occurring risk. The combination of combustible materials (timber, insulation, packaging), ignition sources (hot works, electrical equipment, arson), and incomplete passive fire protection (no compartmentation, open floor voids, missing fire doors) makes active fire precautions essential. Construction site fires are a major cause of property loss in the UK and a significant cause of injury and death.

The legal framework for construction site fire safety comes from multiple sources: CDM 2015 requires fire precautions in the Construction Phase Plan; the Regulatory Reform (Fire Safety) Order 2005 (RRFSO) applies to non-domestic premises during construction (including site offices, welfare facilities, and the partially completed building); the Health and Safety at Work etc. Act 1974 imposes a general duty of care; and Building Regulations Part B requirements for fire safety in the completed building inform the precautions needed during construction.

Hot works — any activity using an open flame or generating sufficient heat to ignite nearby materials — are a particular focus. Torch-applied roofing membrane, soldering and brazing, grinding and disc-cutting, welding, and LPG-fuelled plumbing work are all hot works. A Hot Works Permit system ensures that every hot works activity is assessed, mitigated, and monitored for 60 minutes after completion (the "fire watch" period).

Key Facts

• Regulatory Reform (Fire Safety) Order 2005 — applies to non-domestic parts of the construction site; requires a fire risk assessment and suitable fire precautions
• CDM 2015 Regulation 15 — Construction Phase Plan must include fire precautions and emergency procedures
• BS 5839-1:2017 — Fire detection and fire alarm systems for buildings; Part 3 covers application during construction
• Hot Works Permit — required for any work with open flames, grinding, soldering, torch-applied roofing, or welding near combustibles
• Fire watch period — minimum 60 minutes after completion of hot works; person remains on site checking for smouldering material
• Extinguisher types — Water: Class A (paper, wood, textiles); CO₂: Class B (liquids) and electrical; Dry powder: Class A, B, C; Wet chemical: Class F (cooking oils); Never use water on electrical fires
• Minimum extinguisher provision — one 13A-rated extinguisher (typically 9L water) per 200m² of floor area, maximum 30m travel distance to any extinguisher
• Fire point — a specified location with fire extinguisher, fire action notice, and assembly point direction
• Assembly point — designated and signed; known to all workers before they start on site; included in site induction
• Site induction — must cover fire procedures: location of extinguishers, escape routes, assembly point, alarm signal (whistle, hooter, verbal — describe clearly), who calls 999
• Combustible material storage — flammable liquids (paints, solvents, LPG) stored in ventilated, locked metal or concrete block stores; minimum 3m from structures
• No smoking policy — enforced on all areas of a construction site where combustible materials are present
• Arson risk — unsupervised sites are a high arson risk; remove combustible materials from unfinished buildings overnight; secure the site perimeter

Quick Reference Table

Detailed Guidance

Construction Site Fire Risk Assessment

Under RRFSO 2005, a written fire risk assessment must be carried out for any non-domestic part of the site (including the building under construction where workers are present). The assessment must:

1. Identify fire hazards — ignition sources, fuel sources, and oxygen sources
2. Identify persons at risk — workers, visitors, members of the public near the site
3. Evaluate the risk — likelihood of fire starting and spreading; likely consequences
4. Record findings and implement precautions — document the measures in place
5. Review and update — at each project phase change, after any incident, and when the site layout changes

Key hazards to include:

• Hot works activities
• Electrical equipment and temporary wiring
• Combustible materials (timber, insulation boards, MDF, packaging waste)
• Flammable liquids and gases (paints, solvents, LPG)
• Arson (particularly on unoccupied sites overnight)
• Incomplete passive fire protection (open floor voids, no compartmentation)

Hot Works Permit System

A Hot Works Permit is a document that authorises and controls a specific hot works activity at a defined location. Its purpose is to ensure that precautions are in place before, during, and after hot works. The permit system is not bureaucracy — hot works are the cause of a significant proportion of major construction site fires, often triggered by smouldering material that ignites after the workers have left.

Hot works definition: any work using an open flame, grinding, welding, soldering or brazing, torch-applied waterproofing, disc cutting that generates sparks, or any process generating heat capable of igniting nearby material.

Permit components:

1. Pre-work checks (before starting):

   • Location clearly identified (floor, area, specific work activity)
   • Combustibles removed from minimum 3m radius (or 5m for high-risk activities like roofing torch)
   • Non-removable combustibles protected with fire-resistant blankets
   • Fire extinguisher immediately to hand (type appropriate to fire risk in that area)
   • Water spray available for smouldering prevention
   • Permit authorised by site manager or responsible person

2. During hot works:

   • Competent person carrying out the work
   • Fire watcher present for any work where ignition could spread without immediate detection

3. After hot works (fire watch):

   • All hot work stopped
   • All materials cool to touch where possible
   • Area checked for smoke, smell, or smouldering
   • Fire watcher remains in the area for minimum 60 minutes after completion
   • Final check at end of the 60 minutes and again 30 minutes later (some fire authorities recommend a 2-hour total watch period for roofing work)
   • Permit closed and signed off by the fire watcher

4. End of day:

   • No hot works to be carried out within 1 hour of all workers leaving the site
   • Final check of all areas where hot works were carried out that day

Permit documentation: issue pre-printed permits with a permit number, site address, authoriser, worker, date, time, location, and sign-off sections. File completed permits for minimum 12 months.

Extinguisher Selection and Positioning

Minimum provision (BS 5839-1 and RRFSO guidance):

• One 13A-rated water extinguisher per 200m² of floor area
• Maximum 30m travel distance to any extinguisher
• At each fire point: fire action notice, extinguisher, and directional sign to assembly point
• Additional CO₂ extinguishers at all electrical installations (temporary distribution boards, site office equipment)
• Dry powder or CO₂ at any LPG storage point

On-site specifics:

• Roofing operations (torch-on felt): dry powder or CO₂ immediately to hand at roof level; additional extinguisher at base of access
• Welding: CO₂ or dry powder at the work location
• Plumbing hot works (soldering, brazing): CO₂ extinguisher; never use water near electrical equipment
• Site office: CO₂ for electrical equipment; water for general Class A

Checking extinguishers:

• Visual check weekly: pin in place, gauge in green zone, no obvious damage
• Annual service by a competent person (BAFE-registered service company)
• Extinguishers must carry a current service label; check before deployment to site

Fire Detection and Alarm During Construction (BS 5839-1 Part 3)

BS 5839-1:2017 Annex H (which has effectively been superseded for construction guidance by BS 5839-1 Part 3 in the 2017 version) provides guidance on fire detection during construction of buildings. Key requirements:

• Category of system: during construction, a temporary Category L3 system (detection in escape routes) or Category M (manual alarm only) is the minimum for most projects; large or high-risk projects may require automatic detection
• Coverage: smoke detectors in escape routes and areas of significant fire risk (material stores, welfare facilities)
• Alarm signal: must be audible throughout the site; typically an air horn, electric hooter, or whistle; the signal and what to do must be explained at site induction
• Call points: manual break-glass call points at all fire exits from the site welfare facilities and site office

For the completed building, fire detection requirements are set by BS 5839-6 (domestic) or BS 5839-1 (non-domestic). During construction, interim alarm provisions are the principal contractor's responsibility.

Site Fire Plan

The site fire plan should be a brief, clear document included in the Construction Phase Plan and displayed on site. It must cover:

1. Alarm procedure — what the fire alarm signal is; what to do when you hear it
2. Evacuation routes — escape routes marked on a site plan; updated as the project develops
3. Assembly point — location marked on site and on the plan
4. Roll call procedure — who calls the roll; who calls 999; who liaises with fire brigade on arrival
5. Fire wardens — names of designated fire wardens (typically site manager and foremen)
6. Hot works permit issuer — name and contact of person authorised to issue permits
7. Location of fire extinguishers — on site plan
8. No re-entry rule — nobody re-enters until fire brigade declares all clear

Review schedule: the fire plan must be reviewed when the site layout changes, when new trades arrive, and at each project phase change.

Frequently Asked Questions

Do I need a hot works permit for plumbing soldering?

Yes, unless the work is in an area with no combustible material within 3m and the soldering is done with a small, handheld torch on exposed metal pipework with no concealed voids. In practice, any soldering in a wall void, near timber, near insulation, or under a floor requires a hot works permit and fire watch. A common cause of house fires is soldering in a wall void with a bit of expanded polystyrene insulation nearby — it smoulders unseen for hours and ignites overnight.

What if I'm a sole trader — do I need to keep a hot works permit log?

If you're a sole trader, writing a formal permit to yourself may seem unnecessary, but the pre-work checks, fire watch, and end-of-day confirmation are still essential practice. Many sole traders use a simple checklist approach — a laminated card with the checks on it, dated and initialled. If you're working on a principal contractor's site, they will have their own permit system and you must use it.

What's the difference between a fire risk assessment and a Construction Phase Plan fire section?

The fire risk assessment under RRFSO 2005 is a detailed assessment of fire hazards and risks, required for any non-domestic premises (including the building under construction). The Construction Phase Plan fire section under CDM 2015 is the plan for how fire will be controlled and responded to on site. They overlap significantly — in practice, a single document covering both is acceptable as long as it addresses all the required content.

How soon after completing roofing torch work can workers leave site?

Most roofing contractors' fire procedures require a 60-minute fire watch after the last torch work. Some insurers and fire authorities recommend 2 hours. The key risk is that felt substrate material (especially old organic felt) can smoulder for an extended period before igniting. If torch work finishes at 4pm, workers should remain on site until at least 5pm (or 6pm for belt-and-braces compliance) and do a final check of the roof area and any penetrations before leaving.

Regulations & Standards

• Regulatory Reform (Fire Safety) Order 2005 (RRFSO) — applies to non-domestic premises; requires fire risk assessment and precautions

• CDM 2015 — Construction Phase Plan must include fire precautions

• Health and Safety at Work etc. Act 1974 — general duty of care to workers and others

• BS 5839-1:2017 — Fire detection and fire alarm systems; includes guidance for buildings during construction

• BS EN 3 — Portable fire extinguishers; performance, testing, and marking requirements

• PD 7974-6 — Application of fire safety engineering principles; life safety for people in and around buildings

• HSE Construction Fire Safety — HSE guidance on fire precautions during construction

• NFCC (National Fire Chiefs Council) Hot Works Guidance — hot works permit templates and guidance

• Fire Protection Association (FPA) — construction fire safety publications

• BS 5839-1:2017 — fire detection and alarm system standard

• toolbox talks — fire safety as a toolbox talk topic

• natural gas vs lpg — LPG storage safety on site

• pitched roof structure — roofing hot works context

• warm flat roof detail — torch-on flat roofing and fire precautions