Risk Assessments · Mandatory · Pre-Construction

RAMS — Hot Works

This RAMS covers welding, cutting, grinding, and any activity producing sparks, flames, or heat that could ignite materials. It requires a hot works permit, fire watch procedures, removal of combustibles, and fire extinguisher provision. A fire watch must be maintained for a minimum period after hot works cease to detect smouldering materials.

Last reviewed: 29 March 2026 — This guide reflects UK law as of this date. MHSWR 1999 remains current with no amendments enacted as of 29 March 2026. Next scheduled review: 29 March 2027.

Legal basis	MHSWR 1999 Regulation 3 + Regulatory Reform (Fire Safety) Order 2005 + HSG168
Definition	Any process producing open flames, sparks, or heat — welding, flame cutting, grinding, brazing, soldering, torch-applied roofing and waterproofing
Permit to work	Required for all hot works carried out outside a designated safe area
Fire watch	Mandatory during hot works and for a minimum of 60 minutes after completion (4 hours where timber is present)
COSHH link	Welding fumes and work on coated or galvanised metals require a separate COSHH assessment
Enforcing authority	Health and Safety Executive (HSE) and Fire and Rescue Service

1. What It Covers

Hot works encompass any construction activity that generates open flames, sparks, or significant heat — including welding, flame cutting, grinding, brazing, soldering, and the torch application of roofing membranes or waterproofing materials. These processes introduce a direct fire and explosion risk to the work area and its surroundings, and require specific controls that go beyond standard site fire precautions.

Many of the most serious construction site fires in the UK have been caused by hot works. Sparks generated during cutting or grinding can smoulder undetected for hours before igniting combustible materials nearby. The majority of hot-works fires occur after the shift has ended, when no one is present to detect or respond to the ignition. This is why permit-to-work systems, fire watches, and post-work inspections are not optional precautions — they are the primary line of defence against a well-documented and recurring cause of catastrophic loss.

Construction site fires from hot works: a persistent and serious risk

Sparks from cutting and grinding can travel considerable distances and lodge in crevices, insulation, and timber framing where they smoulder undetected. Fires that start after the workforce has left site cause the most damage because there is no one present to raise the alarm or intervene. A robust hot works permit system combined with a disciplined fire watch regime is the only reliable way to manage this risk.

2. Legal Framework

Hot works on construction sites fall under two overlapping legal regimes. The Management of Health and Safety at Work Regulations 1999 (MHSWR), Regulation 3, requires a suitable and sufficient risk assessment for all work activities — including hot works. The Regulatory Reform (Fire Safety) Order 2005 (RRO) places duties on the responsible person to carry out a fire risk assessment and implement appropriate fire precautions across the premises or site. Both obligations apply concurrently, and compliance with one does not discharge the duty under the other.

Enforcement is shared between the HSE, which has jurisdiction over workplace health and safety, and the Fire and Rescue Service, which enforces the RRO. In practice, a hot works incident on a construction site will often attract attention from both regulators.

HSG168: Fire Safety in Construction

HSG168 is the HSE’s primary guidance document for fire safety on construction sites. It sets out the practical standards for hot works permits, fire watches, storage of flammable materials, and emergency procedures. While HSG168 is guidance rather than law, it represents the standard against which compliance will be judged in any investigation or prosecution. Departing from HSG168 without a documented and justifiable alternative approach is difficult to defend.

3. Key Hazards

Hot works generate a range of hazards beyond fire risk alone. The following table identifies the principal hazards, who is at risk, the key risk factors, and the controls required.

Hazard	Who at risk	Risk factors	Controls
Fire ignition	All site personnel, adjacent occupants, public	Sparks travel up to 10 m; smouldering material in concealed spaces; combustible materials within work area	Minimum 5 m clearance from combustibles; fire blankets over materials that cannot be moved; dedicated fire watcher throughout works and post-work period
Welding fumes	Welder, nearby workers	Toxic metal fumes (manganese, chromium, nickel); duration of exposure; confined or poorly ventilated spaces	Local exhaust ventilation (LEV) as primary control; RPE with P3 particulate filter where LEV is insufficient; COSHH assessment specific to fume composition
Burns and eye injury	Welder, nearby workers, passers-by	UV and IR radiation from arc welding; molten metal spatter; hot workpieces	Welding shield with appropriate shade filter; welding screens to protect bystanders; heat-resistant gloves and flame-retardant clothing
Explosion — flammable atmosphere	All persons in vicinity	Residual flammable vapours or gases; work on pipes, tanks, or vessels that have contained flammable substances	Atmospheric gas testing before work begins; never carry out hot works on containers, pipes, or vessels without a gas-free certificate issued by a competent person
Cylinder hazards	Welder, nearby workers	Gas leaks from damaged valves or hoses; cylinders falling; flashback into cylinders	Cylinders secured upright in purpose-built trolleys or racks; flashback arrestors fitted to both torch and regulator; cylinders stored away from heat sources and separated by gas type
Electrical hazards — arc welding	Welder	Electric shock from welding circuit; damaged cables or connections; wet conditions	Equipment compliant with BS EN 60974-1; daily pre-use inspection of cables, connectors, and earth clamp; no arc welding in wet conditions or on wet surfaces without specific precautions
COSHH — coated metals	Welder, nearby workers	Fumes from galvanised steel (zinc oxide), lead-painted surfaces, cadmium-plated components	Separate COSHH assessment for each coating type; galvanised steel requires heavy mechanical ventilation plus supplied-air RPE; biological monitoring where exposure limits may be exceeded

4. Fire Watch

The fire watch is the single most important procedural control for hot works. Its purpose is to detect and extinguish any ignition that occurs during or after the work. The following table sets out the requirements for each phase of the fire watch.

Phase	Requirement
During hot works	A dedicated fire watcher must be present throughout the duration of hot works. The fire watcher must not carry out any other duties during this period and must have a clear view of the work area and surrounding zones.
Immediately after	The fire watcher must remain in position immediately after hot works cease. The work area and all adjacent spaces — including floors above, below, and behind the work surface — must be inspected for signs of smouldering or heat transfer.
Minimum 60 minutes post-work	The fire watch must continue for a minimum of 60 minutes after the last hot works activity. Where timber framing, insulation, or other slow-combustion materials are present, the fire watch must continue for a minimum of 4 hours.
Interim checks beyond 60 minutes	Where the 60-minute minimum applies, additional checks should be carried out at regular intervals beyond the mandatory period — particularly before the site is left unattended overnight or over a weekend.
Fire extinguisher type	A minimum of one fire extinguisher appropriate to the materials present must be immediately available at the point of work. Water extinguishers are suitable for general combustibles; CO2 or dry powder for electrical or flammable liquid risks. The fire watcher must be trained in extinguisher use.
Pre-work check	Before hot works begin, the fire watcher and the operative must jointly inspect the area to confirm that combustibles have been removed or protected, that fire detection systems in the area are functioning, and that escape routes are clear.

The fire watch must cover hidden areas — not just the visible work surface

Sparks from cutting and grinding can travel up to 10 metres and pass through gaps in floors, walls, and ceilings. Heat from welding conducts through metal sections and can ignite combustible materials on the far side of a partition or on a floor below. The fire watcher must inspect all areas where sparks or conducted heat could reach — not just the immediate work surface. Fires in concealed voids are the most common cause of catastrophic loss from hot works precisely because they are not visible from the point of work.

5. Common Mistakes

No permit to work in place

Hot works carried out without a valid permit to work is one of the most frequently cited failures in fire investigations. The permit system ensures that a competent person has assessed the area, confirmed that precautions are in place, and authorised the work. Without a permit, none of these checks have been formally carried out or recorded.

Fire watcher leaves early or is not dedicated

The fire watcher must remain in position for the full duration of the hot works and for the mandatory post-work period. Assigning the fire watch to the operative carrying out the hot works, or allowing the fire watcher to leave before the post-work period is complete, removes the primary detection control. A fire watcher who is also performing other tasks is not a fire watcher.

No COSHH assessment for coated or galvanised metals

Welding, cutting, or grinding galvanised steel, lead-painted surfaces, or cadmium-plated components generates highly toxic fumes that require a separate COSHH assessment. Zinc oxide fumes from galvanised steel can cause metal fume fever. Lead and cadmium fumes pose serious chronic health risks. Standard welding RPE is not sufficient — supplied-air respiratory protection and heavy mechanical ventilation are required.

Combustible materials not removed or protected

All combustible materials within a minimum of 5 metres of the hot works location must be removed. Where removal is not practicable, materials must be covered with fire-resistant blankets or sheeting. Failure to clear or protect combustibles is the single most common precondition for hot works fires.

Hot works on containers or pipework without a gas-free certificate

Any container, pipe, tank, or vessel that has held flammable liquids, gases, or vapours must be certified gas-free by a competent person before hot works are carried out. Residual vapours can ignite or explode when exposed to heat or flame. This is a non-negotiable precondition — there is no safe shortcut.

6. Frequently Asked Questions

Is a hot works permit required by law?▾

There is no single regulation that explicitly mandates a hot works permit by name. However, the Management of Health and Safety at Work Regulations 1999 require a suitable and sufficient risk assessment, and the Regulatory Reform (Fire Safety) Order 2005 requires appropriate fire precautions. In practice, a permit-to-work system is the only recognised way to discharge these duties for hot works. HSG168 sets it out as the expected standard, and any investigation or prosecution following a hot works fire will examine whether a permit system was in place and followed.

How long must the fire watch continue after hot works are completed?▾

The fire watch must continue for a minimum of 60 minutes after the last hot works activity. Where timber framing, insulation, or other materials with slow combustion characteristics are present in or near the work area, the fire watch must continue for a minimum of 4 hours. Additional checks should be carried out before the site is left unattended, particularly overnight or over a weekend.

Does angle grinding count as hot works?▾

Yes. Angle grinding produces a significant volume of sparks that can travel several metres and ignite combustible materials. It falls squarely within the definition of hot works and requires the same permit-to-work system, fire watch, and clearance of combustibles as welding or flame cutting. This is one of the most commonly overlooked points — angle grinding is frequently carried out without a hot works permit, which is a significant compliance failure.

What PPE is required for arc welding?▾

As a minimum: a welding helmet or hand shield with an appropriate shade filter for the arc process and current being used; flame-retardant overalls or a welding jacket; heat-resistant welding gauntlets; safety boots with metatarsal protection; and RPE with a P3 particulate filter where local exhaust ventilation is not sufficient to control fume exposure. Welding screens must be used to protect nearby workers from UV radiation. Where work is on coated or galvanised metals, supplied-air RPE may be required in place of a standard filter.

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