Toolbox Talks · Best Practice · Construction

Toolbox Talk — Hot Works

A toolbox talk on the fire risks associated with hot works such as welding, cutting, and grinding.

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

1. Leading Cause of Construction Site Fires

Hot works are the leading cause of fires on construction sites. The term covers any process that generates open flames, heat, or sparks — including welding, oxy-fuel cutting, grinding, brazing, soldering, and blowtorch work. The regulatory framework includes the Management of Health and Safety at Work Regulations 1999 (MHSWR), the Regulatory Reform (Fire Safety) Order 2005 (RRO), and CITB guidance note GC07.

A hot works permit is required for every hot works activity, every time, without exception. The permit system ensures that a competent person has assessed the area, confirmed controls are in place, and authorised the work to proceed. Permits are time-limited and location-specific — a new permit is required if the location changes or the permit period expires. The permit is not a bureaucratic formality: it is the primary fire prevention control for hot works activities.

Fire watch must continue for a minimum of 30 minutes after hot works cease — 60 minutes is recommended

Most hot works fires do not start during the work itself — they start after the operative has left and smouldering materials ignite. The fire watch period is critical. A minimum of 30 minutes post-work monitoring is required, but 60 minutes is recommended by most insurers and industry guidance. The fire watcher must remain in the area with a suitable fire extinguisher and be trained to raise the alarm. No hot works should be carried out within 2 hours of the end of the shift to ensure adequate fire watch time.

2. Key Talk Points

Talk Point	Detail
Permit required always	No hot works activity may commence without a valid hot works permit signed by an authorised person. The permit must specify the location, duration, type of work, and controls in place. The operative must have a copy of the permit at the work location. Work must stop if the permit expires or conditions change.
Area preparation	Remove all combustible materials within a 10-metre radius of the hot works location. Where combustibles cannot be removed, cover them with fire-resistant sheeting. Seal all floor, wall, and ceiling penetrations within the 10-metre zone to prevent sparks travelling to other compartments. Check the area above, below, and on the other side of walls and partitions.
Fire extinguisher	A suitable fire extinguisher must be immediately available at the hot works location. The extinguisher type must match the potential fire risk — typically a water or foam extinguisher for general combustibles, and a CO2 or dry powder extinguisher where flammable liquids or electrical equipment are present. The fire watcher and operative must both know how to use the extinguisher.
Fire watch	A designated fire watcher must be present throughout hot works and for a minimum of 30 minutes after work ceases (60 minutes recommended). The fire watcher must not be the person carrying out the hot works. They must have no other duties during the fire watch period. They must have a fire extinguisher, a means of raising the alarm, and knowledge of the evacuation route.
End of shift rule	No hot works should be carried out within 2 hours of the end of the working shift. This ensures that the full fire watch period (30 to 60 minutes minimum) can be completed before the site is vacated. Hot works started late in the day with an inadequate fire watch period are a leading cause of overnight fires on construction sites.
Cylinder safety	Gas cylinders must be stored upright, secured to prevent falling, and separated by type (oxygen separate from fuel gases by at least 3 metres or by a fire-resistant barrier). Cylinders must not be stored in confined spaces, below ground level, or near heat sources. Regulators and flashback arrestors must be fitted and in good condition. Empty cylinders must be valved off and stored separately from full cylinders.

3. Common Mistakes

Starting hot works without a permit

The most dangerous and most common mistake. Operatives who are under time pressure or consider the task minor may start cutting, grinding, or welding without obtaining a permit. There is no such thing as a minor hot works task — a single spark can ignite combustible material and cause a major fire. The permit system exists because human judgement alone is not sufficient to assess fire risk in every situation.

The welder acting as their own fire watcher

The person carrying out the hot works cannot simultaneously act as fire watcher. The operative is focused on the task, wearing a welding helmet or visor, and cannot observe the surrounding area for signs of ignition. A separate, dedicated fire watcher must be assigned. This person must have no other duties during the hot works and the subsequent fire watch period.

Abandoning fire watch early

Leaving the fire watch position before the minimum 30-minute post-work period has elapsed is a critical failure. Smouldering material can take 30 minutes or more to develop into open flame. The pressure to move on to the next task, or the perception that the area is clear, does not reduce the risk. The fire watch period is non-negotiable.

Not sealing floor and wall penetrations

Sparks and molten metal can travel through gaps in floors, walls, and ceilings into adjacent compartments where combustible materials may be stored. A spark dropping through a 5mm gap in a floor plate can ignite insulation, timber, or waste material on the floor below. All penetrations within the 10-metre zone must be sealed with fire-resistant material before hot works commence.

Using LPG cylinders indoors without adequate ventilation

LPG is heavier than air and pools at low level in enclosed spaces. A leak from a cylinder, regulator, or connection in an unventilated room creates an explosive atmosphere. LPG cylinders used indoors must have adequate natural or mechanical ventilation at low level. Gas detection should be considered in enclosed areas. Cylinders must never be stored below ground level.

4. Frequently Asked Questions

What is the minimum fire watch period after hot works?▾

The minimum fire watch period is 30 minutes after the last application of heat. However, 60 minutes is recommended by most insurers, the Joint Code of Practice on the Protection from Fire of Construction Sites, and CITB GC07. Some client specifications and insurer requirements mandate 60 minutes. The fire watcher must remain in the area with a fire extinguisher and be trained to raise the alarm. During the fire watch, the area must be continuously monitored for signs of smouldering, smoke, or heat.

Does grinding require a hot works permit?▾

Yes. Grinding generates sparks that can travel several metres and ignite combustible materials. Angle grinding, bench grinding, and cutting with abrasive wheels all fall within the definition of hot works. The same permit, area preparation, fire extinguisher, and fire watch requirements apply as for welding or cutting. The only exception is where grinding is carried out in a dedicated workshop with permanent fire protection measures and no combustible materials present.

What checks must be carried out in the area before starting hot works?▾

Before signing the permit, the authorised person must confirm: all combustible materials removed or covered within 10 metres; floor, wall, and ceiling penetrations sealed; fire detection systems isolated and alternative monitoring in place; area above, below, and on the other side of partitions checked; fire extinguisher present and correct type; fire watcher assigned and briefed; operative has the permit; evacuation route confirmed; and no hot works within 2 hours of shift end. The permit should include a checklist of these items.

Can a hot works permit be extended beyond its original duration?▾

This depends on the site procedure. Some systems allow a single extension signed by the authorised person, provided conditions have not changed and a fresh area inspection has been carried out. Others require a new permit for any extension. Best practice is to issue a new permit rather than extend, because the re-inspection at permit issue is the primary control. An expired permit means work must stop until a new permit is issued — no informal extensions are acceptable.

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