Hot Works Permits for UK Trades — Fire Safety, Permits and the One-Hour Fire Watch (2026)

What Counts as Hot Work?

Hot work is any work that involves a naked flame, sparks or enough heat to ignite combustible material. It is far broader than most people assume — plenty of everyday trade tasks qualify. If you do any of the following, you are doing hot work and the fire-safety rules apply:

• Welding — MIG, TIG, arc and gas welding, including lead welding (bossing and lead burning) on roofs
• Angle grinding, disc cutting and cutting — anything that throws a stream of sparks and hot slag (grinders, chop saws, abrasive wheels)
• Soldering and brazing — plumbing copper joints with a blow torch, brazing pipework and fittings
• Blow torches and hot-air guns — stripping paint, shrinking heat-shrink, heating pipework
• Torch-on and bitumen roofing — gas torches melting felt and pour-and-roll bitumen work, one of the highest-risk hot work activities of all
• Thawing frozen pipes with a torch or other heat source
• Cutting metal with oxy-acetylene or plasma equipment

Roofers, plumbers, metalworkers, builders and multi-trades all touch hot work regularly, often without thinking of it as a special category. Recognising that you're doing hot work is the first control — because everything else follows from it.

Why Hot Work Is So Dangerous

The danger is not the flame in front of you. The danger is the heat that travels and hides. Sparks and globules of hot slag from grinding or cutting can fly several metres, bounce, roll and drop through gaps you didn't notice. They lodge in dust, in loft insulation, in timber voids, behind plasterboard, in felt, in cardboard and rubbish, in the cavity on the other side of a wall.

Once lodged, they smoulder. A smouldering ember can sit unnoticed for hours, slowly building heat in a hidden pocket of combustible material, then break into open fire long after the operative has left site. That delay is exactly why post-work monitoring is the most important control in the whole process. The fire that destroys the building is almost never the one you can see while you're working — it's the one that ignites in an empty building at six o'clock when the last person locked up at five.

The Law and Your Duties

Several pieces of UK legislation place hot work fire risk squarely on the people doing and managing the work:

• Regulatory Reform (Fire Safety) Order 2005 — the "responsible person" for premises must take general fire precautions and manage fire risk, including risk introduced by contractors doing hot work on the premises.
• Management of Health and Safety at Work Regulations 1999 — the general duty to carry out a suitable and sufficient risk assessment of your work activities, which for hot work means assessing and controlling the fire risk before you start.
• Construction (Design and Management) Regulations 2015 (CDM) — on construction projects, fire is a recognised significant risk that must be planned for and managed throughout the works.

The common thread is simple: you have a duty to assess the fire risk created by hot work and to control it. Ignoring it isn't just dangerous, it's a breach of the law — and after a serious fire, that becomes the question investigators and your insurer ask first.

Avoid Hot Work First

The single best control for a hot work fire is to not do hot work at all. The hierarchy of control starts with elimination, and on a surprising number of jobs there is now a cold alternative that does the same task without flame, spark or heat. Before you reach for the torch or grinder, ask whether you genuinely need it.

• Cut metal with mechanical shears, a nibbler, a hacksaw or a cold saw instead of an abrasive disc that throws sparks
• Use push-fit or pressed (press-fit) plumbing fittings instead of soldering or brazing joints in place
• Use a hot-air gun rather than a naked-flame blow torch where heat alone will do the job
• Do the fabrication or cutting off-site or in a designated safe area, then carry the finished part to position

Only do hot work on site when there is genuinely no reasonable alternative. Where you can move the spark-producing part of the job into a controlled bay, a workshop, or out into the open away from the building, you remove the risk rather than just managing it.

The Hot Work Permit

On higher-risk sites — most commercial projects, occupied buildings, refurbishments and anywhere with significant combustible content — hot work is managed under a permit-to-work system. A hot work permit is a formal document issued before the work starts. It is not paperwork for its own sake; it forces a structured check that the precautions are actually in place before anyone strikes a torch.

A typical hot work permit records and controls:

• The exact work to be done and the equipment being used
• The specific location, and the precautions to be taken there
• A defined time window during which the permit is valid
• Who is responsible for the work and who issued the permit
• The fire watch arrangements during and after the work
• A sign-off confirming the area has been checked and left safe at the end

The permit is usually issued by the principal contractor, site manager or the building's responsible person, and it is only signed off when the area is confirmed safe — including after the post-work fire watch. Permits are standard on commercial sites and are required by many insurers as a condition of cover. As a subcontractor, expect to operate under the site's permit system, and don't start hot work until your permit is in your hand.

Controls During Hot Work

When hot work cannot be avoided, the area has to be made safe before you start and kept safe throughout. The core controls are well established and most of them cost nothing but a few minutes of preparation:

• Clear combustible materials away from the work within a safe radius — commonly taken as around 10 metres — or where they can't be moved, protect them with fire blankets or non-combustible screens
• Remove or cover flammable liquids, gases, packaging, dust and rubbish
• Have the correct fire extinguisher(s) immediately to hand and know how to use them (water/foam and CO2 or dry powder as appropriate to the materials)
• Check voids, ducts, gaps and the other side of any wall or floor you're working on — sparks and heat travel through and behind structures
• Never carry out hot work in or near a flammable atmosphere (fuel vapours, gas, solvent fumes)
• Ensure adequate ventilation, and that only trained, competent operatives use the equipment

Checking the far side of a wall and the voids around the work is the step people skip most often, and it's the one that catches the spark before it becomes a fire.

The Fire Watch — The Most Important Hour

This is the part that matters most, and the part most often cut short. A fire watch means keeping a competent person actively watching the work area for signs of fire — not just during the hot work, but continuing for a sustained period after it finishes.

The widely accepted standard is to maintain the watch during the work and for at least one hour after it finishes. Many insurers and permit systems now require up to 60 minutes of continuous monitoring once the torch or grinder is switched off, plus a further inspection of the area — some specify a final check 60 minutes after that continuous watch ends. During the watch you check the immediate work area and, just as importantly, the adjacent spaces, voids and the other side of walls and floors, because that's where a smouldering ember will be hiding.

Do not leave site straight after finishing a hot work task. The hour after the flame goes out is precisely when most preventable hot work fires are caught — or, if no one is watching, when they take hold unnoticed. Build the fire watch into your job time so it is never the thing you skip to get away on time.

Insurance — Conditions That Can Void Your Claim

For a trade business this is where hot work bites hardest. Insurers know hot work causes catastrophic fires, so they commonly attach specific hot work conditions or warranties to liability and contract works policies. Break one of these and the insurer can refuse the claim — leaving you personally exposed to a six- or seven-figure loss.

Typical insurer hot work conditions include:

• A hot work permit must be issued and followed
• A fire watch must be kept during the work and continued for a set period (often 60 minutes) afterwards
• Suitable fire extinguishers must be available at the point of work
• Hot work must stop a set time before close of works — frequently no hot work in the last hour of the working day, so the fire watch finishes before everyone leaves
• Specific precautions for torch-on / bitumen roofing, which many insurers single out by name

These are not suggestions — they are conditions of cover. Breaching them can void a claim entirely. Read your policy wording, know exactly what your insurer requires for hot work, and make sure everyone on your team works to it. If you sub-contract torch-on roofing, check their precautions too, because their breach can become your loss.

What It Means for a Small Trade Business

You don't need a safety department to manage hot work well. You need to recognise when you're doing it and follow a handful of habits every single time:

• Recognise the moment a task becomes hot work — grinder, torch, welder, soldering iron, hot-air gun, torch-on felt
• Prefer a cold method whenever one will do the job
• Follow the site's permit system and don't start until the permit allows it
• Clear and protect combustibles, and keep the right extinguisher to hand
• Always keep the fire watch, and continue it for the full hour after finishing
• Never do hot work late in the day and then leave — stop early so the watch ends before you do

Quick Reference: Hot Work and Safer Cold Alternatives

Frequently Asked Questions

What counts as hot work?

Hot work is any task involving a naked flame, sparks or heat capable of igniting combustible material. That includes welding and lead welding, angle grinding, disc cutting and abrasive cutting, soldering and brazing, blow torches and hot-air guns, torch-on and bitumen roofing, oxy-acetylene cutting and thawing pipes with a heat source. If the task produces sparks, slag or open flame, treat it as hot work.

How long should a fire watch last after hot work?

The accepted standard is a continuous fire watch during the work and for at least one hour after it finishes. Many insurers and permit systems require up to 60 minutes of continuous monitoring once the equipment is switched off, plus a final inspection of the area afterwards. Check the work area and adjacent voids and spaces before leaving site — the hour after the flame goes out is when most preventable fires are caught.

Do I need a hot work permit?

On higher-risk sites — commercial projects, occupied buildings and most refurbishments — yes, hot work is typically managed under a permit-to-work system, and many insurers require one as a condition of cover. The permit is issued before work starts, sets out the precautions, time window and fire watch, and is signed off only when the area is confirmed safe. Even where no formal permit is in force, you still have a legal duty to assess and control the fire risk before you begin.