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What is a hot work permit, and when do you need one on site?

Last checked 24-10-2026. A plain guide, not legal advice: check the official guidance below for your job.

A hot work permit is a written authority for one defined piece of hot work, naming the place, the time, the precautions and who is in charge. The law does not ask for a permit by name, but HSE guidance recommends one wherever hot work cannot be avoided.

What counts as hot work

HSE's guidance on fire safety in construction (HSG168) defines hot work as any process that generates flame, sparks or heat. It lists oxy-fuel heating, cutting and welding, grinding and cutting metal, torch-applied roofing, heat guns and soldering irons. Brazing is not named, but it makes flame and heat, so it fits the definition.

HSG168 recommends cold methods wherever reasonably practicable, such as push-fit pipework instead of soldered joints, and roof systems that avoid naked flames.

Why a permit is used: the law

The reason is fire risk, and the law on it comes from two places:

  • The Construction (Design and Management) Regulations 2015 (CDM 2015), regulation 29, requires suitable steps to prevent, so far as is reasonably practicable, injury from fire or explosion. Regulation 32 says nobody may do work with a particular fire risk unless suitably instructed.
  • In England and Wales, the Regulatory Reform (Fire Safety) Order 2005 applies to most premises that are not domestic. The responsible person must take general fire precautions and make a fire risk assessment (articles 8 and 9). On an occupied building, expect the occupier to have hot work rules too.

Neither text mentions a permit. HSG168 says that where hot work cannot be avoided you should use a formal system such as permit-to-work. That is guidance: HSE says following it is not compulsory, but doing so will normally be enough to comply. Insurers and main contractors often require a permit, so check your policy and contract.

What goes on a permit

HSG168 says a permit is for a clearly defined piece of work and a set period, not a blanket permission to do hot work anywhere on site. It should normally include:

  • The location and nature of the work.
  • The proposed time and duration, and how long the permit is valid.
  • The precautions before, during and after the work.
  • How to raise the alarm.
  • The person in direct control of the work.
  • The person authorising and closing the permit.

The precautions in HSG168 include: visiting the area first and recording what you find; clearing loose combustibles from around the work, below it and from the far side of a wall; covering what cannot be moved with non-combustible board; at least two suitable extinguishers within reach; and, if the fire alarm is isolated, a firm way of switching it back on when work stops.

Fire watch: during and after

HSG168 recommends a careful watch for fire while the work is going on, and in the area at breaks. Afterwards it recommends a continuous watch for at least an hour, then at least one more check two hours after the hot work ends. It says to finish hot work two hours before the end of the working day so those checks can happen.

These periods are HSE guidance, not law: neither CDM 2015 nor the Order sets a fire watch length. HSG168 says some materials can smoulder for a long time before they ignite, so treat the times as minimums. For high-risk buildings such as timber frame it suggests thermal imaging and a longer watch. Your risk assessment or insurer may ask for more.

Who issues and closes it

HSG168 says only people with clearly assigned authority should issue or close a permit, and they need enough information about the work to spot the hazards and precautions. For high-risk buildings it says the system should be strict and controlled by the principal contractor. On a small job, decide before the work starts who has that authority, usually the person running the site. HSE does not say who should sign; as good practice, a second person checks rather than the welder signing off their own work.

To close a permit, HSG168 says to inspect the work area, including any thermal images from the watch. A permit ends when the work at that location is finished or its time has run out. A full permit may not be needed where the risk is low, such as a designed hot work area, but an extinguisher and fire watch are still required.

Brief the crew and the fire watch on the permit before they start. Our guide on fire safety on construction sites covers the wider duties.

Sources

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