Hot Works Permit Guide: Fire Prevention on Construction Sites

A single spark from a grinder can burn down a building under construction. Hot works permits exist to prevent exactly that. This guide covers when you need a hot works permit, what it should contain, the fire watch process, common failures that lead to construction site fires, and why your insurance policy almost certainly requires one.

What Are Hot Works?

Hot works are any activities that produce heat, sparks, or open flame, creating a potential fire ignition source. On construction sites, the most common hot works include welding (MIG, TIG, arc, and oxy-acetylene), cutting with oxy-acetylene or plasma cutters, brazing and soldering, grinding and disc cutting, and the use of bitumen boilers or hot air guns. Any task that generates enough heat to ignite nearby combustible materials falls under the definition.

Fire is one of the most devastating risks on a construction site. A single spark from a grinding disc can ignite insulation, timber, dust, or flammable liquids and cause millions of pounds of damage within minutes. The Grenfell Tower fire, while not a construction site incident, highlighted how rapidly fire spreads through building materials. On active construction sites, the combination of combustible materials, temporary services, incomplete fire compartmentation, and sometimes inadequate fire detection makes hot works an extremely high-risk activity.

When Do You Need a Hot Works Permit?

A hot works permit to work should be issued before any of the following activities begin:

• Any welding operation (including tack welding)
• Oxy-acetylene or plasma cutting
• Brazing and soldering (including copper pipework)
• Grinding, disc cutting, or any use of abrasive wheels that produce sparks
• Bitumen boiling or application of hot applied waterproofing
• Use of heat guns above 300 degrees C
• Lead work involving a gas torch
• Any operation producing open flame or sustained heat near combustible materials

The permit system is not optional. While there is no single regulation titled "Hot Works Permits," the requirement flows from the Regulatory Reform (Fire Safety) Order 2005, the CDM 2015 Regulations, and the general duty under the Health and Safety at Work Act 1974 to provide safe systems of work. Most insurance policies also explicitly require a hot works permit system as a condition of cover. Failure to operate one can void your site insurance.

What a Hot Works Permit Should Contain

A properly structured hot works permit includes:

Identification Details

• Permit number (sequential for tracking)
• Date and time of issue
• Exact location of the hot work (building, floor, room, grid reference)
• Description of the work to be carried out
• Name of the person carrying out the hot work
• Name of the permit issuer (usually the site manager or safety officer)
• Permit duration (start time and end time -- maximum 8 hours, shorter where possible)

Pre-Work Checks

Before the permit is signed and issued, the permit issuer must confirm the following:

• All combustible materials within a 10-metre radius have been removed or covered with fire-resistant sheeting
• Floor openings, gaps, and voids within the area have been sealed to prevent sparks travelling to other areas
• Fire detection systems in the area have been isolated (with notification to the alarm monitoring company) and temporary detection arranged if needed
• Sprinkler heads in the immediate area have been protected from accidental damage (but NOT isolated unless absolutely necessary)
• A suitable fire extinguisher (minimum 9-litre water or CO2, depending on the materials present) is positioned within 3 metres of the hot work
• A fire watch person has been designated and briefed
• The nearest fire alarm call point and escape route have been identified and are clear
• Adequate ventilation is provided (particularly for confined or enclosed areas)
• Gas cylinders are secured upright, regulators and hoses are in good condition, and flashback arrestors are fitted

Fire Watch Requirements

The fire watch is the single most important control measure in hot works. A designated fire watch person must:

• Be present throughout the hot work and for a minimum of 60 minutes after the work finishes (some insurers require 2 hours)
• Have no other duties during the fire watch -- they cannot be "keeping an eye out" while doing something else
• Have access to a fire extinguisher and know how to use it
• Know how to raise the alarm and call the fire service
• Monitor adjacent areas, floors above, floors below, and voids where sparks could have travelled
• Record the fire watch period on the permit

The post-work fire watch is where most hot works fires start. Smouldering material can take 30-60 minutes to develop into visible flame. Ending the fire watch early is gambling with the entire project.

The Hot Works Permit Process Step by Step

1. Request -- the operative or their supervisor requests a hot works permit from the site manager or designated permit issuer, specifying the work, location, and duration
2. Area inspection -- the permit issuer physically visits the work area and completes the pre-work checklist. This cannot be delegated or done remotely
3. Controls implemented -- combustibles removed, fire extinguisher positioned, fire watch person designated and briefed, fire detection isolated (if required)
4. Permit issued -- both the permit issuer and the operative sign the permit. One copy stays at the work location, one copy goes to the site office
5. Work carried out -- the operative conducts the hot work within the permitted area and time. If conditions change (e.g. new combustible materials brought into the area), work stops and the permit is reassessed
6. Work complete -- the operative notifies the site office that hot work has finished. The fire watch period begins
7. Fire watch completed -- after the specified post-work fire watch period, the fire watch person signs off the permit confirming no fire has been detected
8. Permit closed -- the permit issuer (or delegate) visits the area for a final check, confirms the area is safe, and closes the permit. Fire detection systems are reinstated

Common Hot Works Failures and How to Prevent Them

Analysis of construction site fires repeatedly shows the same failures:

• No permit issued -- operatives carrying out "quick jobs" without going through the permit process. Prevention: enforce a zero-tolerance policy. Any hot work without a permit is a disciplinary matter
• Inadequate area preparation -- combustibles left within range because "it'll only take five minutes." Prevention: the permit issuer must physically inspect the area before signing
• Fire watch abandoned early -- the fire watch person leaves after 10 minutes because "it looked fine." Prevention: record fire watch start and end times on the permit and spot-check compliance
• Sparks travelling through voids -- sparks from grinding fall through floor gaps into the level below. Prevention: seal all openings, and include floors above and below in the fire watch zone
• Permits left running overnight -- a permit issued in the morning is still "active" when everyone goes home. Prevention: all permits must be closed before site closes. No overnight hot works permits unless 24-hour fire watch is arranged
• Fire extinguishers missing or wrong type -- a CO2 extinguisher near timber, or no extinguisher at all. Prevention: include extinguisher type and serial number on the permit

Alternatives to Hot Works

The best hot works control is elimination. Before issuing a permit, consider whether the work can be done differently:

• Mechanical cutting instead of oxy-acetylene cutting
• Push-fit or press-fit pipework instead of soldering
• Cold-applied waterproofing systems instead of bitumen torching
• Bolted connections instead of site welding
• Pre-fabrication in a workshop (with proper fire protection) instead of site hot works

Where hot works cannot be eliminated, they should be scheduled for the start of the day so the fire watch can be completed well before the site closes.

Digital Hot Works Permits

Paper permit systems work but have weaknesses: permits get lost, duplicated, or left unsigned. There is no real-time visibility of active permits across the site. Digital permit systems solve these issues by providing a live dashboard of all active hot works permits on site, automatic alerts when permits are due to expire, GPS-tagged permit locations, mandatory photo evidence of area preparation, digital signatures with timestamps, and automatic reminders for fire watch completion.

With FORGE Command, site managers can manage all their permit to work processes digitally, ensuring nothing falls through the cracks. When HSE arrives for an inspection, you can pull up every permit issued this month in seconds rather than searching through filing cabinets.

Insurance and Hot Works

Construction insurance policies almost universally include hot works conditions. Typical requirements include:

• A written hot works permit system in operation
• Pre-work inspections documented
• Fire watch of at least 60 minutes post-completion (some require 120 minutes)
• No hot works within 30 minutes of site closing
• Gas cylinders removed from the building at the end of each shift

Non-compliance with these conditions can void your insurance. In the event of a fire, the insurer will request your hot works permits and fire watch records. If they do not exist or are incomplete, the claim may be rejected. Given that construction site fires regularly cause losses exceeding one million pounds, this is a risk no site manager can afford to take.