Permits to Work · Mandatory · Construction
Permit to Work — Hot Works
The Hot Works Permit authorises welding, cutting, grinding, and any activity that generates sparks or open flames on a construction site. It mandates combustible material clearance, fire extinguisher provision, and a fire watch for a minimum period after works cease. The permit is time-limited and must be reissued for each shift or change of location.
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.
| Hot work definition | Any process producing open flames, sparks, or significant heat — welding, flame cutting, grinding, brazing, soldering, torch-applied roofing and waterproofing |
| 15-metre rule | All combustible materials must be removed or protected within a minimum of 15 metres of the hot works location; reduced to 5 metres only where a robust fire risk assessment justifies it |
| Fire watch duration | 30 minutes minimum post-work; 60 minutes recommended; 2 hours or more where highly combustible materials (timber, insulation, bituminous products) are present |
| Maximum duration | One day or one shift — the permit must be closed and re-issued for each new shift |
| FPA passport | The Fire Protection Association hot works passport scheme provides a recognised standard of competence for operatives and fire watchers |
1. Why Hot Works Require a Formal Permit
Hot works are one of the leading causes of catastrophic fire on construction sites in the United Kingdom. The permit to work for hot works exists because the fire risk associated with these processes cannot be managed through standard workplace controls alone. A formal permit system ensures that the work area has been inspected, combustible materials have been removed or protected, fire detection and firefighting equipment is in place, a dedicated fire watcher has been appointed, and the post-work fire watch period has been defined before the first spark is generated.
The legal framework for hot works permits derives from the Management of Health and Safety at Work Regulations 1999, the Regulatory Reform (Fire Safety) Order 2005, and HSG168 (Fire Safety in Construction). The hot works permit is the practical mechanism through which the duty to implement a safe system of work is discharged for these activities. An insurer will typically require evidence that a hot works permit system is in operation as a condition of fire insurance cover.
The hot works permit is a specific type of permit to work. It incorporates all the elements of the generic PTW lifecycle — request, authorise, issue, monitor, handback — but adds fire-specific checks and controls that are unique to hot works, most importantly the pre-work area inspection, the fire watch during and after work, and the formal close-out that confirms the fire watch has been completed.
Smouldering fires can ignite hours after hot works are complete
Sparks from cutting and grinding travel up to 15 metres and can pass through gaps in floors, walls, and service penetrations. They lodge in insulation, timber framing, and concealed voids where they smoulder undetected for hours before producing open flame. The majority of construction site fires caused by hot works occur after the workforce has left site for the day. This is precisely why the post-work fire watch is the most critical element of the hot works permit — and why it must never be cut short.
2. Hot Works Permit Required Checks
The hot works permit must contain the following fields, each of which must be completed and signed before the work is authorised. These checks form the minimum standard — individual sites may add further requirements based on their specific risk profile.
| Field | Required content |
|---|---|
| Work description | Specific description of the hot works task (e.g. welding steel connections at Level 2, grinding bolts on steelwork at Grid B3), the type of hot process, and the equipment to be used |
| Area preparation | Confirmation that all combustible materials within the specified clearance zone have been removed or covered with fire-resistant blankets; floors swept clean of dust and debris; gaps in floors, walls, and ceilings sealed or covered |
| Services check | Confirmation that gas pipework, fuel lines, electrical cables, and other services in the work area have been identified and either isolated, relocated, or protected from sparks and heat |
| Gaps, voids, and penetrations | Confirmation that all openings through which sparks could travel to adjacent areas — including floor penetrations, service holes, ceiling voids, and wall cavities — have been sealed or covered with non-combustible material |
| Fire detection | Status of fire detection and alarm systems in the work area: confirmed active, or temporarily isolated with the knowledge of the fire alarm management system and a compensating fire watch in place |
| Firefighting equipment | Minimum of one appropriate fire extinguisher immediately available at the point of work; type appropriate to the materials present (water for general combustibles, CO2 or dry powder for electrical or flammable liquid risks) |
| Fire watch person | Named individual appointed as the dedicated fire watcher; must hold a current FPA hot works passport or equivalent competence; must not carry out any other duties during the fire watch; must have a clear view of the work area and surrounding zones |
| Post-work fire watch | Defined duration of the post-work fire watch based on the materials present: minimum 30 minutes, 60 minutes recommended, 2 hours or more where timber, insulation, or bituminous products are within the clearance zone |
| No hot work within final 2 hours | Confirmation that no hot works will be carried out within the final 2 hours before the site is left unattended (e.g. overnight or over a weekend) — unless an extended fire watch covering the full post-closure period is in place |
| Issue, acceptance, and close-out | Signatures of the issuer (confirming preconditions are in place), the permit holder (accepting responsibility for compliance during the work), and the close-out signature (confirming the fire watch is complete and the area is safe) |
3. Common Mistakes
Fire watcher leaves before the post-work period is complete
The fire watcher must remain in position for the full duration of the post-work fire watch. Leaving early — even by 10 minutes — removes the primary detection control during the period when smouldering fires are most likely to develop into open flame. The fire watch period is not negotiable and must not be shortened to accommodate shift patterns or site closure times.
Hot works carried out within the final 2 hours before site is left unattended
If hot works are completed at 16:00 and the site closes at 17:00, there is only one hour of post-work fire watch available. This is insufficient. Hot works must be timed so that the full post-work fire watch period can be completed before the site is left unattended. Planning the work schedule around this constraint is essential.
Combustibles not removed from concealed areas
Removing visible combustibles from the work area is not enough. Sparks travel through service penetrations, gaps in floors, and openings in walls. Combustible materials on the far side of a partition, on the floor below, or in a ceiling void above the work are just as vulnerable. The area inspection must cover all spaces where sparks or conducted heat could reach.
Angle grinding treated as a low-risk activity
Angle grinding produces a high volume of sparks that can travel several metres. It falls squarely within the definition of hot works and requires the same permit, fire watch, and area preparation as welding or flame cutting. Treating grinding as routine work that does not require a hot works permit is a common and dangerous compliance failure.
Fire detection isolated without compensating measures
Fire detection systems in the work area are often isolated during hot works to prevent nuisance alarms. This is acceptable only if the isolation is formally recorded, the fire alarm management system is notified, and a compensating fire watch is in place for the full period of isolation. Isolating detection without these measures removes both the automated and manual detection controls simultaneously.
5. Frequently Asked Questions
Does the fire watcher need a specific qualification?▾
There is no single legally mandated qualification, but the fire watcher must be competent. The Fire Protection Association (FPA) hot works passport is the most widely recognised standard in the UK construction industry. Many principal contractors and insurers require fire watchers to hold this passport as a condition of working on site. At a minimum, the fire watcher must be trained in the use of fire extinguishers, know how to raise the alarm, and understand their role in the post-work inspection of the work area and surrounding spaces.
Can the operative carrying out the hot works also be the fire watcher?▾
No. The fire watcher must be a separate, dedicated person whose sole task during the hot works and the post-work period is to watch for signs of fire. An operative who is welding, cutting, or grinding cannot simultaneously maintain the level of vigilance required of a fire watcher. The roles must always be assigned to different individuals.
What clearance distance is required for combustible materials?▾
HSG168 recommends that all combustible materials are removed from the work area. The specific clearance distance depends on the nature of the hot work process and the type of combustibles present. As a general standard, a minimum clearance of 5 metres is commonly applied, extending to 15 metres for processes that produce high volumes of sparks (e.g. angle grinding, flame cutting). Where combustibles cannot be removed, they must be covered with fire-resistant blankets or sheeting. The clearance distance must be determined by the fire risk assessment and stated on the permit.
Is a hot works permit required inside a designated workshop?▾
A designated hot works area or workshop that has been specifically designed and equipped for hot works — with non-combustible surfaces, fixed ventilation, permanent fire detection, and no combustible materials — may not require a permit for each individual task, provided a standing risk assessment is in place and the workshop conditions are maintained. However, any hot works carried out outside a designated safe area require a permit. The boundary between the designated area and the rest of the site must be clearly defined and communicated.
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