How are hot works managed in an occupied building?

Welding, grinding, cutting and soldering in an occupied building are the activities most likely to cause a fire, and the fire usually starts after the work has finished.

Which is why hot works are permitted activities with a mandatory watch period afterwards, rather than ordinary trade tasks.

The permit

A hot works permit is issued for a specific task, in a specific location, by a named operator, within a defined time window.

It records what the work is, what the ignition risk is, what controls are in place, who is on fire watch, and when the permit expires. It is issued before the work starts and closed after the watch period ends.

Which means it is a control document rather than a form. A permit signed after the fact to satisfy paperwork has provided no control at all, and the permit regime is auditable under the quality system described in [quality assurance, ITPs and hold points](/answers/quality-assurance-itps-and-hold-points).

On a school or a government site, the permit is frequently countersigned by the facility, so the operator knows hot works are occurring in their building.

Preparing the work area

**Remove combustibles** within the required radius, horizontally and vertically. Vertically is the part that is missed, because sparks fall and travel further than people expect, and a timber floor two levels down is in the risk zone.

**Protect what cannot be removed** with fire blankets or screens.

**Seal openings,** because sparks travel through penetrations, cable trays, floor gaps and ceiling voids into spaces nobody is watching. This is the mechanism behind most hot works fires in existing buildings.

**Check the other side of the wall.** Conducted heat through a steel member or a masonry wall can ignite material on the far face, and that face is frequently in an occupied part of the building.

**Clear the roof space,** where work is near a ceiling, because dust and debris in a roof space is a fuel load. The access considerations are in [ceiling replacement and access panels](/answers/ceiling-replacement-and-access-panels).

**Extinguishers at the work point,** the right type, checked, and the operator trained in their use.

Detection isolation, and putting it back

Welding and grinding set off smoke detection, which on a school or a public building means an evacuation and a fire brigade attendance.

So the affected detection zone is isolated before the work, by the appropriate person, with the isolation recorded.

And it is reinstated the same day, verified rather than assumed. A zone left isolated overnight is a building with no detection in it, which is a far larger risk than the hot works were. That reinstatement is a hold point, and it connects to the systems work in [fire services and detection upgrades](/answers/fire-services-and-detection-upgrades).

Where isolation is not possible, the alternative is a different method: mechanical cutting rather than thermal, bolted connections rather than welded, or the work relocated off site entirely.

The fire watch

Somebody stays at the location during the work and for a defined period after it stops, usually at least an hour and longer where the risk assessment requires it.

Their job is to watch, not to assist. Which means they are not the operator and they are not doing anything else, and they have an extinguisher and a means of raising an alarm.

The watch period exists because smouldering material takes time to develop into a fire. A crew that packs up and leaves at the moment the grinder stops has removed the only control that addresses the most likely scenario.

Timing it around the occupants

On an operating site, hot works are scheduled away from the people.

After hours, in a break, or in a zone that has been decanted, which is the approach in [decanting and temporary accommodation during works](/answers/decanting-and-temporary-accommodation-during-works). On a school, never during exams or assessment periods, per [working during exams and sensitive periods](/answers/working-during-exams-and-sensitive-periods).

And the facility is told: what is happening, where, when, that detection is isolated for a period, and who to contact. That notification is part of the regime in [construction in live environments](/answers/construction-in-live-environments).

Where it most often comes up

Structural steel installation, handrail and balustrade fixing, roof sheeting work, plumbing with soldered joints, and demolition cutting.

Each of those is routine work that becomes a controlled activity the moment it happens inside an occupied building, which is why the permit system covers the trade rather than the project.