Hot Work Permit

A hot work permit is the authorisation a site issues for the work that produces the spark, the flame, or the heat that can ignite the combustible — the welding, the cutting, the grinding, the brazing, the soldering — and it is the permit-to-work control that sits between the torch and the fire. Before the permit is issued, the area is tested for the flammable atmosphere at the LEL, the combustibles are removed to the 35-foot radius or shielded with the fire blanket, the fire watch is assigned and staged with the extinguisher, and the permit specifies the location, the duration, and the precautions. The permit is the record that the controls were verified before the spark, not after.

The hazard the hot-work permit governs is the smoulder. The spark that ignites the combustible does not always start the fire at the moment of the work — the slag that rolls under the floor, the heat that conducts into the wall cavity, and the ember that smoulders for hours are the fires that kill after the crew has gone home, and the post-work fire watch the permit requires is the control that catches the smoulder before it becomes the fire. The 30-to-60-minute watch is the minimum, and the serious permit extends it past the shift, because the fire that starts in the wall in the early morning is the one the morning crew finds. The relationship to LOTO is the isolation the hot work runs alongside, and the LEL is the atmospheric test the permit starts with. See permit to work, LEL, and LOTO.