The construction rule
In construction, OSHA's welding and cutting fire prevention section requires:[1]
- Suitable fire extinguishing equipment immediately available in the work area and ready for use
- Additional personnel assigned to guard against fire when normal precautions are not sufficient, during the work and for a sufficient period after it, so no possibility of fire remains
- Those personnel instructed on the specific fire hazards expected and on how to use the firefighting equipment provided
- The same precautions on the opposite side when the work is on walls, floors or ceilings
The construction text does not set a fixed number of minutes. It says "a sufficient period of time."
The general industry rule
The general industry standard is more detailed. Fire watchers are required where:[2]
- Other than a minor fire might develop
- Appreciable combustible material is closer than 35 feet to the work
- Combustibles are farther than 35 feet away but easily ignited by sparks
- Wall or floor openings within 35 feet expose combustibles in adjacent areas, including concealed spaces
- Combustibles sit on the opposite side of metal partitions, walls, ceilings or roofs and could ignite by conduction or radiation
It also requires the watch to continue for at least a half hour after the work, and the area to be inspected and precautions set, preferably in a written permit, before work starts.[2]
Which one your site follows
Check your hot-work permit program. It can set a longer watch or stricter triggers than either rule, and on data center work near finished or occupied space the owner's permit may add conditions of its own. The permit and the contract set what is expected of your crews.
Fire watch vs. safety observer
A fire watch is assigned to one hot-work operation and stays with it. A safety observer checks that the permit is posted, the fire watch is present and the extinguisher is at hand, and writes it down. NSC Enterprises observers do that by default; serving as the fire watch itself is a separate assignment under your permit. See high-risk work monitoring.
Sources
- [1]29 CFR 1926.352, Fire prevention (welding and cutting). (d): suitable fire extinguishing equipment immediately available in the work area. (e): when normal fire prevention precautions are not sufficient, additional personnel are assigned to guard against fire during the welding, cutting or heating and for a sufficient period after completion, and are instructed on the anticipated fire hazards and the equipment. (f): work on walls, floors and ceilings requires the same precautions on the opposite side.
- [2]29 CFR 1910.252(a)(2)(iii)-(iv), Fire watch (general industry). Fire watchers are required where other than a minor fire might develop, or where appreciable combustibles are within 35 feet, farther but easily ignited by sparks, exposed through wall or floor openings within 35 feet, or on the opposite side of metal partitions, walls, ceilings or roofs. Fire watchers have extinguishing equipment and training, and the watch continues at least a half hour after the work. The area is inspected and precautions designated, preferably in a written permit, before work is authorized.
Sources read 2026-11-02. General information, not legal advice; check the current rule and your contract.