What 29 CFR 1910.252 requires (plain English)
29 CFR 1910.252 sets the general requirements for welding, cutting, and brazing in general industry: the "hot work" that produces sparks, flame, and molten slag capable of igniting combustibles far from the point of work. Hot work is a leading cause of industrial fires because sparks travel, roll into cracks, and smolder undetected for hours before flaring up. The standard's fire-prevention provisions ensure the area is cleared, the work is authorized, and a fire watch catches any ignition: during and after the job.
Before hot work begins, the individual responsible for authorizing it must inspect the area and confirm the fire-prevention precautions are in place, preferably issuing a written permit. If the object to be welded or cut cannot be moved, all movable fire hazards in the vicinity must be taken to a safe place; if they cannot be removed, guards must be used to confine the heat, sparks, and slag. Combustible materials should be relocated at least 35 feet from the work site where practicable, and where combustible debris is on the floor, the floor must be swept clean for a 35-foot radius. Suitable fire-extinguishing equipment must be maintained ready for instant use.
The fire watch is the standard's signature protection. A fire watcher is required whenever welding or cutting is performed in a location where other than a minor fire might develop, for example, where appreciable combustibles are within 35 feet, or where wall or floor openings could expose combustibles in adjacent areas. Critically, the fire watch must be maintained for at least a half hour (30 minutes) AFTER the welding or cutting operation is completed, to detect and extinguish smoldering fires, because many hot-work fires start after the crew has moved on. Hot work is prohibited in areas not authorized, in sprinklered buildings while protection is impaired, and in explosive atmospheres.