What 29 CFR 1926.352 requires (plain English)
29 CFR 1926.352 sets the fire-prevention rules for welding, cutting, and heating operations in construction (part of Subpart J, Welding and Cutting). Hot work generates sparks, slag, and heat that can ignite combustible materials nearby or at a distance, so the standard requires precautions before and during the work.
The first requirement is to control the fuel: when practical, the objects to be welded, cut, or heated are moved to a designated safe location; if they cannot be readily moved, all movable fire hazards in the vicinity are taken to a safe place, or otherwise protected (for example, with fire-resistant shields). Suitable fire extinguishing equipment must be immediately available and maintained in a state of readiness.
The standard also requires a fire watch where welding or cutting is done in a location where a serious fire might develop, or where more than a minor fire could occur, with the fire watcher equipped and remaining after the work. Additional precautions apply for hot work near combustible walls, floors, and partitions and for guarding ducts and conveyors that could carry sparks to distant combustibles. Together these requirements pair naturally with a hot-work permit program, which many construction sites use to enforce them.