OSHA's welding and cutting standard sets the basics: relocate combustibles at least 35 feet from the work where practicable, otherwise protect them with fire-resistant covers or shields; keep suitable fire-extinguishing equipment ready; sweep combustible debris from the floor within 35 feet; and post a fire watch where more than a minor fire could develop.
Why welding starts fires
Welding spatter and cutting sparks travel farther than most people expect, roll across floors, drop through cracks and lodge in gaps where they smoulder unseen. Plasma cutting throws a stream of molten metal out of the back of the cut. OSHA's welding standard (29 CFR 1910.252) is built around that behaviour: it treats any combustible within 35 feet as within reach of sparks.
OSHA's 35-foot rule
- Relocate combustibles at least 35 feet (10.7 m) from the work where practicable.
- Where relocation is impracticable, protect combustibles with flameproofed covers or shield them with metal guards or curtains.
- Where combustible material such as paper, wood shavings or textile fibres is on the floor, sweep it clean for a 35-foot radius.
- Cover or close floor openings and cracks so sparks can't drop onto combustibles below; take the same precautions with wall cracks, open doorways and broken windows.
- Protect or shut down ducts and conveyors that could carry sparks to distant combustibles.
- Provide fire-resistant shields where work is near combustible walls, partitions, ceilings or roofs.
Garages are full of exactly what OSHA lists: cardboard, sawdust, rags, fuel cans, a car. Move what you can, cover what you can't.
Extinguishers and fire watch
OSHA requires suitable fire-extinguishing equipment kept ready for instant use: pails of water, buckets of sand, a hose or portable extinguishers, depending on what's exposed. In a home shop, a multipurpose dry-chemical extinguisher within reach of the bench is the practical minimum.
OSHA calls for a fire watch whenever more than a minor fire could develop, including when appreciable combustibles are within 35 feet, when combustibles farther away are easily ignited by sparks, when wall or floor openings within 35 feet expose combustibles in hidden spaces, or when combustibles sit on the far side of a metal wall that could be heated through. The fire watch keeps extinguishing equipment ready and watches all exposed areas, and the watch continues for a period after the work stops, because smouldering fires show up later.
Where not to weld or cut
OSHA prohibits welding and cutting in explosive atmospheres, including inside uncleaned tanks or equipment that held flammable materials, and in areas where combustible dust has accumulated. At home that means never cutting into a fuel tank, oil drum or gas cylinder that hasn't been properly cleaned and prepared, and keeping fuel cans and solvents well away.
| Before | During | After |
|---|---|---|
| Clear or cover combustibles within 35 ft | Watch where sparks land | Stay and check for smoulder |
| Sweep the floor; close floor and wall gaps | Keep the extinguisher within reach | Check behind walls you heated |
| Move fuel cans and solvents out | Keep bystanders back | Unplug the machine and close the gas |
Plasma cutting specifics
Plasma cutters push molten metal out the back of the cut with compressed air, so sparks go down and away from the torch. Cut over a metal table or a bed of sand, not a wooden bench, and check the floor under the work. The compressor and its hose should be out of the spark stream.
A worked example
You're cutting a steel plate with a plasma cutter in an attached garage. The car is 15 feet away and there's a pile of cardboard boxes by the wall. Pull the car out, move the boxes outside, sweep the floor, cut over a steel table with a sand tray, and keep an extinguisher within reach. After the last cut, stay in the garage and check under the table, along the walls and in corners before closing up.