Hot Work Safety

Hot work means any job that makes a flame, sparks or enough heat to start a fire. Welding, torch cutting, brazing, soldering, grinding, thawing pipe and using a heat gun on roofing all count. The danger is that sparks and hot slag travel, land out of sight, and smolder. Hot work fires often show up after the crew has packed up and left. The way to prevent them is simple: move the fuel, get a permit, and post someone to watch.

What You Will Be Able to Do

• Say when a hot work permit is needed and what it should check.
• Prepare a work area, including openings, walls and floors.
• Carry out the duties of a fire watch.
• Explain why containers and enclosed spaces need extra care.

Why Hot Work Starts Fires

Fire needs fuel, heat and oxygen. Hot work brings the heat. Sparks from cutting and grinding can fly 35 feet or more across a floor and much farther when they drop from a height. They can pass through cracks, gaps around pipes, open ducts and floor openings. Slag can sit inside a wall or in dust on a ledge, smoldering for a long time before it breaks into flame.

OSHA covers this in 29 CFR 1910.252 for general industry and 1926.352 for construction. NFPA 51B, the national fire prevention standard for hot work, adds detail, and insurers and local fire codes often require it. Your site's rules may be tighter than either one.

First, Ask Whether You Need to Do It Hot

Before you plan a permit, ask if there is another way. A pipe can be cut with a mechanical cutter, and a joint can sometimes be bolted or crimped instead of welded. If the part can be moved to a welding shop or a safe outdoor area, that is usually the best answer.

Where Hot Work Is Not Allowed

Do not do hot work:

• In an area the site has not authorized for it.
• In buildings where the sprinklers are impaired, unless your site has a plan for it.
• Where flammable vapors, gases or dust could be present.
• Near large amounts of exposed, easily ignited material.
• On a tank, drum or pipe that may have held something flammable and has not been cleaned and tested.

The Hot Work Permit

A permit is a written check that the area is ready, signed by someone with the authority to approve it. OSHA requires the employer's authorized person to inspect the area and approve the work, preferably in writing, and many sites require a written permit for all hot work outside a designated welding shop. In a welding shop built for it, a permit is usually not needed each time.

A permit typically confirms:

1. The location, the work and the time limit.
2. Sprinklers and alarms are in service.
3. Fire extinguishers are ready, and the right type is on hand.
4. Combustibles are moved or covered.
5. Floors are swept, and gaps are sealed or covered.
6. The atmosphere has been tested if vapors could be present.
7. A trained fire watch is assigned.

Permits are usually good for one shift or one job. If the conditions or location change, get a new one.

Prepare the Area

1. Clear 35 feet. Move all combustibles at least 35 feet from the work in every direction.
2. Cover what cannot be moved. Use welding blankets or curtains rated for the job. A plain tarp is not rated.
3. Sweep the floor. Remove dust, lint, sawdust and oily rags. Wet down wood floors where appropriate, and take care with electrical hazards.
4. Close the gaps. Cover floor openings, wall cracks, ducts and pipe chases within 35 feet.
5. Check the other side. Heat passes through metal walls, pipes and beams and can ignite material you cannot see. Inspect the far side of any wall, ceiling or floor you are working on, and post a second watch if needed.
6. Shut down conveyors or ducts that could carry sparks somewhere else.
7. Test the air with a gas meter where flammable vapors might collect. Stop if the reading reaches 10% of the lower explosive limit, or a lower limit set by your site.

Warning: Never weld, cut or heat a drum, tank or pipe that has held a flammable or unknown substance until it has been cleaned, tested and made safe. A small amount of residue can vaporize and explode, even in a container that looks empty.

The Fire Watch

A fire watch is a trained person whose only job is to look for fires. OSHA requires one wherever a fire could develop beyond the minor, such as where combustibles are within 35 feet, where wall or floor openings could carry sparks, or where a metal partition could carry heat to the other side.

The fire watch must:

• Be familiar with the alarm and how to call for help.
• Have an extinguisher ready, and be trained to use it.
• Watch the whole area, including below the work and on the far side of walls.
• Have the authority to stop the work.
• Do nothing else. Holding parts or running tools for the welder is not allowed.
• Sound the alarm first if a fire starts, then fight it only if it is within their training and the capacity of the equipment.

How Long to Stay

OSHA requires the watch to stay at least 30 minutes after the hot work ends. NFPA 51B has called for at least 60 minutes since its 2019 edition, and many insurers and sites now use 60 minutes. Some add further monitoring afterward, for up to three hours. Follow the longer of your site rule and the legal requirement.

Worked example: You finish torch cutting at 2:15 p.m. on a site that follows NFPA 51B.

1. The fire watch stays until at least 3:15 p.m., checking the area and below it.
2. At 3:15 the watch signs off and the permit is closed.
3. If the site requires 3 hours of extra monitoring, someone checks the area until 6:15 p.m.

The watch must not leave early for a break or end of shift. Plan the end of hot work so someone can stay.

Hot Work in Enclosed Spaces

Enclosed spaces raise the stakes. Fumes build up quickly, the work uses up oxygen, and sparks can ignite residues. Coatings on the steel can give off toxic gases when heated. Treat any tank, vessel or vault as a confined space until proven otherwise, ventilate it, keep monitoring the air, and keep gas cylinders outside. Never ventilate with oxygen, because enriched air makes everything burn much harder.

After the Work

1. Check for hot spots, including under blankets and on the other side of walls.
2. Turn off gas at the cylinders and shut down equipment.
3. Stay for the full watch time.
4. Close out the permit.
5. Return equipment, and report any problems.

Common Mistakes

Check Your Understanding

1. You need to cut a bracket off a steel column. There are wood pallets 20 feet away and you cannot move them. What do you do?

Have them covered with a welding blanket, or find another way to do the work. Combustibles inside 35 feet must be moved or protected, and a fire watch is needed.

2. An empty drum needs a hole cut in it for a parts washer. The label is gone. Can you use a torch?

No. Assume it held something flammable. It must be cleaned, tested and made safe first. Use a method that does not make heat if you can, or get a different drum.

3. The welder asks the fire watch to hold the end of a pipe for a moment. Should the fire watch do that?

No. The fire watch has one job. Get someone else to hold the pipe.

4. You finished at 4:30 p.m. and your site uses the 60-minute rule. Your crew leaves at 5:00 p.m. What must happen?

Someone must stay on watch until at least 5:30 p.m. If nobody can, stop hot work earlier.

Key Takeaways

• Hot work includes welding, cutting, brazing, soldering, grinding and any other flame or spark work.
• See if a cold method or a safe shop location can replace the job.
• Clear or cover combustibles for 35 feet in all directions, and close the gaps.
• Get a permit, and check the far side of walls and floors.
• A fire watch does nothing else and stays at least 30 minutes by OSHA rule, and 60 minutes under NFPA 51B.
• Never work on a container until it has been proven safe.