The Definition of Hot Work

Definition of Hot Work

Hot work is any work that involves open flames or produces sparks or heat capable of igniting flammable or combustible materials. The most common examples are welding, oxy-fuel cutting, plasma cutting, brazing, soldering, abrasive grinding and torch-applied roofing. Less obvious activities also count, such as thawing frozen pipes with a torch, using a heat gun to strip paint, or hot riveting.

Hot work is one of the leading causes of industrial and construction fires. The heat source is easy to see, but the danger often is not. Sparks and molten slag can travel 35 feet or more, drop through floor openings and cracks, roll under doors and settle in dust, insulation or packaging, where they can smolder for an hour or longer before bursting into flame. Heat can also conduct through metal walls, pipes and decks and ignite materials on the other side, in a room no one is watching. Add flammable vapors or gases in the area, and a single spark can cause an explosion.

Because of these risks, hot work is controlled through a combination of OSHA rules, the consensus standard NFPA 51B (Standard for Fire Prevention During Welding, Cutting, and Other Hot Work), insurer requirements and site permit systems.

Regulations and Standards for Hot Work

OSHA general industry

OSHA's fire prevention requirements for welding and cutting in general industry are in 29 CFR 1910.252(a). The core principle is that if the object to be worked on cannot be moved to a safe location, all movable fire hazards must be moved away from it. If neither can be moved, guards must be used to confine the heat, sparks and slag. The standard requires fire extinguishing equipment to be ready for instant use and sets out when a fire watch is required. Management must also establish areas and procedures for safe hot work and designate an individual responsible for authorizing it.

OSHA specifies places where cutting or welding is not permitted, including areas not authorized by management, sprinklered buildings where the sprinklers are impaired, explosive atmospheres or areas where they may develop, and areas near large quantities of exposed, readily ignitable materials.

OSHA construction

In construction, 29 CFR 1926.352 requires that combustible materials be moved or protected, that fire extinguishing equipment be immediately available, and that additional personnel guard against fire during and after the work when it is done near combustibles.

NFPA 51B

NFPA 51B sets out detailed responsibilities and procedures and is often stricter than OSHA. It defines roles for management, the permit authorizing individual, the hot work operator and the fire watch, and it requires a written permit for hot work outside designated areas. Many insurers and corporate standards adopt it as their baseline.

The Hot Work Permit Process

Most organizations manage hot work through a written permit, which is a specific type of permit-to-work. A typical process looks like this:

1. Ask whether hot work is necessary. Cold methods, such as mechanical cutting, bolting or crimping, eliminate the hazard and sit at the top of the hierarchy of controls.
2. Inspect the area. The permit authorizing individual checks the work area and surroundings, including floors above and below and the far side of walls and partitions.
3. Apply the 35-foot rule. Combustibles within 35 feet of the work are moved away or protected with fire-resistant covers, metal guards or welding curtains. Floors are swept clean, and openings in floors and walls within that range are covered.
4. Test the atmosphere. Where flammable gases or vapors could be present, such as in tanks, pipelines, confined spaces or near fuel storage, a calibrated gas detector is used to confirm the atmosphere is well below the lower explosive limit before and during work. See explosion hazard for why this matters.
5. Check fire protection. Sprinklers and alarms must be in service. Suitable extinguishers or charged hoses must be at the work location.
6. Assign a fire watch. Where required, a trained fire watch is assigned with no other duties.
7. Issue and post the permit. The permit is signed, posted at the work location and limited to a specific time period, often a single shift.
8. Close out. After work ends, the fire watch continues for the required time, followed by monitoring, before the permit is signed off.

Fire watch duration

OSHA's general industry rule requires a fire watch for at least 30 minutes after hot work is completed where a fire watch is required. Since its 2019 edition, NFPA 51B calls for at least one hour of fire watch after hot work, followed by fire monitoring of up to three additional hours as determined by the permit authorizing individual. Many sites have adopted the NFPA times because smoldering fires can take well over 30 minutes to appear.

Health Hazards of Hot Work

Fire is not the only risk. Hot work also creates health hazards that need their own controls:

• Welding fume: metal fume containing manganese, iron oxide and other metals. Welding stainless steel produces hexavalent chromium, which has its own OSHA standard. Local exhaust ventilation and, where needed, respiratory protection are the main controls.
• Gases: carbon monoxide, ozone and nitrogen oxides can build up, especially in confined spaces. Shielding gases such as argon and carbon dioxide can displace oxygen and act as asphyxiants.
• Ultraviolet and infrared radiation: arc welding can cause "arc eye" and skin burns, requiring filter lenses of the right shade and screens to protect nearby workers.
• Burns and electric shock: from hot metal, spatter and welding circuits, especially in wet conditions.
• Heat stress: from the work itself combined with heavy protective clothing.

Example of Hot Work

A cold storage warehouse hired a contractor to weld new brackets onto steel columns to support a conveyor upgrade. The contractor's welder checked the floor around the column, saw nothing combustible and began work without a permit, as the warehouse's procedure had not been explained to him. On the other side of the column, an insulated metal wall panel with a foam core sat about 10 feet away. Heat and sparks traveled along the bracket and into the panel joint. The welder finished and left. About 75 minutes later, smoke detectors activated and the fire department found a fire spreading inside the panel cavity, which damaged a section of the roof and forced the warehouse to discard refrigerated stock.

The warehouse's review found that contractors were not briefed on the hot work program, no permit was issued, the insulated panels had not been identified as a hazard, and there was no fire watch. The site rewrote its contractor orientation to cover hot work, required permits for all hot work outside a designated welding shop, added insulated panels to its permit checklist with a thermal camera check before sign-off, and adopted NFPA 51B fire watch and monitoring times.

Frequently Asked Questions: Hot Work

Is grinding considered hot work?

Yes. Abrasive grinding produces sparks that can ignite combustibles and flammable vapors, and NFPA 51B includes it within the scope of hot work. Many sites require a permit for grinding outside designated areas, just as for welding.

What is a designated hot work area?

A designated area is a permanent location, such as a maintenance welding shop, that has been specifically designed or approved for hot work. It is built from noncombustible materials, kept free of combustibles and has fire protection in place. Hot work in a designated area generally does not need an individual permit for each job.

Can hot work be done in a building with sprinklers turned off?

OSHA prohibits cutting and welding in sprinklered buildings while the sprinkler protection is impaired. If sprinklers must be taken out of service, hot work should be postponed, or the impairment must be managed through a formal process with the fire official and insurer before any work proceeds.

Who can issue a hot work permit?

The permit should be issued by a person designated by management who understands the hazards and the site's fire protection, often called the permit authorizing individual. That person should not be the welder doing the work. Contractors should follow the host site's permit system unless the host has formally accepted the contractor's program.