Property fires and explosions, personal injury/death, process interruption, business loss, and insurance costs. 

Hot Work Activities
Hot work activities include a variety of equipment and procedures that can lead to ignition sources for unplanned fires and explosions, such as welding, cutting, brazing, soldering, and grinding. These activities may also include unsuspected tool use, such as cutoff saws, power saws, drills, roofing and other heating torches, space heaters, tar pot heaters, nail and staple guns, spark-potential iron/steel hammers, and other hand tools. Welding, cutting, and brazing are in the broad description headings for related OSHA regulations under General (29CFR1910 Subpart Q) and Construction standards (29CFR1926 Subpart J). OSHA also references NFPA 51B as a compliance requirement (NFPA 51B, Standard for Fire Prevention During Welding, Cutting, and Other Hot Work [2019 edition]). 

This review sheet focuses primarily on property risks, but hot work includes personal injury risk as well. Examples of personal risk include UV and IR radiation, eye flash burns, oxygen depletion, toxic metal fumes and process gases, heat stress, burns, and confined-space entry risks. Controls often extend to other regulations, including confined-space entry procedures, ventilation and gas testing, lockout/tagout controls, personal protective equipment, process safety management, and training. 

Factors Leading to Hot Work Fires and Explosions
The three basic elements for fire are contained in hot work activities: oxygen, fuel, and ignition. A cutting torch, for example, uses a 100% oxygen gas cylinder, acetylene gas cylinder, and a spark igniter to use. Welding equipment and other tools use electricity to generate the heat to work with oxygen (or other gases) in melting the metal alloy welding rods and joining metal pieces together. Each of these produces working flame or arc, along with molten metal that can travel to surrounding areas and ignite combustibles and flammable gases. Transferred heat through tank walls or roofs may ignite gases or insulation on the opposite side of the work as auto-ignition temperatures or the gases or insulation are reached.

As an example, pneumatic truck tires have become over-pressurized due to welding heat transfer through axles and rims from connected hot work. Some have blown the tires with injury to welders. In other instances, the inside of the tire caught fire and burned until inside oxygen was depleted, or the tire burst from pressure buildup. 

Where flammable gases exist, a simple spark from an iron hammer may ignite a flash or an explosion. Grinders and cutoff saws generate steady spark streams, which can ignite flammable gases or suspended combustible dusts with a single spark. They can also pool the flying sparks that land in the same spot and create a molten metal patch that can retain and transfer heat to combustible surfaces. Overheated drill bits can lead to charred wood or hot metal slivers. (Drill bit coolants are often used for metal drilling to avoid overheating and to maintain sharp cutting edges.)

Open-flame torches used for spot heating of pipes or tar, as in plumbing or roofing, can easily ignite nearby or hidden lumber framing in buildings, which may then continue to smolder and burn long after the torch is removed. Building construction codes help prevent the ignition and spread of such fires. 

Hot Work Property Risk Controls
The following are recommended to control hot work risks:

  1. NFPA 51B Standard for Fire Prevention During Welding, Cutting, and Other Hot Work should be the beginning for establishing an effective hot work safety program. It is included in OSHA requirements. In addition, OSHA General (Subpart Q) and Construction (Subpart J) regulations address welding, cutting, and brazing risks. 
  2. Educate all personnel affected by or working with hot work applications. In addition to general principles, be sure to teach and follow task-specific procedures. 
  3. Hot work procedures should be written, taught, and applied to include the NFPA standards and OSHA requirements. Include hot work permit applications in the procedure. 
  4. Task-specific planning is important for each hot work assignment. Use standard job hazard analysis (JHA) methods to help identify controls to implement for each hot work task. Many routine hot work tasks can be completed in permanent welding shops or in designated welding zones at construction or other temporary sites. These can be isolated, screened, and ventilated to control exposures to other areas and workers. 
  5. Hot work permits, including the process of correctly using the permits, is one of the best methods to control fire and explosion risks. Every point on the permit checklist should be included as a routine, even if some don’t apply to most applications. Use a new permit each new day or when restarting interrupted hot work. Include key personnel in the permit, such as a fire safety supervisor, one or more designated and trained fire watches, and those completing the hot work. The fire watch assignments should be exclusive of other distracting work tasks and should extend 60 minutes (or longer as determined) after stopping the hot work activity (NFPA 51B – 2019 edition). In addition, we recommend that someone, such as a second shift supervisor or security guard, walk through the hot work zone four hours after the activity to monitor for smoldering or fires.
    Key points of a hot work permit include:
  • Instructions for using the permit, including permit posting
  • Fire suppression systems and/or extinguishers in order  
  • Hot work equipment inspected and in good condition
  • Removal or control of all combustibles and flammables within the zone to 35 feet distance, including all potential floors or zones above or beneath the hot work zone
  • Flagging and signs to limit access and exposure to non-essential personnel
  • Ventilation and gas testing to remove and control flammable atmospheres
  • Lockout/tagout applications to control systems/risks that may impact the work
  • Combustibles and flammables removed from opposite sides of area walls, floors and ceilings, or additional fire watches in place in those areas
  • Application of confined space permitting or other risk controls specific to the area/task
  • Permit authorizing individual, fire watch, and all worker signatures before starting
  • Fire watch signature following the 60-minute post-work period
  • Area monitor signature following the four-hour area recheck 
  1. Hot work permit/task review is recommended as a final fire safety supervisor step. The submitted permits should be checked for accuracy. Any incidents, such as combustible or flammable ignitions, should be reviewed with management and workers (as with any safety incident) to learn what can be improved. Adjustments can then be added to the overall or task-specific hot work procedures.