Author(s): Samuel A Oyewole, Vidisha Parasram, Reepa Shroff, Johnnie Banks. Published on May 1, 2017.

Hot Work, Safe Work

Key lessons from the U.S. Chemical Safety and Hazard Investigation Board investigations of hot work incidents


Recently, hot work has been a topic of concern among the fire and inspectional communities. Hot work was blamed for, or suspected as the cause of, a series of large fires involving residential housing complexes under construction around the country, resulting in tens of millions of dollars in losses. In Boston, hot work was blamed for a 2014 residential fire that killed two firefighters. Last year, the city’s fire prevention code was amended to require all persons engaged in hot work operations to obtain a Hot Work Safety Certificate. So far, more than 13,000 workers in a variety of construction industry jobs have participated in the NFPA-designed hot work certificate program.

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Sidebar, 5 Hot Work Misconceptions:
Safety training shed light on common inaccuracies surrounding the practice.

Boston Hot Work Safety Certificate:
The Boston Hot Work Safety Certificate 1-Day Program provides in-person training.

Hot work is any work process that involves welding, soldering, brazing, cutting, grinding, drilling, burning, or melting of substances capable of creating a spark or flame of sufficient temperature to ignite flammable vapors and/or combustible material. (NFPA’s definition includes flame-producing activities, spark-producing activities, and heat production, either through conduction or radiation/convection.) Common sources of ignition during hot work include open flames; electrical, friction, or impact sparks; hot surfaces; hot bearings; welding or cutting torches; and heated gases, coils, or resistors. All hot work involves inherent fire risks and hazards, and all fire hazards should be considered and evaluated before commencing hot work operations. Special procedures and permits are required when hot work is to be performed in a confined space, tank, vessel, or pipeline.

Hot work accidents occur throughout many industries in the United States, including food processing, pulp and paper manufacturing, oil production, fuel storage, and waste treatment. Most hot work incidents occur due to the ignition of combustible materials (e.g., a roofing fire) or the ignition of structures or debris near the hot work activity. Although the hazards associated with hot work are well documented, the frequency and severity of hot work–related incidents have been overwhelming in the last two decades. In order to fully benefit from the lessons learned from these incidents, it is important that industry and safety organizations adopt more stringent health and safety standards to ensure that hot work activity is conducted safely, that workers are aware of the hazards, and that they are fully protected.

Aerial view of the Boston fire that killed two firefighters.

Consequences Hot work was blamed for a 2014 fire in Boston that killed two firefighters. The event helped spur a hot work safety training program developed by NFPA. Photograph: Getty Images

The U.S. Chemical Safety and Hazard Investigation Board (CSB) has found that hot work is one of the most common causes of worker deaths among incidents investigated by the agency. The CSB continues to see hot work incidents and has found a significant subset of occurrences—those involving piping, tanks, or containers where flammables are present—to be particularly dangerous. In addition, the CSB repeatedly observes hot work incidents involving tanks or containers at high-hazard facilities such as refineries and chemical plants that typically result in injuries and fatalities and have the potential to result in major catastrophic accidents.

Since 2001, the CSB has deployed to and investigated 14 hot work–related incidents that have resulted in 25 fatalities and 21 injuries to employees and members of the public. The CSB continues to monitor hot work incidents where continuous monitoring could have alerted workers to the changing conditions in areas where hot work activity was conducted. In an education session at the upcoming NFPA Conference & Expo, a CSB investigator will present a case study of an investigation into a 2016 hot work–related flash fire at an oil terminal in Texas.

Need for investigation

The CSB began investigating hot work hazards following a July 17, 2001, explosion at the Motiva Enterprises refinery in Delaware City, Delaware. A work crew was repairing a catwalk above a sulfuric acid storage tank farm when a spark from their hot work ignited flammable vapors in one of the tanks. Corrosion had caused holes in the roof and shell of the tank, allowing sulfuric acid to leak. The tank collapsed, and one of the contract workers was killed; eight others were injured, and a significant volume of sulfuric acid was released to the environment.

The CSB began systematically tracking hot work incidents following the July 29, 2008, accident at the Packaging Corporation of America (PCA) in Tomahawk, Wisconsin. Workers were performing welding work above an 80-foot-tall storage tank that contained highly flammable hydrogen gas, the product of bacterial decomposition of organic fiber waste—a mixture of recycled paper pulp and water—inside the tank. This was a new hazard, identified by the CSB. Hot work ignited flammable vapors, resulting in an explosion that killed three workers and injured another.

In the 10 months following the explosion at PCA, the CSB investigated five additional incidents where hot work ignited flammable gas or vapor, including an explosion at MAR Oil in La Rue, Ohio, that killed two contractors in October 2008; an explosion that killed one and injured another at EMC Used Oil in Miami, Florida, in December 2008; an explosion that killed a contract welder at ConAgra Foods in Boardman, Oregon, in February 2009; an explosion at A.V. Thomas Produce in Atwater, California, in March 2009 that severely burned two employees; and the explosion of a massive gasoline storage tank that killed three workers at a TEPPCO Partners fuel distribution facility in Garner, Arkansas, in May 2009.

In November 2011, two contractors at the E. I. DuPont De Nemours Co. located in Buffalo, New York, were performing welding atop a 10,000-gallon slurry tank when hot sparks ignited flammable vapors, causing an explosion that killed one contractor and seriously injured another. The CSB’s final report and safety video, entitled “Hot Work: Hidden Hazards,” were released at an April 19, 2012, public meeting. A primary cause of the blast was established by the CSB as the failure of the company to require that the interior of storage tanks—on which hot work was to be performed—be monitored for flammable vapor. The CSB issued a recommendation urging DuPont to require monitoring inside and around storage tanks prior to performing any hot work.

Hot work best practices

In February 2010, the CSB released “Seven Key Lessons to Prevent Worker Deaths during Hot Work in and Around Tanks,” a safety bulletin that provided summaries and findings from 11 investigations. (It also notes that 60 fatalities occurred due to hot work between 1990 and 2010.) In addition, the bulletin provided seven key lessons aimed at preventing worker deaths during hot work in and around storage tanks containing flammable materials. These include:

    Use Alternatives: Whenever possible, avoid hot work and consider alternative methods.
    Analyze the Hazards: Prior to the initiation of hot work, perform a hazard assessment that identifies the scope of the work, potential hazards, and methods of hazard control.
    Monitor the Atmosphere: Conduct effective gas monitoring in the work area using a properly calibrated combustible gas detector prior to and during hot work activities, even in areas where a flammable atmosphere is not anticipated.
    Test the Area: In work areas where flammable liquids and gases are stored or handled, drain and/or purge all equipment and piping before hot work is conducted. When welding on or in the vicinity of storage tanks and other containers, properly test and, if necessary, continuously monitor all surrounding tanks or adjacent spaces—not just the tank or container being worked on—for the presence of flammables and eliminate potential sources of flammables.
    Use Written Permits: Ensure that qualified personnel familiar with the specific site hazards review and authorize all hot work and issue permits specifically identifying the work to be conducted and the required precautions.
    Train Thoroughly: Train personnel on hot work policies/procedures, proper use and calibration of combustible gas detectors, safety equipment, and job–specific hazards and controls in a language understood by the workforce.
    Supervise Contractors: Provide safety supervision for outside contractors conducting hot work. Inform contractors about site-specific hazards, including the presence of flammable materials.

Between 2010 and 2013, the CSB reviewed 187 hot work incidents, 85 of which resulted in a fire or explosion while hot work was being conducted on or near a tank or container. These incidents resulted in 48 fatalities and 104 significant injuries. Twenty-three percent of injuries and 42 percent of fatalities involved contractor workers.

The CSB continues to see catastrophic incidents involving hot work on tanks and containers containing flammable vapors. Our past investigations into these incidents demonstrate a lack of awareness of the hazards of conducting hot work on containers that in some cases had previously been cleaned. The CSB recently deployed to two hot work incidents, one at the Sunoco Logistics LP terminal in Nederland, Texas, and the other at the PCA facility in DeRidder, Louisiana. At Sunoco, seven contractors were injured in a flash fire while conducting hot work on a pipeline on August 12, 2016. On February 8, 2017, three contractors were fatally injured in an explosion at the PCA facility while conducting hot work.


Due to the frequency and severity of hot work accidents, the CSB has designated safe hot work practices as one of the five elements of its newly developed Drivers of Critical Chemical Safety Change Program. The CSB’s Drivers of Critical Chemical Safety Change are based on recommendations resulting from CSB investigations and studies. The goal of the program is to pursue implementation of changes most likely to achieve important national-level safety improvements.

The CSB has continued to advocate for best practices and recommended improvements of consensus standards, specifications, recommended practices, technical reports, and codes to address hot work activities. NFPA standards and codes referenced by the CSB in its hot work investigations include NFPA 51B, Fire Prevention During Welding, Cutting, and Other Hot Work; NFPA 326, Safeguarding of Tanks and Containers for Entry, Cleaning, or Repair; and NFPA 70E®, Electrical Safety in the Workplace®. In addition, the CSB has continued to push for the adoption of its recommendations aimed at preventing hot work incidents by emphasizing the need for increased hot work hazard awareness among workers and the need for stronger oversight and responsibility for hot work activities.

SAMUEL A. OYEWOLE, PH.D., VIDISHA PARASRAM, MPH, REEPA SHROFF, MS, AND JOHNNIE A. BANKS, CFEI, are chemical incident investigators at the U.S. Chemical Safety and Hazard Investigation Board (CSB) in Washington, D.C. The CSB is an independent, scientific federal agency whose mission is to independently investigate significant chemical incidents and hazards and effectively advocate for implementation of the resulting recommendations to protect workers, the public, and the environment. Top Photograph: iStockPhoto

5 Hot Work Misconceptions

Safety trainings shed light on common inaccuracies surrounding the practice


Despite repeated fires started by hot work and an NFPA standard on safe hot work practices—NFPA 51B, Fire Prevention During Welding, Cutting, and Other Hot Work, which was first issued in 1962—hot work–related blasts and blazes continue to occur. According to the NFPA report “Structure Fires Started by Hot Work,” issued last September, fire departments in the United States responded to an average of 4,400 structure fires a year involving hot work from 2010 to 2014.

In March 2014, two Boston firefighters died responding to a fire that was started by hot work. As a result of that tragedy, NFPA has been working with the city and its fire department since September to deliver hot work safety training to construction workers in the Boston area. So far, over 13,000 workers have participated in the NFPA-designed program. I have led over 40 of these trainings, and in my experience, these are some of the major misconceptions surrounding hot work.

THE MISCONCEPTION: Hot work is just welding and torch cutting.

The truth: As defined by NFPA 51B, hot work is any work that involves “burning, welding, or a similar operation that is capable of initiating fires or explosions.” It’s not just work that involves flames. After all, you don’t need a flame to generate heat. Activities such as drilling, soldering, brazing, tapping, grinding, heat treating, chipping, thawing pipes, and abrasive blasting—often referred to as sand blasting—are all considered hot work.

THE MISCONCEPTION: Soldering, which is often involved in plumbing-related tasks, is not a big problem.

The truth: According to the NFPA report on hot work structure fires, soldering causes 34 percent of hot work fires started in homes. (We don’t have the data on whether the work is performed by contractors or homeowners engaged in DIY repairs.) Nevertheless, because this work must usually be performed close to combustible construction materials and insulation, it can be a significant hot work safety challenge.

THE MISCONCEPTION: The hazard goes away once the hot work operation ceases.

The truth: NFPA 51B and other hot work safety practices require someone—normally a trained fire watch—to remain at the work site for a minimum of 30 minutes after hot work has stopped to monitor the site for any smoldering conditions or reignition from hot embers or retained heat. And heat has a way of sticking around. Insurance data indicates that retained heat has contributed to reignition conditions up to four hours after the hot work was performed.

THE MISCONCEPTION: Hot work safety is the responsibility of the person in charge.

The truth: NFPA 51B requires establishing a hot work safety team consisting of three individuals: the person in charge (referred to in NFPA 51B as the permit authorizing individual, or PAI); a hot work operator; and a fire watch. The standard defines their duties as being responsible for safety on the work site and identifying any change in conditions so that hot work stops until the conditions are reevaluated. This is a particular point of emphasis in the training we are conducting for Boston. Essentially, our message on the job site for all workers is if they see something that might be an unsafe change in condition, they need to tell someone so it can be checked.

THE MISCONCEPTION: Hot work residue, including sparks, slag, spatter, and heat transfer, are usually only transmitted a limited distance.

The truth: Many types of hot work, such as welding, grinding, and torch cutting, produce sparks, slag, or spatter that can reach well beyond the immediate work area. For that reason, NFPA 51B establishes a minimum safe distance of 35 feet in all directions from the location of the hot work. In other words, combustible materials must be moved at least 35 feet away from the work to prevent contact with the hot work residue, such as sparks or slag. That distance is only a minimum, and conditions such as wind or proximity to dry grass might necessitate a greater distance. While working at an elevated location, for instance, where sparks can fall vertically, I have seen hot work residue travel distances in excess of 100 feet.

GUY COLONNA is NFPA division director of technical services.