When, why, and how fires and explosions occur
June 27, 2002
This article provides some statistical analysis, causes for, and tips to consider regarding welding and cutting fire and explosions. It includes a sidebar about governing codes and questions to ask regarding fires and explosions when welding or cutting is suspected in an incident.
Last June a spark from a welding torch started a 15-acre fire in Lake Piru, Calif. Welders working inside the Chicago Theater in September called the fire department after a welding torch ignited debris between the walls. In November welding sparks ignited rags on a workbench near an employee who was welding, damaging a Chicago-area industrial building.
These are just a few true stories that demonstrate what can happen when safety precautions aren't taken while welding or cutting.
Many times we focus on the proactive approach, learning how to weld safely during classroom or on-the-job training. Unfortunately, some lessons aren't learned until a welder makes a mistake.
Fires and explosions can be caused by any number of things, including flammable liquid inside a closed chamber; a new flange being welded on a pipeline; or flammable debris, such as wood or clothing.
"Most of the time the welding itself doesn't cause the fire," said Lynn Mead, who has been an applications consultant for 18 years at Praxair Inc., Danbury, Conn. Praxair supplies atmospheric, process, and specialty gases; high-performance coatings; and related services and technologies. He helps fabricators with their applications, advises them how to do jobs, and determines root causes in fire investigations.
Mead said he looks for three things when he investigates a fire or explosion: ignition, a combustible, and an oxidizer. These help lead him to discover the cause.
"It usually comes down to operator error—someone didn't purge out a pipeline, for instance," he said.
And that operator error can be as simple as taking the wrong action when a fire first breaks out.
"Even the smallest little variable can make a big difference in the outcome of a case," said Chris Bloom, CJB Fire Consultant, Grants Pass, Ore., a fire consultant and member of the National Fire Protection Agency (NFPA, www.nfpa.org).
"If a guy turns around and sees a small puff of smoke, runs over, and grabs a fire extinguisher immediately, he may be able to put out the fire. But the fire may be too big for him to contain. It's always recommended that you call 911 first because property can be replaced, human beings cannot."
In Mead's 25 years with Praxair, he's seen only seven fires or explosions. He said he's seen other safety-related accidents, such as suffocation, more often than he has seen fires and explosions.
In the cases he has seen, however, he's noticed that some of the accidents happened because of a welder's lack of knowledge."Steel can burn in the right situation, and some people don't know that," he said. "It's not always the person's fault."
National estimates based on the National Fire Incident Reporting System (NFIRS) and NFPA survey of torch fires in the U.S. rank residential fires as the highest number of incidents among cutting, welding, and other torch structure fires by occupancy, per year, from 1994 to 1998, with an average of 4,640 fires per year.
"Generally speaking from my observations, most issues have more to do with the mom-and-pop shops, such as the sole proprietorship or the single shop where someone works out of his garage. They do cutting, they do welding and body work, the whole deal," Bloom said.
Many fires start in attics, ceiling or roof assemblies, and concealed spaces, according to the study. An average of 580 fires originated in such areas per year from 1994 to 1998. Bloom attributes many of these to activities such as pipe sweating and torch-applied roofing.
"As with anything with welding or cutting, you're dealing with a component that is generating a lot of heat, whether it be direct heat from a flame or direct heat from an arc," he said. "In confined areas such as attics, ceilings, roofs, or concealed spaces, it is extremely important to make sure that you don't have any flame penetration or sparks or arcs that can sit back and smolder up against a combustible material.
"And if it's in a concealed space or in an attic, it's very hard to get up and around to check the entire area to see if you have slag running into that area or if you have direct flame impingement from the cutting torch," Bloom said.
Bloom emphasized two points about these findings. First, fires are categorized by the fire departments on the scene. The categories in the study are general. Second, it's good to read up on causes of fires, but statistics only refer to fires allegedly caused by welding. Just because welding or cutting was performed and is alleged to have started a fire doesn't mean it definitely did. Other unrelated factors may be involved and may have played a substantial role in the fire loss.
"It's important to remember with these incidents how many welders we have out there and what type of work they are doing. You'll find that the majority of them are extremely safe, and it's just a very small percentage of people who are—for lack of a better term—not totally careful about how they do their work," he said.
Burning Debris. The setting: a cold-storage warehouse for fruit in a rural setting. The scene: A welder is working on 25-foot-tall scaffolding, installing new refrigerant lines for a compressor. While he's torch welding, slag drops below him and starts two small fires, one of which is on the scaffolding. He immediately sees this fire—he feels the heat at his feet—and immediately puts it out. However, he doesn't check the combustibles in the area—a 2- by 4- by 3-ft. pile of debris below the scaffold.
The warehouse's owners sweep up the debris into a pile, which includes leaves and broken-off pieces of insulation. No fire blankets were present to protect these nearby combustibles. When the welder looks down, he sees a small fire in that pile. But by the time he gets down from the scaffold, the fire has consumed a significant portion of the pile, a fire beyond the capabilities of his fire extinguisher.
The fire spreads to an adjacent building—which is encased in polyurethane foam—and nearly engulfs it in flames. Fortunately, no one is injured.
The welder in this case is not certified, which is part of the problem.
"The fire could have been significantly hindered or prevented if there had been proper safety procedures in place, such as a fire blanket to protect the debris below and its movement; if proper welding procedures had been used, such as not letting the slag drop down in that area; and if proper safety equipment had been used," Bloom said.
Body Shop Blaze. The setting: a body shop. The scene: a car shop mechanic who welds and cuts on the side is working on a vehicle body.
The welder burns a hole through the car body while trying to weld structural pieces into place because he has held the electrode on it too long, putting slag inside the passenger compartment. When he pulls away, checking to see what he has done, the electrode comes off and hits the adjacent wall. When he sees the electrode hit the wall, he runs over to it because he notices a small fire has started. At that point, however, he doesn't see the small fire burning inside the vehicle, and the vehicle ends up fully involved in flames. In this case, as well, no injuries occur.
Sometimes even the best welders can have an accident, one in which someone doesn't walk away.
Flash Fire. The setting: simultaneous painting and welding in a three-story warehouse under renovation. The scene: A welder works on a metal plate that separates the second and third floors. Painters are working on the first and second floors, so the welder has two fire watchers, one on the third and one on the second floor.
So the welder continues his work. Although he's doing everything correctly, welding slag drops from where he's working, and it's coming down at a temperature far exceeding the ignition temperature of any combustible. Slag falls down to the second floor and ignites, resulting in a flash fire that ignites the rest of the contents in the building. One of the painters dies because the fire flashes and he isn't able to get out in time.
The painters are using volatile materials for paint thinners, according to fire cause and origin consultant Joseph Bloom, Bloom Fire Investigation, Grants Pass, Ore.
"Everybody smelled the odors, and the welder was very, very specific— he said, 'I smell something bad; is this stuff OK?' And on two or three occasions, he was told, 'Yeah, this stuff is fine, don't worry about it, there are no problems,'" Joseph Bloom said.
"The only thing I can think of that might have prevented this is if somebody had provided the welder with an MSDS [material safety data sheet] on what the material was. The painters are very good painters, the welder's a very good welder, but it's just something that somebody overlooked," Joseph Bloom said.
"Coming on two different days might have helped, but people try to get jobs done as quickly as possible—that's just human nature. That's why we put up pads, why we hire people as fire watchers, and why we have extinguishers around. But once in awhile you have what's called an accident. This was an unfortunate chain of events."
From their experiences, Joseph and Chris Bloom offer some tips that address welder safety in the case of fires and explosions.
Associate Editor Stephanie Vaughan can be reached at email@example.com.
By Chris Bloom
Welding and cutting sparks are blamed as the cause of many fires each year. In most cases in which welding is determined to be the cause, national standards and rules governing such operations have been violated.
If welding is suspected of causing a fire, adjusters should ask questions about the welding operation itself. These questions, when asked during their initial fact-gathering, can help determine if the welding operation or something else was responsible for the fire.Questions to ask include the following:
Recommended welding and cutting practices are outlined in references such as the "National Fire Code NFPA-51B, ANSI Z49.1," the "National Fire and Protection Agency (NFPA) Handbook," and other fire and trade publications.
Sparks and molten metal slag produced during cutting and welding operations can reach temperatures as high as 5,000 degrees F. Sparks and slag can travel for long distances, especially those produced by oxyacetylene cutting. Because of this, a minimum clear distance of 35 feet is required between welding operations and combustible material. If this requirement cannot be met, the combustible materials must be covered or shielded with metal or fire-resistant guards to prevent ignition.
A welder should maintain a fire watch for at least 30 minutes after welding or cutting ends. This time period allows the welder to detect smoke or fire caused by hot metal fragments entering cracks or concealed spaces.
Proper precautions must be taken to minimize the chance of a fire spreading. First, an appropriate fire extinguisher should be available for the type of material which might be involved. The extinguisher must be properly charged, functioning correctly, and located in the vicinity of welding operations.
These are not the only considerations to examine. Noncompliance with national standards covering cutting and welding operations accounts for about 6 percent of industrial fires, 8 percent of commercial fires, and numerous residential fires each year.
Even if it is determined that noncompliance is the cause of a fire, the fire scene still should be examined by a cause and origin investigator to rule out other possible causes or confirm other factors which may have contributed to the amount of fire damage.