Welding Fires

Exactly What is Welding?

Welding is an industrial process that cheaply, effectively, and permanently joins two pieces of metal. Essentially, the two pieces of metal are melted together at a seam by an intense and concentrated heat source. This heat is generated in one of two ways. Most welding is done using a powerful arc of electricity to generate heat. Welding machines use a low voltage and a very high current in order to generate the necessary heat. There are many different variations on the basic concept of arc welding, and some of them can produce temperatures of 11,000 degrees Fahrenheit or more. Sometimes a fuel gas is burned to produce the required heat. The gases, such as acetylene or natural gas, are mixed with pure oxygen and burned, resulting in a very hot flame that can be used for cutting or welding. A filler metal can be used to help join the two pieces of metal together. Welding with filler metals is a bit like using a hot glue gun. The flame or arc melts the filler-metal, and it re-hardens in the joint, providing extra strength to the weld or joining two different metals that would not otherwise hold together. In addition, shielding gases are often used while welding to keep melted metal from reacting with air or to increase the intensity of an electric arc.

Fire Hazards in Welding

Due to the high temperatures involved, welding equipment can provide an excellent ignition source for all sorts of accidental fires. There are four major sources of ignition present in any welding situation.

1. Slag-Droplets of melted metal from a welding operation are called slag. They are easily hot enough to ignite paper or other flammable materials.
2. Hot metal-When a workman cuts or welds metal, some of the intense heat from the spot being welded is conducted throughout the rest of the piece. If the metal becomes hot enough, it might ignite flammable material that touches it.
3. Sparks-A welding spark is a tiny piece of metal that is hot enough to glow. Sparks can travel as much as 35 feet and still be hotter than 2500 degrees Fahrenheit. To protect from sparks, move all combustible materials away from the area. Any flammable object that cannot be moved should be carefully covered by metal shields or fire blankets.
4. The flame or arc itself-Almost any material that comes into contact with the flame or arc will rapidly ignite. If the welding torch is dropped, or if it malfunctions, a fire could start very quickly.

Four Welding Dangers

1. Holes, Openings, or Cracks-Anywhere that a spark or drop of slag can find to hide and smolder is a danger. Tiny fires have been known to smolder unnoticed for hours before breaking out. (National Fire Protection Association Fire Protection Handbook 10-68, 1986.)
2. Flammable Materials-Anything that can burn will, if given the opportunity. A pile of sawdust, a few rags, or even flammable dust in the air will burn if they have enough heat and oxygen. Fires may ignite suddenly and violently, or smolder undetected for hours before flaring up. (National Fire Protection Association NFPA 51B Standard for Fire Prevention in Use of Cutting and Welding Processes, 1994.)
3. Vapors and Gasses-Flammable vapors or gasses can cause powerful explosions if they mix in the right proportion with air. Some sources of flammable vapors are fuel tanks and volatile liquids left by other workers. Flammable gasses might come from faulty gas lines or tanks, or even from leaks in the welding equipment itself. (American Welding Society ANSI Z49.1-1988, -Safety in Welding and Cutting.)
4. A Special Welding Hazard-Welding on tanks or pipes that have contained flammable liquids or gasses presents a unique safety challenge. Tanks or pipes should emptied and thoroughly cleaned, then tested for flammable material before welding begins. As an added safety precaution, tanks should be filled with water to within a few inches of the welding area. (American Petroleum Institute API Publication 2009 -Safe Welding and Cutting Practices in Refineries Gas Plants, and Petrochemical Plants, August 1988.

Tips on Investigating Welding Fires

It is a natural reaction to blame the welder for any fire resulting from a welding job. However, sometimes the welder is not to blame, even if he or she provided the ignition source for the fire. For instance, someone else might have introduced a flammable vapor or gas into the area, resulting in fire. Perhaps the welding equipment was defective. Keep an open mind, and investigate all possible ignition sources. It may be that the fire was started by something else, and just happened to occur near a welding operation. Here is a list of points to check out:

1. Determine the exact source of ignition. Was it welding-related, or is the welding equipment just a coincidence? Use the process of elimination to rule out all other plausible sources of ignition.
2. Determine the origin of the fire. Remember that a welding spark can travel as much as 35 feet. As with the ignition source, eliminate all other places of origin.
3. If the fire was started by welding equipment, then what was the general cause of the incident? Were the welders negligent? Did a piece of equipment malfunction? Was there an accidental or unnoticed release of flammable material in the area? Did someone else fail to completely inform the welders about the hazards of a specific job?

There is a good potential for successful subrogation in many welding-related fires. Welding is safe when it is done correctly, but it requires many careful precautions. When something goes wrong, the odds are good that someone has violated a basic welding safety rule, causing an accident. Consider the case from all possible angles before deciding anything.

Suggested Reading

1. National Fire Protection Association, NFPA 51B Standards of Fire Prevention in Use of Cutting and Welding Processes. 1994 edition.

2. John Kennedy and Patrick M. Kennedy, Fires and Explosions, Determining Cause and Origin. 1985.