Combustible Dust Hazards in the Welding and Cutting Environment

It is important to understand that combustible dusts create a serious workplace hazard. Airborne clouds of combustible dusts are easily ignited and can result in a rapid, violent spread of fire or deflagration.
When confined inside of a structure, pressure build-up can easily initiate an explosion. Deflagration or explosion can cause severe injuries, death, and property damage.
Welding, cutting, and other hot work processes are the cause of many workplace dust explosions. Combustible dust trails on surfaces can act as a fuse to serve as a source of ignition in other areas.

Industries that process or generate combustible dusts include:

  • metallurgical
  • textile
  • mining
  • plastics
  • rubber
  • pharmaceutical
  • lumber
  • food processing
  • agriculture
  • and a wide range of manufacturing processes

  • Dusts can become airborne when conveyed, dumped, mixed, and transferred during the processing of combustible solids and powdered materials.
    These dusts may also collect on surfaces and present a potential hazard if released into the air.
    To prevent combustible dust from escaping into the work environment, process controlls should be used for collection.
    Dust control equipment must be designed to prevent dust explosion or deflagration hazards. Sufficient housekeeping practices must be in place to avert fugitive dust from accumulating on surfaces.

    Nature of the Hazard - Combustible Dusts

    Not all dust is combustible. In fact, limestone dust is used in coal mines to reduce explosion hazards. However, materials which can burn or corrode in contact with oxygen can form combustible dusts. These reactive materials include:

  • metals
  • plastics
  • coal
  • carbonaceous materials
    • grains
    • wood
    • paper
  • organic compounds such as
    • additives
    • solid food products
    • pharmaceuticals

  • Dusts vary in their potential for combustion and in how violent their airborne dust deflagrations may be.

    For a dust deflagration to occur, a large and dense cloud of dust needs to become airborne at one time and make contact with an energy source that is strong enough to cause ignition.
    For certain dusts, a static spark is enough to ignite a dense cloud vs. others that may require an open flame or contact with a hot surface.
    To understand how dense a dust cloud is and what type of energy sources are required to create an ignition hazard can only be learned through specialized lab testing.
    A small explosion or shock can stir up settled dust into the air creating a big cloud which is often ignited by the heat of the first explosion. It's important to note that finer dust particles become airborne and ignite more easily.

    How to Avoid Combustible Dust Hazards

    If dusts or powders are processed or handled in a workplace or if dusts are visible in the air or on surfaces, it's important to know or find out what the dust is made up of. Request Safety Data Sheets (SDSs), and look them over for flammability and combustibility data.
    Find out if the dust is reactive or combustible. Combustible dusts should not be allowed to collect on surfaces to depths >1/32”. Compressed air should never be used to clean combustible dust deposits on surfaces. Proper cleanup requires unique tools such as explosion-proof vacuums.
    Dusts that are contained inside of processing equipment and/or ventilation systems can deposit into ducts and become concentrated in collection devices like bag houses.
    Equipment that is used to store, collect or handle combustible dusts requires special design features to reduce the risk of deflagration.

    Combustible Dust Precautions

  • Understand the materials that may be present in your working environment and find out what they are if you are not sure.
  • Never use compressed air for cleaning powdered materials and dusts.
  • Welding or other hot work processes should never take place where combustible dusts are present on surfaces or where they might become airborne. Check adjacent and concealed spaces for dust. Consult a supervisor or safety professional if you are unsure about the risks or safety requirements.
  • Never work on equipment that handles or collects combustible dusts unless you are authorized to do so and have had the required training.
  • Always be extra careful about electrical safety, including static charge buildup
  • Follow all safety precautions, hot work procedures, and any other steps designed to prevent dust explosions.

  • Resource: AWS Health and Fact Sheet No. 41 - Combustible Dust Hazards in the Welding and Cutting Environment