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 American Welding SocietySafety and HealthFact Sheet No. 41 September 2013 © 2013 American Welding Society 

COMBUSTIBLE DUST HAZARDS IN THE WELDING

 AND CUTTING ENVIRONMENT

 American Welding Society8669 Doral Blvd.Doral, Florida 33166E-mail: info@aws.orghttp://www.aws.org

Fact Sheet No. 41 – 09/13 

 AWS disclaims liability for any injury to persons or to property, or other damages of any naturewhatsoever, whether special, indirect, consequential or compensatory, directly or indirectlyresulting from the publication, use of, or reliance on this information. AWS also makes noguaranty or warranty as to the accuracy or completeness of any information published herein.

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INTRODUCTION

Combustible dusts are a serious workplacehazard. Airborne clouds of these dusts areeasily ignited, resulting in the rapid, violentspread of fire, or “deflagration.” If confinedinside a structure, the pressure can buildup creating an explosion. Deflagration or

explosion can cause loss of life andproperty damage. Welding and other hotwork operations initiate many workplacecombustible dust explosions. Dust trails onsurfaces can act as a fuse to serve as asource of ignition in other areas. Therefore,welders should understand the factors thatcontribute to combustible dust hazards.

Industries that process or generatecombustible dusts include: metallurgical,textile, mining, plastics, rubber,pharmaceutical, lumber, food processingand agriculture, and a wide range ofmanufacturing processes. Duringprocessing of combustible solids andpowdered materials, dusts can becomeairborne when conveyed, dumped, mixedand transferred. These dusts may alsocollect on surfaces and present a potentialhazard if released into the air. Processcontrols should be used to collect thesedusts to prevent them from escaping intothe work environment. Dust controlequipment must be designed to avoidcreating dust explosion or deflagration

hazards. Housekeeping practices must besufficient to prevent fugitive dustaccumulation on surfaces.

NATURE OF THE HAZARD—

COMBUSTIBLE DUSTS

Not all dust is combustible. In fact,limestone dust is used in coal mines toreduce explosion hazards. However,materials which can burn or corrode incontact with oxygen can form combustibledusts. These “reactive” materials include:metals, plastics, coal and othercarbonaceous materials, grains, wood andpaper, and many organic compounds suchas additives, solid food products andpharmaceuticals. Dusts vary in theirpotential for combustion and in how violenttheir airborne dust deflagrations may be.

For a dust deflagration to happen, it takesa big enough and dense enough cloud ofthe dust to become airborne at one timeand then contact an energy source strongenough to cause ignition. For some dusts itmay take only a static spark to ignite adense cloud, while others might require anopen flame or contact with a hot surface.Understanding how dense is a dust cloudand what kinds of energy sources areneeded to make an ignition hazard canonly be learned though specialized labtesting.

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 American Welding Society8669 Doral Blvd.Doral, Florida 33166E-mail: info@aws.orghttp://www.aws.org

Fact Sheet No. 41 – 09/13 

 AWS disclaims liability for any injury to persons or to property, or other damages of any naturewhatsoever, whether special, indirect, consequential or compensatory, directly or indirectlyresulting from the publication, use of, or reliance on this information. AWS also makes noguaranty or warranty as to the accuracy or completeness of any information published herein.

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 A small explosion or other shock will stir upsettled dust into the air. This makes a bigcloud, which is often ignited by the heat ofthe first explosion.

It is also important to understand that finer

dust particles become airborne more easily- and also ignite more easily.

HOW TO AVOID THE HAZARD— WHAT

TO LOOK FOR

If dusts or powders are processed orhandled in a workplace, or if dusts arevisible in the air or on surfaces, find outwhat is in the dust. Ask for Safety DataSheets (SDSs), and look them over forflammability and combustibility data. Findout if the dust is reactive or combustible.Combustible dusts should not be allowedto collect on surfaces to depths > 1/32”.Compressed air or steam should never beused to clean such dust deposits onsurfaces. Proper housekeeping requiresspecial tools like explosion proof vacuums.

Dusts contained inside processingequipment and/or ventilation systems candeposit in ducts, and become concentratedin collection devices like bag houses.Equipment used to store, collect or handlecombustible dusts requires special designfeatures to reduce the risk of deflagration.

PRECAUTIONS:

  Always understand the materialsthat may be present in theenvironment, and check when youare not sure.

  Never use compressed air forcleaning powdered materials anddusts.

  Never weld or do other hot workwhere combustible dusts arepresent on surfaces or where they

might become airborne. Checkadjacent and concealed spaces fordust. Consult with your supervisoror safety professional if you areunsure about the risks or safetyrequirements.

  Never work on equipment thathandles or collects combustibledusts unless you are authorized todo so and have the required

training.

  Always be extra careful aboutelectrical safety, including staticcharge buildup.

  Always follow all safety precautions,hot work procedures and othersteps designed to prevent dustexplosions.

SUMMARY

It is important to understand the materialspresent in the work environment and if anyof their dusts might be flammable orcombustible, or have other hazards. Thedusts or powdered forms of certain types ofsolid materials can be ignited by asufficient energy source if enough of it getsairborne at one time. This makes it doublyimportant for those who conduct welding

and its allied processes to know if thishazard is present and to take theappropriate steps to prevent potentiallydevastating dust explosions.

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 American Welding Society8669 Doral Blvd.Doral, Florida 33166E-mail: info@aws.orghttp://www.aws.org

Fact Sheet No. 41 – 09/13 

 AWS disclaims liability for any injury to persons or to property, or other damages of any naturewhatsoever, whether special, indirect, consequential or compensatory, directly or indirectlyresulting from the publication, use of, or reliance on this information. AWS also makes noguaranty or warranty as to the accuracy or completeness of any information published herein.

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INFORMATION SOURCES

Chilworth Technology, Inc., “Testing to Assess Explosion Characteristics of DustClouds”; Vahid Ebadat, NFPA Symposiumon Dust Explosion Hazard Recognition andControl, Balimore, May 13-14, 2009.

Chilworth Technology, Inc., Presentation:“Dust Explosion Prevention andProtection”; Dehong Kong; Princeton, NJ.May 13, 2008.

CEP Magazine, Suzannne Shelly,Contributing Editor, “Update PreventingDust Explosions”; March 2008.Powder and Bulk Engineering,Presentation: “Dust Collection: MinimizingDust Generation in Solids HandlingEquipment”; Gary Q. Johnson; November5, 2008.

National Fire Protection Association(NFPA). Standard for the Prevention ofFire and Dust Explosions from theManufacturing, processing, and Handlingof Combustible Particulate Solids (NFPA654), available from National FireProtection Association, 1 BatterymarchPark, P.O. Box 9101, Quincy, MA 02269– 9101, telephone: 800–344–3555, website:www.nfpa.org.

Occupational Safety and Health Administration (OSHA). Combustible Dust.Website: www.osha.gov.

 American Welding Society (AWS). Safetyand Health Fact Sheets, published by the

 American Welding Society, 8669 DoralBlvd., Doral, FL 33166; telephone800-443-9353; website: www.aws.org.