Flammable atmospheres may be produced by flammable fuels, paint, cleaning solvents, combustible dust (such as metal), naturally occurring reactions that produce methane gas, or hydrogen from boiler cleaning or battery charging. Many deaths and injuries in the shipyard have been caused from fires and explosions caused by flammable atmospheres.

In the OSHA shipyard standards, a flammable atmosphere is defined as any atmosphere that contains 10% or more of the Lower Explosive Limit (LEL), or Lower Flammable Limit (LFL) for any substance.

  • Spaces and adjacent spaces that contain or have contained flammable liquids or gases must be tested for flammable atmospheres before entry. Examples of spaces are: [29 CFR 1915.12(b)]
    • Fuel tanks
    • Pump rooms
    • Pipelines
    • Recently painted or solvent-cleaned spaces
    • Sewage tanks
    • Any adjacent spaces to the above spaces
    • Cargo tanks (For tank ships)
  • If any space contains 10 percent or more LEL, it must be labeled "Not Safe for Workers - Not Safe for Hot Work". [29 CFR 1915.12(b)]