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Confined or Enclosed Spaces and Other Dangerous Atmospheres » Toxic Atmospheres


A high number of toxic products and cargoes are found in shipyard employment. Additionally, many shipyard operations use toxic materials or produce toxic atmospheres. Because of the confined and enclosed nature of the spaces where these products are generally located, the hazard is increased.

In addition to materials that are inherently toxic, certain maritime cargoes and shipyard operations produce toxic gases as a by-product.

One such by-product is hydrogen sulfide (H2S), a naturally occurring poisonous gas  is hard to detect and could cause shipyard fatalities. Hydrogen sulfide is found in tanks that have carried sour crude oil, bunker oil, or drilling mud, as well as in fish holds and sewage tanks. The OSHA Maritime PEL for H2S is 10 ppm. The American Conference of Governmental Industrial Hygienists (ACGIH) sets the threshold limit value (TLV) at 10 ppm, with a 15 ppm short-term exposure limit (STEL).

Carbon monoxide (CO) is another common toxic gas found in shipyards. It is produced by combustion processes such as welding, spontaneous combustion, and internal combustion engines. Carbon monoxide is odorless and colorless, making it especially dangerous. It has a PEL of 50 ppm and an ACGIH TLV of 25 ppm.


Requirements and Example Solutions
  • Spaces that have contained toxic, corrosive, irritating, or fumigated atmospheres or residues must be tested for these materials before entry. Examples of these spaces include: [29 CFR 1915.12(c)]
    • Cargo tanks
    • Ship holds
    • Fuel tanks
    • Sewage tanks
    • Adjacent spaces
    • Piping and pumps that carry toxic material
  • In order for the space to be labeled "Safe for Workers," the toxic atmosphere must be less than the OSHA PEL, and not be immediately dangerous to life or health (IDLH). [29 CFR 1915.12(c)]
  • In the absence of a specific OSHA PEL, employers should consult with other available sources that provide guidance with respect to the concentration and duration of employee exposure to a toxic substance. These sources include the ACGIH TLVs, NIOSH Recommended Exposure Limits (RELs), and the American Industrial Hygiene Association Workplace Employee Exposure Limits (WEELs).
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