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Enclosed or Confined Spaces in Ships
The atmosphere in any enclosed spaces not continuously or adequately ventilated, such as cargo or other tanks, cargo holds, pump rooms, cofferdams, duct keels and stores, may contain toxic or flammable gases or be deficient of oxygen to the extend of being incapable of supporting human life.
What is an Enclosed Space
- A space contained or having last contained combustible or flammable cargoes.
- A space containing or having last contained, cargoes or stores of a toxic, corrosive, oxygen absorbing or irritant in nature. Toxic gases may emerge from certain bulk cargoes. Residues from cleared bulk cargoes and leakages from packaged cargoes also offer same risks.
- Cargo spaces, ballast spaces, or other spaces which have been inerted or fumigated.
- Spaces wherein heating stoves, boilers or internal combustion engines are installed.
- Refrigerated cargo spaces in ships fitted with direct expansion plants, from which refrigerant may leak.
- Spaces in which welding has taken place leaving residual fumes.
- Spaces in which fires have occurred which consume oxygen and usually produce toxic combustion products.
- Spaces immediately adjacent to the spaces referred to the above, especially pump rooms and duct keels which may contain toxic fumes released from leakages of cargo, and including cofferdams and double bottom tanks around and beneath cargo spaces.
Lack of Oxygen
If an empty tank has been left sealed for a time, the oxygen content of the atmosphere may be reduced due to oxygen combining with the steel in the process of rusting. Lack of oxygen may also occur in a laid up boiler or other vessels where oxygen absorbing chemicals have been used to reduce rusting. Depletion of oxygen may occur in holds when oxygen absorbing cargoes are carried. For example vegetable products which have begun to rot or ferment, wood chips, steel products which have begun to rust, etc.
Presence of Toxic Gases
There is possible presence of hydrogen in a cathodically protected cargo tank used for ballast which will be readily dispersed upon opening the tank covers. Even after dispersing, there are chances of trapped gas pockets in the corners and upper side of the tank which displace oxygen, creating a dangerous atmosphere to enter. Also there is a risk of fire hazard since hydrogen is a combustible gas.
If carbon dioxide or steam has been discharged, for example to extinguish or prevent a fire, the oxygen content will be reduced in the affected space. The use of inert gas in the cargo tanks of tankers for permanently inerting those spaces, results in only minimal amounts of oxygen being present.