Possible cargos for these vessels are acids, alkaline, alcohol, monomers, chlorinated alkenes, and other chemical substances. This type of vessel has a higher safety grade than a product tanker. The cargo tanks are separated from the outer shell/ double bottom by ballast tanks. Between the cargo tanks, engine room and forepeak there is a narrow, empty space called cofferdam meant to create a safe division so that in case of leakage the consequences are reduced. A cofferdam is also required in case two cargo tanks are filled with different, incompatible products. In the cofferdam there is usually a sounding pipe, a bilge connection and a connection with open air.
The chemical tankers are categorised in classes subject depending on the protection they offer against pollution: I for the most toxic cargos, II and III for less dangerous substances, for instance. The cargo can be divided in classes of toxicity: A, B, C and D; A is the most toxic and D the least; the degree of toxicity and which ships are allowed to carry such substances is well defined by the IMO. Have a look at this interactive graph of a...