LNG Ships

By F. R. Chowdhury

Image Credit: Liquefied Gas Carrier.com

Properties of LNG:

LNG is actually METHANE. Purity of cargoes ranges from 67% to 99.5%, according to geographical location. Impurities consist mainly of Ethane and Propane. LNG is:
Non – toxic
Non – corrosive
In its gaseous form it is lighter than air. Its ratio of volume as liquid to gas is 1:600.

Lower flammable limit is approx. 4% in air. Upper flammable limit is approx. 14% in air. There is no LEL or UEL as such because there is no explosive effect upon ignition at any concentration. Auto ignition temperature is approx. 585° C and there is therefore little chance of ignition from engine or boiler exhausts. Methane has a slow travelling flame front and can be effectively extinguished with dry powder. Ship superstructure or other vulnerable areas may be protected by water spray, which imparts heat to the vapour cloud, resulting in immediate upward evaporation. CO2 injection firefighting systems are not fitted due to the possibility of ignition by static electricity being generated. Read more