Safe Operational Practice on Liquefied Gas Tankers
This domain tests the special hazards of LNG and LPG: cryogenic cold, pressure, boil-off, vapour dispersion and rapid phase change. The exam expects you to apply containment, ESD and gas detection controls.
Cargo control
Liquefied gas is carried at low temperature, under pressure, or both. Cool-down must be controlled to avoid thermal stress. Boil-off gas is managed by reliquefaction, burning in the boilers or venting only under controlled conditions. Pressure relief valves must never be isolated. The ship/shore link and ESD system allow either side to stop transfer.
Hazard control
Cold burns and brittle fracture are cryogenic risks. Methane and LPG vapours are flammable; cold LNG vapour is initially denser than air. Gas detection, ventilation, dry powder or suitable foam and water spray for vapour dispersion are key. Personnel need cryogenic PPE and breathing apparatus where required.
Worked example
LNG spills onto water during transfer. Activate ESD, stop transfer, notify the terminal, remove ignition sources, monitor gas and use water spray to disperse vapour. Do not direct a water jet into the liquid; the rapid vaporisation and cold cloud can spread the hazard. Reasoning: LNG vaporises quickly and forms a flammable cloud, so control the vapour and ignition sources rather than the liquid.
Traps that cost marks
Treating LNG as explosive in liquid form; isolating pressure relief valves; using a direct water jet on a spill; forgetting rollover and stratification; assuming LPG vapour is lighter than air.