Inert Gas System

An inert gas system maintains the atmosphere in tanker cargo tanks at an oxygen concentration below 8% by volume, making the space non-explosive regardless of hydrocarbon vapour concentration. SOLAS Chapter II-2/4 and the International Safety Guide for Oil Tankers and Terminals (ISGOTT) require inert gas systems on crude oil and product tankers of 8,000 DWT and above. The inert gas supply is provided either by scrubbed boiler flue gas or by a dedicated inert gas generator, and is distributed to each cargo tank through a deck main and individual tank connections. Proper inert gas management is one of the most safety-critical tasks aboard a tanker. Chief officers and pump room engineers must ensure tanks are purged of air before cargo loading and that inert gas pressure is maintained positive at all times — typically at least 100 mm water gauge above atmospheric — to prevent air ingress. The P/V breaker and deck water seal in the distribution system provide back-pressure protection. Oxygen content and pressure must be logged continuously during cargo operations and the records retained for inspection. Failure of the inert gas system during crude oil washing or high-rate cargo discharge has preceded several catastrophic tanker explosions.