MARS 200833

Major gas leak

Official report: MAIB www.maib.gov.uk/publications/ investigation_reports/2007/ennerdale.cfm

A fully pressurised gas tanker experienced a major leak of liquefied propane during loading from a shore terminal. The leak was sealed 29 hours later, after an estimated 66 tonnes of propane had been lost to atmosphere.

After completion of loading, a cargo surveyor boarded to take samples of the cargo. In order to ensure a truly representative sample, the chief officer arranged to keep the cargo in circulation during the sampling, using the tank’s deep well pump.

After having taken the first tank’s sample, and while the chief officer was engaged in securing that tank, the cargo surveyor proceeded to the second tank. As he turned the ship’s connection to engage his sampling device, the sampling valve assembly came off in his hand, causing free release of pressurised gas from the open end of the branch pipe.

The chief officer saw and heard a leak and activated the emergency shut down (ESD) system. As gas continued to escape, it soon became apparent that the ESD valve before the detached sampling connection was not completely shut.

The ship’s crew made several attempts to refit the sampling valve, but due to the high pressure of the escaping gas and the formation of ice on the pipe, these were unsuccessful.

The emergency services arrived promptly and maintained a continuous water spray on the deck to disperse the gas cloud. Soon afterwards, a decision was taken to close the port to all traffic, and other vessels at the terminal were moved to safety.