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Tank explosion case onboard a chemical tanker

Prior to loading cargo the vessel was required to gasfree and clean her cargo tanks. To accomplish this, the de-humidifier system was used to gas-free the tanks. The system consisted of a blower within the forward store, a main line along the deck and branch lines to each cargo tank.

Recognising the risk of cargo vapours passing along the line to the forward store, the system was fitted with individual tank valves, a main line isolation valve, a non return valve and a spool piece, which the Company required to be removed when the system was not in operation to isolate the forward store from the cargo side of the system.

The day after loading her cargo of Naptha, and three days prior to the incident, five crew members entered the forward store as part of a familiarisation tour conducted by a junior deck officer. They were met by a strong smell of cargo, however this was not reported to a senior officer.
tank explosion case
Fig: Exploded ford store

Two days later and with the vessel now at sea, the ventilation flaps, hatch and door of the forward store were secured. The following day the Bosun opened the door of the forward store and turned on the ventilation fan. An explosion occurred and the Bosun was killed.

What Went Wrong ( Critical Factors ):

Several valves in the de-humidifier system were passing and the spool piece was not removed after the tank cleaning operation. It was therefore possible for cargo vapours to enter the forward store and with the store room secured for sea, an explosive atmosphere was created. The ventilation fan provided the ignition source.

Five crew members smelt cargo vapour in the forward store but did not report this to a senior officer. Some of them were new to the vessel and junior in rank. The spool piece was not removed as required by the Company. Designed as the last line of defence, it was found that the position and design of the spool piece made it difficult to handle. The spool piece is 2 metres above deck height and 50kg in weight.

Lessons learned & Recommendations:

* Use your senses! Any irregularities must be reported to a senior officer.

* On completion of operations spool pieces must be removed and the blanks properly fitted. In order to make them conspicuous, all portable bends, and spool pieces are to be conspicuously marked and labelled with intended purpose.

* Vessels with awkward and heavy spool pieces on the dehumidifier system, as in this case, should consider alternative arrangements with their Superintendent. In this case, the Managers replaced the spool pieces on the dehumidifier system with a flexible hose.







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Special tank cleaning method

Determining proper tank cleaning by acid wash method

Supervision of all tank cleaning and gas freeing operations

Disposal of tank washings, slops and dirty ballast - safe method

Type & condition of tank coatings - maintenance guideline

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Tank cleaning fatality- case study & lessons learned

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Tank explosion case study

Rubber lined tanks, for the transport of phosphoric acid, waste acids and hydrochloric acid.



Following reference publications provide useful guidance and international regulations for carrying hazardous chemicals at sea.



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