Ventilation systems in many chemical tankers are not built in accordance with IBC code or SOLAS requirements says the Casualty Investigation Unit of Sweden’s Transportstyrelsen, Transport Agency, releasing its report into the overpressure and explosion aboard the chemical tanker Vingatank on 23 February, 2010.
Says STA: “the chemical tanker Vingatank arrived at Brofjorden on the Swedish west coast after a ballast trip from Kristiansand in south Norway. It was very cold with a temperature of 10ºC below zero.
The second officer checked the P/V valves after arrival and the loading of vacuum gasoil started at 20.05 on 22 February.
Just before midnight a high pressure alarm sounded from tank no. 2 port. The OOW shifted the loading over to tanks no. 3 starboard and port. He reset the alarm and ordered the AB to check the P/V valve. The AB saw fumes coming out of the valve which made the OOW think that it was OK to commence loading. The pressure in no. 2 port tank was normal when the loading of the tank started after the first alarm.
After a while there was a second high pressure alarm from tank no. 2 port. Also at this time the AB saw fumes coming out of the P/V valve. The OOW then assumed that the sensor did not work properly.
At 00.35 just a few minutes after the second alarm there was an explosion in no. 2 port tank.
At the shipyard an ice plug was discovered in the ventilation pipe. The ice plug did not choke up the pipe completely so it was obvious that some fumes passed the ice and could be seen by the AB when he checked the P/V valve.
Eight tonnes of steel was replaced at the shipyard. No personal injury or environment damage occurred.
In our opinion the ventilation system in many chemical tankers are not built in accordance with IBC code 8.2.2 and SOLAS II-2, 188.8.131.52. … The OOW did not follow standing orders.
STA casualty investigator Sten Anderson tells MAC: “The IBC code 8.2.2 says ‘The venting system should be connected to the top of each cargo tank and as far as practicable the cargo vent lines should be self-draining back to the cargo tanks under all normal operational conditions of list and trim’. Normal condition for a tanker, is to our experience, trim by the stern and then the forward tanks are not self draining. This is however something for the classification societies to think about.