This incident refers to a ballast tank explosion of an offshore rig during shipyard repairs. During a repair job in a pre-load tank (ballast tank) on board a rig at a repair yard, an explosion occurred in the tank. The rig was undergoing extensive repairs. During the break time, workers using gas torch inside the pre-load tank, had shut the gas torch valves and left the tank. After the break, when they went in again for continuing their job, there was an explosion in the tank as soon as they ignited the gas torch.
Two workers were seriously burned and hospitalised, and one of them died a few days later.
The most probable cause of the explosion was ignition of gas coming from the gas torch. On investigation it was found that valve on the gas torch was not tight, hence gas had accumulated inside the tank during the break, as there was no proper ventilation.
Such incidents highlight the following lessons to be learned, which apply not only to repairs in shipyards but also on similar kind of repairs in enclosed spaces:
- The conditions for the validity of the issued “hot work certificate” may change quickly during a work shift and need frequent follow-up.
- Continuous proper ventilation is a condition when work is carried out in any enclosed space. In this case this could have avoided or at least reduced the accumulation of gas causing the explosion.
- Gas equipment including hoses to be used in enclosed spaces is to be well maintained so as to perform as desired.
- While temporary leaving a work place, proper precautions are to be taken. In this case by having closed the main gas cylinder valves.
Note: Photos and drawings contained in this post are not actual photos/drawings of the rig where the accident occurred.
Source: DNV
Officer of the Watch 
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