Thoughts please - feel free to ask additional questions. Welding onto a back deck on a ship, weld is about 8cm deep. Fuel tank directly underneath, the weld covers a small corner where the fuel tank is located. Tank is 22cm from the deck, no void space. Tank is 75% full of fuel oil. Is there an explosion risk? Any pointers to experts in this area would also be welcome. Thanks.

Yes -very high risk of explosion. Tk should be m/t and certified gas free. In my day it was a job for the shipyard welder. Have it p/p out or transferred to another f/o tk. "Back deck on a ship" - not exactly marine speak . Can you offer further and better particulars? Jon

Safetygirl, I'd suggest the only route you should take is to get someone competent to evaluate the task, look at the drawings, visit the site and advise properly. Anything less would not be robust!

Emma Just to clarify: Was the welding carried out on the body of the fuel tank itself or on something else above the tank? If it was the tank itself, then appropriate stringent precautions would have been needed to prevent the risk of an explosion through heating of the air and oil inside the tank. However, if it was the latter scenario, the crucial question was surely whether or not the extent and duration of the welding process could have imparted a sufficient amount of heat onto and through the tank body to pose the explosion risk. Some years ago someone told me that the Royal Navy would carry out repairs to the outsides of fuel oil tanks PROVIDED that the tanks were full of oil or water so as to totally exclude air. However, perhaps this only applied to urgent repairs needed at sea and during wartime conditions. Can anyone expand on this?

It does yes. It's all about reaching flammable limits which depend on the fuel / oxygen / heat balance. It's how you can extinguish a fire by putting excess fuel on it. So too much fuel means it can't enter flammable limits. But I wouldn't recommend it as a sole method of control!