Cutting Out a Fuel Tank

[Mike Sibley]

I have to replace the 30-year old steel fuel tank in my Pearson 365 sailboat. Unless I remove the engine first (Boooo), the only way to get the old tank out is to first cut in in half and then remove it through the cockpit locker. I plan to use a reciprocating saw. Although I can remove almost all the diesel fuel from the tank, some will undoubtedly remain at the bottom. What can I do to the remaining fuel or to the tank to insure that it doesn't all go up in flames when I start cutting and a few sparks fly?

(I plan to replace the old 50-gallon tank with two 25-gallon tanks that can be installed through the cockpit locker.)