Scuttle fuel tank repairer request.

[A G Wood]

Excluding oxygen by replacing with non-combustible carbon monoxide is the chemical explanation.

Thank you Duncan, I thought there would be a simple explanation, either way, it worked and seemed a lot easier than filling the tank with water.

Not wishing to impugn the knowledge and empirical experience of long-time and esteemed contributors to this forum, but I need to mention that carbon monoxide, despite being toxic to air breathers, is actually combustible. It was in fact the major constituent of coal gas [the sort produced at the gasworks] and the gas produced by automotive wood gas generators of the WW2 era. We were taught the best safe purge for hot work [i.e. open flames] on containers which have held flammables is nitrogen, and even then care is needed to make sure all traces of flammables have been removed.