What is the safest way to cut the straps off a gas tank when can't reach the bolts and they are rusted fast?

I have a leak in the line above my gas tank and one of the straps that is almost rusted through. To get to the rubber line at the top of my plastic gas tank I have to cut the other strap off as well as remove the one that is almost rusted through. There is about a quarter tank of gas and am worried about cutting them off with the grinder and the fumes igniting the tank... I have gotten lots of advice but none seems truly "safe". Any suggestions would be appreciated.

Thanks,
Todd Garrety