Dear D.Knopper:When I was a kid back in Olde England(40 yrs ago),a scrap metal merchant started to cut open a tank just like yours. The explosion was felt two miles away, he and his helper were never found! He did't know about filling the tank with inert gas and cutting it with a recip' saw. Better still, save yourself the trouble & get the help of licensed,insured,insured (yes I said insured twice)professional.Good luck buddy. Brian Wood,the water guysers.