Before breaking out the cutting torch [u][b][size:14pt]watch this video[/size][/b][/u] , can happen with any wheel and tire, inflated or not.
Tire Pyrolysis

The service manual explains how to disassemble the rim.
Being as you're not saving the rim you may find it's easier to use a saws all on the tire, only difficult part is the steel in the bead, a cold chisel works on them if you cant get the saw in there.

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
---All pictures---
"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-