I read that 20 years ago in a science magazine handed to me by my marine corps college room mate, so i don't have a link lol.
The article was not necessarily about heat. It had to do with deadly rays produced as EMP waves pass through steel. The waves outside are not exactly healthy, but the rays produced inside the tank are deadly. Hence they were showing how the guys inside a tank, though they might expect to be better protected, would be more impacted by EMP. The whole article was about EMP.