I watched "Indestructible Man" with Lon Chaney a couple nights ago, hoping it was one I remembered from my childhood. No such luck. The movie I remember was about a man who became nearly invincible, but it started with an atomic blast; I have memory of people watching in horror from the viewing room as he was caught in the explosion. My only other memory is that he was destroyed with flamethrowers, leaving an outline of ash at the end of the movie.

Anyone know what movie this is?

Did he grow into a bald giant? If so, it's The Amazing Colossal Man