Emergence by John Birmingham
Dave Hooper has the hangover from hell, a demonic ex-wife and the claws of the tax office sinking into him. So the last thing he needs is an explosion at the off-shore oil rig where he works.
But this is no ordinary industrial accident, and despite the news reports, Dave knows that terrorists aren't to blame for the disaster. He knows because he kills one of the things responsible.
When he wakes up in a hospital bed guarded by Navy SEALs, he realises this is more than just a bad acid trip. Yet his shock and anger are cut short by a startling self-discovery; his contact with the creature has transformed the overweight, balding safety manager into something else entirely. A goddamned superhero.