Edvard stated: source post
No idea, but it takes 18 minutes of high agony for some reason.
Bullet to the head or explosions are the best choices, although I have no idea why it takes 1-2 minutes to die...I thought it was pretty much instant death.
Those who I have seen blow themselves up was instant I assure you... as was the shotgun to the head... and one rifle to the head... one pistol to the head they said he may have been a live a few minutes...
The carbon monoxide dudes were the ones I think suffered agony the most...