Well, uh, I have some, um, facts to contribute. Not sure if this thread needs facts.
We occasionally get in dead (motionless, non-zombie) people who have been charred all over. They vary from people who still have recognizable features (mostly killed by breathing smoke - zombie-irrelevant) to charred lumps. The commonest are people who are in between those two extremes. These people have lost almost all of their skin, sparing maybe the area under the jeans-n-underwear and in the gluteal cleft, with everything else charred.
These people are found in the “pugilistic posture”, so named because ages ago, people thought they died fighting. They have their arms drawn up as if in a parody of a boxer at bay. This is because the flexor muscles are stronger than the extensor muscles (don’t ask me why - empirically observed), so they are all flexed and adducted. Their hands crumble early, so they don’t have fingers any more, and often don’t have palms any more. Feet go just as early if they are barefoot; take longer if there are shoes on (no oxygen = no burning; shoes have to burn off, takes time).
I would think a zombie would be pretty powerless to do you significant harm once they assume the pugilistic posture, even before their hands burn off. And though I have no hard data on how long this takes, seems like in a house fire, which is much cooler than napalm or crematorium, it takes under half an hour. In a car fire, less than twenty minutes.
The brain does boil and blow off the top of the head, but that takes much longer than the pugilistic posture; in a body in the trunk of a car that is torched, maybe it takes, I dunno, forty-five minutes? An hour? And that’s heat in a confined compartment. Takes longer if not enclosed; our house fire people don’t generally have boiled brains and burst crania. After the scalp burns off, they do have fire fractures of the skull sometimes, and fire epidural hemorrhage, none of which was sustained during life. (Makes my job more difficult, is all)
Incidentally, even a person who has been burned until the abdomen pops open and lets out a few coils of small bowel, will generally have otherwise intact viscera, except for the brain; when we do the autopsy, there’s hardly anything that’s really cooked, and those mostly only at the edges. We get liquid blood out to do the tox. We get liquid urine.
And of course I’m not telling you what, in our morgue humor, we call such people.
It is my personal plan to defend myself in the zombie war with a scalpel. I will leave eviscerated struggling zombies everywhere with divided spinal cords and absent viscera. Band together behind me. I’ll be at the morgue; that’s where the best saws are.
)