"I'm wondering about the usefulness of a "wildfire shelter" that doesn't keep the interior air "cool" as the fire passes by. If the air is heated to 1832F that it's going to expand (create a wind) and try to enter through cracks and such in any shelter."

The shelter that Mollison advised is like an underground bunker. It is at least halfway dug into the ground, with a non-wood structure over it (filled sandbags would be good, forming a dome over the hole). Then the structure is covered with a foot or two of soil (preferably planted to something with a good root system, like white clover).

With a shelter like this, it will help you to survive a moving firestorm. Only the temps outside are that high. It would take quite a while of sustained heat to heat up the soil around the shelter to the point that it would be a real oven. The moving flames might also use all the oxygen in the area, which I understand can cause you to pass out for a while. (This is why you are advised, when wading into a watersource from a local fire, that you may pass out and drown when the oxygen in the air is depleted.)

I had also read somewhere that someone built an underground shelter and had an open pipe extending from the shelter down into a hand-dug well (above water level). Since heat, by its very nature, must rise, the air inside the well would be cooler, and would/might provide oxygen for the shelter. I don't remember if this was actually done, actually tested, or was just theory. I'm just tossing it out here as an idea to consider. Maybe someone else here can say if it's a viable plan.

Sue