Life after 800 deg day?

There was a show on the science channel last night about the results of a comet or asteroid impact with the Earth. One of the results was a day where the temperture reached 800 deg for about a day. After that they showed small groups of survivors struggling to survive. Other than being in cellars and a cave the show was sketchy on how these groups survived the 800 deg temps. How would anyone survive? I do not see a cellar being enough protection from the heat. How far underground would you need to be to survive this?

I imagine that submariners would be best placed to survive (briefly) such an event. They’re in a medium with a high heat capacity and have their own air supply. Even if the atmosphere hit 800 degrees (did they really say that? Seems unlikely that the entire atmosphere would hit that.), the oceans aren’t going to boil away in any short period of time, and I suspect that even relatively close to the surface the temperature would remain temperate. Of course, you’d have tsunamis and other tectonic events that might put the submariners into the mixmaster, but you didn’t ask about those.

800 degrees for 24 hours would penetrate a few feet at best. Earth (ground dirt) is a poor conductor of heat.

10 feet underground should be safe and stick to around 68 degrees.

The fact that nothing on the surface would survive that would make survival after you return to the surface unpleasant.

To illustrate the insulation powers of soil, think about how hot it is on the other side of the crust. It’s over 800 degrees all the time.

Why doesn’t anybody talk about those kinds of temps after the asteroid hit 65M years ago? The extinction then was not caused by heat but presumably by dust in the air that blocked sunlight, causing a collapse of the food chain. Is the object described in this show lots, lots bigger?

I’d think all the surface water would evaporate as well. There’d be nothing to drink, and the air would be incredibly humid - it also wouldn’t just pop right back down to 75 degrees overnight.

It’s just my WAG, but I’m betting at least a month underground to survive that.

Because, as you said, the big problem wasn’t the heat (at least not after the very brief firestorm), but the cold that followed. But there was a Firestorm that spanned a signifcant portion of the globe.

Also think about the moon.

Hotter than crap on the surface for about 2 weeks, then really cold for about 2 weeks.

A few feet down below the surface and the temp only swings a few degrees either way.