Thanks for asking, because I feel bad that I might have helped a myth to spread. So I am glad to be given opportunity to correct what I said on the radio broadcast.Spaced Out Radio
I said in the interview that for a trek to be considered category III difficulty the hikers need a certain number of nights where they don't lit a fire i.e. "cold nights". This is not true
. The closest to this is that they need certain number of overnights in a tent, not refuge, cottage, house, etc
. So where the group pitched their tent doesn't really matter for the category of difficulty. Seasoned hikers explained the choice of place for the tent the night of Feb 1st on the slope without a stove with the fact that the group was training for an expedition in the Subpolar Urals where there is little wood. Hiking groups often had to sleep without a stove. But this is not a requirement. Dyatlov group was under no pressure to meet any requirements or go in any places they were not ready for.