In the conditions in which you’re jumping into one of these you don’t really want much ventilation - too much heat/smoke, and potentially even the fire burning through some of the oxygen from the contained air. Underground might not be an ideal place to be but IMO it’s likely the best of a set of bad choices if you can’t get out ahead of time - dirt is a pretty good thermal insulator.
In the conditions in which you’re jumping into one of these you don’t really want much ventilation - too much heat/smoke, and potentially even the fire burning through some of the oxygen from the contained air. Underground might not be an ideal place to be but IMO it’s likely the best of a set of bad choices if you can’t get out ahead of time - dirt is a pretty good thermal insulator.