may be dug deeper into the cave floor to provide a place for the coldest air to gather, away from the occupants. the cave entrance may be closed up with chunks of snow to deflect wind and retain heat, although it is vital to prevent drifting snow from completely plugging the rest of the entrance in order to maintain a constant air supply. Some prefer to place a ski pole or a ski up from the cave out through the roof or side wall. This can provide an emergency air hole should the main entrance become blocked. Skis can also be placed to cover the entrance or used to secure blocks of snow at the entrance. A snow shovel should always be kept inside the cave when participants are inside. Dangers It is possible to sleep several consecutive nights in a snow cave, but care must be taken since a slight ice crust may develop on the inside of the cave from moisture in the exhaled air of the inhabitants. This is thought to result in reduced air ventilation through the snow cave walls and roof, and thus increase the risk of suffocation. As a precaution, it is common to scrape off a thin layer from the inside of the cave ceiling each night spent in the cave. See also Maternity den Mountaineering Quinzhee Igloo References External links Survival Skills: Building a Snow Cave at PBSkids.com Denali Building Snow Caves for Fun & Recreation at Outdoors With Dave Why are snow caves dangerous? at TraditionalMountaineering.org Mountaineering techniques Outdoor recreation Buildings and structures made of snow or ice