My snow shelter of choice when the temps dip below minus 40 degrees Fahrenheit (standing temps, not windchill) on a multi-day, dead-of-winter operation is the trench shelter. And if I don't have enough snow depth for a trench, then I simply shovel it into a pile that I can dig a trench into.
Source: This article was adapted from the Field Manual for the United States Antarctic Program (USAP), 6th edition (2001), edited by Bill McCormick. Prepared by the Raytheon Polar Services Company (RPSC) field support staff for the Office of Polar Programs (OPP), National Science Foundation (NSF).A trench with a tarpaulin roof is the quickest shelter you can build. This is very important in an emergency.
- The size of the trench you dig is dependent on the size of the covering and on the support items used to span the trench. Support items could include skis, ski poles, bamboo flags, rope(s) stretched tight, etc.
- Span the trench with support items, cover with a tarp, and anchor the edges of the tarp with snow blocks or heavy equipment. Improvise with trench coverings. A trench can be covered with a tent fly, skidoo cowlings and covers, Nansen sleds, sled tanks, plywood, pallets, cardboard, plastic, etc.
- Shovel a light skiff of snow over the tarp to add extra insulation; too much snow will collapse the tarp.
If I was in a survival situation, I would make the trench as small as possible, sleeping as close to the top of the shelter as possible since this is where the warmest air is located, with the coldest air being at the bottom, in the cold well Dan is referring to.
ReplyDeleteSince we are a heavy team with season-appropriate equipment, we generally build them: so we just can sit up in them without knocking the snow or frost down onto ourselves from the ceiling with our heads; wide enough so we can roll over without bumping the sides and knocking snow onto ourselves; and a foot longer than we are tall, so we don't bump the head end and shower ourselves with snow. I am 6-2, 195, so mine are usually 7 foot or so in length, 3 foot in width, and about 40 inches tall.
To make them easier to roof, and quicker to excavate, we generally dig an initial trench the width of our shovel, and then carefully carve it wider down near the ground level, keeping it dome like for strength and support; for less digging, we also sometimes make the trench torso length, and excavate a low tunnel at the foot end, for our legs.
We also enter from one end through a tunnel (not the roof) which is closed off with a double thermal door: two hanging contractor-grade/size garbage bags (used to line rucksacks or stuff sacks when we are underway, in case we run into wet snow or rain) spaced about a foot apart, with the area between them filled with gear that effectively gives the door one foot of insulation (or we fill one bag full of snow and pull it into the tunnel like a plug, to seal it off thermally.
We also make sure the roof will support 6 to 8 inches of fluffy snow (and any storm loads) to reduce heat loss through it. If possible, we excavate the trench down to Mother Earth, thereby capturing the heat continuously radiating from below (often the ground is not frozen, so it is a good source of 32-plus-degree warmth, when compared to minus 40 to minus 80 ambient temps outside).
A high vent, angled upward and outward from the edge of the ceiling, about an inch or two in diameter, is a good idea, as is a low one, at the bottom edge of the door, especially if you are going to occupy the trench for more than one night as the once breathable snow will eventually ice up inside.