SPEAR lesson 13 Shelter 1.2 Rule of 3, Heat Transfer and Shelter Selection

Lesson 13  Shelter 1.2 

Rule of 3, Heat Transfer, Shelter Selection

For survival you have a lot of options.

1. You can simply stay in your house
2. You can build a primitive shelter from sticks and branches
3. You can tunnel into the snow and make a cave
4. You can set up a tent or tarp
5. You can stay in a vehicle
6. You can find any other abandoned structure
7. Or you can take the shelter of someone else.

With all these options, and many more I didn't list, you have to identify what makes one shelter better than another.  If you have to build a shelter what do you have to know to make it work the first time.  This lead us into the rule of threes:

• You can live three weeks without food
• You can live three days without water
• You can live three hours exposed to the elements 
• You can live three minutes without air.

Most survivalist know this list and use it to prioritize the actions in an emergency.  Preppers use a similar formula in how they prepare for the unknown.  If you can go three weeks without food then that gets knocked off the top of the "to do" list.  Water is a little more pressing but if you are without shelter and the temperature is getting down below freezing you better put shelter on the top of that list.  The three minutes without air will come in later.

The number one reason for shelter is to protect our core body temperature.  If it goes up or down more than a couple of degrees we are facing death.  So the first thing to consider for a shelter is whether or not it will retain heat.  This brings me to the next list which is basic heat transfer:

• Conduction- This form of heat transfer comes when things are touching.  Think of electrical wire. You electricity is conducted through wires but it doesn't work if the wires aren't touching
• Convection- This is simply hot air.  Or heat that is transferred by the air.  It can transfer to your body or away from it.  To remember this think about a convection oven.  It is different from a regular oven by that is has a fan that blows the hot air around.
• Radiation-  This heat is best illustrated by a magnifying glass as it concentrates the radiant energy of the sun.  Another good example is when you are sitting in front of a fire and you can feel it heating your face.  It is the radiant heat that is doing this not the convected air.

Your shelter needs to hold in convection that comes from your body or from a fire that you build.  A solar blanket can be used to reflect back the radiation from the fire.  And by building your shelter off the ground you can avoid the loss of your body heat through conduction to the ground.

Insulation that is in our homes uses this same principle of stopping heat loss.  It creates lots of small air pockets that eliminates convection and due to the poor conduction rate of the trapped air it takes a long time for heat to transfer through it.  You winter clothes are designed to do the same thing.  If you find yourself stuck out without shelter you can fill the clothes that you do have with anything you can find that will produce those small pockets of air.  You can use crumpled up paper, dry grass, strips of cardboard or whatever you may be able to find.

The last item of heat transfer that you need to understand is evaporation.  When you want to turn water into steam you have to add heat.  When you want to turn water into ice you need to remove heat.  Anytime you change the state of an element the price you have to pay is paid in heat.  If you lick the back of your hand and blow across it you can feel it get cooler.  The saliva is evaporating and taking your heat with it.  When we sweat we do so for this very purpose.  The sweat that we generate evaporates to keep our core temperature down when it is hot or we are exerting ourselves.  If it is really cold outside that sweat will freeze and take much more heat than your body designed.

          The other thing that happens when we sweat and it it cold our clothes get wet.  The reason this is bad goes back to conduction.  Remember all those little air pockets in our clothes, well they are now filled with water.  Water transfers heat ten times more effectively than air does.  If you get wet and it is cold you need to get out of those wet clothes and into dry ones as soon as possible.  If you don't have dry clothes you need to build a fire and dry your clothes if front of the fire.  Don't wear them when you are drying them.  The steam could burn you but it is better to take your chances with the cold air then it is to let the cold water suck the heat out of you.

Oh yeah.  The three minutes without air.  Don't make a shelter so tight and closed up that you don't let in any fresh air.  If you sleep in the cab of a vehicle and there are a couple of people with you the air will only last a couple of hours with the windows all closed up.  Make sure that you have a fresh source of air to keep from falling off into that sleep that you don't wake up from.

Continue on to Lesson 14

Start at the beginning:  Lesson 1

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