In survival , the rule of threes is a quick reference guide for how to survive in a survival emergency. 
Normally, it contains the following:
- You can survive three minutes of severe bleeding , without breathable air ( unconsciousness occurs), or in icy water.
- You can survive three hours in a harsh environment (extreme heat or cold).
- You can survive three days without drinkable water.
- You can survive three weeks without edible food.
These conditions are assuming that the one (s) above it are met. For example, if you have a large quantity of food and water, then the harsh conditions rule applies. These rules are also useful in determining the order of priority when in a situation.
- Jump up^ “Wilderness Survival Rules of 3 – Air, Shelter, Water & Food” .