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The Rule of Threes

In survival, the rule of threes involves the priorities in order to survive. The rule, depending on the place where one lives, allow people to effectively prepare for emergencies and determine decision-making in case of injury or danger posed by the environment.

Normally, the rule of threes contains the following:

• You can survive three minutes without breathable air (unconsciousness) generally with protection, 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 food.

Each line assumes that the one(s) before it are met. For example, if you have a large quantity of food and water yet are exposed to the environment, then the harsh conditions rule applies.
The Rule of Threes is useful in determining the order of priority when in a life-threatening situation, and is a generalization (or rule of thumb) rather than a scientifically accurate fact.

Additional generalizations may be presented with the rule, though they are not typically considered part of the "Rule of threes." For example, it might be said that it takes a three-second psychological reaction time to make a decision during an emergency, or that an individual can last three months without companionship or hope.