What is the rule of three as it relates to survival?

The Rule of Threes states, humans can survive

3 minutes without air

3 hours without shelter

3 days without water.

Explanation:

Human can survive for 3 Minutes without air (oxygen) or in icy water. Human can survive for 3 Hours without shelter in a harsh environment (unless in icy water) Human can survive for 3 Days without water (if sheltered from a harsh environment) human can survive for 3 Weeks without food (if you have water and shelter)