The recommended size of ones circle of awareness when in a foriegn, uncertain, or dangerous situation. The size is based on the theory that most attackers, bumblers, and other potential irritants can cover twenty-one feet in about one and a half to two seconds which happens to be the minimal required timefor most people to notice a threat and decide on a preventative plan. It is actually the radius that should be 21 feet and not the diameter of the bubble.

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