The blood circle, also known as a safety circle, is a term used by the Boy Scouts

Scouting

Scouting, also known as the Scout Movement, is a worldwide youth movement with the stated aim of supporting young people in their physical, mental and spiritual development, that they may play constructive roles in society....

 to describe the area within the radius of the arm and blade length combined, when using a pocket knife

Pocket knife

A pocket knife is a folding knife with one or more blades that fit inside the handle that can still fit in a pocket. It is also known as a jackknife or jack-knife...

, knife

Knife

A knife is a cutting tool with an exposed cutting edge or blade, hand-held or otherwise, with or without a handle. Knives were used at least two-and-a-half million years ago, as evidenced by the Oldowan tools...

 or axe

Axe

The axe, or ax, is an implement that has been used for millennia to shape, split and cut wood; to harvest timber; as a weapon; and as a ceremonial or heraldic symbol...

. This area can be envisioned as a sphere

Sphere

A sphere is a perfectly round geometrical object in three-dimensional space, such as the shape of a round ball. Like a circle in two dimensions, a perfect sphere is completely symmetrical around its center, with all points on the surface lying the same distance r from the center point...

 with a person and a sharp instrument at its center. Presumably, anyone within this radius is at risk of being wound

Wound

A wound is a type of injury in which skin is torn, cut or punctured , or where blunt force trauma causes a contusion . In pathology, it specifically refers to a sharp injury which damages the dermis of the skin.-Open:...

ed by an accidental slip of the blade. Therefore, it is desirable to keep other people outside of the circle at all times.

Delimiting the blood circle

The circle is found by holding the blade of the cutting instrument (never the handle) in the hand used for cutting, and slowly swinging the arm in a 360° arc. The far end of the handle marks the limits of the circle. Any person or thing within this circle is considered to be at risk of injury. While it is never a good idea to enter another person's blood circle, it is customarily the responsibility of the knife-holder to clear the circle, or to move if the circle cannot be cleared.