The Ergonomics of Reaching Upwards and Over

The distance a man can reach determines the minimum height of guards or the minimum distance of barriers from the machines they are intended to fence.

Reaching Upwards
How do we answer the question whether a dangerous part of a system is fenced as to provide security away from the dangers? The average limit of reach when on tiptoes at about 95 inches (Schroeder in Anatomy for Interior Designers places). There is no doubt that some individuals can reach further, which is likely why the International Safety Code published by the International Labor Office establishes about 102 inches as the dividing line beyond which positional safety is considered.

Reach Over Barriers
It is one practice with certain types of machinery to use a fence guard to regard it as safe. We usually want to figure out how far that barrier should be? The reach over a barrier is interrupted by the body at the point of contact with the barrier. If the barrier is low, the body can be bent and therefore the extent of reach is longer than the arm. If the barrier is at armpit height, reach is equal to the length of the arm. If the barrier is above shoulder height, interruption is at the elbow, or when even higher, at the wrist or fingers. Various heights should be from dangerous parts of various heights to conform to these principles of average human reach.  An arm reaching over a barrier can be describe as a curve that determines what distances from the barrier dangerous parts of machinery of varying heights are safe by position.

The manner of measuring the guard distance is important. The distance of the guard is the horizontal measurement from the plane of the guard of the height shown or dangerous part. The point at which the measurement is to be taken is where the transmission or dangerous part contacts the reach curve. This is not necessarily the part of the transmission that is nearest to the plane of the guard.