Stairway Fall Prevention

STAIRWAY FALLS

Although falls occur while ascending stairs, those which occur while descending usually involve more serious injury. Descending stairs is a modification of level walking. The body first "commits" itself by moving its center of gravity forward in the direction of the step below while swinging the trailing leg forward, to become the leading leg, to a position over the step on which it will be placed. Weight is then lowered to the next step by bending the knee of the opposite, now trailing leg, with the leg extensors performing most of the work in controlling the rate at which the leg is bent and therefore the rate at which gravity pulls the body down. As the knee bends, the heel of the trailing foot is raised, and support of the body is momentarily transferred to the ball of the trailing foot. In an instant, however, body weight and balance is transferred to the ball of the foot of the forward leg as the foot falls or bounds onto the step below.

As this occurs, the ball of the forward foot is placed on the step first approximately 2 inches from the step leading edge. As the ball of the foot strikes the step, the ankle joint adjusts immediately to avoid jarring and to help cushion and lower the weight. The heel may drop entirely to the step, or it may be kept slightly elevated, depending primarily on the rate of descent. As body weight continues to move forward and downward, the forward leg becomes the trailing leg as the trailing leg swings forward to the next descending step.

Although balance is maintained while descending stairs through a complex system involving continuous physical and physiological feedback and adjustment, several key aspects of stair design interface with this process to assist or hinder the safe descent of individual stairs.

Critical components of stair design related to fall prevention include surface coefficient of friction (especially at and near the step leading edge), nosing or leading edge cross-sectional contour, tread-riser dimensions, fall arrest features such as handrails, lighting conditions, various trip hazards, and the conspicuity of stair features and potential hazards.

First, as discussed, when the knee of the trailing leg begins to bend and its heel begins to rise, balance is transferred momentarily to the ball of the foot. This position of the foot is supported by the first few inches of the step leading edge (the forward portion of the tread near the leading edge and then, as the body progresses forward, the step nosing, being the "leading edge" of the step). As the forward foot is being lowered to the step below, the trailing foot (shoe sole) rocks forward over the edge of the nosing and is supported largely by this leading edge of the step immediately before transferring all weight to the foot below. At this critical moment, when body weight is supported by the trailing leg held in place on the step by the friction or grip characteristics of the step leading edge, the potential for a "slip" type fall is increased. The safe condition of step surfaces and leading edges (nosings), in terms of their dimensions and frictional characteristics, is therefore critical to the safe use of stairs while descending. Important stair features are level slip-resistant steps, and a slightly rounded step leading edge having good slip-resistance (1/8 to 1/4 inch maximum radius for wood stairs, 1/4 to 1/2 inch maximum radius for stairs with good friction characteristics).

A second critical moment in stair descent related to stair design is the moment at which the leading foot is lowered and contacts the forward portion of the step below. Here, the ball of the foot contacts the step first at various angles of attack and suddenly bears the complete weight of the body. Initial contact area of the foot may vary only between 6 and 10 square inches and produce pressures between 15 and 30 pounds per square inch or greater. At this critical moment, when the leading foot first contacts the step below, and the foot must be held in place by the frictional characteristics of the tread surface, the potential for a "slip" type fall is increased. Important desirable stair features here include level steps, adequate tread depth, uniform tread-riser dimensions, sound and properly dimensioned step and upper landing leading edges (nosings), and a surface friction level (of landings, steps, and nosings) that is highly slip-resistant. Once again, good friction is especially critical in the area of the nosing and for about 4 or 5 inches back from the step (or landing) leading edge.