Trip Type Falls

LEVEL WALKING

People learn to walk while giving the walking task (the walking process) very little conscious thought. The difficulties of normal walking on level slip resistant surfaces are largely overcome in early childhood by learning, practice, and experience, coupled with physical growth and development.

Although, to an adult, walking may at first be characterized as merely putting one foot in front of the other, human walking is an extremely complex locomotor activity. The human body has a relatively high center of gravity combined with a relatively small base of support, producing a rather unstable object in terms of fall prevention. To remain upright, one must maintain the center of gravity over and within one's base of support. If a slip or other misplacement of a foot moves the center of gravity outside the base of support, a fall will occur.

During the walking process, as the center of gravity moves forward, weight and balance are continually being transferred from one foot to the other. As each foot contacts the walking surface, and at every other phase of the walking cycle, coordination of muscle and bone, weight and balance, are continuously and precisely adjusted and timed to prevent the loss of stability. At the same time, the user of various walking surfaces must contend with a variety of surface characteristics such as surface friction, slope, texture, and subtle protrusions. Physical characteristics of walking surfaces may assist people in maintaining stability by offering design features that are compatible with human needs, or they may seriously hamper stability and create conditions that are clearly or deceptively dangerous.

During the walking process, the upper body's center of gravity moves forward at a fairly constant rate, its support being continuously shifted from leg to leg. More than this, the upper body actually "commits" itself in a forward direction and then relies on the successful movement and proper placement of the forward leg in order to maintain (regain) support and prevent a fall. Walking can be thought of as the process of repeatedly losing and gaining body support by one leg and then the other, with one leg taking over support of the upper body as the other leg begins to lose support.

Balance of the upper body during walking activity is also a dynamic process. Not only is balance of the whole body being shifted from leg to leg while walking, such balance must be continuously adjusted on the stationary leg during the time of opposite leg swing.

Analysis of how people walk has shown that during the walking process, as the forward foot is initially placed on the walking surface, it contacts the surface so that only the rear edge of the heel strikes first, and begins to bear an increasing portion of body weight.  At the same time the trailing foot momentarily remains in contact with the walkway, continuing to bear part of the load until the forward heel rocks forward, gradually accepting the full load as the entire foot contacts the walking surface.

THE "TRIP" TYPE FALLS

On any walking surface, a trip type fall occurs when an object, unevenness, or other characteristic of the walking surface prevents or even momentarily delays the trailing leg from swinging forward to achieve a timely and accurate positioning of the foot on the surface ahead for proper body support and balance at the critical moment of contact. Since the process of walking requires split second timing in the transfer of support and balance from leg to leg, the slightest disruption of this process, or the rhythm of this process, can produce imbalance of the upper body and result in a fall produced as the upper body continues to move forward, beyond a base of support, according to the law of inertia.

The trip type fall accident has been well recognized in the safety literature and through common experience. Not only have large objects been recognized as tripping hazards but also small objects have been recognized as particularly dangerous due to their relative "hidden" nature. Traditionally noted small tripping hazards include turned-up (non-flat) floor rugs and mats, abruptly edged (abrupt edge sloped) floor mats, loose and slightly raised floorboards, bent-up floor plates, excessively raised door thresholds, uneven sections of sidewalk, cracked and raised sections of flooring, and the infamous poorly placed electric extension cord.  Further, as people tend to minimize the walking distance between point A and point B, when persons round corners in a hallway, protruding floor edge molding can produce a trip type fall; or if a chair legs extends back further than the upper backrest of a chair, persons guided by the chair back, routinely trip over an extended chair leg.

When any aspect of a walking surface produces a sudden and abrupt rise between sections of such flooring, the term used to describe this hazard is change of elevation.  Numerous standards address acceptable and unacceptable (unsafe) changes in elevation.  These include the (a) National Fire Protection Association’s Life Safety Code (NFPA-101), (b) the American National Standards Institute’s Facilities Accessibility Standard (ICC/ANSI-A117.1), also as referenced and required by the International Building Code (ICC),  (c) the Accessibility Guidelines (ADAGG) under the Americans with Disabilities Act (ADA), and (d) the American Society for Testing and Materials’ Standard Practice for Safe Walking Surfaces (F-1637).

These standards have similar requirements to protect against falls due to abrupt changes in elevation.  Basically, these codes, standards, and regulations require that (a) any change of elevation (change in level) less than ¼ inch in height may be without edge treatment, (b) any change of elevation (change of level) between ¼ inch and ½ inch shall be beveled with a slope not steeper than 1:2 (or 26.57degrees), and (c) any change of elevation (change in level) greater than ½ inch shall be transitioned by means of a ramp that complies with applicable building codes, regulations, standards, or ordinances, or all of these.  Such building universally stipulate that a ramp for pedestrian use must have a slope no steeper than 1:12 (or 4.76 degrees).

Tripping hazards are particularly difficult to detect when potential victims are engaged in any task or activity that involves their attention away from the specific location of such hazards.

INSPECTION AND MAINTENANCE

Because of the frequency and potential severity of falls, walking surfaces must be inspected on a systematic and timely basis. How quickly a defect or unsafe condition can develop will dictate the frequency of inspection. Discovered defects must be repaired or barricaded immediately.

For additional information, see the Nelson & Associates Fact Sheets (.pdf) below:

Five Types of Same-Level Falls

Human Vision During the Walking Process

Dark Adaptation

Application of ADA to Private Entities

Application of ADA to Public Entities

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