Slip Potentials on Ramps

Abstract

Falls are a major cause of injuries at work, in public places and at home. In over 50 percent of falling accidents, slips led to the injury. Ramps have the potential to be particularly hazardous with regards to slips and falls since higher shear forces are created. The purpose of this study was to determine the effect of ramp angle on slip potential at the feet during downward and upward gait. This was accomplished by investigating the relationship between the horizontal and vertical foot forces during gait as a function of ramp angle. A ramp was designed and built which incorporated a force plate. Foot forces were measured while subjects walked up and down the ramp. The ramp angle was varied from 0 to 20 degrees in 4 degree intervals. Normal forces were divided into the shear forces, thus calculating a “required” coefficient of friction (RCOF) for the entire trial. The results showed shear forces increase both in magnitude and duration as ramp angle is increased. The RCOF also increased as ramp angle increased. The maximum RCOF for each trial increased almost linearly as the ramp angle was increased (r² = .92; p < .01), with levels often over 0.6 at angles of 20 degrees. Most guidelines for ramp design suggest a surface with a minimum COF of 0.5; however this study indicates that high ramp angles can generate RCOF values greater than this recommended level. Thus, the guidelines may be too low and a higher surface COF necessary.