Study of Human Impact Tolerance Using Investigations and Simulations of Free-Falls

A study of free-fall accidents and resulting injuries was conducted to determine how useful these types of data could be in establishing human injury tolerance limits. “Tolerance” was examined primarily for children at two levels - reversible injury and threat to survival. The specific objectives were to investigate specific free-falls in sufficient depth to permit biomedical or mathematical reconstruction of the fall, simulate selected free-falls to estimate impact response, and compare predicted responses with observed injuries as a means of estimating human tolerance levels. From more than 2100 reported free-falls, 110 were investigated on-site. Seven head-first and three feet-first falls were then simulated using the MVMA 2-D Crash Victim Simulator. Newspaper reports of free-falls showed that males fell six times as often as females and most often while at work. Children fell from windows and balconies more often than from any other hazard. Case investigations showed that children were generally injured less severely than adults under similar fall circumstances, and tended to land on their heads a greater proportion of the time. The investigations also indicated that for impacts onto rigid surfaces: Both children and adults may be expected to suffer skull fractures in head-first falls of greater than 10 ft; adults are likely to incur lumbar spine fracture if they land in a sitting position after falling 10 ft; and adults will probably sustain pelvic fracture in feet-first falls of more than 30 ft. The head-first fall simulations predicted skull acceleration responses that were higher than previously considered survivable, although five of the six child subjects whose falls were simulated did survive. Analysis of simulation results indicated that, for some children under eight years old, peak accelerations of as high as 350 G, with a rate of onset of up to 200 000 G/s and a duration of up to 3 ms (approximate HIC = 1700-2800), would produce only moderate, reversible injury (as defined by AIS 2). For this same age group, the survival limit for head impacts - the level at which most people would sustain AIS 5 or greater injuries - was estimated to be as high as 600 G peak acceleration and 300 000 G/s for a duration of up to 3 ms (approximate HIC = up to 11 000). In feet-first simulations, the model predicted forces in the leg bones that correlated with observed injuries. The combination of in-depth on-site investigation and computer simulation of representative cases was found to be an effective method of studying impact injury tolerance.

This research was sponsored by the Insurance Institute for Highway Safety, Washington, D.C.