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To understand the possible mechanisms of ladder accidents and possible role current designs may play in these accidents, a multi-year study was initiated. Failure analysis of the structural members of the ladder and finite element models of the structural assembly were used to assess possible failure modes. Results indicated that structural failure is likely, and may often be a result of a combination of buckling, bending and torsion in the side rails. Experiments with commercially available ladders instrumented with strain gages indicate that measured strains and the resulting stresses were much higher than those predicted from static analysis, and suggest a dynamic factor of at least 2.5 is necessary to adequately account for the loads applied to the structure. This dynamic load phenomenon was found to exist for both aluminum and fiberglass step ladders. These results suggest that current designs that utilize open-channel side rails may not meet the safety factor requirements set for in the ANSI standards for portable ladders.