Characterization of Task Specific Force Systems and the Rational Selection of A-Frame Ladders

Abstract

Because it is inexpensive, an A-Frame ladder is routinely chosen to perform specific aerial work tasks. Presently, these death defying activities cannot be evaluated a priori using information furnished by ladder manufacturers relative to the resistance of their ladders or by trade organizations who cannot define the reasonably foreseeable load environment for various construction tasks. This paper proposes a methodology for rationally evaluating the safety of A-Frame ladders for specific overhead work tasks. A force-plate, normally used in gait testing, is used to safely support workers engaged in a specific work task. The force-plate output can be used to characterize the loading environment for a menu of important operations such as tuck pointing, painting, installation of lighting fixtures, speakers, and ceiling fans. Using statics, the loading menu may be accessed to simulate the forces applied to any ladder under any user profile. The overturning resistance of A-Frame ladders must be established by testing; static stability calculations are unconservative. When the loading environment associated with the installation of a typical ductwork detail was compared to the resistance of a special duty A-Frame ladder, the applied forces sometimes exceeded its lateral resistance. This is consistent with our field experience involving six death cases of sheet metal workers.