Ladders Expert Witnesses On Stepladder Accidents Part 2

Ladders and scaffolds expert witnesses at Technology Associates write on stepladder instability:
Three-leg contact can develop under a number of situations such as set-up on an uneven surface or when climbing, sliding, pivoting or “walking” a flexible ladder along the ground as the user’s work progresses. Dr. John Morse has cited a subtle type of unperceived three-leg stepladder contact named “Type-II racking”, which occurs during climbing as follows.

After the climber has one foot on the floor with his other foot on the first step, and one or both hands on the front rails at chest height, he pulls himself upward with one arm and attempts to keep his body straight. This imposes a torque about a vertical axis to the ladder. This torque, combined with the climber’s pulling force (which is necessary to raise his weight to the next step), tends to unload the rear legs. With these legs offloaded, and while this torque is still applied, the ladder twists or “racks” in the direction of the applied torque. When the climber’s foot then leaves the floor and reaches the first step, weight is shifted back onto the rear legs of the racked (slightly twisted) ladder. When this occurs, only one of the ladder’s rear legs can contact the ground. If this goes undetected, the climber has unknowingly created a three-legged ladder and the potential for instability, should center of gravity diagonal-crossover occur later after subsequent climbing or use.