ARCCA’s expert conducted an investigation of the evidence to determine the root cause of the accident, as well as the role that the design of the incident MEWP played in the accident.
During testing of the incident MEWP, some issues with the control console were discovered. The controls had an intermittent connection with the machine, which made responses to the controls inconsistent and unpredictable. Taking extreme care not to alter the evidence, ARCCA experts used X-ray imaging and 3D CT scans to identify improperly seated wire connections in the control console plug that were consistent the control issues identified during testing.
Based on the evidence ARCCA experts determined that the accident was most likely caused by a control malfunction leading to a Sustained Involuntary Operation (SIO) event. In a SIO event, contact with an obstruction pushes the operator into the controls, which causes the machine to drive harder into the obstruction. Some MEWPs are equipped with safety devices to guard against SIO events, but the subject MEWP was not. ARCCA experts designed, built, and tested a prototype automatic safety device that connected to an identical scissor lift to the incident machine. In laboratory tests, the ARCCA anti-SIO device greatly reduced the force exerted when the machine contacted an obstruction.