Mobile Elevated Work Platforms (MEWPs), such as scissor lifts, boom lifts, and vertical mast lifts, are mobile machines that allow a worker to maneuver themselves and their tools to reach elevated work areas like ceilings, power poles, vertical storage areas, etc. A major hazard of operating a MEWP is entrapment, where the occupants of the MEWP become entrapped or pinned between the work platform and an obstruction. In this case, a welder was trapped between the railing of their scissor lift and an overhead beam. The welder experienced extreme forces and died as the result of their injuries.
Steps Taken:
A team of ARCCA experts conducted a thorough investigation of the evidence to determine the root cause of the failure, as well as the origin of the components involved in the failure by:
- Reviewing the initial documentation including OSHA investigation reports and supporting documents, worker statements, accident reports by the controlling contractor, invoices, maintenance records, training records, technical data sheets, and the plaintiff’s product liability complaint.
- Analyzing patents and publications describing safety devices available on the market for MEWPs manufactured at or before the manufacturing date of the incident MEWP.
- Preforming a joint inspection and testing of the evidence and incident MEWP with experts representing each of the involved parties present.
- Electrical testing of various components and systems in the incident MEWP and its control console.
- X-ray imaging and taking 3D Computer Tomography (CT) scans of the incident MEWP control console and its connectors.
- Designing an automatic safety device to detect entrapment of the operator or collision with an obstruction, stop the machine, sound an alarm, and allow the operator or rescuers to engage a momentary bypass to re-activate the machine and free the operator or clear the obstruction.
- Designing a control console that could only be installed in a location where accidental engagement of the controls was unlikely.
- Constructing and preforming laboratory testing of a prototype safety device that could successfully stop the same model of MEWP as the incident scissor lift in the event of operator entrapment or collision with an obstruction.
Final Findings:
ARCCA’s experts 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.
