John R. Yannaccone, P.E., Principal Mechanical Engineer

Case Summary: Plaintiff set out to trim his hedges using a battery-operated hedge trimmer.  As he removed the blade guard, the trimmer started running while his thumb was in the area of the blade, resulting in severe injuries.

Expert Analysis: The hedge trimmer’s instructions indicated it was equipped with two switches, both of which had to be activated for the trimmer to operate.  One switch was located on the forward grip, and the other switch was located on the rear grip.  When functioning properly, the separate locations of the switches would require the user to have both hands clear of the blade before the trimmer would run.  On the day of the incident, Plaintiff had been holding the front grip in one hand while removing the blade guard with his other hand.  Since nothing was in contact with the rear grip, the trimmer should not have run.

Inspection of the hedge trimmer confirmed it was equipped with two switches, one on each grip.  The trimmer was in good condition and did not have any obvious damage that would affect the operation of the unit.  However, the hedge trimmer would occasionally run when only the front switch was activated.  This was an intermittent issue that occurred repeatedly during the inspection, with no clear outward indications prior to these occurrences.  

Further inspection determined that the rear switch, located inside the housing unit of the rear grip and activated by depressing the trigger, would sometimes fail to fully return to the off position when the trigger was released.  However, the difference in the trigger’s position when the trimmer would malfunction was less than ¼ inch, which would be virtually impossible for the operator to detect.  No attempt was made to determine the cause of the trigger sticking as that would have required disassembly of the trimmer.

Result:  Following the inspection where the hedge trimmer repeatedly malfunctioned, the defendant settled with the plaintiff.

John R. Yannaccone, P.E., Principal Mechanical Engineer with DJS Associates, Inc., can be reached via email at experts@forensicDJS.com or via phone at 215-659-2010.

Categories: Case Studies | John R. Yannaccone, P.E. | Mechanical Engineering

Tags: Equipment Failure | Mechanical Inspection | Personal Injury