Mechanical Engineering Expert Opines on Unsafe Power Tool


Mechanical Engineering Expert WitnessThis case takes place in Massachusetts and involves injuries that were sustained by a construction worker due to alleged manufacturing defects in a large angle grinder. At the time of the accident, the worker was using the grinder to cut a large section of metal piping. The worker was wearing appropriate clothing and safety equipment, including eye and ear protection, and was working in accordance with accepted best practices for operator safety. At some point the cutting disk attached to the grinder broke, causing the operator to immediately lose control of the tool, which deflected into the man’s leg. The remains of the cutting wheel had continued to spin at high speed and caused a devastating laceration. Following the incident, it was discovered that the grinding wheel had a potentially defective weld that may have caused the wheel to break. Additionally, it was claimed that the grinder itself lacked important safety features, such as a retractable protective guard, which may have prevented the injury after the grinding wheel failed. An equipment appraisal expert witness was needed for this matter.

Question(s) For Expert Witness

  • 1. Do you have extensive experience working at a company that manufacture's grinders similar to the one noted above?
  • 2. Could this accident have been prevented if proper safety mechanisms were installed on the grinder?

Expert Witness Response

I have extensive experience in the design of equipment used in the cutting and forming of metal, including angle grinders as described in the summary above. I served as the chief product engineer at some of the country’s top tool design and manufacturing companies, and have great familiarity with handheld power tools. I am the author of one of the most widely cited articles on power tool safety engineering, and have spoken and taught about the engineering aspects of power tool engineering at the national level. I invented and currently hold a patent on an “Inertial Safety Device” which is designed to prevent injury due to kickback in hand held circular saws. Similar systems are commonly installed on power tools sold by the overwhelming majority of manufactures, and are considered standard. It is my opinion that the injuries could have been prevented or mitigated with properly designed and installed safety devices. While a defect in the cutting disk may have caused the accident here, the lack of a retractable guard to prevent injury after catastrophic failures is the true issue.

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