Defective Material Casting Linked to Catastrophic Failure of Power Tool

This case involves a man who suffered serious injuries when an angle grinder exploded while he was using it to remove a seized bolt. The grinder was equipped with a metallic safety cover that shattered when the grinding wheel exploded, sending metal fragments into the man’s arm. It was claimed that the safety guard, which should have prevented or at least mitigated some of the injuries suffered by the tool’s user, was defectively designed and / or manufactured.

Question(s) For Expert Witness

1. Please describe your experience in product failure analysis as a metallurgist.

2. Would you be able to review this case and give an opinion as to why this part may have failed?

Expert Witness Response E-039290

I have over twenty-five years of expertise in the determination of root cause and problem resolution, and extensive experience designing and conducting field and laboratory testing. My background also extends to the areas of materials characterization, fractography, metallography, and mechanical testing. It sounds like the tool may have been fabricated incorrectly. These tools often times are heat treated incorrectly, which may create a brittle product. Subsequent impact use may cause a piece to spall from the tool, creating a projectile with sharp edges. Additionally, an improper quench can cause thermal cracking, which can also lead to a chunk breaking off during use. It sounds like the tool was not properly manufactured.