Mechanical Engineering Expert Opines on Tree Stand Failure


Product Liability Expert WitnessThis case involves a hunter who was seriously injured after a failed stitching on a tree stand caused him to fall from a tree. The stand in question was recently purchased from a sporting goods store, and had straps that served to secure it to the tree. At some point, the stitching on both straps malfunctioned. The Plaintiff fell from a great height, resulting in serious injuries. It is alleged that the stand was defectively manufactured, and that the Plaintiff had been using the stand in accordance with the provided instructions at the time of the accident.

Question(s) For Expert Witness

  • 1. Please discuss your background in designing and engineering tree stands.
  • 2. Is it possible that the straps were defective?
  • 3. Should the product have included warnings?

Expert Witness Response E-001114

I have 40+ years of industry experience and I am one of the leading authorities in the US on the failure of sports equipment, stools, and chairs. I am also a bow deer hunter and have used many different tree stands over the years, including ones that I designed for my own personal use. It is most likely that the straps and stitching are synthetic polymeric materials like polyester or nylon. I am an expert in synthetic materials including their strength properties and failure modes. I have a network of labs that can analyze the straps and stitching materials to determine if they are defectively manufactured. I believe that any device that supports body weight which would result in bodily injury if failure occurred, should have clear warnings regarding use and required maintenance. I have served as an expert in over 150 cases involving the failure of all kinds of plastic parts including pulleys, latches, pipes, hoses, stools, chairs, sports equipment, medical devices, toys, fabrics, bags, containers, helmets, etc. I believe that basic part design and material failure principles that have governed my forensic failure analysis projects over the past 40+ years also apply to tree stands.

Expert Witness Response E-006336

I have investigated several tree stand accidents and determined if a product defect contributed. I have extensive design engineering experience, my specialty being mechanical design, and analysis using finite element analysis (FEA). It is possible that the straps were defective. I am curious as to whether it was the straps that secure the top part of the stand failed, or the cable attachments that support the foot platform. It is also possible if it is the nylon straps that the failure is due to UV degradation, particularly if the stand was left in the tree. The failure could have been caused or exacerbated by the design of the stand such as the strap running across a sharp surface, or bending repeatedly. The product should have included warnings, and likely did. Most tree stands have warnings and/or instructions regarding not leaving the stand up but rather taking stand down after every use, which no one actually does and is unreasonable to expect, or base the safety of the stand on. I have worked on failure cases involving tree stand accidents. I am a licensed professional mechanical engineer, with a bachelor of science in Mechanical Engineering, and experience in mechanical design.

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