Third Circuit Confirms That Alleged Defect in “Simple” Component of More Complex System Must Be Proven by Expert Testimony When Facts Surrounding Defect Claim Are Beyond Common Knowledge


A plaintiff who alleges that a product is defective usually has to offer expert testimony in support of that allegation.  This should come as no surprise for complex products – if it took a team of scientists and engineers to bring the product to market, then a lay jury should not be asked to evaluate an alleged defect in that product without the aid of expert testimony.  But what if a plaintiff alleges a defect in the design of a relatively simple, more familiar component of a complex product?  The Third Circuit recently addressed that question in an opinion that, although nonprecedential and in some respects peculiar to New Jersey law, illustrates how a court should approach the issue.

In Kuhar v. Petzl Co., 2022 WL 1101580 (3d Cir. Apr. 13, 2022), Plaintiff fell and injured himself while using a safety harness that he had purchased as part of a kit seven years earlier.  He alleged that the fall occurred because a bolt attached to the carabiner of the safety harness had snapped due to a design and/or “indeterminate” or manufacturing defect.  In support of his claims, Plaintiff proffered a metallurgical and materials sciences expert who identified two alleged design defects – a “sharp profile change” and “sharp threads on the bolt” – and machining grooves that the expert deemed a manufacturing defect, some combination of which he claimed had caused the accident.  But some of the expert’s defect and causation opinions were “net opinions” – New Jersey parlance for “ipse dixit” opinions – and were excluded for lack of supporting data.  Other opinions were excluded because the expert failed to define his terms or explain his reasoning.  The Third Circuit agreed with the district court that the expert’s opinions lacked both reliability and fit, and affirmed its exclusion of all of the expert’s opinions.

This left Plaintiff without any expert testimony to support his defect claims.  He argued that his claims could proceed regardless, as a defect can sometimes be shown through circumstantial evidence such as proof of proper product use and the nature of the malfunction under New Jersey law.  Plaintiff contended that the alleged defects existed in a simple bolt and that a lay juror could “understand the function of a bolt, or whether a bolt is supposed to break.”  But, as the Third Circuit observed, the bolt was merely one component of a more complex system, and the issue under New Jersey precedent was not whether the instrumentality is categorically simple or complex – it is whether the factfinder’s common knowledge allows it to draw an inference of negligence or defectiveness, or whether it needs expert guidance to fairly draw such an inference.  On the facts, jurors would be unlikely to understand “the engineering design considerations; metallurgical aspects of plating the bolt; or the principles of physics at work on the bolt when in use.”  Thus, expert testimony would be required to establish the defects that Plaintiff alleged.  Lacking supporting expert testimony, the design defect claim was properly rejected.

Plaintiff argued that New Jersey’s indeterminate product defect test – a product liability variation on res ipsa loquitur – can be satisfied without expert testimony.  That test allows a jury to infer a defect where (1) the incident that harmed the plaintiff was of a kind that ordinarily occurs as a result of a product defect, and (2) the incident was not solely the result of causes other than product defect existing at the time of sale or distribution.  But the court held that an indeterminate product defect, like a specific defect, must be established by expert testimony when the critical inference is beyond the common knowledge of the factfinder.  Thus, it was once again not sufficient to argue that a lay jury should know “whether a bolt is supposed to break.”  Rather, one would need to understand how the bolt functions as part of the larger system, which in turn would require “scientific, technical, or other specialized knowledge.”  The lack of expert testimony compelled summary judgment in the defendants’ favor.

Kuhar is a fine example of a court requiring an expert to explain and support his opinions and, having concluded the expert failed to meet that standard, refusing to allow a plaintiff to simply punt the expert question to a lay jury.  It also nicely focuses on the right question to ask when evaluating the need for expert testimony when a plaintiff alleges a defect in a “simple” component of a more complex system.  In such cases, it is not enough to argue that a jury can conclude that the component should not fail.  If a jury cannot appreciate how the component functions in context and what demands the system makes on it, then the jury will need expert testimony to conclude that the component is defective.

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About the Author: Eric M. Friedman

Eric Friedman guides clients through all stages of product liability litigation, particularly working with expert witnesses to present the science behind clients' products. By leaning on his pre-law history as a biochemist, he is able to identify key arguments for and against clients and craft winning strategies for both motion practice and trial.

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