In some circumstances, a plaintiff lacking direct evidence of an identifiable, specific defect may be permitted to use circumstantial evidence to prove that a product malfunctioned and create a triable inference of a product defect. Some courts may treat proof of a product malfunction as circumstantial evidence of a product defect because a product will not ordinarily malfunction (or perform outside the reasonable safety expectation of the consumer) in the absence of a defect. This circumstantial evidence doctrine, commonly known as the “malfunction theory,” may provide plaintiffs with a pathway to establish a prima facie case of a product defect.
While the malfunction theory sometimes allows plaintiffs to bring a claim for a product defect where the product is no longer available or a specific defect cannot be identified, plaintiffs often attempt to stretch the theory beyond its logical bounds. In a recent case from Idaho, Black v. DJO Global, Inc., the Idaho Supreme Court rejected use of the malfunction theory when the alleged product “failure” (or malfunction) was the occurrence of a known risk, i.e., one that could occur even when the product performs as intended. Black v. DJO Glob., Inc., 488 P.3d 1283, 1288 (Idaho 2021).
The malfunction theory is a principle of circumstantial evidence akin to the doctrine of res ipsa loquitur. Under negligence law, the doctrine of res ipsa loquitur allows a jury to infer a defendant’s negligence when the circumstances of an accident suggest that the accident could not have occurred in the absence of the defendant’s negligence. However, because res ipsa loquitur is designed to establish negligence rather than product defectiveness, most courts decline to apply it to strict liability products liability or breach of warranty claims. Instead, malfunction theory allows a plaintiff to establish a prima facie case of a product defect by showing that the product failed in proper use under circumstances that raise a reasonable inference of a product defect.
Under the malfunction theory, a product may be inferred to be defective by circumstantial evidence that demonstrates: (1) the product malfunctioned; (2) the malfunction occurred during proper use; and (3) the product had not been altered or misused after leaving the defendant’s control in a manner that probably caused the malfunction.
In Black, the Idaho Supreme Court emphasized that for the malfunction theory to apply, “the product at issue must be of a type which permits a jury to infer that an injury would not have occurred had there not been a defect attributable to the manufacturer.” The plaintiff had suffered burns from electrode pads used during electric stimulation therapy. The operating manual that accompanied the product specifically noted that skin irritation and burns beneath the electrodes have been reported with the use of muscle stimulators. The Court reasoned that because “Black suffered an injury that is the precise type of injury that is known to result” from use of the product, “this fact precludes a jury from inferring that an injury would not have occurred had there not been a defect attributable to the manufacturer.” The Court held that because burns were a known risk, their occurrence did not mean that the product had “malfunctioned.” Thus, the Idaho Supreme Court held that plaintiff’s defect claims failed, and the manufacturer was entitled to summary judgment.
While resort to the malfunction theory may be permissible when the circumstances of a case combine to prevent the plaintiff from establishing defectiveness and causation by ordinary methods of proof, such as in cases where the product is lost, damaged, or otherwise destroyed, courts and juries should not be allowed to apply the doctrine broadly. Inferring a malfunction when the product performed within the bounds of expectations, as in the occurrence of a known risk or side effect, is a bridge too far, particularly when the product is available for inspection and analysis. No shortcut to proof of defect is needed. The Black case is a good example of the doctrine’s limits.
