I have been doing product liability cases since 1985. The thing to understand about a defective product case is that the product is on trial, not human conduct. Pennsylvania follows the Restatement (Second) of Torts, Section 402A. Under Pennsylvania Law, someone who sells any product in a defective condition unreasonably dangerous to the user or consumer or to his or her property is subject to liability for physical harm caused to the ultimate user or consumer, or to his property, if the seller is engaged in the business of selling such a product, and the product is expected to and does reach the user or consumer without a substantial change in the condition in which it is sold. This is also known as strict liability.