In Johnson v. American Standard, Inc. (2008) 43 Cal.4th 56, the California Supreme Court held that the "sophisticated user" defense applies in California. "The sophisticated user defense exempts manufacturers from their typical obligation to provide users with warnings about the products' potential hazards. The defense is considered an exception to the manufacturer's general duty to warn consumers, and therefore, in most jurisdictions, if successfully argued, acts as an affirmative defense to negate the manufacturer's duty to warn." (Id. at p. 65.) "Under the sophisticated user defense, sophisticated users need not be warned about dangers of which they are already aware or should be aware. Because these sophisticated users are charged with knowing the particular product's dangers, the failure to warn about those dangers is not the legal cause of any harm that product may cause. The rationale supporting the defense is that 'the failure to provide warnings about risks already known to a sophisticated purchaser usually is not a proximate cause of harm resulting from those risks suffered by the buyer's employees or downstream purchasers.' " (Johnson, supra, 43 Cal.4th at p. 65.) In Johnson, the plaintiff was a trained and certified heating, ventilation, and air conditioning (HVAC) technician. (Johnson, supra, 43 Cal.4th at p. 61.) The plaintiff asserted negligence, strict liability failure to warn, strict liability design defect, and breach of implied warranties causes of action based on the defendant's alleged failure to warn the plaintiff of the potential hazards of exposure to R-22, a refrigerant commonly used in large air conditioning systems. (Id. at p. 62.) The California Supreme Court held that as an HVAC technician, the plaintiff knew or should have known about the hazards of R-22 exposure. (Id. at p. 74.) The court thus affirmed the granting of summary judgment in favor of the defendant. (Id. at p. 75.)