In Hooker v. Department of Transportation (2002) 27 Cal.4th 198, a crane operator was killed when the crane tipped over because of instability caused by the crane operator's contraction of outriggers so that traffic could pass through a narrow overpass. The crane operator was an employee of an independent contractor hired to construct the overpass for the California Department of Transportation (Caltrans). His widow sued Caltrans on the theory that Caltrans had negligently exercised control over safety conditions at the worksite. The Caltrans construction manual provided that Caltrans was responsible for obtaining the contractor's compliance with all safety laws and regulations, being familiar with construction zone traffic management, being able to recognize and anticipate unsafe conditions, and visiting construction sites periodically to observe the operation and traffic conditions. The manual gave the Caltrans resident engineer authority to set compliance schedules for the correction of dangerous conditions and to shut down affected operations until they were corrected. The Caltrans representative at the jobsite had previously observed crane operators retract their outriggers to let vehicles pass and realized that the crane would be unstable if its boom were extended over its side when its outriggers were retracted. (Hooker, supra, 27 Cal.4th at pp. 202-203.) The California Supreme Court found that under these circumstances, the plaintiff had failed to show a triable issue of fact regarding whether Caltrans had affirmatively contributed to the injuries of the contractor's employee. (Id. at p. 212.) Hooker cites with approval Kinney v. CSB Construction, Inc. (2001) 87 Cal.App.4th 28. Kinney holds that where "(1) the sole factual basis for the claim is that the hirer failed to exercise a general supervisory power to require the contractor to correct an unsafe procedure or condition of the contractor's own making, and (2) there is no evidence that the hirer's conduct contributed in any way to the contractor's negligent performance by, e.g., inducing injurious action or inaction through actual direction, reliance on the hirer, or otherwise," the hirer should not be subject to liability. (Kinney, at p. 36.) In McKown v. Wal-Mart Stores, Inc. (2002) 17 Cal. 4th 219, a companion case to Hooker, the high court considered whether an employee of an independent contractor is barred from pursuing a lawsuit against the hirer of the independent contractor on the theory the hirer negligently provided unsafe equipment. (McKown v. Wal-Mart Stores, Inc., at p. 223.) The court answered that question in the negative and affirmed the decision of the appellate court holding a hirer liable for negligently providing an unsafe forklift for use by an independent contractor on the hirer's premises. It reasoned that "when a hirer of an independent contractor, by negligently furnishing unsafe equipment to the contractor, affirmatively contributes to the injury of an employee of the contractor, the hirer should be liable to the employee for the consequences of the hirer's own negligence." (Id. at p. 225.) Liability of the hirer arises where the hirer's conduct has affirmatively contributed to the injury. (Hooker, supra, 27 Cal.4th at pp. 211-212.) In footnote 3, the opinion explains: "Such affirmative contribution need not always be in the form of actively directing a contractor or contractor's employee. There will be times when a hirer will be liable for its omissions. For example, if the hirer promises to undertake a particular safety measure, then the hirer's negligent failure to do so should result in liability if such negligence leads to an employee injury." (Id. at p. 212, fn. 3.) In sum: The California Department of Transportation (CALTRANS) hired a contractor to construct an overpass. The contractor's employee was killed while operating a crane. It was alleged CALTRANS was liable for the death of the crane operator because it allowed traffic to use the overpass during construction, which lead to the crane operator's death. The question presented was whether an employee of a contractor may sue the hirer of a contractor for the tort of negligent exercise of retained control. (Id. at p. 201.) "We conclude that a hirer of an independent contractor is not liable to an employee of the contractor merely because the hirer retained control over safety conditions at a worksite, but that a hirer is liable to an employee of a contractor insofar as a hirer's exercise of retained control affirmatively contributed to the employee's injuries. In this case, although plaintiff raised triable issues of material fact as to whether defendant retained control over safety conditions at the worksite, plaintiff failed to raise triable issues of material fact as to whether defendant actually exercised the retained control so as to affirmatively contribute to the death of plaintiff's husband. Therefore, the trial court properly granted summary judgment in favor of defendant, and the Court of Appeal erred in reversing that judgment." (Hooker, supra, 27 Cal.4th at p. 202.)