GOV § 840.2

An employee of a public entity is liable for injury caused by a dangerous condition of public property if the plaintiff establishes that the property of the public entity was in a dangerous condition at the time of the injury, that the injury was proximately caused by the dangerous condition, that the dangerous condition created a reasonably foreseeable risk of the kind of injury which was incurred, and that either:

(a) The dangerous condition was directly attributable wholly or in substantial part to a negligent or wrongful act of the employee and the employee had the authority and the funds and other means immediately available to take alternative action which would not have created the dangerous condition; or

(b) The employee had the authority and it was his responsibility to take adequate measures to protect against the dangerous condition at the expense of the public entity and the funds and other means for doing so were immediately available to him, and he had actual or constructive notice of the dangerous condition under Section 840.4 a sufficient time prior to the injury to have taken measures to protect against the dangerous condition.