Our Supreme Court decided nearly 30 years ago in Greenman v. Yuba Power Products, Inc. (1963) 59 Cal. 2d 57, 27 Cal. Rptr. 697, 377 P.2d 897, that a person injured by a defective product did not need to rely on contractual theories, such as breach of express or implied warranty, to hold a remote manufacturer liable for injuries caused by a product. "A manufacturer is strictly liable in tort when an article he places on the market, knowing that it is to be used without inspection for defects, proves to have a defect that causes injury to a human being." (Id. at p. 62.) "The purpose of such liability is to insure that the costs of injuries resulting from defective products are borne by the manufacturers that put such products on the market rather than by the injured persons who are powerless to protect themselves." (Id. at p. 63.) The elements the plaintiff must prove were set forth succinctly in Greenman and have not changed substantially over the years: (1) "that he was injured"; (2) "while using the product in a way it was intended to be used"; (3) "as a result of a defect in design and manufacture . . . that made the product unsafe for its intended use"; (4) "of which plaintiff was not aware . . . ." (Id. at p. 64.) The concept of strict liability for engaging in ultrahazardous activities has long been recognized. In Green v. General Petroleum Corp. (1928) 205 Cal. 328, 270 P. 952, where an oil well suddenly erupted, showering the defendant's neighbor's property with oil and mud, the court held that liability would be imposed without proof of negligence. In Luthringer v. Moore (1948) 31 Cal. 2d 489, 190 P.2d 1, the court explained the principle which underlay its holding in Green: "The important factor is that certain activities under certain conditions may be so hazardous to the public generally, and of such relative infrequent occurrence, that it may well call for strict liability as the best public policy." (Luthringer v. Moore, supra, at p. 500.) The factors to be considered in determining whether a particular activity is abnormally dangerous or ultrahazardous are: (a) existence of a high degree of risk of some harm to the person, land or chattels of others; (b) likelihood that the harm that results from it will be great; (c) inability to eliminate the risk by the exercise of reasonable care; (d) extent to which the activity is not a matter of common usage; (e) inappropriateness of the activity to the place where it is carried on; (f) extent to which its value to the community is outweighed by its dangerous attributes.'" (SKF Farms v. Superior Court (1984) 153 Cal. App. 3d 902, 906, 200 Cal. Rptr. 497.) Only a limited number of activities have been classified as ultrahazardous, including blasting with explosives in the vicinity of populated areas (Balding v. D.B. Stutsman, Inc. (1966) 246 Cal. App. 2d 559, 564, 54 Cal. Rptr. 717), fumigating with industrial strength pesticide (Luthringer v. Moore, supra, 31 Cal. 2d at p. 500), and crop dusting with toxic chemicals (SKF Farms v. Superior Court, supra, 153 Cal. App. 3d at p. 905). The act of discharging a firearm has been held not to constitute an ultrahazardous activity. (Orser v. George (1967) 252 Cal. App. 2d 660, 672, 60 Cal. Rptr. 708, citing Jensen v. Minard (1955) 44 Cal. 2d 325, 328-329, 282 P.2d 7 and Tucker v. Lombardo (1956) 47 Cal. 2d 457, 463, 303 P.2d 1041.)