An ultra hazardous activity in the common law of torts is one that is so inherently dangerous that a person engaged in such an activity can be held strictly liable for injuries caused to another person, even if the person engaged in the activity took every reasonable precaution to prevent others from being injured.

The following factors determine an activity as ultra hazardous:

• The relative possibility of harm.
• The level of seriousness of potential harm.
• If the possibility of harm is decreased with the utmost care.
• Whether the risk of the activity outweighs its social value.
• Inappropriateness of the activity in the area it is commenced

In some jurisdictions liability for damages to an adjoining owner from ultra hazardous activities on one’s land is predicated upon negligence[Klostermann v. Houston Geophysical Co., 315 S.W.2d 664 (Tex. Civ. App. San Antonio 1958)].  An adjoining landowner has a non delegable duty of reasonable care if he or she knows or should know that inherently dangerous activities are being performed on his or her property even by independent contractors,[ Kinsey v. Spann, 139 N.C. App. 370, 533 S.E.2d 487 (2000)] and thus any negligence on the part of the workers may be imputed to the property owner.  In the United Kingdom, this area of law is governed by the rule established in Rylands v Fletcher.