An ultrahazardous 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. In the Restatement of the Law 2d, Torts 2d, the term has been abandoned in favor of the phrase "inherently dangerous activity."

Categories of ultrahazardous activity

Several categories of activities are commonly recognized as being inherently hazardous; those who engage in them are subject to strict liability. These include:

Someone who is injured by one of these inherently hazardous activities while trespassing on the property of the person engaged in the activity is barred from suing under a strict liability theory. Instead, they must prove that the property owner was negligent.

In the United Kingdom, this area of law is governed by the rule established in Rylands v Fletcher.

Determining if an activity is ultrahazardous

Factors determining an activity is ultrahazardous:[2]

  1. The relative possibility of harm.
  2. The level of seriousness of potential harm.
  3. The level of activity – most persons would not regularly engage in ultrahazardous activities.
  4. Whether decreasing the possibility of harm requires exceptional measures of caution.
  5. Whether the risk of the activity outweighs its social value.
  6. Inappropriateness of the activity in the area where it is engaged in.


  1. ^ The injury, however, must arise from what makes the animal dangerous. See Alwin v. State Farm Fire and Casualty Co., 610 N.W.2d 218 (Wis. Ct. App. 2000).
  2. ^ See, e.g. Langan v. Valicopters, Inc. (1977)