abnormally dangerous activity

An abnormally dangerous activity is related to tort law. The Restatement of Torts defines it as an activity that (1) is not of common usage, and (2) creates a foreseeable and highly significant risk of physical harm even when reasonable care is exercised by all actors. A person who is found by a court to have carried on an abnormally dangerous activity will be subject to strict liability for physical harm resulting from that activity. 

Origin of the Rule

In Rylands v. Fletcher, an English case from 1868, the opinion read that "[a] person who for his own purposes brings on his lands and collects and keeps there anything likely to do mischief if it escapes, must keep it in at his peril." American courts often cite this case as providing the origin of the rule on abnormally dangerous activities. In US jurisdictions, courts have never required that the activity take place on the defendant's land. However, they retained the requirement of "unnatural use" in the form of "not of common usage", meaning an activity that is unreasonable or inappropriate in light of the circumstances. 

Key Elements

The first factor is common usage. In the 2021 case Shuck v. Beck, the court found common usage if many people in the community “customarily carry on” the activity. Other states also look at frequency. For instance, in Vacation Vil. Homeowners Assn. Inc. v. Town of Fallsburg, a sewage treatment plant was deemed common usage because they are in most developed municipalities. So, driving cars is common usage, but storing toxic chemicals is not. The rationale is that there is no need for strict liability when many people impose a risk on each other, because of the principle of reciprocity: all of them enjoy the benefits and share the risks of the activity. On the other hand, if a dangerous activity is unusual, the persons engaging in it impose a risk on others who do not benefit, hence the need for strict liability. 

The second factor requires a highly significant risk of physical harm. Highly significant risk of physical harm: the term "physical harm" generally includes both bodily harm and property damage. A risk of physical harm is deemed "highly significant" if any of the following is true:

  • The likelihood of physical harm is unusually high, even though the severity of that harm is ordinary.
    • For example, using explosives in a residential neighborhood is very likely to result in physical harm, but the harm may be limited, in most cases, to moderate property damage.
  • The likelihood of physical harm is relatively low, but the severity of the potential harm is very high.

In any case, courts must evaluate the likelihood of physical harm and the potential severity of that harm in the context in which the activity took place. 

[Last updated in June of 2022 by the Wex Definitions Team]