Abnormally Dangerous Activities

Abnormally Dangerous Activities

An abnormally dangerous activity is an activity that creates an unusually serious risk of harm even when the person conducting it exercises reasonable care.

Under the traditional rules of tort law, a person who engages in an abnormally dangerous activity may be held strictly liable for certain harm resulting from that activity. The plaintiff generally does not have to prove that the defendant acted negligently.

The central principle is simple:

When an activity creates an extraordinary and unavoidable risk, the law may place responsibility for resulting harm on the person who chooses to conduct the activity.

This doctrine is an important exception to the ordinary negligence system. Most accidental injuries are governed by negligence: the plaintiff must show that the defendant failed to act as a reasonably careful person would have acted.

Abnormally dangerous activity doctrine takes a different approach.

Even if the defendant took every reasonable precaution, the defendant may still be responsible for harm caused by the special risks that make the activity unusually dangerous.

But the doctrine is deliberately narrow. Not every dangerous activity is abnormally dangerous. Modern life contains countless activities that carry substantial risks, yet those activities are ordinarily governed by negligence rather than strict liability.

Understanding that distinction is essential.

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What Makes an Activity Abnormally Dangerous?

The phrase “abnormally dangerous” does not simply mean “very dangerous.”

A motorcycle can be dangerous.

A construction site can be dangerous.

A commercial kitchen can be dangerous.

Driving a vehicle can be dangerous.

Operating a factory can be dangerous.

Yet these activities are ordinarily subject to negligence principles.

The question is therefore not simply:

“Could this activity hurt someone?”

Almost every human activity can.

The more important question is:

Does this activity create a special type of serious risk that justifies imposing liability even when reasonable care is exercised?

That inquiry requires consideration of several factors.

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The Modern Restatement Approach

The modern American formulation is associated with the Restatement of Torts.

Rather than relying on a single definition, courts generally consider several factors when determining whether an activity is abnormally dangerous.

These include:

1. the degree of risk of harm;
2. the likelihood that the resulting harm will be great;
3. the inability to eliminate the risk through the exercise of reasonable care;
4. whether the activity is a matter of common usage;
5. whether the activity is inappropriate for the location where it is conducted;
6. the extent to which the activity’s value to the community is outweighed by its dangerous attributes.

No single factor necessarily decides the question.

The analysis is contextual.

An activity may be abnormally dangerous in one setting but not another, depending on the circumstances and applicable law.

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1. High Degree of Risk

The first consideration is the degree of risk created by the activity.

An activity involving only a minor possibility of harm is unlikely to justify strict liability.

For example, painting the exterior of a house creates some risk.

But that risk is ordinarily manageable through reasonable precautions.

By contrast, activities involving explosives, certain highly dangerous substances, or comparable hazards may create risks that are fundamentally different in character.

The greater the inherent risk, the stronger the argument for strict liability.

But high risk alone is not enough.

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2. Potential Magnitude of Harm

Courts also consider how serious the consequences could be if the risk materializes.

An activity that creates a small possibility of catastrophic injury may raise different concerns from an activity that creates a small possibility of minor property damage.

Consider controlled blasting.

Even if the probability of an accident is relatively low, an accident could cause:

• serious bodily injury;
• death;
• destruction of buildings;
• flying debris;
• structural damage; or
• widespread property damage.

The potentially extraordinary magnitude of harm is therefore relevant.

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3. Can Reasonable Care Eliminate the Risk?

This is one of the most important factors.

Negligence law assumes that many risks can be reduced through reasonable precautions.

Strict liability becomes more attractive when reasonable care cannot eliminate the inherent danger.

Imagine two activities.

Activity A

A company operates heavy machinery. Proper training, maintenance, inspection, and supervision can substantially eliminate the risk.

Activity B

A company uses explosives. Even with extraordinary care, the physical characteristics of explosives create risks that cannot be completely eliminated.

The second activity presents a stronger case for strict liability.

The doctrine therefore focuses not merely on whether the defendant was careful, but on whether care itself can adequately control the relevant risk.

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4. Common Usage

Courts also consider whether the activity is a matter of common usage.

An activity that is widespread and ordinarily undertaken by members of the community is less likely to be treated as abnormally dangerous.

Driving provides an obvious example.

Millions of people drive automobiles every day. Driving can cause catastrophic injuries, but it is a common activity governed primarily by negligence rules.

By contrast, an unusual activity involving extraordinary hazards may receive different treatment.

This factor reflects an important policy consideration:

The law is reluctant to impose strict liability for activities that are ordinary and socially integrated parts of everyday life.

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5. Appropriateness of the Location

Location can matter.

An activity that is reasonable in one location may create extraordinary risks in another.

Consider an industrial activity involving substantial hazards.

Conducting it in a remote industrial area may create different risks from conducting the same activity in the middle of a densely populated residential neighborhood.

The location may therefore affect whether an activity should be considered abnormally dangerous.

This does not mean that an otherwise dangerous activity automatically becomes strict liability simply because it occurs in the wrong place.

Rather, location is one factor in determining whether the activity has the unusual characteristics that justify strict liability.

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6. Social Value vs. Dangerousness

The law may also consider the social value of the activity.

An activity can be highly useful and still be dangerous.

The fact that society benefits from an activity does not necessarily eliminate strict liability.

Instead, the law may ask whether the activity’s value and ordinary character justify treating the risks under negligence principles or whether the unusual danger warrants strict liability.

This factor reflects a broader policy judgment.

Tort law is not simply trying to eliminate risk.

If the law imposed strict liability on every activity that could seriously injure someone, enormous portions of modern life would become legally impractical.

The objective is to distinguish ordinary socially accepted risks from exceptional risks.

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Classic Examples of Abnormally Dangerous Activities

Examples traditionally associated with strict liability include certain activities involving:

• explosives;
• blasting;
• large quantities of hazardous substances;
• certain toxic or dangerous chemicals;
• highly dangerous industrial operations; and
• other activities that create extraordinary risks that cannot be adequately eliminated through reasonable care.

The precise boundaries vary among jurisdictions.

An activity should never be classified as abnormally dangerous merely because it appears frightening or technologically sophisticated.

The legal test must be applied to the particular circumstances.

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Explosives and Blasting

Blasting is one of the clearest illustrations.

Suppose a construction company needs to remove a large quantity of rock.

It uses explosives.

The company:

• hires qualified professionals;
• carefully calculates the amount of explosive material;
• establishes safety zones;
• inspects the site;
• follows all applicable regulations; and
• takes reasonable precautions.

Despite these precautions, the explosion sends debris onto neighboring property and damages a house.

A negligence claim might fail if the company exercised reasonable care.

A strict-liability claim may nevertheless succeed if the blasting activity qualifies as abnormally dangerous under applicable law and the injury resulted from the characteristic risk of blasting.

This demonstrates the central principle of the doctrine:

The defendant’s carefulness does not necessarily eliminate liability.

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The Importance of the Characteristic Risk

Strict liability does not make an operator responsible for every injury occurring during an abnormally dangerous activity.

The harm generally must arise from the type of risk that makes the activity abnormally dangerous.

This is a critical limitation.

Imagine that a company is conducting controlled blasting.

At the same time, a pedestrian trips on an ordinary crack in the sidewalk several blocks away.

The pedestrian cannot simply argue:

“The company was conducting an abnormally dangerous activity, therefore it is strictly liable for my injury.”

The blasting activity did not cause the accident.

Likewise, suppose an employee at the blasting company carelessly leaves a toolbox in a walkway and a visitor trips over it.

The resulting injury may be governed by ordinary negligence principles rather than the strict-liability rule associated with blasting.

The doctrine is tied to the special danger, not merely to the defendant’s participation in a dangerous activity.

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Abnormally Dangerous Activities and Causation

Causation remains essential.

A plaintiff generally must establish that the defendant’s abnormally dangerous activity caused the injury.

Two questions are particularly important:

Factual causation

Did the activity actually cause the harm?

Scope of liability

Was the harm sufficiently connected to the special risk that makes the activity abnormally dangerous?

The second question is particularly important because strict liability is not unlimited.

The defendant is generally responsible for the consequences of the extraordinary risks that justify imposing strict liability—not every conceivable event that happens while the activity is being conducted.

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Strict Liability Without Negligence

The defining feature of this doctrine is that the plaintiff generally does not need to prove negligent conduct.

Consider two cases.

Case One: Negligence

A company stores ordinary construction materials.

An employee carelessly stacks the materials.

They fall onto a neighbor’s property.

The plaintiff must establish the elements of negligence.

Case Two: Abnormally Dangerous Activity

A company conducts blasting.

The company exercises reasonable care.

The blast nevertheless creates the type of harm that makes blasting abnormally dangerous.

The plaintiff may be able to recover under strict liability without proving that the company was careless.

The difference is therefore not simply the level of care.

It is the legal classification of the activity.

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Why Impose Strict Liability?

Several theories support the doctrine.

Risk Allocation

The person choosing to conduct an unusually dangerous activity creates a special risk for others.

The law may therefore assign the resulting costs to that person.

Loss Spreading

Commercial operators may be better positioned to insure against unusual risks and distribute those costs through the economic structure of the enterprise.

Deterrence

Strict liability can encourage businesses to consider whether extraordinarily dangerous activities are justified and whether safer alternatives exist.

Corrective Justice

When an extraordinary risk imposed by one person’s activity causes harm to another, compensation may be considered appropriate even when the defendant was not negligent.

These theories are complementary rather than mutually exclusive.

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Strict Liability Is Not a Judgment That the Activity Is Wrong

This distinction is important.

An activity can have enormous social value and still generate strict liability.

The law does not necessarily say:

“You should not do this.”

Instead, it may say:

“If you choose to conduct this unusually dangerous activity, you should bear responsibility for certain harms that result from its inherent risks.”

That is a fundamentally different proposition.

Strict liability therefore does not necessarily prohibit dangerous activities.

It allocates their costs.

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Strict Liability and Negligence Can Coexist

An abnormally dangerous activity can generate both strict-liability and negligence issues.

Suppose a company conducts blasting.

The activity itself may trigger strict liability.

But suppose the company also violates a basic safety rule by allowing unauthorized people into the blast zone.

That additional conduct may constitute negligence as well.

The plaintiff may therefore have multiple possible theories.

Strict liability does not make negligence irrelevant.

Instead, the two doctrines can operate alongside one another.

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Regulatory Compliance Does Not Necessarily Defeat Strict Liability

A defendant may argue:

“We followed every government safety regulation.”

That can be relevant evidence.

But regulatory compliance does not necessarily eliminate strict liability for an abnormally dangerous activity.

Government regulations may establish minimum safety requirements.

The common-law strict-liability doctrine asks a different question:

Who should bear the risk of harm arising from the extraordinary characteristics of the activity?

Consequently, compliance with regulations does not automatically answer the tort question.

The precise effect of compliance varies by jurisdiction and by the governing statutory framework.

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Location and the Community

Location is particularly important because the same activity can create radically different risks depending on where it occurs.

Imagine an activity involving hazardous materials.

In an isolated industrial area, the population exposed to the risk may be relatively small.

In a densely populated residential area, thousands of people may be exposed.

The law can therefore consider whether the activity is appropriate to the place where it is conducted.

This illustrates an important idea in tort law:

Danger is not always an intrinsic characteristic of an activity; sometimes danger depends on the relationship between the activity and its surroundings.

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Common Activities Are Usually Governed by Negligence

A common misunderstanding is that any activity with significant risks should trigger strict liability.

That would make strict liability extraordinarily broad.

Consider:

• driving;
• construction;
• operating machinery;
• farming;
• commercial transportation;
• operating restaurants;
• using electrical equipment.

All of these activities can cause serious injury.

Yet society generally treats them as ordinary activities that should be regulated primarily through reasonable-care standards.

The law therefore distinguishes between ordinary risks of modern life and exceptional risks associated with unusual activities.

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The Historical Development of the Doctrine

The roots of strict liability for dangerous activities can be traced to the famous nineteenth-century English case Rylands v. Fletcher.

In that case, the defendant constructed a reservoir, and water escaped onto neighboring property.

The case became associated with a principle under which a person who brings something onto land and keeps it there in circumstances involving an extraordinary risk may be responsible for resulting harm.

American law developed its own approach.

Modern American tort law generally treats the doctrine through the more structured concept of abnormally dangerous activities, rather than applying a broad rule to every unusual accumulation or use of property.

The historical development is important because it shows how tort law moved from broad ideas of responsibility for dangerous conditions toward more carefully defined categories and factors.

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Abnormally Dangerous vs. Ultrahazardous

Students may encounter both expressions:

• abnormally dangerous activity
• ultrahazardous activity

Historically, courts and commentators have used both terms.

Modern American tort law generally prefers abnormally dangerous activity.

The terminology matters less than the underlying legal question:

Does the activity create a special and extraordinary risk that remains even when reasonable care is exercised?

When reading older cases, however, students should recognize that “ultrahazardous” may refer to substantially similar concepts.

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Abnormally Dangerous Activities vs. Dangerous Products

These doctrines should not be confused.

An abnormally dangerous activity concerns the activity itself.

Products liability concerns the condition of a product and whether the product is defective under applicable law.

For example:

Activity

A company conducts blasting with explosives.

The danger arises from the activity.

Product

A manufacturer sells a defective pressure vessel that unexpectedly explodes.

The claim may involve products liability.

Both doctrines can involve strict liability, but they rest on different legal foundations.

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Abnormally Dangerous Activities vs. Negligence

The distinction can be summarized:

Question	Negligence	Abnormally Dangerous Activity
Must plaintiff prove unreasonable conduct?	Generally yes	Generally no
Is the activity itself central?	Usually no	Yes
Is reasonable care a defense to liability?	Generally yes	Not necessarily
Must causation be established?	Yes	Yes
Does the doctrine apply to ordinary risky activities?	Yes	Generally no
Is strict liability involved?	No	Yes
Is the risk unusually dangerous despite precautions?	Not required	Important factor

The conceptual difference is therefore straightforward:

Negligence regulates conduct. Strict liability for abnormally dangerous activities allocates extraordinary risks.

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Defenses and Limitations

Strict liability does not mean that the defendant has no possible defenses.

Depending on jurisdiction and circumstances, issues may include:

• assumption of risk;
• consent;
• comparative responsibility;
• contributory negligence;
• causation;
• misuse or other plaintiff conduct;
• statutory limitations;
• intervening causes; and
• whether the harm actually arose from the characteristic risk of the activity.

The exact effect of plaintiff negligence is particularly jurisdiction-dependent.

A plaintiff who knowingly and voluntarily encounters an extraordinary danger may raise a different question from a person who is unexpectedly exposed to the risk.

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The Role of Foreseeability

Foreseeability operates somewhat differently here than in ordinary negligence.

In negligence, foreseeability is central to determining whether a duty exists, whether conduct was unreasonable, and whether harm falls within the scope of liability.

In strict liability for abnormally dangerous activities, the central inquiry is instead whether the activity is sufficiently dangerous to justify strict liability and whether the harm resulted from the activity’s characteristic risk.

That does not make foreseeability irrelevant.

But the doctrine is not based on the defendant’s failure to foresee harm in the ordinary negligence sense.

This distinction is important when analyzing an examination problem.

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A Practical Exam Framework

When confronted with an abnormally dangerous activity problem, work through the following sequence.

Step 1: Identify the activity

What exactly was the defendant doing?

Do not describe it merely as “dangerous.”

Be precise.

Step 2: Ask whether the activity is abnormally dangerous

Consider:

• degree of risk;
• potential magnitude of harm;
• ability to eliminate risk through reasonable care;
• common usage;
• appropriateness of the location;
• social value.

Step 3: Identify the characteristic risk

What makes the activity unusually dangerous?

Is that the risk that actually caused the plaintiff’s injury?

Step 4: Establish causation

Did the activity cause the plaintiff’s harm?

Step 5: Determine whether the plaintiff’s harm falls within the doctrine

Strict liability is not unlimited.

The injury must generally be connected to the special danger that justifies the rule.

Step 6: Consider defenses

Examine consent, assumption of risk, plaintiff conduct, causation, and other applicable defenses.

Step 7: Consider alternative theories

Even if strict liability is uncertain, ask whether the facts support:

• negligence;
• trespass;
• nuisance;
• products liability; or
• another tort theory.

This approach produces a much stronger legal analysis than simply stating:

“Explosives are dangerous, so strict liability applies.”

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Hypothetical: Careful Blasting

A construction company needs to remove rock beneath a future highway.

It obtains permits and hires experts.

The company calculates the explosive charge carefully and establishes a safety perimeter.

During the blast, rocks are thrown into a neighboring property and destroy a garage.

The homeowner sues.

Analysis

The first question is whether blasting constitutes an abnormally dangerous activity under the applicable law.

If it does, the homeowner generally does not need to prove that the company failed to exercise reasonable care.

The next question is causation.

The blast caused the property damage.

Finally, the court would consider whether the damage resulted from the characteristic risk that makes blasting abnormally dangerous.

If those requirements are satisfied, strict liability may apply.

The company’s extensive precautions would not necessarily defeat liability.

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Hypothetical: Negligent Activity at a Construction Site

A construction company is building an apartment building.

A worker carelessly leaves a heavy piece of equipment unsecured.

The equipment falls and injures a pedestrian.

The construction project is obviously dangerous, but construction itself is ordinarily not treated as an abnormally dangerous activity simply because it involves substantial risks.

The plaintiff would therefore ordinarily analyze the claim through negligence or another applicable theory.

The key distinction is:

Dangerous does not automatically mean abnormally dangerous.

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Hypothetical: Unrelated Injury

A company conducts an activity that qualifies as abnormally dangerous.

A visitor comes onto the property and slips on an ordinary wet floor unrelated to the dangerous activity.

The visitor cannot simply invoke strict liability because the defendant was engaged in an abnormally dangerous activity.

The injury must be causally connected to the special risk created by that activity.

This limitation prevents strict liability from becoming unlimited liability.

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Why the Doctrine Remains Important

Abnormally dangerous activity doctrine illustrates a fundamental principle of tort law:

Legal responsibility does not always depend on moral blame.

A person can behave perfectly reasonably and still bear responsibility for certain consequences of an activity.

This can seem harsh.

But the doctrine rests on a different conception of fairness.

If a person chooses to conduct an activity that imposes extraordinary risks on others, the legal system may decide that the person should bear the costs when those risks materialize.

The person may be free to conduct the activity.

But freedom to create the risk can come with responsibility for its consequences.

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Economic Analysis of Abnormally Dangerous Activities

Economic analysis provides another explanation.

Suppose an activity creates an expected accident cost.

Under negligence, a business can potentially avoid liability by demonstrating that it took reasonable precautions.

Under strict liability, the business must consider the expected costs of injuries resulting from the activity even when it operates carefully.

This encourages the business to ask:

• Is the activity worth undertaking?
• Can the activity be redesigned?
• Can a safer alternative be used?
• Should the activity be moved?
• Should insurance be purchased?
• Should the activity be conducted less frequently?

Strict liability therefore encourages internalization of accident costs.

The enterprise does not necessarily stop the activity.

Instead, it incorporates the risks into the economic decision of whether and how to conduct it.

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Corrective Justice and Abnormally Dangerous Activities

Corrective justice offers a different perspective.

Suppose A’s unusually dangerous activity causes B’s property to be destroyed.

A may not have acted negligently.

Nevertheless, B has suffered a loss because of a risk A chose to create.

Strict liability allows the legal system to say:

A should restore B’s loss, even though A was not careless.

This does not necessarily mean that A deserves punishment.

The purpose is compensation and restoration rather than moral condemnation.

The distinction between wrongdoing and responsibility for risk is therefore central to understanding the doctrine.

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Abnormally Dangerous Activities and Modern Technology

New technologies raise difficult questions about whether traditional categories remain sufficient.

Consider activities involving:

• highly advanced industrial systems;
• autonomous machinery;
• dangerous chemicals;
• biotechnology;
• large-scale energy systems;
• drones;
• experimental technologies; or
• other activities involving unusual and difficult-to-control risks.

The fact that a technology is new does not automatically make it abnormally dangerous.

The traditional factors remain relevant.

The central inquiry is still whether the activity creates an exceptional risk that cannot adequately be controlled through reasonable care and whether strict liability is appropriate as a matter of law.

Modern technology therefore creates new factual problems without necessarily requiring a completely new conceptual framework.

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Key Takeaways

1. An abnormally dangerous activity is an activity that creates an unusually serious risk of harm even when reasonable care is exercised.
2. Abnormally dangerous activities can give rise to strict liability.
3. Not every dangerous activity is abnormally dangerous.
4. Courts consider factors including the degree of risk, magnitude of potential harm, ability to eliminate the risk through reasonable care, common usage, location, and social value.
5. The plaintiff generally must show that the harm resulted from the characteristic risk of the activity.
6. Causation remains essential.
7. Reasonable care may not defeat liability when strict liability properly applies.
8. Regulatory compliance does not necessarily eliminate strict liability.
9. The doctrine is different from products liability, although both can involve strict liability.
10. The deeper justification for the doctrine includes risk allocation, compensation, deterrence, loss spreading, and corrective justice.

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Frequently Asked Questions

What is an abnormally dangerous activity?

It is an activity that creates an unusually serious risk of harm that cannot adequately be eliminated through reasonable care and that is sufficiently exceptional to justify strict liability under applicable law.

What are examples of abnormally dangerous activities?

Traditional examples include certain forms of blasting, use of explosives, and activities involving unusually dangerous substances. The exact classification depends on the jurisdiction and circumstances.

Does negligence have to be proved?

Generally no. If the activity qualifies for strict liability, the plaintiff generally does not need to establish that the defendant acted unreasonably.

Is every dangerous activity subject to strict liability?

No. Ordinary dangerous activities such as driving and construction are generally governed by negligence.

Can careful conduct still result in liability?

Yes. That is a central characteristic of strict liability for abnormally dangerous activities.

Does causation still matter?

Yes. The plaintiff must generally establish that the activity caused the injury and that the injury resulted from the type of risk for which strict liability is imposed.

Does social value prevent strict liability?

Not necessarily. Social value is one factor considered in determining whether an activity should be classified as abnormally dangerous.

Is blasting always an abnormally dangerous activity?

Not necessarily in every jurisdiction or circumstance. Blasting is a classic example, but the legal classification depends on the applicable law and facts.

What is the difference between ultrahazardous and abnormally dangerous?

The terms have been used differently over time, but “abnormally dangerous” is the modern terminology generally used in American tort law.

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Further Reading

For an accessible overview of tort law and related concepts, see the Cornell Law School Legal Information Institute:

Cornell LII — Tort

Cornell LII — Tort Law resources

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Conclusion

Abnormally dangerous activity doctrine represents one of the clearest examples of strict liability in tort law.

The law ordinarily asks whether a person behaved reasonably. But some activities create risks that remain extraordinary even when the person conducting them exercises exceptional care.

In those circumstances, tort law may decide that the person who chooses to create the risk should bear responsibility for certain resulting harms.

The doctrine is intentionally narrow. Danger alone is not enough. The activity must possess characteristics that distinguish it from ordinary risky activities, and the plaintiff’s injury must be connected to the special risk that justifies strict liability.

Ultimately, the doctrine reflects a fundamental choice about responsibility:

When extraordinary risks are deliberately introduced into the world, the person who creates those risks may be required to bear the consequences when those risks become reality.