Strict Liability vs. Negligence Per Se: Legal Responsibility Without a Law Degree

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A defective product, a dog bite and a broken safety rule can each lead to an injury claim, and the claims do not all work the same way. Strict liability can remove the need to prove carelessness. Negligence per se stays inside a negligence claim but uses a law that was broken as the measure of careful conduct.

The details depend on the state; this article uses California’s rules as its main example. There, people who carry out certain dangerous activities remain legally responsible for the harm even if they were careful. California law also treats a qualifying violation of a statute, ordinance or regulation as a presumption of carelessness that the person who broke it can rebut.

Ordinary negligence asks what a careful person would do

California’s Judicial Council Civil Jury Instructions define negligence as failing to use reasonable care to prevent harm to oneself or others. The comparison is with a reasonably careful person in the same situation, and it covers both doing something that person would not do and failing to do something that person would do.

The plaintiff is the person bringing the claim; the defendant is the person or entity being sued. California’s basic negligence instruction requires proof that the defendant was negligent, the plaintiff was harmed, and the negligence was a substantial factor in causing that harm. So careless behavior and an injury are not enough merely because both occurred.

A substantial factor is a contribution a reasonable person would regard as more than remote or trivial; it need not be the only cause of the harm. The California instruction also says conduct is not a substantial factor if the same harm would have occurred without it.

A product defect is different from carelessness

California’s jury instructions on strict liability for products cover a flaw in how a product was made, a flaw in its design and inadequate warnings. In a strict-liability claim over a manufacturing defect, the plaintiff must show that the defendant manufactured, distributed or sold the product, that it was defective when it left the defendant’s possession, that the plaintiff was harmed, and that the defect substantially caused the harm. The plaintiff must first produce evidence that the injury occurred while the product was being used in an intended or reasonably foreseeable manner. The instruction asks about the product and its connection to the injury, rather than requiring the plaintiff to identify a careless act in the production process.

A manufacturing defect exists when the product differs from the manufacturer’s design or specifications, or from other typical units of the same product line.

For a design defect, California’s consumer-expectation test asks whether a product performed as safely as an ordinary consumer would expect during intended or reasonably foreseeable use or misuse. The plaintiff must also show harm and that the failure to perform safely was a substantial factor in causing it.

A second design test, called risk-benefit, weighs the challenged design’s benefits against its inherent dangers. The two tests are alternative ways to prove a design defect: a product can fail the consumer-expectation test even if the benefits of its design outweigh the risks.

California also recognizes strict liability for inadequate warnings. The plaintiff must show that the product had risks that were known or knowable from generally accepted scientific knowledge when it was made, distributed or sold, that the risks presented a substantial danger in intended or reasonably foreseeable use or misuse, and that ordinary consumers would not have recognized them. The plaintiff must also show that the defendant failed to warn adequately, that the plaintiff was harmed, and that the lack of warning was a substantial factor in causing the harm.

Dangerous activities and dog bites have their own conditions

In California, people who engage in what courts call ultrahazardous activities are responsible for the harm those activities cause, regardless of how carefully they carry them out. A 1969 California Law Revision Commission report lists blasting in a developed area as an ultrahazardous example. The plaintiff must prove that the defendant engaged in the activity, that the plaintiff was harmed, that the harm was the kind anticipated from the activity’s risk, and that the activity was a substantial factor in causing the harm. Strict liability is still not an automatic win: the activity has to qualify, and the harm has to be the kind anticipated from its risk.

California courts assess whether an activity is ultrahazardous by considering the degree of risk, the potential seriousness of harm, whether reasonable care can eliminate the risk, how common the activity is, its suitability to the location, and its community value compared with its danger. Whether an activity qualifies is a legal question for the judge.

California’s dog-bite statute gives a different example: a dog’s owner is liable for damages suffered by a person bitten in a public place or while lawfully in a private place. That rule applies regardless of the dog’s former viciousness or the owner’s knowledge of it. A person is lawfully on the owner’s property when there by the owner’s invitation, express or implied, or when carrying out a duty imposed by state law or by federal law or postal regulations.

The same statute limits claims against government agencies for certain military or police uses of dogs, including crime investigation, warrant execution, defense of a person and specified apprehension situations. That limitation does not apply to a bite victim who was neither involved in nor suspected of involvement in the acts that prompted the dog’s use. The limitation also applies only when the agency has adopted a written policy on necessary and appropriate uses of dogs.

A safety violation must match the person and injury

Negligence per se, meaning negligence in itself, uses a legal rule as the standard of care, the measure of careful conduct, in a negligence claim. California’s instructions explain that a plaintiff borrows a statutory standard but still must prove causation.

California Evidence Code Section 669 creates a presumption of failure to use due care when a person violates a statute, ordinance or public regulation and the other specified conditions are met. A presumption is a starting conclusion that the law permits to be rebutted under its stated conditions.

The violation must proximately cause death or injury to a person or property. For this California test, the violation must meaningfully contribute to the injury, rather than be only a remote or trivial factor. The injury must arise from the kind of occurrence the rule was designed to prevent, and the injured person must belong to the class the rule was adopted to protect. The questions are therefore distinct: Was a rule broken, did that violation cause this injury, and was this the person and danger the rule addressed? Breaking a law is not enough by itself: a rule meant to prevent fires, for example, would not create the presumption for an unrelated injury.

California allows the presumption to be rebutted by showing the violator did what would reasonably be expected of an ordinarily prudent person in similar circumstances who wanted to comply with the law. A child who broke the rule can rebut the presumption by showing the care ordinarily exercised by children of the same maturity, intelligence and capacity, but not when the violation occurred in an activity normally undertaken only by adults and requiring adult qualifications.

Not every state gives a violation that effect. Washington’s negligence statute, RCW 5.40.050, generally treats breach of a statutory, ordinance or administrative-rule duty as evidence of negligence rather than negligence per se. It makes negligence-per-se exceptions for electrical fire safety, smoke alarms, specified needle-sterilization and disease-prevention precautions, and driving under the influence of alcohol or drugs. The effect of a broken safety rule therefore has to be checked under the law that governs the claim.

Causation and defenses still apply

Neither doctrine lets a plaintiff skip the rest of the case: causation still has to be proved, and defenses remain. Strict liability leaves room for issues about the injured person’s own conduct: California’s product-liability instruction permits a reduction in damages when the plaintiff’s negligence substantially contributed to the harm. The reduction is based on the plaintiff’s percentage of responsibility. That is called comparative fault, a division of responsibility for the loss.

A plaintiff can plead more than one applicable legal theory for the same incident. California’s court forms for a personal-injury complaint allow one or more cause-of-action attachments. A cause of action is the legal reason offered for a lawsuit.

In a product case, for example, one inquiry would examine a manufacturing defect and its causal role; another would ask whether a violated safety rule protects the injured person against the type of injury at issue. The proof supporting one inquiry does not automatically answer the other.

How a criminal case differs

In California, a personal-injury case is usually filed in the county where the injury happened or where the defendant lives or does business. Identifying the responsible person, property owner or business may require research.

The general deadline to file a personal-injury case in California is 2 years from the injury, with exceptions. Filing too late can lead to dismissal even when the underlying case was otherwise sound. Government-agency claims have different deadlines and requirements, including first submitting a claim to the agency by an earlier deadline. Never rely on a general explanation like this one to work out the deadline for a particular case.

Strict liability also exists in criminal law, where it concerns a different kind of proof. For a strict-liability offense covered by California’s Criminal Jury Instruction No. 254, prosecutors must prove the prohibited act or required omission, but do not have to prove a particular intent or other mental state.

The federal courts’ description of their own criminal and civil cases shows why criminal strict liability is kept separate from the civil injury doctrines discussed here. In a federal criminal trial, the government must prove guilt beyond a reasonable doubt. A federal criminal sentence can include prison, a fine paid to the government and restitution paid to crime victims.

In a federal civil lawsuit, a plaintiff may seek money to compensate for harm or ask the court to stop harmful conduct. The federal civil plaintiff must meet a preponderance-of-the-evidence standard: it must be more likely than not that the defendant is responsible for the harm.

Check the governing statute, the applicable civil jury instructions and the court’s self-help guidance for the place where the claim belongs.