What is an "intervening or superseding cause"?

In tort law, a defendant can only be held liable for injuring a plaintiff if the defendant’s negligence caused the plaintiff’s injuries. There must be a direct link between the negligent behavior and the injury so that the behavior is both the cause in fact and the proximate cause of the injury.

Because causation must exist for the defendant to face liability, a defendant may argue that an intervening cause broke the link between the defendant’s behavior and the plaintiff’s injury. The intervening cause must occur between the defendant’s negligent act and the plaintiff’s injury, and it must have caused injury to the plaintiff.

For instance, suppose that a mechanic at an auto shop accidentally spills some gasoline in the parking lot, but he fails to clean it up.  A customer walking across the parking lot flicks a lit cigarette butt, which hits the gasoline, resulting in a fire that burns the customer. The mechanic may raise the affirmative defense that the lit cigarette the customer dropped was an intervening cause that broke the chain between the mechanic’s spill and the customer’s burns.

The lit cigarette meets the definition of an intervening cause: it occurred between the mechanic’s spill and the customer’s burn injuries, and it caused the customer to be injured. However, the defendant will not be able to escape liability unless the intervening cause is also a superseding cause.

Like an intervening cause,  a superseding cause occurs between the defendant’s action and the plaintiff’s injury, and it is also responsible for the injury. However, a superseding cause is also one that the defendant could not have reasonably foreseen.

In the example above, the mechanic may still be held liable for the customer’s injuries because a fire caused by the spilled gasoline was foreseeable. The mechanic could have reasonably foreseen that spilled gasoline might catch fire and injure anyone in the parking lot, including customers. Here, the lit cigarette is an intervening cause, but it is not a superseding cause.

By contrast, suppose that the customer flicked a lit cigarette near the gasoline spill, but was not burned by the flames. Instead, the customer is so startled by the sudden fire that he has a heart attack. Here, the lit cigarette is most likely a superseding cause of the injury, because the mechanic would not have reasonably foreseen that a gasoline spill would result in a heart attack.

To relieve the defendant of liability, the intervening or superseding cause must be unforeseeable in most cases. However, three exceptions exist. First, a foreseeable intervening cause may still eliminate the defendant’s liability if the intervening cause was an intentional tort or action by another party. For example, if the customer in the parking lot had deliberately dropped a match into the gasoline spill, the mechanic would not be liable for the resulting burn injures. Similarly, a criminal act may intervene to relieve the defendant of liability even if the crime was foreseeable.

Finally, a defendant may escape liability if a third person with the ability to fix the condition that will lead to injury sees the condition but does not fix it. For example, suppose that the manager of the garage sees the gasoline spill, but does not clean it up or have one of the garage’s employees clean it up. In this case, the manager, not the mechanic, may be liable for the defendant’s injuries. The manager may also be liable under a premises liability theory for failing to protect customers from dangerous conditions in the parking lot, such as gasoline puddles.