Legal Definitions - supervening cause

A supervening cause (also known as an intervening cause) refers to an unexpected and independent event that occurs *after* an initial act of negligence but *before* any resulting harm or injury. This new event is so significant and unforeseeable that it breaks the direct link, or "chain of causation," between the original negligent act and the ultimate injury. When a supervening cause is identified, it typically relieves the initial wrongdoer of liability for the harm that follows, because the supervening cause is considered the true, independent cause of the injury.

Here are some examples to illustrate this concept:

• Example 1: Negligent Parking and Intentional Vandalism

  Imagine a delivery driver negligently parks their truck on a steep hill without properly engaging the parking brake, causing the truck to slowly roll down the street. Before the truck hits anything, a group of vandals sees the unattended, rolling vehicle, jumps in, and intentionally steers it into a lamppost, causing significant damage. While the driver's initial negligence put the truck in motion, the vandals' deliberate act of taking control and crashing it is a supervening cause. The driver might be held responsible for the truck rolling unattended, but the intentional act of the vandals breaks the chain of causation for the damage to the lamppost, making the vandals primarily liable for that specific harm.

• Example 2: Unsecured Construction Site and Unforeseeable Natural Disaster

  A construction company leaves a large, unsecured pile of building materials on a public sidewalk overnight, which is a negligent act. The next morning, before anyone is injured by the materials, an unprecedented microburst (a sudden, localized column of sinking air) strikes the area, scattering the materials and causing them to crash through the window of a nearby shop. Although the construction company was negligent in leaving the materials unsecured, the unforeseeable and extreme weather event is a supervening cause. The damage to the shop window is directly attributable to the natural disaster, not merely the negligent placement of the materials, thereby breaking the causal link between the company's initial negligence and the shop's damage.

• Example 3: Faulty Wiring and Unrelated Arson

  A landlord fails to address a tenant's repeated complaints about faulty electrical wiring in their apartment, which is a negligent omission. Weeks later, an arsonist, completely unrelated to the wiring issue, breaks into the apartment through a window and intentionally sets fire to the unit. While the faulty wiring posed a potential fire hazard, the arsonist's deliberate act of setting the fire is a supervening cause. The fire damage to the apartment is a direct result of the arsonist's criminal act, not the landlord's negligence regarding the wiring, thus relieving the landlord of liability for the fire damage itself.