Legal Definitions - efficient intervening cause

An efficient intervening cause is an event or action that occurs *after* an initial act of negligence but *before* the resulting harm. This intervening event is so significant, independent, and unforeseeable that it completely breaks the causal connection between the original negligent act and the final injury. When an efficient intervening cause is present, it becomes the *new* primary cause of the harm, and the person or entity responsible for the initial negligence is typically relieved of liability for the subsequent injury. It essentially cuts off the legal responsibility of the first wrongdoer.

Here are some examples to illustrate this concept:

• Example 1: Unsecured Vehicle and Reckless Theft

  Imagine a situation where a driver, Mr. Henderson, negligently leaves his car unlocked with the keys in the ignition in a parking lot known for high crime. A thief, Mr. Jones, seizes the opportunity, steals the car, and while fleeing at high speed, crashes into a pedestrian, causing severe injuries. While Mr. Henderson's initial negligence in leaving the car unsecured created a *condition* for the theft, Mr. Jones's independent, criminal act of stealing the car and then driving recklessly is likely an efficient intervening cause. Mr. Jones's actions are so extreme and unforeseeable in terms of the specific harm to the pedestrian that they break the chain of causation from Mr. Henderson's initial negligence, making Mr. Jones solely responsible for the pedestrian's injuries.

• Example 2: Construction Site Negligence and Deliberate Arson

  Consider a construction company that negligently leaves highly flammable materials unsecured and exposed overnight at a building site, violating safety regulations. Later that night, an arsonist deliberately breaks into the site and sets fire to these materials, causing extensive damage to an adjacent property. Although the construction company was negligent in securing the site and materials, the *deliberate act of arson* by an independent third party is an efficient intervening cause. The arsonist's criminal act is a new, unforeseeable, and dominant force that directly caused the fire and damage, thereby relieving the construction company of liability for the fire damage to the adjacent property.

• Example 3: Faulty Product and Extreme User Modification

  Suppose a manufacturer produces a power tool with a minor design flaw that could, under specific circumstances, cause a small electrical short. However, a user, Ms. Chen, completely disregards the safety manual and extensively modifies the tool's electrical components in a dangerous way, attempting to boost its power far beyond its intended design. Due to her extreme modifications, the tool catastrophically fails, causing a severe injury. While the manufacturer's initial design flaw was a form of negligence, Ms. Chen's *radical and unauthorized modification* of the tool is an efficient intervening cause. Her actions were so far outside the foreseeable use of the product that they broke the causal link between the manufacturer's original flaw and her injury, making her modifications the direct and primary cause of the harm.