Just because there is an intervening act, between a negligent act and the harm, you can still be held liable for damages, but not always. For example, in the case of Watson v. Kentucky & Indiana Bridge and Railroad, (137 Ky. 619, 126 S.W. 146 (1910)), a railroad negligently derailed a tanker and spilled some gasoline. Some jerk wandered by and intentionally tossed a match and started a fire. The court held that the railroad was not liable because "the intervening agency is something so unexpected or extraordinary that the railroad could not have anticipated it.

• Restatement of Torts §442B says that a negligent defendant, who's conduct creates or increases the risk of a particular harm is not relieved from liability by the intervention of another person, except where the harm is intentionally caused by that person and is not within the scope of risk created by the defendant's conduct.