In general, a negligent defendant is only liable for damages that are foresseable. However, sometimes it is difficult to determine the limits of foreseeability, especially with regard to fires. Smith v. London and South Western Railway (L.R. 6 C.P. 14 (1870)) was one of a number of famous "Fire Cases" from the 1800s. In all of these cases, someone negligently starts a fire and the courts have to decide what the extent of the damages are. In this case, a train caused a fire that damaged a building 200 yards away. In general, the Fire Cases established the doctrine that when the defendant's conduct otherwise qualifies as proximate cause of the plaintiff's harm, the defendant does not escape liability merely because the harm was more extensive than anyone could have foreseen. In this case, one judge said, "When it has been once determined that there is evidence of negligence, the person guilty of it is equally liable for its consequences whether he could have foreseen them or not." So basically, if you start a fire, and that fire gets out of control and burns a lot more stuff than you might have expected it to burn, you are still liable for all of that damage, since it is foreseeable that a fire could burn out of control.