What Is the Defense of 'Necessity' Under Tort Law?

The necessity under tort law is a situation where the law allows you to breach your duty somewhat because something outside the control of society occurred. For example, you might be excused of a trespass, or at least have your damages reduced in a trespass, if there was a fire and you needed to break into someone's water barn to get a hose and attach water to put out the fire. Even though it wasn't your property, because there was a fire, you needed to access someone else's property to put it out. You would still be liable for the damages that occurred assuming that it was a private necessity. But if it was a public necessity, where for the general good of the public it was required for you to violate that privilege such as a trespass or breaching someone's property rights. Under the law public necessity, you would not be liable for damage that you caused.