Necessity : General Defences in Tort
An act causing damage, if done under necessity to prevent a greater evil is not actionable even though the harm was caused intentionally. The defence of necessity is based on the maxim ‘salus populi supreme lex’ which means the welfare of the people is the supreme law. Necessity should be distinguished from private defence. In necessity, there is an infliction of harm on an innocent person whereas in private defence harm is caused to a plaintiff who himself is the wrongdoer.
Necessity is also different from inevitable accident because in necessity the harm is an intended one whereas in inevitable accident the harm is caused in spite of reasonable efforts to avoid it. Examples of necessity include throwing goods overboard a ship to lighten it for saving’ the ship or persons on board the ship, or pulling down a house to stop a further spread of fire; or immediate operation performed by a surgeon upon an accident victim lying unconscious.