What is the defense of necessity in a criminal case?

This defense is said to be available when the actor is faced with a choice of two evils and finds himself in a position where he may "either do something which violates the literal terms of the criminal law and thus produce some harm or not do it and so produce a greater harm." LaFave and Scott, Handbook on Criminal Law (1972) 50, page 387. Thus it is asserted that society will benefit from the greater good that is accomplished by the violation of the literal language of the law. United States v. Simpson, 460 F.2d 515, 517-18 (9th Cir. 1972).

The defense of necessity, where it is recognized to exist, is hedged about with many conditions, at least one of which would prevent its application here: "(T)he assertion of the necessity defense requires that optional courses of action appear unavailable." United States v. Mowat, 582 F.2d 1194 (9th Cir. 1978).