The defence of sudden and extraordinary emergency is set out in section 9AI of the Crimes Act 1958 and states the following:
(1) A person is not guilty of a relevant offence in respect of conduct carried out by him or her in response to circumstances of sudden or extraordinary emergency.
(2) This section applies if and only if the person carrying out the conduct reasonably believes that –
circumstances of sudden or extraordinary emergency exist; and
committing the offence is the only reasonable way to deal with the emergency; and
the conduct is a reasonable response to the emergency.
(3) This section only applies in the case of murder if the emergency involves a risk of death or really serious injury.