In the United States, powers were interpreted from constitutional documents to vest in the President to declare a national emergency. Unfortunately, no written criteria were developed nor were any safeguards developed to end a national emergency.
By 1976, in US v Bishop, the United States Court of Appeals, 19th Circuit, noted that on four occasions a national emergency had been invoked by the American President: 1933, 1950, 1970 and 1971. None had ever been revoked.
In 1976, a new National Emergencies Act ended all previous proclamations although not before the Court wrote:
"A national emergency must be based on conditions beyond the ordinary. Otherwise, it has no meaning. The power of the Soviet Union in world affairs does not justify placing the United States in a constant state of national emergency."
The United States Code (Title 42, Chapter 68, Subchapter I, §5122), now defines emergency and major disaster as follows:
"Emergency means any occasion or instance for which, in the determination of the President, Federal assistance is needed to supplement State and local efforts and capabilities to save lives and to protect property and public health and safety, or to lessen or avert the threat of a catastrophe in any part of the United States.
"Major disaster means any natural catastrophe (including any hurricane, tornado, storm, high water, wind-driven water, tidal wave, tsunami, earthquake, volcanic eruption, landslide, mudslide, snowstorm, or drought), or, regardless of cause, any fire, flood, or explosion, in any part of the United States, which in the determination of the President causes damage of sufficient severity and magnitude to warrant major disaster assistance under this chapter to supplement the efforts and available resources of States, local governments, and disaster relief organizations in alleviating the damage, loss, hardship, or suffering caused thereby."
The Canadian statute, Emergencies Act, defines a national emergency as follows:
"[A] national emergency is an urgent and critical situation of a temporary nature that seriously endangers the lives, health or safety of Canadians and is of such proportions or nature as to exceed the capacity or authority of a province to deal with it, or seriously threatens the ability of the Government of Canada to preserve the sovereignty, security and territorial integrity of Canada and that cannot be effectively dealt with under any other law of Canada."
The United Kingdom's Civil Contingency Act 2004 defines an emergency as follows:
"Emergency means an event or situation which threatens serious damage to human welfare in a place in the United Kingdom,an event or situation which threatens serious damage to the environment of a place in the United Kingdom, or war, or terrorism, which threatens serious damage to the security of the United Kingdom.
"An event or situation threatens damage to human welfare only if it involves, causes or may cause loss of human life,human illness or injury, homelessness,damage to property,disruption of a supply of money, food, water, energy or fuel,disruption of a system of communication,disruption of facilities for transport, or disruption of services relating to health.
[A]n event or situation threatens damage to the environment only if it involves, causes or may cause contamination of land, water or air with biological, chemical or radio-active matter, or disruption or destruction of plant life or animal life."