Whilst some emergencies are self evident (such as a natural disaster which threatens many lives), many smaller incidents require the subjective opinion of an observer (or affected party) in order to decide whether it qualifies as an emergency.

The precise definition of an emergency, the agencies involved and the procedures used, vary by jurisdiction, and this is usually set by the government, whose agencies (emergency services) are responsible for emergency planning and management.

Defining an emergency

In order to be defined as an emergency, the incident should be one of the following:

• Immediately threatening to life, health, property or environment.
• Have already caused loss of life, health detriments, property damage or environmental damage
• Have a high probability of escalating to cause immediate danger to life, health, property or environmentFact: date=May 2007

In the United States, it is generally a requirement in most states that a notice be printed in each telephone book requiring that, if a person requests the use of a telephone line (such as a party line) because of an emergency, the other person must relinquish use of said line immediately, if their use is not also in the nature of an emergency. An emergency is also typically defined by those state statutes as "a condition where life, health or property is in jeopardy, and the prompt summoning of aid is essential."

Whilst most emergency services agree on protecting human health, life and property, the environmental impacts are not considered sufficiently important by some agenciesFact: date=May 2007. This also extends to areas such as animal welfare, where some emergency organisations cover this element through the 'property' definition, where animals which are owned by a person are threatened (although this does not cover wild animals). This means that some agencies will not mount an 'emergency' response where it endangers wild animals or environmentFact: date=May 2007, although others will respond to such incidents (such as oil spills at sea which pose a threat to marine life). The attitude of the agencies involved is likely to reflect the predominant opinion of the government of the area.

Dangers to life

Many emergencies cause an immediate danger to the life of people involved. This can range from emergencies affecting a single person, such as the entire range of medical emergencies which include heart attacks, strokes and trauma, to incidents affecting large numbers of people such as natural disasters including hurricanes, floods or mudslides.

Most agencies consider these to be the highest priority of emergency, which follows the general school of thought that nothing is more important than human life.