The best method for assessing a casualty in an emergency situation is to perform a quick primary survey followed by a more thorough secondary survey.
A primary survey is a quick assessment of a casualty to find and correct any life-threatening issues. It often follows a structure such as DR ABC (or DRSABC).

This involves checking the following things:

  1. Danger – any hazards to yourself or bystanders?
  2. Response – is the casualty unconscious?
  3. Shout for help – if they are unconscious, shout for further help but do not leave their side
  4. Airway – open the airway by tilting the head back and lifting the chin
  5. Breathing – check for normal breathing for up to 10 seconds
  6. Circulation – perform CPR and use a defibrillator if the victim isn’t breathing

A primary survey should be carried out to assess all casualties.