Turnchapel's Automated External Defibrillator (AED) could be used by anyone to save the life of someone who's in cardiac arrest. According to the British Heart Foundation (BHF), there are four steps to take if someone is having a cardiac arrest:
  1. Call 999 and ask for an ambulance
  2. Start CPR
  3. Ask someone to bring a defibrillator if there's one nearby
  4. Turn on the defibrillator and follow its instructions

For more information: see How to use a defibrillator from the BHF and this guide to defibrillators from the Resuscitation Council.