If someone is injured in an incident, first check that you and the person who is injured are not in any danger. If you are, make the situation safe.

When it's safe to do so, assess the person who is injured and, if necessary, dial 999 for an ambulance. You can then carry out basic first aid.

The 3 priorities when dealing with a casualty are commonly referred to as ABC, which stands for:

• Airway
• Breathing
• Circulation

If the person appears unresponsive, ask them loudly if they're OK and if they can open their eyes.

If they respond, you can leave them in the position they're in until help arrives.

While you wait, keep checking their breathing, pulse and level of response:

• Are they alert?
• Do they respond to your voice?
• Is there no response to any stimulus (are they unconscious)?

If there's no response, leave the person in the position they're in and open their airway.

If this is not possible in the position they're in, gently lay them on their back and then try to open their airway.

To open the airway, place 1 hand on the person's forehead and gently tilt their head back, lifting the tip of the chin using 2 fingers. This moves the tongue away from the back of the throat.

Don't push on the floor of the mouth, as this will push the tongue upwards and obstruct the airway.

If you think the person may have a spinal injury, place your hands on either side of their head and use your fingertips to gently lift the angle of the jaw forward and upwards, without moving the head, to open the airway.

Take care not to move the person's neck. But opening the airway takes priority over a neck injury. This is known as the jaw thrust technique.

To check if a person is still breathing:

• look to see if their chest is rising and falling
• listen over their mouth and nose for breathing sounds
• feel their breath against your cheek for 10 seconds

If they're breathing normally, place them in the recovery position so their airway remains clear of obstructions, and continue to monitor normal breathing.

Gasping or irregular breathing is not normal breathing.

If the person isn't breathing or is not breathing normally, call 999 for an ambulance and then begin CPR.

If the person isn't breathing normally, you must start chest compressions immediately.

Agonal breathing is common in the first few minutes after a sudden cardiac arrest (when the heart stops beating).

Agonal breathing is sudden, irregular gasps of breath. This shouldn't be mistaken for normal breathing and CPR should be given straight away.

If the person isn't breathing, call 999 for an ambulance and then begin CPR.

The advice given on this page only covers common first aid situations and is not a replacement for taking a first aid training course.

Basic first aid courses are run regularly in most areas around the UK.

Organisations that offer courses include:

• St John Ambulance
• British Red Cross
• NHS Ambulance Service
• St Andrew's First Aid