What action should you take if a casualty is experiencing a reaction and you need to keep the airway open?

Using the head tilt chin lift method is the recommended action when a casualty is experiencing a reaction that may compromise their airway. This technique is essential because it helps to clear the airway by repositioning the tongue and lifting the jaw, which can be especially important if the person is unconscious or semi-conscious and unable to protect their own airway.

Maintaining an open airway is crucial in any first aid situation since an obstructed airway can lead to serious complications, including suffocation or hypoxia. This method is widely taught in first aid and CPR courses as a standard procedure for ensuring that the airway remains clear, especially in emergencies.

In contrast, administering oxygen is appropriate in certain situations but not as an immediate response if the airway is blocked. Performing abdominal thrusts is meant for choking situations and is not relevant here unless the casualty is actually obstructed. Providing water can pose a risk if the casualty is unable to swallow or is unconscious, which could lead to choking or aspiration.