Under what conditions should a tourniquet be applied?

A tourniquet should be applied specifically in cases of life-threatening extremity hemorrhage that cannot be controlled by more basic methods, such as direct pressure. This choice is correct because the primary purpose of a tourniquet is to rapidly stop significant bleeding in a limb when injury causes major arterial blood loss. In situations where other bleeding control measures, like applying pressure or utilizing hemostatic dressings, have failed or are impractical, the tourniquet can be a critical life-saving intervention. The urgency in controlling severe hemorrhage is paramount as uncontrolled bleeding can lead to shock and death.

Applying a tourniquet for minor bleeding, as indicated in the first option, is not advised because it can cause unnecessary complications and further injury. Tourniquets are not suitable for all traumatic injuries, as indicated by the third option; they should only be used in specific circumstances of severe hemorrhage. Lastly, the fourth option suggests applying a tourniquet only when instructed by a senior medic. However, in emergency situations, timely action is essential, and if a responder recognizes an immediate threat to life from bleeding, they must act independently to apply a tourniquet without waiting for further orders.