Can a non-medical person apply a tourniquet?

Yes, a tourniquet is designed to cease life-threatening bleeding and must be used immediately, without waiting for medical services to arrive, similarly as witnesses of sudden death must start resuscitation as soon as possible. Likewise, a fire extinguisher in the event of fire can and should be used without waiting for the arrival of the fire brigade or a lawfully held firearm used in case of self-defence without waiting for the police.