I've no experience with hornets, so this may be alarmist - or not..
Hornets, like many social wasps, can mobilize the entire nest to sting in defense: this is highly dangerous to humans. The hornet alarm pheromone is used to raise alarm of nest attack, and to identify prey, for example bees. It is not advisable to kill a hornet anywhere near a nest, as the distress signal can trigger the entire nest to attack. Materials that come in contact with pheromone, such as clothes, skin, dead prey or hornets, must be removed from the vicinity of the hornets nest. Perfumes, and other volatile chemicals can be falsely identified as pheromone by the hornets and trigger attack.