I will follow the school's planned procedure for this situation, but I will also talk to my students beforehand and make sure that they understand my expectations.
I will answer any questions that they might have about this drill since it is such a sensitive topic and make sure that they COMPLETELY understand the severity of the situation.
For a tornado drill, I will take my students to our safe spot and bring a book or something to try and keep them distracted while we are in a weird spot.