Along the FBI advice to run, hide, fight, the facility where my wife's restaurant is that has a little over 100 individual business', in the United States, had an active shooter exercise. It was run by the local police department. The, alleged, police officer active shooter was armed with an AR15 (no, it wasn't an assault rifle) that was loaded with mini paint balls. Being shot with one you would know you were hit. It hurt and raised a small welt.
The shooter walked in the back door, you could hear some shots from the rifle he had. We had been instructed that the first thing to do was run from the sound of the shots and try to leave the building. If unable to leave the building then hide. If unable to hide, the last thing we were told to do was fight!
I ran in the direction of the shots. Saw the "police officer shooter" walking down an aisle occasionally shooting his rifle, and hid until he walked by. He shot 3 people he found "hiding" before he reached me. Less than 5 minutes had passed. As he walked by me, I pointed my, finger gun, at his head and shouted bang! He turned quickly and I shouted bang again and yelled head shot, you are dead!
What was the police officer shooters reaction? He said, you can't have a gun, this is a no gun zone!?!? I said you are supposedly an active shooter in a no gun zone too! You are still supposed to be dead from a head shot! ... He then shot me in the stomach with his AR15 paint ball gun (which could still shoot real bullets after changing out the bolt).
The police officer shooter then went on with the active shooter exercise drill that lasted about 45 minutes! Even though he was shot dead!!