The biggest problem i see with active shooters is
they might be from the govern-cement.
So, you expect some lone nut, but you end up with a small team of well coordinated, well armed and armored thugs.
Run, hide, fight is as shtupid as that skit in South Park
"when lava is flowing towards you, remember to drop and cover".
The thing with most offices is that they are literally death traps.
There really isn't a back door. And the fire exits are ... these solid metal doors that you can't see through. So, are you escaping or letting the shooter in?
Fortunately, with most offices having one way in, you know where the shooter is coming from, and there are lots of places to ambush from.