I am not going to speak for
@Muppet , but that is a MCI of epic proportions. On the scene...do-gooders will take injured to several places, there isn't going to be one triage area. For every one bus rider, there will be 10 walking wounded. After you do some semblance of triage, you transport. But to where? There is one level 1 trauma center in Vegas, you think maybe 5 trauma bays at most. Maybe able to clear a dozen, 18 ICU beds. Of course the less wounded would go elsewhere, but how do you shit beds in 4 or 5 hospitals for 400 victims?? You can't. So you put beds in hallways, you board in the ED, you evac by ground and air to other cities.
It isn't a "all hands on deck" at first because you still need busses to respond to regular 911 calls. And hospitals will take whatever comes through the door until a point when the facility declares what we call a Code Triage, which is an external disaster. At that point the level 1 trauma center will divert ambulances to other facilities with non-emergent issues, empty as many ICU beds as possible, discharge people who are with a day or two of being discharged, call in extra staff.
No matter how prepared we like to say we are, we never are. This is a shit sandwich for everyone.