The Central Ohio Trauma System is holding their large-scale disaster drill today in Columbus. Does anyone know which talkgroups they'll be using? It should be interesting to listen to.
All of the above.
Seriously, it could be any of the oodles of talkgroups available. In a major incident, the incident commander would assign talkgroups as needed from what's known to be available, and in a full-scale exercise of this type that's what they should do.
Major pre-planned events like sporting events and concerts would have pre-planned talkgroups, but something like this should rightly be done on the fly as if it were a real incident.