Found this on the Homeland Security Site. The DHS Exercise and Evaluation Program, ie the handbook for drills that somehow are ALWAYS happening at same time as terror/school-shooter attacks.

Pic shows paragraph from sec 3-3 (pg 20 on pdf) on the Logistics section that deals with recruitment and management of actors. Haven't got through it all yet, but reads like a guideline for FF's.

https:// www.fema.gov/media-library-data/20130726-1914-25045-8890/hseep_apr13_.pdf