This really depends on your current infrastructure and how the current inner-operability works. If you are in a state like Ohio where EVERYONE is on a single radio system, and you can simply switch the knob and zone and be on a common channel, then you need to mimic a system failure in the middle of your exercise. Firemen can at least change a channel. They have a dispatch and several fireground channels typically. Police... you get assigned a patrol zone the first day and never leave it, you never leave the channel, for 20 years. Finding the ITAC and ICALL zone in the radio should produce some high comedy. And you need to dictate the cell network being down at the start of the exercise as well. What the actual situation this is wrapped around isn't relevant. Plane crash, housing development on fire, hazardous waste spill, have the fire people pick that. The communications is what you need to be concerned with. Unless you are a fire guy, and then you pick... but it still don''t matter. The last one I was part of was a plane crash with fire in a housing development. Large wreckage field with multiple sites of damage. IC announced 1 hour in that the radio system had failed and they needed to work out communications on an alternate system or repeater. ANd fall back to simplex operations for the fireground operations. Of course there was some confusion and cross talk until they got each fireground on a separate simplex channel, and IC needed to assign a communications officer and command channel for teh chief's to use to communicate back to IC but it got squared away and they made it work. Public safety communications is a funny thing. They just expect it to work and when it don't it becomes very confusing. As hams we just know to spin the dial and where to go. Public safety guys don't necessarily KNOW how that all works. And when you have 36 zones in a radio with 16 channels per zone. It becomes even more confusing. Because their radios may have every other button worn clean from use except that zone button. That one is a scary rabbit hole for many.