There are talkgroups labeled in some radios that read "EMSCOM" and "FIRECOM," which are statewide talkgroups. However, I have never heard them used before nor has anyone else for that matter. That being said, there are a couple of DNR freqs on VHF-High band that are being used for fireground comms, in addition to 154.295 MHz.
Moreover, if a lot of fire departments need to communicate during a major disaster, they can contact the NCC, and use a few of the statewide event channels. This would provide all of the agencies involved several common talkgroups they could use to quickly establish direct contact with each other.
73's
Ron