ERRV means Emergency Response and Rescue Vessel
Every platform or group of platforms in a close vicinity will have a dedicated ERRV so no need for the rig to have it's own open boat cos they jump from the ERRV.
FRC means Fast Rescue Craft Used to be Searider 6's with twins or Delta's now moving towards hard tube diesels with jets for safety. Check out Norsafe or Delta
ARCC Means BP got a lot of money some of which it gave to Delta for some pretty fancy RIBS