I have, on many occasions, seen Crash trucks deployed to various entry points to control 'exercise demonstrators' but that was, I suspect, in 'exercise water cannon mode' rather than expending expensive foam compounds
Pure reportage ... My normal DISTAFF role was to dismantle ATC, Base Ops and other key functions, instead of overseeing 'rabble control'. That's what RAF Regt DISTAFF are for.