I played lots of Airsoft matches (back in Poland) in buildings. Ruined factories, housing projects, one abandoned mental health facility, some old abandoned forts, etc.
Most of the time the floors were literally covered with BB's (as they have seen many airsofters and games in their time) and I've never tripped on them.
I have always worn my Jungle Boots to games and didn't have a single accident involving BB's and concrete
So I guess you have nothing to worry about.