How many adults?

Usually there have been 2 or more adults in the lab at any given time. I have been alone with the kids only for short periods of time, thus I have not experienced an entire afternoon as the only adult. I think it would be "doable", but I definately prefer having 2 adults who stay for the entire afternoon. This allows one to be in each room at all times. With our current location, that works well. The kids view the consistent adults as the people to go to with questions or concerns. Also the consistent adults are naturally more familiar with the kids, equipment, etc. I also want other adults to feel welcome to come in and out as they please to play, observe, whatever.