Yes silica has become a major concern for OSHA regulations. The implementation date for the new OSHA regulation was pushed back from June 28th to September 22nd, 2017(might be slightly off on the day), but I'm sure the procedures weren't followed. Dust now has to be controlled/collected and if it is collected the HEPA vac needs to meet certain requirements. There are a lot of other things that go into this regulation along with medical testing and air monitoring as well, but I digress. It sounds like you have done what you can to remove the dust. I'd continue cleaning the room and games a little more regularly until you stop collecting the concrete dust.