I imagine they have special air hose quick connects that purge some volume upon connection. A cursory googling finds Trellchem suits use this type: http://www.

I imagine they have special air hose quick connects that purge some volume upon connection. A cursory googling finds Trellchem suits use this type: http://www.cejn.com/products/fluids/couplings-nipples/series-221-breathing-air/ http://www.cejn.com/products/fluids/couplings-nipples/series...