I am studying NFPA 497. I am looking at figure 5.10.4(c) and 5.10.4(e). (c) uss the terminology "Unloading via a closed transfer system", and (e) uses the terminology "unloading via an open transfer system". What do the terms open/closed transfer system mean in this context? Also, (e) refers to a "dome". What does "dome" mean in this context?