The safe usage and storage of Hydrogen gas H2 requires a decent level of purity- say above 98%. Those who have researched hydrogen production using electrolysis would be aware of several methods of separating out the small amounts of heavier gases like oxygen that are often present. Here is another concept that just may work. Consider the following:- The Sand drum method. You have a container that is shaped like an old fashioned spinning top - a conical shape on top pointing upwards - and a conical shape on the bottom pointing down- the two halves sealed together. The container is filled with clean beach sand of a smooth partical type. In the Esperence region of Western Australia we have perfect white beach sand whose grains have smooth rounded egdes. It squeaks under your feet when you walk on it. Now 90% pure H2 is piped into the lower/mid centre (the core) of this sand filled container at a low flow rate. I suppose that the H2 would slowly disperse upwards to the H2 exit pipe at the apex - and O2 would settle to the O2 exit pipe at the bottom?? It would also double as a flash-back arrester? Any objections or feed-back to this idea? Thanks.