The Scuba Doctor offers a large variety of manifolds and gas switch blocks for recreational, technical, rebreather, sidemount and commercial diving applications.
Every time we sell a manifold or switch block, we shudder a little bit. The gas switch block is used in primarily by hookah surface supply divers to switch from surface supply to emergency bailout gas. Manifolds are primarily used in gas distribution systems. But the key here is that there are not different gas mixtures involved.
Unfortunately divers sometimes get the idea to match these products up with multiple cylinders and/or or quick disconnects to create some type of elaborate system for rapid switching between different gas mixtures and/or cylinders. Gas switching errors are very often involved in technical diving accidents. Over the years we've learned about several near misses and fatalities that were directly attributable to mistakes with switch blocks that were connected to different gas mixtures. No matter how careful the diver, or how many safeguards, we think using switch blocks with different mixtures is a very bad idea.