You see them at gas stations, factories, etc... Since the cylinders are on the sprue it is easy to paint them in any color that you see gas cylinders in from sliver to black to green, whatever. Then place them around the layout to add that human factor.

I do like Tichy train accesories. These are the small things that add realism in my opinion. Nothing really to assemle just paint as you like Oxy/acetylene torch, nitrogen, ammonia, whatever. These are always sitting around a train repair facility.