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Deco and Stage BottlesDecompression bottles store the gasses used on the ascent from a dive. They should be made of aluminum (instead of steel) since these types of tanks swing from slightly negative to slightly positive as their contents is consumed and so they don't adversely affect the diver's trim. Typical sizes are 30 Ft3 and 40Ft3. Stage bottles are used to provide additional gas on dives where the back-mounted tanks alone cannot carry a sufficient quantity by themselves. Like deco bottles, stage bottles should be aluminum (instead of steel) for their superior buoyancy characteristics. The most commonly used size is 80 Ft3. Both type of bottles, deco and stage, are clipped to the divers left side only. The bottles are clipped to the left shoulder and left hip D-ring. The right hip has no D-ring since this is where the light canister is mounted on the waist strap. The goal in rigging these bottles is to keep the top of the bottle in close to the diver to minimize drag, and to keep the bottom of the bottle fairly free to swing into the slipstream such that water can flow longitudinally along the length of the bottle. This has the benefit of minimizing the frontal area the bottle presents to the flowing water as the diver swims, thereby minimizing drag. The points of attachment on the bottles should be snap-bolt clips and rope. Never use suicide clips or any metal-to-metal connections. Suicide clips will entrap line when you least expect and have killed many divers over the years. Metal-to-metal connections have also killed many divers who became trapped and were unable to cut themselves free. This is why you should attach your clips to the bottles only with rope that can be cut free if necessary. Additionally, deco and stage bottles should be permanently marked with the Maximum Operating Depth (MOD) of the gas they're intended to contain. The single largest cause of death among technical divers today is breathing the wrong gas. This happens when a diver gets confused and inadvertently opens the wrong valve or grabs the wrong regulator. If you can find a way to reduce the chance of this happening to you, you'll have drastically improved your odds The best way to do this is to mark your bottles with the MOD in big, bold lettering. Three inch high numbers are the way to go. Such clear markings permit you to positively identify the bottle you intend to breathe, and more importantly, permit your buddy to see which bottle you're attempting to breathe. With two people independently identifying the bottles at each gas switch, the chances of making a mistake (one that's missed by two people) is drastically reduced. To deploy the stage/deco gas, you first identify the bottle and open only that valve. All other valves should be kept closed unless you're breathing from them. If only the valve attached to the bottle with the correct MOD is opened, only the correct regulator will deliver gas. Even if the other regulators were pressurized to keep water out, they will only deliver a fraction of a breath before stopping; only the correct regulator attached to the intended gas will deliver. Once you've done the gas switch and you and your buddy have double-checked that you're on the right gas, you shut down the stage/deco valve you were breathing before. You can mark the oxygen fraction on a sticker near the neck if you like, but keep in mind that the FO2 is almost meaningless underwater. You don't want to be looking at a sticker with "31%" written on it than have to do a bunch of mental arithmetic to figure out if at your current depth that gas will kill you or not. With the MOD in big, bold lettering on each tank, all you have to do is check how deep you are to know if you can breath from a cylinder. Below are some pictures of the best way to rig your decompression and stage bottles.
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