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  • Air Management
    Text by Michael McCrory

    What the heck does air management mean? Well, if you're not familiar with this term, you need to read on. Have you ever been halfway through a dive, looked at your console and noticed you've consumed more air than you thought? Or, have you ever been on a dive boat and heard the divemaster say, "Let me know when you get down to 1,000 psi?" Even more annoying, have you been on a dive and heard one of those low air alert alarms going off? If you have experienced any of the above, I think you'll appreciate the need for air management skills. If you run out of gas in your car, you have an inconvenience. If you run out of fuel in a boat, you have a problem. If you run out of air underwater, you have a tragedy in the making.

    The technical diving community has been utilizing gas management techniques for many years. This skill allows the technical diver to plan and execute extended range dives with a greater margin of safety. However, it appears the modern recreational diver has a tendency to let dive computers do most of the work on pre-dive planning and post-dive analysis. While a computer is a valuable tool when used properly, it is of little help when its user has poor air management skills.

    Once recreational divers reach a certain comfort level in open water, the need and desire to constantly monitor air consumption is diminished. In some cases the diver becomes so enthralled with the underwater environment he or she just simply forgets. At this point, failure to monitor depth, air consumption and bottom time could create a hazard for the diver and his/her dive buddy. Dive a little too deep, stay a little too long, surface a little too fast and guess what? A great opportunity for decompression illness has reared its ugly head. Every diver's goal is to prevent such a situation. With small amounts of pre-dive planning, including air management, we can achieve that goal.

    Let's review some basic air management skills and applicable formulas to get started. First, you always have the old standard "Be back on the surface or at the boat with no less than 500 psi/33.3 bar in your cylinder." The 500 psi/33.3 bar rule is relatively standard with dive operators worldwide. Now, let's consider the depth of the dive. It is always a good practice to allow at least 100 psi/6.6 bar per atmosphere of depth for the ascent phase of your dive, i.e. 33 fsw/10 m = 100 psi or 6.6 bar and 66 fsw/20 m = 200 psi or 13.3 bar and so on. Considering these two factors alone, we have a good start on managing air.

    If we consider a typical open water dive having the same entry and exit point, we can perform a little pre-dive planning with the information given. Assuming we started the dive with a 3,000 psi/200 bar cylinder, we should deduct 500 psi/33.3 bar from the total pressure, i.e. 3,000 psi/200 bar minus 500 psi/33.3 bar leaves us 2,500 psi/166.7 bar of usable air. Our planned diving depth is 66 ft./20 m. If we also allow 100 psi/6.6 bar for each atmosphere of depth, we now must subtract 200 psi/13.3 bar from the 2,500 psi/166.7 bar usable air. This means that we now use 2,300 psi/153.3 bar for our dive planning. We will use one-half of our usable air going away from the entry point and the other half on the return trip. One-half of our useable air would be 1,150 psi/76.7 bar. Subtract one-half of your usable air from the full cylinder and you now have your turnaround pressure reading. So, we start our dive going away from the entry point. When until the remaining cylinder pressure is 1,850 psi/123.3 bar, we turn around and head back. Upon reaching the exit point, our remaining cylinder pressure should be 700 psi/46.7 bar. This allows us enough air to make a slow ascent to the surface not exceeding a rate of 30 ft./10 m per minute, plus make a safety stop at 15 ft./3 m for three to five minutes.

    As you can see, with a small amount of air management skill, it becomes evident that low air or no air problems can be prevented. This type of information is easy to cover in a pre-dive plan. It's also a good idea to take your air management information in the water with you-just for reference. Remember the old saying "A short pencil is better than a long memory." Write the figures on an underwater slate, attach it to your BCD or put it in your pocket and you have instant access.

    There are a few other safety aspects of diving to consider during a pre-dive plan, such as depth, bottom time or residual nitrogen. Air management is just one of the many. In future articles, we can address these additional aspects in greater detail. Until then, happy diving and remember, "If you always return to the surface with at least 500 psi in your cylinder, you will never run out of air underwater!"