you should stop at 5 meters (15 feet) for an additional 3 minutes. However, you determine your Letter Group using the dive schedule of 21 meters/45 minutes (70 feet/45 minutes). You can also include the 3 minutes as part of your ADT as an extra precaution. You document your precautionary decompression stop on your NAUI Dive Planning Worksheet next to a short horizontal line drawn through the ascent line of the dive profile. Required Decompression If you accidentally exceed a Maximum Dive Time or Adjusted Maximum Dive Time, you must decompress by stages. You must stop at 5 meters (15 feet) during your ascent and stay there for a specified time to allow your body to offgas nitrogen. You must keep your physical activity to a minimum during your decompression stop. It is useful to have a means of support to maintain a constant depth during your stop. An ascent line, a decompression bar suspended from a boat, or the contour of the bottom in shallow water are all examples of support (figure 5-17). Without something to grasp, it is difficult to remain at one depth in shallow water. Swimming and hovering decompression are possible, but not easy, and the activity might offset the benefit of offgassing nitrogen. Table 1 gives you required decompression times for each depth. To the right of the Maximum Dive Times for each depth are split squares containing two sets of numbers. The top number represents dive time. The lower number represents the decompression time required for that dive time. The decompression time is the length of time you must spend at 5 meters (15 feet) to help avoid DCS. For example, if your TNT on a 24-meter (80-foot) dive was 45 minutes, you would have to perform a 10-minute decompression stop. Time spent decompressing is considered neutral time. It does not count as part of your ADT. You document your required decompression stop on your NAUI Dive Planning Worksheet next to a short horizontal line drawn through the ascent line of the dive profile. Omitted Decompression If you surface and discover you omitted a required decompression stop, take the following steps: 1. Discontinue diving for 24 hours no matter how well you feel. 2. Breathe 100% oxygen, if available. If only a small, portable unit is available, breathe the oxygen until the cylinder is depleted. 3. Drink plenty of fluids. 4. Rest. 5. Watch for symptoms of DCS. If you suspect that you have DCS, you must seek medical help. If there is an operational chamber nearby, go there. Otherwise, have medical help call Divers Alert Network (DAN) at (919) 684-9111, which is their 24-hour emergency line. They will advise you of the procedure to follow to obtain chamber treatment. Never go back into the water to try to make up for the omitted decompression stop. Cold or Strenuous Dives If you get cold, do strenuous physical work during or after a dive, or both, use the next greater time for your dive schedule. For example, a dive to 18 meters (60 feet) with a TNT of 40 minutes would become a 50 minute dive. NAUI Scuba Diver 138 Decompression, Dive Tables, and Dive Computers FIGURE 5-17. IT IS USEFUL TO HAVE A MEANS TO HELP MAINTAIN A CONSTANT DEPTH DURING YOUR DECOMPRESSION STOP.
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