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Planning Your Surface Intervals Planning your surface intervals carefully is a good way to control your residual nitrogen and your AMDT for repetitive dives. The longer you remain on the surface between dives, the less nitrogen remains in your body, and the longer you can stay under water on your next dive. You must be able to determine how long a surface interval is required to carry out a planned dive without nearing the no-decompression limits. Surface intervals must be at least 10 minutes in length. NAUI recommends that you spend at least an hour on the surface between dives. Choosing to spend more than an hour on the surface between dives gives you more time to offgas nitrogen and will give you more time under water on your next dive. If you use the same example from the previous Chapter 5- Decompression, Dive Tables, and Dive Computers section, you have a Letter Group of H after your second dive of the day. For your third dive, you want to go to 18 meters (60 feet) for at least 25 minutes. If you look at the 18-meter (60-foot) column on Table 3, you see that you must have a Letter Group of E to be able to spend a maximum of 25 minutes at 18 meters (60 feet). To find out how long you must stay on the surface to change from a Letter Group of H to a Letter Group of E, follow the E row from Table 3 back to Table 2. At the same time, follow the H column down from Table 1. Find the block where the E row and H column intersect. It should have a minimum time of 1:42 and a maximum time of 2:23. By spending one hour and 42 minutes on the surface between your second and third dives, you can dive to 18 meters (60 feet) for 25 minutes. Limiting Your Depth Your third option in dive planning is to increase your bottom time by limiting your depth. If you were not able to extend your surface interval between the second and third dives in the previous example and you did not want to make a dive shorter than 25 minutes, you could dive to a shallower depth and spend more time there. If you have a Letter Group of G following a one hour SIT and you know you want to spend at least 25 minutes on your dive, follow the G row in Table 3 until you find a column that has an AMDT of at least 25 minutes. In this example, the depth of 12 meters (40 feet) has an AMDT of 57 minutes. Therefore, by diving six meters (20 feet) shallower, you can make a 25 minute dive. These examples show how you can use the dive tables to your advantage. SPECIAL RULES There are a number of special rules and procedures you must also learn to handle special situations. These situations include decompression, cold or strenuous diving, flying after diving, and altitude diving. Decompression Diving Intentionally exceeding the Maximum Dive Time is unwise, unsafe, and discouraged. As you will learn in advanced or specialty training for deep diving, you must meet many requirements to carry out decompression dives properly. In normal recreational diving decompression dives are still discouraged, even if you meet all the requirements. Diving is only a sport – why risk injury? Some divers engage in technical diving, an extremely advanced recreational diving activity. Technical diving can involve planned decompression dives. You must have special equipment and training as well as extensive diving experience to participate. In addition, this type of diving is much more hazardous than other recreational diving. Technical divers accept the fact that risk of DCS or other problems is much greater. Precautionary Decompression Stops You should stop at 5 meters (15 feet) for 3 minutes at the end of each dive for a precautionary decompression stop or safety stop. Taking this action is recommended to help prevent DCS and to maintain control of your ascent near the surface. Time spent decompressing is considered neutral time. It does not count as part of your ADT. For example, if you dive to 21 meters (70 feet) for 45 minutes, Decompression, Dive Tables, and Dive Computers 137


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