One of the dive table models that is available to NAUI divers is the Reduced Gradient Bubble Model, or RGBM. The RGBM model was designed by NAUI member Dr. Bruce Wienke. The RGBM is called a “dual-phase” model because it recognizes that in addition to the nitrogen dissolved into our blood and tissues when we dive, we also have nitrogen present in the form of gaseous “microbubbles,” which must also be controlled. This can become significant in technical and decompression diving. The full RGBM tables for technical diving are available in both a printed manual and as software. In 2001, using Dr. Wienke’s tables, NAUI published a set of RGBM no-calculation dive tables for recreational diving. The NAUI RGBM dive tables are for both air and nitrox, and can be used for elevations up to 10,000 feet (3048 m) above sea level. Many dive computers use the RGBM model when making their calculations. If you do not yet have your own dive computer, the RGBM recreational dive tables can be used in conjunction with a depth gauge and timing device. They are waterproof and will fit in your BC pocket. There is a set of RGBM tables for each of the three common scuba breathing gases: air, EAN32 and EAN36. (You will learn about EAN32 and EAN36 in your NAUI Nitrox class. These gas mixtures are beyond the scope of this course.) For each of the gas types, there are three tables, one for each of the three altitude ranges: sea Level to 2,000 feet (610m), 2,000 to 6,000 feet (610 to 1829m) and 6,000 to 10,000 feet (1829 to 3048 m). For any given dive, you will use only one of the RGBM tables, but it is essential that you be aware of and use the appropriate table. Using the incorrect table for your gas mix and/or altitude range could result in serious injury (figure 5-19). How to Use the RGBM Tables On the back of each table are printed the specific rules for that particular table. Be sure to read those rules and follow them in your dive planning and diving to help reduce your risk of decompression sickness (DCS). Some of the rules may be the same from table to table, such as “Depth measuring devices may require correction for use at altitude and in fresh water to determine a diver’s actual dive depths....” Other rules vary from table to table. For example, the minimum surface interval time (SIT time) for the sea level to 2,000 feet, (610m) between dives is one hour. On the 2,000 to 6,000 feet (610 to 1829 m) table the SIT time is a minimum of 90 minutes. Be sure to read and understand the rules you are using for each individual table (figure 5-20). As you look at the front of the appropriate table, you will see that there are either two or three sections, one for each dive of the day. You can conduct up to three dives in one 12-hour day for the sea level to 2,000 (610m) table, while you are limited to two dives for the higher altitude tables (figure 5-21). Each dive has three columns, max depths in feet of seawater (fsw), max depths in meters of seawater (msw) and maximum dive time (MDT) for each depth. Using the table is straightforward and easy. Find the first dive’s planned maximum depth (in feet or meters) in the Dive One columns. If your depth is not specifically listed, always round up to the next greater depth. Then follow that row, to the right, to find the MDT. Your planned and actual dive should not exceed the MDT for that depth. After the appropriate surface interval for the table you are using, move to planning the second NAUI Scuba Diver 142 Decompression, Dive Tables, and Dive Computers FIGURE 5-20. EACH INDIVIDUAL RGBM TABLE HAS INSTRUCTIONS PRINTED ON THE BACK THAT ARE SPECIFIC TO THAT PARTICULAR TABLE.
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