Surface decompression is a technique for fulfilling all or a portion of a diver's decompression obligation in a recompression chamber instead of in the water, significantly reducing the time that a diver must spend in the water. Also, breathing oxygen in the recompression chamber reduces the diver's total decompression time. Other variations will be handled in accordance with paragraph 9-6.2.
Surface decompression offers many advantages that enhance the divers' safety. Shorter exposure time in the water keeps divers from chilling to a dangerous level. Inside the recompression chamber, the divers can be maintained at a constant pressure, unaffected by surface conditions of the sea. Divers shall be observed constantly by either the inside tender or topside personnel, and monitored for decompression sickness and oxygen toxicity. Using an inside tender when two divers undergo surface decompression is at the discretion of the dive supervisor. If an inside tender is not used, both divers will carefully monitor each other in addition to being closely observed by topside personnel.
If an oxygen breathing system is installed in the recompression chamber, conduct surface decompression according to the Surface Decompression Table Using Oxygen (Table 9-6). If air is the only breathing medium available, use the Surface Decompression Table Using Air (Table 9-10).
Residual Nitrogen Timetables have not been developed for Surface Decompression Repetitive Dives. Repetitive surface decompression dives may be accomplished in accordance with paragraph 9-10.1.5.
9-10.1 Surface Decompression Table Using Oxygen. Using the Surface Decompression Table Using Oxygen (referred to as Sur D O2) requires an approved double-lock recompression chamber with an oxygen breathing system as described in Chapter 22. With Sur D O2, divers ascend at a constant rate of 30 fpm. The divers are decompressed to the first decompression stop (or to the surface if there are no water stops required) at an ascent rate of 30 fpm. The travel rate between stops and from 30 fsw to the surface is also 30 fpm (::20 per 10 fsw). Minor variations in the rate of travel between 20 and 40 fpm are acceptable.
Once the divers are on the surface, the tenders have three and a half (:03::30) minutes to remove the breathing apparatus and diving dress and assist the divers into the recompression chamber.
Pressurizing the recompression chamber with air to 40 fsw should take approximately 30 seconds (descent rate not to exceed 80 fpm). The total elapsed time from when the divers leave the 30-foot stop to when they reach the 40-foot recompression chamber stop must not exceed 5 minutes with the following exception: If no in-water stops are required, the time from reaching the surface to arrival at 40 feet in the chamber must not exceed 4 minutes. During descent in the recompression chamber, if a diver cannot clear and the chamber is at a depth of at least 20 fsw, stop, then breathe oxygen at 20 fsw for twice the 40 fsw chamber stop time. Ascend to 10 fsw and breathe oxygen again for twice the 40 fsw chamber stop time. Then ascend to the surface. This "safe way out" procedure is not intended to be used in place of normal Sur D O2 procedures.
If the prescribed surface interval is exceeded and the divers are asymptomatic, treat them as if they have Type I decompression sickness (Treatment Table 5, Chapter 21). If the divers are symptomatic, they are treated as if they have Type II decompression sickness (Treatment Table 6, Chapter 21), even if they are only displaying Type I symptoms. Symptoms occurring during the chamber stops are treated as recurrences (Chapter 21).
Upon arrival at 40 fsw in the recompression chamber, the divers are placed on the Built-in Breathing System (BIBS) mask breathing pure oxygen. The designated 40-foot stop time commences once the divers are breathing oxygen. The divers breathe oxygen throughout the 40-foot stop, interrupting oxygen breathing after each 30 minutes with a 5-minute period of breathing chamber air (referred to as an "air break"). Count the air breaks as "dead time" and not part of the oxygen stop time. If the air break interval falls on time to travel, remove oxygen and commence traveling to the surface at 30 fpm. This procedure simplifies time keeping and should be used whenever using the Surface Decompression Table Using Oxygen. Remove the O2 mask prior to leaving the 40 fsw stop for the surface.
9-10.1.1 Example. A dive is planned to approximately 160 fsw for 40 minutes. The dive is to be conducted using Sur D O2 procedures. Figure 9-12 shows this dive profile.
In the event of oxygen system failure, it is important to be familiar with the appropriate air decompression schedules. If the oxygen system fails while the divers are in the water, the divers are shifted to the Standard Air Decompression Table or the Surface Decompression Table Using Air. During the chamber phase, use the procedures listed below in the event of oxygen system failure or CNS oxygen toxicity.
9-10.1.2 Oxygen System Failure (40-fsw Chamber Stop). Follow this procedure when there is an oxygen system failure at the 40 fsw chamber stop:
1. Complete remainder of 40-fsw stop on air.
DIVING CHART-AIR (lOVt) Date 11 Deo 96
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