A "Pyle stop" is an additional short deep-water stop, which is increasingly used in deep diving (named after Richard Pyle, an early advocate of deep stops). Typically, a Pyle stop is 2 minutes long and at the depth where the pressure change halves on an ascent from the bottom to a shallow water decompression stop. For example, on an ascent from a maximum depth of 196 feet (60 metres) at 100 psi (7 bar) to a decompression stop at 65 feet (20 metres) at 40 psi (3 bar), the Pyle stop would take place at the halfway pressure, which is 70 psi (5 bar) at 130 feet (40 metres).
DAN wrote:Adding A Deep Stop
On the other hand, it was found that even in repetitive dives, bubbles could be avoided as long as the leading tissue nitrogen was kept below 80 percent of the allowed M value, or less than 11 mbars (1 bar = surface pressure). The M value is the safe calculated partial pressure of nitrogen that can be safely allowed. A practical way to achieve this was by the introduction of an additional deep stop. This simple procedure lengthened the ascent time from 11.2 mins to 18.55 minutes, without changing the ascent rate, and reduced the previously recorded 30.5 percent incidence of high-grade bubbles to zero.
International DAN research studies have recently clearly confirmed these hypotheses: 15 divers were enrolled in a study and each given eight possible combinations of ascent rates, and either a shallow stop, or a deep and a shallow stop. The repetitive dives were to 80 feet (25 meters) for 25 minutes; the surface interval was three hours, 30 minutes; and the final dive was to 80 feet for 20 minutes. Ascent rates were 60, 30 and 10 feet per minute. The matrix is shown in Table 3 and the results of 181 dives are shown in Table 4.
Clearly, the best decompression schedule is Profile 6 (see highlights in both tables). With an ascent rate of 33 feet (10 meters) per minute, and two stops at 45 feet (13.5 meters) and 9 feet (2.7 meters) respectively, this profile had the lowest bubble score of 1.76.
Other Experiences with Deep Stops
From time to time in diving history, the concept of the "deep stop" has reappeared. Brian Hills noted that Australian pearl divers, who previously endured many fatalities and severe DCS in places like Broome and Thursday Island, eventually devised their own means of decompressing to stop this. The whole secret to their success was empirically adding deeper initial stops.
In more recent times, recreational technical divers have also devised their own decompression methods which have led to two so-called "bubble models" for computation. The Wienke Reduced Gradient Bubble Model (RGBM) and the Yount Variable Permeability Model (VPM) both attempt to predict when bubbles form and then calculate decompressions to prevent bubble formation before surfacing.4
NAUI technical divers have used the Wienke RGBM model quite extensively with no recorded incidence of DCS. This data as well as the results of this IDAN research in divers were discussed at a NAUI workshop in Florida in early 2003. As a result, NAUI has now suggested that a deep stop might well be incorporated in recreational diving by taking a one-minute stop at half the depth and followed by a two-minute safety stop at the 15- to 20-foor level instead of the three minutes currently recommended. We are currently testing this concept with our Italian diver research teams.
Azza wrote:The idea of the deep stops is more to slow your ascent, and limit bubble formation, than anything really.
aquakiwi wrote:I'm not really familiar with them but understand they can be beneficial, at what depth? and can they take the place of the 5m stop.
ChuckyBob wrote:Decompression dives are a bit different. The shallower stops are probably much more important and deep stops are more of a normal dive profile.
aquakiwi wrote:Thats pretty much what I wanted to hear, frequently conditions make the 3m stop uncomfortable.
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