I have had many discussions with students, potential students, and even other instructors about why I no longer teach the “standard” safety stop for recreational diving. In this article, I will discuss a new way to ascend from a dive. I’m using a depth of 100 feet as an example. This “new” method is safer in my opinion. This article will introduce the concept of a deep stop for recreational diving.
A deep stop is a “pause” for 30 seconds to one minute at a depth that is half of the depth for the dive. In our example, we’ll use an average depth of 100 fsw (33 msw). The reasoning why a diver would want to do this is to slow the ascent and give the body a chance to adjust to the change of pressure. The body will start to off gas at 75% of the average depth for the dive. In our example, we’ll start off gassing at 75 fsw. The deep stop will allow our bodies to adjust to the pressure change and start off gassing. It also gives us a quick chance to clean up any gear that may be “untidy”. Such as turning off lights and clipping off light heads.
For the 15 feet for 3 minutes, PADI put that into their curriculum when the DSAT Doppler study years ago showed a tremendous decrease in symptomatic and asymptomatic bubbling when the stop was done and using the standard 60 fpm, at the time, recommended ascent rate. They now recommend 30 fpm.
I do understand the rationale for the stop at 50 feet, as that would be indicated as a “recreational deep stop”. I know that NAUI has used the RGBM and Bruce Wienke’s recommendation of 50% of max depth of any dive past 40 fsw for the recreational deep stop and then 3 minutes at 15 feet and a 30 fpm ascent rate.
We then take that 3 minutes at 15 feet safety stop and stretch it out so that the stops are divided equally at 1 minute at 30 feet, one minute at 20 feet, and one minute at 10 feet. This gives us a smoother ascent profile vs. the one stop at 15 feet for 3 minutes, this decreases rapid reduction in ambient pressure and gives cleaner deco vs. ascending to one stop at a shallower depth and waiting the whole time there. This also begins to shape our thinking regarding deco as we progress to more aggressive profiles. In other words, we start to accustom ourselves to this “smoothing” of the deco curve as we ascend and lengthen the shallow stops as we ascend.
The reason why we do this comes from decompression research that shows a tremendous reduction in bubbling if we address decompression from a dual phase approach. This dual phase approach says that inert gas exists in two different forms in the body. One phase is called the “free phase” or bubble phase, and one form is the dissolved gas phase. In a nutshell, the bubble phase of off gassing is addressed at the deep stops and the dissolved phase is addressed at the shallow stops. The two different phases use different driving gradients to eliminate inert gas. The bubble phase gradient is increased w/increased depth (hence stopping deeper) and the dissolved gas driving gradient is increased w/reduced depth (thus the shallow stops).
Deep stops limit sudden reduction in ambient pressure and thus limit the size & formation of more bubbles by keeping ambient pressure high.
This is a very simple explanation of a complex process that is still not fully understood even by the experts. I would recommend doing a bit of research on the subject on the Net…any search for Brian Hill, Yount, WKPP deep stops, Richard Pyle deep stops, Bruce Wienke, RGBM (Reduced Gradient Bubble Model), VPM (Varying Permeability Model), etc. will yield a ton of info.
Thanks to Brandon Schwartz for providing some of this information.
Dive Safe,
Duane
Precision Diving
