Deep Stop Scuba, Why Is It So Controversial?

My name is Víctor Córdoba, and I have the challenge of explaining the controversy about deep stop scuba to the readers of this blog.

Why me? What gives me the authority to write about deep stop scuba? – You probably ask yourself. The answer is my expertise. Let me introduce myself.

I studied biology, and I am a diver. I am a PADI Course Director, and IANTD Training Instructor specializing in Cave, Trimix, and Rebreather diving. Besides, I work as the Director of Human Resources for Dressel Divers. During more than 35 years of diving, I have made more than 5000 dives. With these credentials, I write to you.

It is possible that this is the first news you have about deep stop scuba, and you do not know what it is. I’ll tell you now.

Perhaps, you have already heard of deep stops and are interested in learning more about the discussion and whether or not to perform them. Perfect, you are in the right place!

It is also possible that you are an expert on this topic. In this case, we invite you to send us your contributions and help shed light on deep stop scuba. 😉

Anyway, we are facing an exciting topic that has the world of diving in check. Take a look at the table of contents and find out how we approach it.

1. What Is Deep Stop Scuba?

 We could define deep stop scuba as a type of diving where a stop is made earlier than traditional dive algorithms indicate.

I should not start the house from the roof. Let’s lay the foundation first.

If a dive’s objective is something, it is to return to the surface without suffering from decompression sickness (DCS). As all divers know, nitrogen is absorbed by the tissues as far as we descend. The depth and diving time influence this. During ascent, nitrogen is eliminated little by little when exhaling.

Dissolution algorithms were born to avoid DCS. It is the way we name conventional models, those that every diver knows. They indicate when and how long a diver has to stop for a given depth and specific bottom time. So far, nothing new.

However, some technical divers claimed a few years ago that, although they made the established stops, after a few dives, they felt fatigued. In contrast, if they made deep stops earlier than the dissolution model required, post-dive symptoms improved.

The truth about this statement and what it means for recreational diving is what we try to clarify in the following points.

2. Decompression stops according to the different models

 To understand the debate about deep stop scuba it is interesting to review decompression models their history.

2. 1. Dissolution decompression models

 We owe the first decompression tables to Dr. John Scott Haldane, a Scottish physiologist. The Royal Navy’s Deep Diving Committee required his services in 1908.

The physiologist worked on the hypothesis that the dissolution of nitrogen in human body tissues is heterogeneous. That is, different body tissues have different saturation and elimination times. Haldane established 5 compartments to help him establish the mathematical formula for decompression diving time.

Furthermore, Dr. Haldane believed that tissues sustain a certain level of nitrogen saturation before producing bubbles. He concluded that a diver could ascend without DCS to the depth where a compartment’s nitrogen pressure does not exceed twice the pressure that it would support at ambient pressure at that depth. According to him, using that 2:1 ratio, we could avoid decompression sickness by ascending in stages and stopping there until the nitrogen level in the compartment dropped enough. Then the diver could ascend again to the next stop while maintaining the 2:1 ratio.

Subsequently, the work of doctors Robert D. Workman and Albert Bühlmann improved Haldane’s calculations by introducing the concept of M-Value.

This value indicates the maximum saturation each compartment can support at a given depth. So, no one follows the 2:1 ratio anymore because not all tissues work at the same velocity, and the ratios range from 1.55:1 to 3.15:1.

It meant that shallower dives required less decompression diving time, while longer deep dives involving slowly dissolving tissues increased decompression diving time.

2. 2. Bubble decompression models

 Spencer and Huggins used ultrasonic Doppler scanners to reveal the existence of microbubbles in the tissues of divers emerging from a dive. These initially asymptomatic bubbles can be a problem in repetitive dives. In other words, a diver does not have to exceed an M value to generate bubbles. Whoops!

Thus, new models emerged to improve bubble-based decompression tables. The most significant are the Bruce Wienke Reduced Gradient Bubble Models (RGBM) of the NAUI and the Variable Permeability Model (VPM) that D.E. Yount and D.C. Hoffman developed at the University of Hawaii.

The main feature of these models is deep stops in that in the most complicated dives, the divers made the first stops earlier than in the dissolution models.

2.3. Dr. Pyle and his deep stops

To the new models based on bubbles, we have to add the stir caused by Dr. Pyle.

In the mid-1990s, Richard Pyle, an ichthyologist (a scientist who studies fish) also based in Hawaii, disclosed to the diving community that although he made decompression stops following dissolution patterns, he found himself weary after a few dives and after others not. The explanation that Dr. Pyle gave for this fact was the following.

The ichthyologist went down to great depths to capture fish to study and make their taxonomy. In the process, he had to stop and prick the swim bladder of the specimens with a hypodermic needle so that it would not burst on the ascent. He did that stop at a deeper depth than that established by the decompression tables. When he failed to catch fish, he did not make that previous stop. Pyle claimed that he was much better off when he did deep stop scuba. So, he developed his own model of it.

At this moment, the entire diving community opened its arms and accepted deep stop scuba; especially technical divers. It was the Nirvana discovered! Or not?

3. First stop depth debate

To get the decompression process optimization that the new models supposed, NEDU (US Navy) wanted to verify them.

So, Dr.David J. DOOLETTE and his team conducted an experiment. The goal was to show that deep stops were better and more effective. In this way they could reduce the decompression times of their tables and optimize their performance. It was assured by Dr. Doolette in a personal conversation with me. But they did not expect the surprise they were going to get.

There were two dive profiles in the experiment. Both carried out with air, at a depth of 50 meters/ 164 feet, for 50 minutes of bottom time and with a total duration of 174 minutes.

One of the profiles followed dissolution decompression patterns. The other made deeper stops according to a US Navy VVal algorithm.

The experiment subjects’ performance was in a temperature-controlled hyperbaric chamber. The subjects had to do constant exercise on an ergonomic bicycle with the same intensity. Measurements were made by reducing the variables involved in decompression sickness.

The surprise was maximum when after making 200 exposures of each profile, 11 decompression sicknesses occurred in the deep stop’s scuba profile and only 3 with the traditional profile, two of those having only weak symptoms, according to Dr. Doolette.

In the conversation, Dr. Doolette was asked if he thought the same thing would happen to him using Trimix. He confessed that he was collaborating in a Swedish navy investigation whose results pointed in the same direction.

This study has had a lot of controversy due to the scientific protocol. However, other studies, such as the one by Jean-Eric Blatteau in France, also offered deep stop scuba disappointing results.

What is the explanation for these results? It is easy. During the time you are in the deep stop, the fast elimination and saturation tissues really discharge, but the slow and medium tissues continue to load with nitrogen. So, when you get to the surface, you have the middle tissues crammed with nitrogen.

• OK, I understood. So, we dismiss deep stop scuba completely, don’t we, Victor?
• No, at least not entirely.

Dr. Christian R Gutvik of the University of Norway conducted another study with anesthetized pigs, because they are physiologically more similar to humans.

Gutvik made 2 profiles with two variants each. In the first one, he submerged the pigs to 30 meters/98 feet with a 70-minute permanence at the bottom and evaluated them with deep stop scuba and traditional stops. In the second, he took them up to 60 meters/ 197 feet, but he only had them in the bottom for 20 minutes and subjected them to both types of stops.

The result of the ultrasound was interesting. It indicated that pigs that had deep stalls while shallow and a lot of bottom time had fewer bubbles than traditional stalls.

In contrast, the pigs that made deep stops, descended to 60 meters/ 197 feet and spent 20 minutes at the bottom had more bubbles than those that made traditional stops.

It indicates that it is vital to assess the severity of the dive and diving time. Doing a shallow dive with a lot of bottom time can be riskier than diving deeper for a short time. So, in this type of diving, deep stops do make sense.

4. Recreational divers, how do we take advantage of deep stops?

Dr. Frans J. Cronje, Professor Alessandro Marroni (President of DAN Europe), and Dr. Richard Vann (DAN Vice President of Development and Head of PSD Work) also conducted a study that demonstrated the validity of deep stops for recreational diving.

They measured the formation of microbubbles in divers who had repeatedly descended to 25 meters using air. In the study, it combined 3 ascent speed ranges (3 m/minute|10ft/minute, 10 m/minute|33ft/minute, and 18 m/mimute|59ft/minute) with different ascent profiles: (no stops, 5 minute safety stop at 6 meters and 2 stops: a 5-minute deep stop at 15 meters/ 49 feet and the 5-minute safety stop at 6 meters)

Divers who ascended at a speed of 10m/m. performing a deep stop at 15 meters/ 49 feet and the safety stop at 6 meters showed a percentage close to 0% of microbubbles.

Therefore, deep stops work on square dives (with a fixed bottom time), such as a wreck dive.

Why are they not always used? Because in recreational diving, these types of dives are not frequent. Recreational divers usually start a dive, reach the desired depth and gradually ascend during the dive.

5. How do we use deep stop scuba in technical diving in 2022?

The fact that deep stops have not been a definitive solution for technical diving does not mean we don’t use them anymore. In fact, the traditional system continues to cause decompression stress in divers’ bodies that we are still trying to correct. Currently, technical divers use gradient factors over the dissolution algorithm. With this, we try to modify the traditional decompression profile with deep stops at less depth. The topic of gradient profiles applied to deep stop scuba is for another article. Are you interested in this topic? Let us know, and I’ll tell you. Write to us!