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Digging Deeper: A Fresh Case for Deep Stops

“Deep stops”—the practice of making deep decompression stops, originally popularized by deep diving ichthyologist Richard Pyle in the early 1990s—has largely fallen out of favor with the tech community over the last decade as a result of a number of studies and experiences. However, as DAN’s Reilly Fogarty explains, deep stops may yet provide some value according to the work by DAN Europe researchers. The devil’s in the details.



by Reilly Fogarty
Header photo by Jong Moon Lee.

For nearly two decades a vocal minority in the diving community has been gathering their pitchforks and protesting against deep stops, and anyone who would commit the thought-crime of considering them. The data has appeared to legitimize this pursuit, with several studies failing to confirm benefits or indicating negative outcomes with the addition of deeper decompression stops. Endless debates among academics and divers alike ultimately made it taboo to promote deep stops in the North American dive community. 

Across the pond the backlash against those who would perform their decompression marginally deeper has been similarly negative but rather less dramatic. Whether that contributed to the ongoing research in deep stops is hard to say, but some theories have indicated that deep stops may yet provide value. Data from some of the biggest names in diving research has indicated a potential decrease in decompression risk with some profiles, and while the data is far from conclusive, it warrants a closer look. 

Dr. Costantino Balestra and JP Imbert are two proponents of continued research, and their research seems to show a correlation between the addition of deep stops and a decrease in post-dive bubbling in some cases. Here’s what we know:

DIY, This Is Not

Most discussions about deep stops veer into the realm of specific practices. All too often technical divers see promising research results and apply derivations of the latest hypotheses immediately. In the case of deep stops, this usually manifests in the manual addition of deeper decompression stops either during their dive planning or on the fly. It is theoretically possible that Balestra’s and Imbert’s hypotheses are correct, and the added deep stops might happen to coincide with their recommendations in some fashion, but the typical outcome is an increase in bottom time and, potentially, in decompression risk. 

Short deco stop at the mouth of a cave. Photo courtesy of David Rhea.

On-the-fly implementation of theoretically suggested practices was common enough that a paper from 2011 aimed to study the models divers were modifying rather than finding the ideal application for deep stops (Cronje, 2011). Research to determine if deep stops have any benefit whatsoever is still being performed, so the range and specific applications of those stops are still a ways off. 

Even just the three papers cited at the end of this article show three separate deep stop protocols, and those are carefully calculated protocols designed for research purposes. The reality is that we don’t yet know enough for divers to be adding these to their profiles. Confounding the issue further, there is so much about decompression science that we don’t yet understand that any benefit or trouble from the addition of these stops might be caused by factors that appear unrelated.  

Crunching the Numbers

Broaching a topic that many consider to be put to rest long ago is tough, and it requires excellent data. Balestra and Imbert point to several papers as background and supporting documents for their ongoing research. Each of these focused on the addition of a decompression stop significantly deeper than the first indicated by their decompression model of choice and looked at the rate of DCS incidence in the participants. The first used a stop added at half the maximum depth (Cronje, 2011), another added a stop at 50 feet following a test dive to 25 m/82 feet (Bennett, 2007), and a third used a range of ascent rates and compared a each to a range of deep and shallow stop protocols following a 25 m/82 ft dive. (Marroni, 2004). 

The Cronje paper was actually written in response to end-user modification of dive tables to add deep stops at half the maximum depth with anecdotal or Doppler evidence to support them. Significant debate over the efficacy of the modifications at various depths ensued, and the aim was to determine whether those modifications put divers at risk for spinal DCS. An animal model was applied; it involved compressing groups of rats to 3.5-6.0 atm for one hour and then using a 7-minute decompression schedule with and without a 5-minute stop at half the maximum depth. 

Interestingly, this profile is known to cause spinal DCS in anesthetized rats, but no rats displayed symptoms of DCS. Thus another trial was conducted to determine the threshold for DCS in the subject participants. This trial involved compressing 11 animals to 4.93 atm (without results) and another 14 animals to 5.4 and 5.9 atm with and without deep stops, also without results. Across all models there were two deaths and two breathing abnormalities (both in the group compressed to 5.4 atm without deep stops) and zero instances of spinal DCS or other symptoms. It’s difficult to point to a reason for the apparent fortitude of these rats, but the lack of symptom evolution in any subject — using a proven DCS-causing profile — illustrates the wide variability in DCS onset. 

The Bennett and Marroni papers had somewhat greater success with their subjects, and their work provides a foundation for an ongoing interest in deep stops among researchers like Balestra and Imbert. The Bennett paper compounded on prior work indicating a correlation between deep stops and a decrease in precordial Dopper-detectable bubbles. This paper focused on optimizing the stop times from the initially applied 5-minute stop at 15 m/50 ft following a dive to 25 m/82 ft with an ascent rate of 9 m/30 ft of seawater (fsw) per minute. 

Subjects were asked to perform 20- and 25-minute dives to 25 m/82 ft with an ascent rate of 10 msw/33 fsw/min and apply one of 15 profiles with stop times ranging from 1 to 10 minutes at 15 m/50 ft and a second shallower stop performed at 6 m/20 ft. Decompression stress was estimated with the use of precordial Doppler bubble counts. Data indicated that deep stops of 1 minute actually increased bubble counts, leading to the greatest bubble evolution of any profile tested, but a 2.5-minute deep stop followed by a shallow stop of 1-5 minutes led to the lowest bubble counts. 

Increasing time at the shallow stop did not measurably decrease bubble count. The results led the researchers to recommend a deep stop of “at least 2½ minutes” at 15 m/50 ft in addition to a stop at 6 m/20 ft for 3-5 minutes following dives to 25 m/82 ft, but the authors noted that they could not extrapolate those recommendations beyond those profiles without further study. 

Making a shallow stop. Photo courtesy of Jong Moon Lee.

The Marroni paper also relied on precordial Doppler bubble counts to measure decompression stress, although its focus was more specifically on spinal and neurological DCS. The authors of the paper hypothesized that introducing deep stops would reduce bubble formation specifically in fast tissues and result in a decreased risk of neurological DCS, measurably by a lower bubble count. 181 dives to 25 m/82 ft were performed by 22 volunteers, with bottom times of 20 and 25 minutes and 3.5-hour surface intervals. Eight ascent profiles were utilized with ascent rates of 3, 10, 18 msw/min (10, 33 and 60 fsw/min) combined with no stops, a shallow stop at 6 m/20 ft, and a deep stop at 15 m/50 ft plus a shallow stop at 6 m/20 ft. 

The greatest bubble counts were found in divers utilizing the slowest ascent rate, while the lowest were found in divers using the 10 msw/min (33 fsw/min) ascent rate with a 5-minute stop at both 25 m/50 ft and 6 m/20 ft. These divers showed nearly half the bubble load of the control group at 5 minutes post-dive and 70% of the bubble load at 10 minutes postdive. As with the Bennett paper, the researchers could not extrapolate the data to other profiles but did find the use of deep stops correlated with a reduced overall bubble load.

Decompression research is a tough field because of the variability inherent to individual subjects and symptom onset, but that’s no surprise given the breadth of factors involved. It’s disheartening to wade through a decade of research just to discover that we have, at best, anecdotal data on the application of deep-stops, but that’s where things currently stand. There is significant data that indicates that deep stops in a small range of researched profiles may decrease bubble load, and more research is warranted. 

What we don’t yet know is how the deep stop profiles compare to profiles using the same decompression time or tissue gradients but at shallower depths, how those deep stops affect decompression at technical depths, or how they can be applied in the field. The nature of the work makes it difficult and time-consuming to collect research subjects and data, and it’s unlikely that we’ll have answers to these questions in the immediate future, but the possibilities are fascinating to consider. 

Additional Resources:

Decompression, Deep Stops and the Pursuit of Precision in a Complex World:


  1. Cronje FJ, Meintjes WA, Bennett PB, Fitchat S, Marroni A & Hyldegaard O. (2011). Analysis of clinical outcomes of linear vs. deep stop decompression from 3.5 to 6 atmospheres absolute (350 – 600 kpa) in awake rats. Undersea Hyperb Med 38, 41-48.
  2. Bennett PB, Marroni A, Cronje FJ, Cali-Corleo R, Germonpre P, Pieri M, Bonuccelli C, Leonardi MG & Balestra C. (2007). Effect of varying deep stop times and shallow stop times on precordial bubbles after dives to 25 msw (82 fsw). Undersea Hyperb Med 34, 399-406.
  3. Marroni A, Bennett PB. (2004). A deep stop during decompression from 82 fsw (25 m) significantly reduces bubbles and fast tissue gas tensions. Undersea Hyperb Med 31, 233-243.

Reilly Fogarty is a team leader for risk mitigation initiatives at Divers Alert Network (DAN). When not working on safety programs for DAN, he can be found running technical charters and teaching rebreather diving in Gloucester, Mass. Reilly is a USCG licensed captain whose professional background includes surgical and wilderness emergency medicine as well as dive shop management.


Fact or Fiction? Part 2: Interview with World Record Holder Ahmed Gabr




by Michael Menduno

See Part 1: Fact or Fiction? Revisiting Guinness World Record Deepest Scuba Dive 

The day before this issue of InDepth was to go LIVE with Gabr’s world record story—I had reached out to him to comment but he declined—I received an email from Gabr. He apologized for any previous confusion and told me that he had checked my credentials and legitimacy and was now willing to grant me an interview. An hour later, we were speaking on FaceTime. Gabr was animated and very talkative. He would frequently go off on tangents and I had to keep bringing him back to my questions. At first, he seemed a bit nervous, but he started to relax more as the conversation went on.

After we briefly talked about his military background—note that he made the dive while still a colonel in the Egyptian army—I began by asking Gabr why he thought these allegations were surfacing now, six years after he conducted his world record dive. He said he believed it was because a documentary of his dive had been completed, and his detractors wanted to get back at him. “Their agenda is to discredit me and the movie,” he said. I asked him if he knew who Scuba Sam was, and he told me that he was a former disgruntled member of his team that had fled Egypt under legal suspicion and wanted to get back at him.

Gabr verified that the head cam video included in Scuba Sam’s email was accurate. I asked him why he hadn’t carried a camera and filmed the dive to begin with. He explained at the time he had an 8-year old child and a pregnant wife, and he said it would have been a huge stressor for him to know that they might see the video if he had died. For that reason, he hadn’t videoed his training dives either.

What About The Depth Timer?

I asked Gabr about Scuba Sam’s first allegation, whether his Scubapro 330 m Depth Timer with blacked out corners—that only showed his Maximum Operating Depth—was metric or imperial. He answered by first saying that computers were not required as part of the validation and launched into a detailed explanation of Guinness’s measurement methodology.

Guinness’s procedure for validating the dive was twofold. First, Gabr had to retrieve one of the unique, signed, and wrapped depth tags from the certified descent line. More on procedure surrounding the tags later. In addition, Gabr’s deep support diver, who met him at 90 m/295 ft, instead of 110 m/361 ft, as planned, was supposed to video him giving a special hand sign indication “3-5-0,” which was requested by the Guinness adjudicator shortly before the dive. In addition, he was to display the retrieved tag, which was the 335 (335 m/1094 ft) tag as shown in the video. He said that only the adjudicator, deep support diver, and Gabr knew the sign. Computers were not required. However, Gabr told me that he was so excited that he held out his Depth Timer (DT) which showed a max depth of 330. The question is whether it was feet or meters.

I asked him why he had blackened out the three corners of the Depth Timer so that only the max depth was showing. Note that only the last digit of the current depth reading, and part of the preceding digit, in the upper left-hand corner is showing. He explained that he did that before his last training dive because he was worried that breathing helium beyond 300 meters would give him hallucinations, so he wanted to keep his brain focused by having a single number. Is max depth the best number? His account contradicts the explanation that two of his team members independently gave me. They reported that Gabr told them it was to insure the integrity of the device under pressure as per the manufacturer.

Gabr explained that he made the dive with four measuring devices: two computers, the Depth Timer, and a Swiss military watch which was rated to extreme depth. He told me that he clipped one of the computers on the line at 90 m/295 ft on his way to depth, as he was worried that it would fail and he wanted it to keep track of his overall dive time compared to his runtime table. He later retrieved the computer which is shown in his hand with double enders in the video. Gabr then said that the main computer died (went blank) at 290m/796 ft during his descent.

OMG! How did he monitor his depth with no working computer and a depth timer only showing MOD? Gabr explained that he used the rope as his “depth tool,” and his watch to keep the time?!? Wow. Can you imagine? What if you got blown off the line? The rope was NOT marked in 3 m/10 ft increments. Rather, according to the engineering report, it was marked in 5-meter increments from 320-350m, and 50-meter increments from 300-150 m, then 10m increments from 120-100 m, and the 3m increments from 96-90 m, where he met his first safety diver. In other words, it would be very difficult to follow as a depth guide, particularly if he were suffering confusion. Gabr reported to me that he was mentally confused and feeling drained at depth. 

Note also that Gabr’s first three planned 1-min deep stops (186 m, 171 m, 150 m) were not marked on the rope, nor his stops at 140, 130, 123 (see the partial runtime deco table shown in Part 1). On the video, Gabr gave his first safety diver the OK upon meeting him at 90 m and later reported that the dive went according to plan. No mention of computer problems or the lack of a depth-keeping device at depth.

Again,  I asked him about the Depth Timer, whether it was the imperial (feet) version as alleged, or the metric version. Specifically, if it were the metric unit, why wasn’t the decimal showing before the last digit of current depth? [See the analysis in Part 1] Note that the Scubapro metric unit shows the current depth shallower than 100 m in three digits XX.X, to the tenth of a meter. Gabr said that the device “wasn’t in feet.” 

What happened, he explained, was that the depth timer began to flood on ascent, and as a result, the decimal point indicating that it was a metric unit and the temp reading had disappeared by the time he reached 90 m/295 ft. He said that eventually the face of the depth timer went blank. Again, Gabr pressed the point, “Why do I need to fake something that is not even required [for the record]?” 

One source told me that Gabr had been wearing his metric depth timer on his previous training dives with a standard strap mounting. However, the depth timer in the video has bungee cords. Was the metric device swapped out for an imperial version for this dive?

What About the Gas?

I asked Gabr about arriving at his 90 m/295 ft stop, where he met his deep safety diver, roughly eight-minutes (21 meters shallower) earlier than the plan. He explained that it wasn’t an issue and was within his calculated safety limit. He said that he had reached the 335 m/1099 ft depth tag between 12-14 minutes, and in the absence of a working depth monitor, he ended up making his first stop from depth at 150 m/492 ft using the rope markings. The plan called for slowing his ascent rates as he ascended through various depth zones. 

I next asked him about the video which shows him breathing his back gas (trimix 4/85) as he is met by his safety diver at approximately 90 m: “Why were you breathing your bottom mix?” Gabr answered immediately, “I ran out of deco gas.” He then launched into an explanation about Isobaric Counter Diffusion (ICD), and why it wasn’t a big concern for him to switch back to his back gas because the differences in nitrogen were minor. But what about the oxygen?!?

Note also, that none of the tanks had SPGs. I asked him about this. “It’s a weak point for failure,” he explained. However team members told me that all cylinders were triple checked, analyzed, and marked for proper contents prior to the dive.

Deco plan for the dive. Photo courtesy of

In the video, the safety diver descends to Gabr, asks in sign, Are you Ok? Gabr, who appears very relaxed, responds with an OK sign. No mention of an out-of-gas issue. Gabr then displays his retrieved 335 tag, shows his Depth Timer reading 330, and makes the sign requested by the Guinness adjudicator 3-5-0. “The first thing I wanted to do was secure the record, and do the whole video process,” Gabr explained. He next secured the tag to his support diver to prepare it for its trip topside. “My nightmare was that my deep support would lose the tag so I zip-tied it to his D-ring.” 

After the Guinness protocol was accomplished, the safety diver switched out Gabr’s empty stages and passed him his stage bottle with trimix 12/75 deco gas, that was supposed to be breathed from 120 m up to 90 m. Gabr then went back on his deco gas. The support diver also sent up a status slate to the surface indicating Gabr was OK. The 90 m safety diver met them soon after, and facilitated Gabr’s gas switch to trimix 16/69.

There were several things that were a bit inexplicable. First, if you had just completed a 330+ meter diver, lost a computer, and then ran out of deco gas prior to your 90 m stop while you were facing another 14-hours of decompression, would you give your safety diver, who was carrying back-up deco gas the OK sign? Again, according to Guinness and other news reports, Gabr said that the dive went as planned. Second, were Gabr’s priorities. Wouldn’t you switch to your deco gas and then do the record protocol?

Finally, most troubling, Gabr had four 12L cylinders of 12/75: three staged on the line and one in a carried stage bottle. According to the plan, Gabr was to breathe 12/75 from 120 m to 90 m, for a period of 15 min at an average depth of 110 m or 12 atm. You do the math. For example, with a high 20L surface consumption rate for example, he should have burned through 20L/min x 12 ATM x 15 min=3600 liters. That’s roughly 1.5 12L cylinders, not four. Was he in that depth range longer? Gabr acknowledged that he had burned through lots of gas between those depths and was crazily coughing and had some chest pain. He thinks he had mild pulmonary edema. 

Lines, Tags and Fitness

The fourth allegation concerns the angle of the descent line. The video, 50-minutes into the dive, shows the line at what is estimated to be 25º angle, which performing a trigonometric analysis, would mean that the 335m tag would be at approximately 303 m/989 ft short of the record. Gabr explained to me that the Guinness adjudicator and the calibration engineer who was on board measured the angle of the descent line at 15 minutes into the dive. Accordingly they subtracted 2.65 meters to arrive at the record of 332.35 m/1094 ft and 4.5 inches.

The fifth allegation is that there was a broken chain of custody with the tags, meaning that they could have been altered or replaced prior to the dive. Gabr disputed the claims. Though he wasn’t present for all of it, he said that the tags were under the control of the adjudicator the whole time, who even had his own locks to secure the tagged line the night before the dive. That is in Guinness’ bailiwick to determine. Gabr said that the adjudicator watched him dress and searched him prior to the dive. Eye witnesses reported that Gabr and his lead support diver were not searched thoroughly for tags before entering the water, and that the diver who escorted Gabr to depth was not searched.

Gabr showing off his record to his friends. Photo courtesy of

Finally, I asked Gabr about his reported high energy level following the dive, which contrasted sharply with Gomes’ experience who had to be helped to walk (See Part 1). Gabr, who is reportedly very fit, explained that, unlike Gomes, he removed his quads at 21 m/70 ft and so only wore them for 4.5 hours. Gabr said that he also hydrated and ate every hour during his shallower deco stops, which he asserted Gomes’ did not. He also pointed out that at 41-years old at the time of the dive, he was 12-years younger than Gomes when he set his record. Ouch! I later checked with Gomes’ who said that he also hydrated and ate. As discussed in Part 1, Gomes insists the quads were not an issue for him. We ended the post-dive discussion with Gabr pointing out that its difficult to compare one person to another.

What now?

I asked Gabr what he intended to do. To my surprise he launched into a story about a sustainability project he was involved in with the first Egyptian to climb Mt. Everest. He then told me about a shipwreck exploration project in the Mediterranean in late September that he planned to do a pilot film about. I finally interrupted him. “But what about the allegations?” 

“I have no idea,” he said. “What do you think?” “It’s up to Guinness,” I offered. “No, Guinness is done with it. It’s over,” he said. I asked Gabr if he had been in touch with or heard from Guinness or his project leader. He said he hadn’t, adding that, “They have a bullet-proof system.” He went on. “I am confident in what I did. But it bothers me that my reputation has been targeted. Why do I have to justify myself? I am confident, but I’m being hurt,” he said. 

He went on. “Why are they doing this now, after six years,” he asked rhetorically. “Usually people try to discredit a record at the time it is made. But why six years later?”

“Do you think it’s because of the documentary film?” I asked. “I’m sure about that,” Gabr replied. “It’s the same person who was with the team. He was trying to sell helium illegally in my name and got me into trouble. He wants to discredit my whole record and the movie,” he said.

I asked if Netflix was going to release the documentary, which several people had told me about. Gabr said, no, that the documentary, which had investors, had not been sold yet. “Netflix didn’t buy it?” I asked. “No,” he said. I asked him several times if he had a financial stake in the film but did not get a clear answer, though he acknowledged he was under contract. 

Gabr then said about his anonymous accusers. “They are not searching for the truth. They only mention half the truth. There was no peer review from professionals. My record would be discredited if I had relied on one of the computers. For sure. But that was not the measurement methodology.”

I asked Gabr if he would be willing to have a peer group review all the information and possibly clear him. Gabr said that he was open to anything. He said that he has been using the same video in his talks as presented in the emails and is always willing to sit and discuss things at every dive show he attends. “I don’t mind talking about my dive,” he said.


There is obviously a lot of information to unpack, and numerous additional details, as well as information protected by confidentiality that I have omitted here. It’s clear to me that I am not in a position to render a judgement, nor is it my job. My job has been to ask questions, lay out what appear to be the facts as best and fairly as I can and point out inconsistencies as I see them. 

As I said before in Part 1, it’s up to Guinness to decide if they want to investigate the allegations or not, and on that basis to determine if Gabr completed a record dive or not. However, given the widespread distribution of allegations about the record, and what seem like surprising discrepancies, it’s likely that his record will remain under a shadow until the full truth is known, whether by Guinness or perhaps, as Gabr suggests, through a peer review by professionals. 

Michael Menduno is InDepth’s editor-in-chief and an award-winning reporter and technologist who has written about diving and diving technology for 30 years. He coined the term “technical diving.” His magazine aquaCORPS: The Journal for Technical Diving (1990-1996), helped usher tech diving into mainstream sports diving. He also produced the first Tek, EUROTek, and ASIATek conferences, and organized Rebreather Forums 1.0 and 2.0. Michael received the OZTEKMedia Excellence Award in 2011, the EUROTek Lifetime Achievement Award in 2012, and the TEKDive USA Media Award in 2018. In addition to his responsibilities at InDepth, Menduno is a contributing editor for DAN Europe’s Alert Diver magazine and X-Ray Magazine, a staff writer for, and is on the board of the Historical Diving Society (USA).

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