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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.

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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:
https://gue.com/blog/decompression-deep-stops-and-the-pursuit-of-precision-in-a-complex-world/

References:

  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.

Latest Features

OSHA vs. The Houston Aquarium: What Constitutes A Scientific Dive?

The Houston Aquarium recently won a pitched legal battle against the Occupational Safety & Health Administration (OSHA). At stake was whether the aquarium’s fish-feeding, scientific divers should be required to meet the more rigorous commercial diving regulations. As British dive journalist Victoria Brown explains, the case has served as a wake-up call for diving scientists to modernize their diving standards and establish global buy-in.

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by Victoria Brown
Header photo courtesy of the Downtown Houston Aquarium

Disgruntled employees, unwanted Santa outfits, 19th Century brotherhoods, and knowledge of different types of algae? We take a detailed look at the almost decade-long litigation that has plagued a very public, but little-known, tentacle of the scientific diving community. The good news? This saga could inadvertently prove to be the catalyst for modernizing this self-regulating community of divers.

Landry’s Downtown Houston Aquarium has recently won an eight-year long legal dog fight against the U.S. Department of Labor’s Occupational Safety and Health Administration (OSHA). The latest ruling, one that has not and now cannot be challenged by the Department, ruled in favor of the Aquarium, finally putting the matter to rest. Despite this being described as “the battle of our time” by the Houston Aquarium’s Corporate Dive Program Manager, Todd Hall, scientific divers across the USA—and the world—have been relatively silent on the matter, and the win has been under-celebrated. 

If OSHA had challenged the ruling. it would have seen the case tried in the Supreme Court, the highest court in America. In this article, we dive under the surface of the case and draw attention to how this landmark ruling could benefit the global scientific diving community in years to come. 

Scientific Diving Guidelines

The guidelines governing scientific diving were born out of challenges to the original 1977 OSHA publication of standards for commercial diving operations. These applied to any diving in the natural or artificial inland body of water, as well as diving along the coast of the US and other listed territories. These standards made no provisions for diving performed solely for scientific research and development purposes, despite many dive programs operating safely and independently before the publication of the standards. 

Surface-supplied aquarium divers. Photo by Todd Hall

The educational institutions who championed this niche in diving quickly argued for exemption on the grounds that there were already standards in place before the OSHA publication, pointing to the University of California Guide for Diving Safety adopted in 1973. Furthermore, and perhaps more poignantly, they cited their impeccable safety record which was a result of efficient self-regulation. 

The main crux of their argument was that the educational/scientific and commercial diving conditions are not congruent, therefore they cannot be subject to the same standards. This pressure led to OSHA deciding, in August 1979, to officially look into the matter, as they wanted to better understand the issue at hand. This move on the part of OSHA opened the gateway for non-educational scientific diving organizations such as the American Academy of Underwater Science (AAUS) to be formed, strengthening the case for exemption. 

The scientific diving community proved victorious on November 26, 1982, when OSHA, after extensive consultation and public hearings on both the east and west coasts, granted a dispensation to divers that met their definition of scientific diver. [Recreational diving instruction was also deemed exempt from commercial regulation]. They also stipulated that scientific divers must operate under a diving program that utilized a safety manual and that had an adequate diving control board in place. In a bizarre twist, this was challenged by the Brotherhood of Carpenters and Joiners Union, which filed for a judicial review, seeking further guidance on what type of enterprises could be exempt. 

This legal challenge led to the publication and adoption of the guidelines in place today, fatefully titled, “Commercial Diving Operations-Exemption for Scientific Diving-Final guidelines.”

These guidelines stated that the exemption is valid as long as the diving programs operated under a diving control board with autonomous and absolute authority, utilised a diving manual covering all diving operations specific to the program including standards and practices, emergency assistance plans that cover recompression and evacuation, as well criteria for diver training and certification. 

The Case Against The Aquarium

Fast forward to 2012, and this exemption became the fighting ground for an appeal by the Downtown Houston Aquarium for relief from approximately $20,000 worth of penalties issued by an OSHA inspector, who during an inspection had applied commercial diving standards to the program despite its scientific status. It was not the cost of the penalties that spurred the appeal but the implications of accepting the inspector’s citations. This included the associated costs of adapting the program to commercial diving standards and, more importantly, the potential increased risk to divers of applying those standards. 

Photo courtesy of he Downtown Houston Aquarium

It was a tough pill for this little known part of the scientific community to swallow given its good safety record, and there was also the danger of a domino effect with other programs being treated in the same way, something which would seriously hinder future research from both a financial and safety point of view. 

Indeed, this created unrest among aquarium programs causing some to make the costly switch to commercial standards in anticipation. Mauritius Bell, the president of the Association of Dive Program Administrators (ADPA) and program administrator at California Academy of Sciences,  reported in an interview that in a recent ADPA survey of their members, more than 50% of zoos and aquariums were operating under commercial standards. He believed that the percentage would have been much lower before the citation. 

The Landry’s Houston Aquarium operates a six-acre entertainment complex with a 500,000-gallon aquatic tank that houses over 300 species from all around the globe, reptile and bird exhibits, large dining halls, and a selection of white Bengal tigers amongst their jam-packed entertainment attractions. Despite this touristic facade, Landry’s Aquarium also operates as a scientific research center and the tanks are maintained as best as possible to replicate the natural ecosystems for marine life. 

In 2011, a employee who was partaking in the diving program was asked to leave his post apparently after a disagreement relating to a Santa outfit. This disgruntled employee, in turn, complained to OSHA and accused Houston Aquarium of not following the commercial diving standards on dives they executed as part of the daily aquarium operations. He sent OSHA portions of the Code of Federal Regulations, along with his complaint detailing his concerns with the diving practices, and accusing Houston Aquarium of not following commercial diving standards on dives that, it could be argued, were not for the purposes of data capture. 

Note the bailout tanks. Photo by Todd Hall

OSHA—and rightfully so—has a policy of deploying an inspector to investigate any complaints of this nature. Mark Chapman, the local Compliance Health and Safety Officer, was assigned to the case, and after visitation, deemed that everything was in order according to the scientific diving exemption of the commercial diving regulations. Chapman documented the aquarium’s stringent record-keeping across a long history, that their appropriate dive medicals were in place and up to date, and that all safety equipment was in the right place.

These findings were challenged by the ex-employee who lodged a further complaint with the national OSHA office, leading to a second investigation in February 2012. During this inspection, Chapman uncovered new evidence that formed the basis of the Citation and Notification of Penalty that was issued on July 10, 2012. It was determined that divers who clean the tanks and feed the animals were not conducting scientific dives, and, as a result, those dives were subject to the more stringent commercial diving operation standards. This is the only time OSHA has issued such a citation to an aquarium program that claims scientific status. 

It was determined that divers who clean the tanks and feed the animals were not conducting scientific dives, and, as a result, those dives were subject to the more stringent commercial diving operation standards. This is the only time OSHA has issued such a citation to an aquarium program that claims scientific status. 

What is a Scientific Dive?

The aquarium realized the potential impact on the broader scientific community, as well as their program, and decided to appeal. This led to the case being heard by an Administrative Law Judge (ALJ) in February 2019, a little less than seven years later.

The proceedings identified three types of dives: feeding/cleaning dives, event dives, and mortality dives (during which dead animals are removed and taken to the Aquarium’s lab for examination). During the initial three- day hearing, the ALJ ruled some activities did not fall within the exemption, namely the feed, clean, and event dives. Consequently, on February 15, 2019, the majority of OSHA’s Review Commission panel affirmed the ALJ’s determinations that these did not meet the plain text definition; interestingly, the Chairman of the Commission dissented. 

The aquarium conceded that the event dives were extraneous to the scientific research being conducted, but strongly disagreed that the feed and clean dives could be seen in the same light, chiefly because these dives underpinned the research conducted by the aquarium. It was reported at the time that Landry’s general counsel and executive vice president, Steve Scheinthal, was of the opinion that OSHA had overstepped its bounds and vowed to appeal. His challenge to the ruling was launched on April 16, 2019, when the aquarium, led by senior diving officer Todd Hall, petitioned a higher court to review the judge’s ruling, focusing on the decision to side with the lay testimony of an OSHA Compliance Officer whilst excluding expert testimony. 

Photo courtesy of he Downtown Houston Aquarium

Furthermore, they took issue with the OSHA declaration that the application of commercial diving safety regulations should be enforced on the aquarium because they were not performed by “employees whose sole purpose for diving is to perform scientific research tasks,” despite it being substantiated during the hearing that the Aquarium’s employees all hold scientific bachelors and masters degrees. Another citation was issued for not having decompression tables at the exhibits, but they were proven to be nearby in the dive locker which was fully accessible by the divers. All in all, there were many grounds for a challenge.

And so we arrive back at the landmark decision reached by the fifth circuit Federal Court Of Appeals (just below the Supreme Court) in July of this year, which can no longer be contested by OSHA. The court was sensitive to the fact that the divers completing these activities are trained scientists and learned that there was a requirement for them to observe animal health and behaviors, eating patterns, and the types of algae growing in the tank. 

Furthermore, during the appeal it was proven that this information was recorded upon completion of their dives, thus meeting the criteria of data capture which is the basis for the criteria of what defines a scientific dive. The court also listened and agreed with expert testimony stating that adhering to the OSHA commercial standards in the context of a scientific dive would make the divers and animals “less safe.” Indeed, Todd Hall had testified from the beginning that this was the case, pointing out that a diver could get to the surface quicker than switching to a second air supply and that extra equipment in the exhibits created a hazard to the animals. When asked to comment on the ruling Hall said, “It took eight and a half years to come full circle. The take away was that we were right all along because the judge used our exact logic from day one of why we were safe and why more equipment doesn’t make us safer.”

The Quest for Global Scientific Diving Standards

This was not just a victory for one aquarium, as over the last few months many that had made the switch to the OSHA commercial standards have quickly reverted to the more appropriate and safer scientific standards that they followed before the 2012 citations. It could also be argued that this was also a win for the scientific diving community as a whole which, through organizations such as the American Academy of Underwater Sciences (AAUS), has been vocal that there is a need for more clarity from OSHA on the criteria for exemption. 

Jessica Keller, a NOAA employee and the current secretary of AAUS, believes this is a long-standing issue. “There’s a question of when to apply commercial diving standards vs. when to apply the scientific exemption. We needed clarification in these grey areas.” 



When speaking with her colleague Derek Smith, President of AAUS and a previous expert witness for the Aquarium put forward by ADPA, he echoed Keller’s sentiment and sees this very much as the beginning rather than the end of the matter. “Celebrating the victory is short-lived, as this landmark is cementing the practices followed not only by the Houston Aquarium, but a large majority of aquariums across the USA and the world,” he said.  “It’s a silent victory about practices they have carried out for years and years. I believe there is now the opportunity to dive headfirst into a new battle and push for updating of the standards for Commercial Diving Operations (CDO) and its exemptions.”

It must be noted—and this was highlighted by Derek Smith—that the ruling pertains to the three states that the Fifth Circuit has jurisdiction over, and cannot fully be used as a precedent. Having said that, he went on to say that it is certainly a case that can be referenced. The AAUS has offered to work with OSHA in assessing exemption claims; as an organization that oversees the standards for one hundred and fifty-two scientific diving programs, AAUS argues that they are better placed to make the call on what is exempt, since they have access to  decades of accrued data. 

Photo by Todd Hall

Derek Smith confirmed that the AAUS has begun this partnership work and is hopeful that this will prevent any other aggressive and baseless enforcement against programs claiming exemption. Keller also celebrated this move, stating, “The most important thing is now we have opened the lines of communications, and I’m glad that OSHA is interested in having a better pulse on what’s happening in the field.” 

This case has also given rise to conversations around the modernisation of the standards followed by scientific divers and the benefits to science this could yield. For example, Todd Hall believes that using a rebreather would allow for closer and improved observation of the animals, as well as minimising the impact on the ecosystem. 

The ripple effect has not stopped there, as the global scientific community looks to the US when setting standards. Smith and the AAUS are certainly playing a role in painting what that future looks like for the community as a whole. When asked to talk about what is next, Smith passionately explained: 

We are trying to unify everyone on a world level. I’m heading up (for the AAUS) a scientific diving training council which is akin to the recreational scuba training council, we have all the major scientific diving standard-setting organizations across the world to agree to a common standard that we will all follow. It’s at the stage now where it’s going out to all our boards, Canada, the US, Mexico, and we have about 100 countries represented so far. [We are seeking] unified training standards so we can enjoy some level of formal recognition of prior training so scientists can move freely across the world to work.

According to Smith, the goal is to establish a global organization that will mirror the role that The World Recreational Scuba Training Council (WRSTC) plays in recreational diving in protecting the worldwide safety of the recreational diving public, primarily through the development of worldwide minimum training standards. The World Scientific Diving Training Council (WSDTC) was established last year, putting foundations for minimum training standards  into the ground. This is a tall task, as there are no doubt some territories that have their own entrenched standards. For example, the Health and Safety Executive in the UK has a strong hold on this type of diving dating back to the Diving at Work Regulations 1997, Approved Code of Practise and Guidance. 

The World Scientific Diving Training Council (WSDTC) was established last year, putting foundations for minimum training standards  into the ground. This is a tall task, as there are no doubt some territories that have their own entrenched standards.

What will be the impact of this global action? Keller was quick to point to the the potential benefits, both in the short and longer term, of this new consolidated way of working in the scientific community:

Photo by Todd Hall

Let’s create this global minimum standard for science so that reciprocity and international collaboration can be easier and so we can trade information. Our oceans are in trouble with sea level rise, and we need to understand it better. Moving forward we need it to be easier. If we can get our own house in order that will help us globally, [and] having an organization to help set these standards will help save the world.

This is yet to be proven, but what is more certain at this point is that this sensational court case has drawn attention to the fact that scientific diving has self-regulated without incident for the pastthree decades. It could be viewed that the case was an unnecessary eventuality born out of a plot of revenge by a disaffected actor; but, it could also be viewed as a necessary evil that may just have ensured that this community of divers continues to keep each other safe.


Additional Resources




Avidly exploring the underwater world since she was twelve, Victoria Brown has been a professional diver for sixteen years and is now based back in the UK following many years touring the snowiest peaks and deepest green seas. From safety diving on media projects to creating content for the coolest brands in the diving industry, she has diving written all over her.

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