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Heart Rate Variability, or simply HRV, is becoming more and more used in different fields, from an instrument able to diagnose cardiovascular anomalies, to a tool instrumental in improving high performance sports training. Many of us who are seriously into physical activities and sports practicing are familiar with or even have used one of the many apps available for watches or smart phones. But do we really know what they are?
Well, HRV is simply the variance in the interval between two heat beats. Or to be more precise, the changes in the interval between successive normal heartbeats. Usually, this is assessed through the timing between QRS complexes, which are main spikes as seen in a continuous electrocardiographic recording (ECG). HRV is the result of the balance between the sympathetic and the parasympathetic branches of the autonomic nervous system (ANS), as well as of other non-neural sources of variation. From a practical standpoint, it is as simple as a collection of time intervals, or for those more familiar with mathematical terms, it is a time series (a series of data points indexed by time).
Typically, these time intervals are not fixed or static but can vary widely moment to moment in response to input from the sympathetic and the parasympathetic branches of the autonomic nervous system, which control the contraction and relaxation of the cardiac muscle. Each system is activated by multiple receptors, responding to arterial pressure (baroreceptors), oxygen, and CO2 levels, as well as endogenous substances, emotions, immunological alterations, among other stimuli.
The parasympathetic branch, which regulates your energy and helps your body recover during rest periods, is mediated mainly by acetylcholine and is responsible for maintaining homeostatic heart frequencies and contractility without exhausting. It is responsible for short-term fluctuations of the heart frequency, and it operates in a frequency between 9 to 25 cycles per minute or 0.15Hz to 0.4Hz. Note that Hertz (Hz) is an international metric of frequency and is defined as one cycle per second (cpm).
Conversely, the sympathetic branch, which regulates your “fight or flight” stress impulses, is mediated mainly by norepinephrine, and its activity is triggered by stress, increasing cardiac energy demand by increasing heart rate . This branch is responsible for longer-term fluctuations of the heart frequency, operating in a lower bandwidth of 0.04Hz to 0.15Hz (or 2 to 9 cycles per minute).
HRV is commonly studied in the time and frequency domains, that is as a function of time and frequency. Different HRV indicators have been associated with sympathetic or parasympathetic activity. Additionally, there is an important association between specific frequencies and the baroreflex function, which provides a rapid negative feedback loop to adjust our heart frequency in order to maintain blood pressure at nearly constant levels.
But wait, what do time and frequency domains mean?
Let us start with the simpler one, time domain. In mathematics, the domain of a function is the set into which all of the input of the function is constrained to fall; therefore, when the term time domain is used, it simply means that we are doing our analysis based on time intervals extracted from the ECG recording. There are many indicators that have been created to study the variance in the intervals but here we will discuss only two of them, SDNN and RMSSD.
SDNN is the standard deviation, a measure of variation, of the time interval between heart beats (the R-R interval), and reflects all the cyclic components responsible for variability. The greater the SDNN, that is the variation between beats, the better. RMSSD is the square root of the mean squared differences of successive R-R intervals, or the variance of the variance of our time series, and is considered to be related to the parasympathetic activity. Both, SDNN and RMSSD are powerful indicators of our cardiovascular health, since the loss of variance between intervals is associated with many cardiovascular and/or inflammatory diseases. As shown below in Figure 3, we want our heart rate frequency to fluctuate a lot over time.
Now that the main time domain indicators have been defined, let us move to the frequency domain. But first, we need to understand one important math concept: any function or time series—think of the graph of a curve—can be re-written as a summation of sine and cosine functions, which are used to model phenomena such as sound and light waves. This idea was first introduced by Jean Baptiste Fourier in 1882 in his work Théorie analytique de la chaleur and later became known as Fourier series.
Figure 1 shows an example, using an arbitrarily chosen function:fx=x3+ x2+3x+5, plotted in the interval ]-π to π [. The resulting data shown as a curve can be reconstructed using a summation of sines and cosine functions through a Fourier series. In this case, twenty sine/cosine functions were used to approximate the curve, while in Figure 2, fifty functions were used.
It is easy to see from the diagrams that, the more functions we use, the greater the precision in the reconstruction of the original data. In both cases, we are using the sum of sine and cosine or “wave” functions to approximate the curve fx=x3+ x2+3x+5 in an ordered way. Each of the component sine and cosine functions correspond to a specific frequency. In this way, a curve can be broken down into its constituent frequencies.
Figure 3 shows the intervals between heart beats i.e., the R-R intervals extracted from a ECG recording and plotted against the time domain, which shows the variation of the heart rate frequency over time.
The next step is to approximate the waveform or curve formed by the heart beat data displayed in Figure 3 as a summation of functions through the Fourier series. This enables us to determine all the frequencies that are acting in our system. The frequency domain indicators are thought of as the “power” associated with each frequency—think of it as the relative contribution of that frequency in the re-construction of the curve formed by the data and calculated through a Fourier transform. These are usually plotted in a spectrogram, a graph where the x axis corresponds to the frequencies and the y axis to each frequency’s power or contribution, like the one displayed in Figure 4.
Now we are ready to define each one of the frequency domain indicators, categorized according to its associated frequency. They are:
- Ultra-low and Very-low Frequencies: 0.01 to 0.04 Hz, not relevant in most cases, due to the relatively short ECG recording usually used.
- Low Frequencies (LF): 0.04 to 0.15 Hz
- High Frequencies (HF): 0.15 to 0.4 Hz
In the beginning of this article, we noted that the branches of the autonomic nervous system (ANS), that is the sympathetic and the parasympathetic branches operate in different frequencies. Based on that, we can see that different HRV indicators in the frequency domain might be associated with sympathetic or parasympathetic activity.
High frequencies are highly impacted by the respiratory pattern, while low frequencies are affected by both the sympathetic and the parasympathetic branches of the ANS. Therefore, by analyzing the power or contribution associated with different frequencies, we can make inferences about the activity of each of the branches of the ANS and their interaction with other systems.
So, why does that matter?
Going back to the beginning of this article, most of the applications, i.e., “apps” used by smart phones and watches to track HRV perform their analysis are based on SDNN, which is a simple-to-calculate and powerful HRV indicator. It’s use is based on the idea that after a workout, the activity of the sympathetic branch temporarily prevails, reducing the overall variability and hence the SDNN.
In this sense, the tool can be used to avoid overtraining, adjusting the intensity of the training session according to the monitored HRV, until the measured SDNN returns to its pre-training values. The same concept can be used to measure stress levels. In theory, all other factors being the same, the more stressed we are, the less variability, and therefore a lower SDNN can be expected. In both cases, the exercise and the stress will likely induce a temporary preponderance of the sympathetic branch.
Now that we know how to analyze it and we understand that different systems are likely to be associated with different frequencies, we can understand why historically HRV was seen as a good measure of imbalances in the ANS. Probably the best way to describe HRV would be as a surrogate measure of the complex interaction between the brain and the cardiovascular system.
So how does that relate to diving?
It has been demonstrated by many studies that a reduced HRV is related to decreased life expectancy. A reduction in HRV has been reported in several cardiological and non-cardiological diseases, ranging from diabetes to renal failure, to mention a few [2,3,4]. A reduction in HRV, when analyzed in the frequency domain has also been associated with inflammatory processes [4, 5].
It is interesting to note, however, that due to huge inter-individual variance, it is difficult to establish expected HRV parameters for a population, and although some interesting studies have been published over the years, there is no consensus on standard values for each one of the HRV parameters. On the other hand, intrasubject analysis, that is the variation of HRV for the same individual over time, can offer very important insights.
Scuba diving is known to trigger oxidative and inflammatory processes, causing a variety of alterations in our physiology, ranging from loss of endothelial function , that is the capacity of the vascular endothelium to respond to vasodilator stimulus, to the activation of the innate immune system and production of microparticles  i.e., particles shed by different cells, which carry nuclear components of their originating cells, like RNA and DNA, and are involved in cell signaling and communication.
As one could imagine, scuba diving is also related to alterations in HRV  and by studying the pattern of these alterations we could infer how our bodies are responding to a dive and, in particular, to the decompression. Our recent study demonstrated that HRV is negatively associated with the production of microparticles and that, using a model built with machine learning, it was possible to predict the pre to post dive variation of the HRV, based on the variation of specific inflammatory markers, linking inflammation and oxidative stress to HRV in scuba diving.
In the past decade, many studies have demonstrated that the presence of inflammatory processes are linked to lowering HRV (either in the time or frequency domains). In our study we demonstrated the inflammatory and oxidative process related to diving are also related to changes in HRV and, interestingly enough, to a preponderance of the sympathetic branch in cases where the volunteers presented more intense responses to the decompression. This fact is also probably linked to the loss of endothelial function, long observed to happen after diving, although the mechanisms are, at this point, not completely clear.
There is still a lot to be understood about the relationship of HRV alterations and diving. The hyperoxia, i.e., exposure to pressures of oxygen higher than 0.5 ATA associated with diving, has its own effects on HRV, making interpretation of HRV variations in diving even more complex. The long-term goal of our research is to better understand individual responses to decompression. We believe HRV variations can be a powerful tool to achieve this objective.
Our team has been working in cooperation with DAN Europe, which has a huge database of diving profiles and outcomes, and some interesting models are being created to model the oxidative and inflammatory processes, but there is still a long way to go before these models can be used in any practical application. However, it is a promising field, and its comprehension will surely help in the full understanding of decompression physiology, making this subject certainly something interesting for the diving community. We could even dream about being able to adjust our dive profiles based on individual responses, right? Watch this space.
- Ernst G. Heart-Rate Variability—More than Heart Beats? Front Public Heal. 2017;5(September):1-12. doi:10.3389/fpubh.2017.00240
- Malliani A, Pagani M, Lombardi F, Cerutti S. Cardiovascular neural regulation explored in the frequency domain. Circulation. 1991;84(2):482-492. doi:10.1161/01.CIR.84.2.482
- Appel ML, Berger RD, Saul JP, Smith JM, Cohen RJ. Beat to beat variability in cardiovascular variables: Noise or music? J Am Coll Cardiol. 1989;14(5):1139-1148. doi:10.1016/0735-1097(89)90408-7
- Sloan RP. Heart Rate Variability Predicts Levels of Inflammatory Markers: Evidence for the Vagal Anti-Inflammatory Pathway. 2015;(Bernik 2002):94-100. doi:10.1016/j.bbi.2014.12.017.Heart
- Adam Moser, Kevin Range and DMY. Relationship between Heart Rate Variability, Interleukin-6, and Soluble Tissue Factor in Healthy Subjects. Bone. 2008;23(1):1-7. doi:10.1038/jid.2014.371
- Brubakk AO, Duplancic D, Valic Z, et al. A single air dive reduces arterial endothelial function in man. J Physiol. 2005;566(3):901-906. doi:10.1113/jphysiol.2005.089862
- Thom SR, Bennett M, Banham ND, et al. Association of microparticles and neutrophil activation with decompression sickness. J Appl Physiol. 2015;119(5):427-434. doi:10.1152/japplphysiol.00380.2015
- Schirato SR, El-dash I, El-dash V, Natali JE, Starzynski PN, Chaui-berlinck JG. Heart rate variability changes as an indicator of decompression-related physiological stress. Undersea Hyperb Med. 2018;Mar-Apr 20:173-182.
- Schirato et al. Association between Heart Rate Variability and decompression-induced physiological stress. Front. Physiol. Front. Physiol., 03 July 2020
- Schirato’s Talk at the 2019 GUE Conference: Heart Rate Variability: What it is and Why it Matters
- From GUE’s membership magazine QUEST: Decompression: Revisiting Old Assumptions by S.Rhein Schirato
Brazilian scientist, Sergio Rhein Schirato, is a hedge fund manager and a researcher at the Laboratory of Energetics and Theoretical Physiology of the Biosciences Institute of the University of Sao Paulo (USP). He holds a PhD in Sciences, a Masters in Finance jointly granted by New York University and London School of Economics and post graduation in applied Math. His current research includes the application of neural networks in decompression modeling and heart rate variability. Additionally, he is a GUE Fundamentals and Rec 1, 2 and 3 instructor, as well as GUE Rebreather certified diver.
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.
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.
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.
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.
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.
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.
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.
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.
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:
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.
- The Secretary of Labor vs. Houston Aquarium Inc.
- Oral Arguments: The Court Recordings
- American Academy of Underwater Scientists
- OSHA Commercial Diving Operations (CDO): 1910 Subpart T App B – Guidelines for scientific diving
- OSHA EXEMPTION, AAUS, AND SCIENTIFIC DIVING
- Health & Safety Executive (HSE): Scientific and archaeological diving projects. Diving at Work regulations 1997. Approved Code of Practice and guidance
- Dive Safety Manual Standards For Scientific Diving, University of California Santa Barbara
- Manual for Diving Safety: Scripps Institution of Oceanography University of California, San Diego
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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