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by Peter Buzzacott
Most technical divers understand and know how to calculate their Surface Air Consumption (SAC) rate, which is typically used in gas planning. But did you know that SAC rates can also be used to measure various workloads—for example, the difference in workload when diving doubles vs. singles, using various techniques, or under different environmental conditions?
Let’s use an example to recap the theory; I’ll use metric throughout this blog for simplicity. A diver is at 10m depth, which is 2 ATA in the sea. The diver’s tank is a standard 12-liter tank filled with 200 bars (plus a safety margin); therefore the diver has 2,400 usable liters of gas at the surface. At 10m depth, that would be down to 1,200 breathable liters, and if the diver used the whole 1,200 L of usable gas over one hour, then the diver’s surface equivalent breathing rate would be 1,200/60, which is 20 liters per minute—a common, if slightly high, breathing rate. One might argue the actual breathing rate is 40 liters per minute, and that the equivalent of 40 liters per minute comes out of the tank, but it is actually compressed down to 20 liters because the diver is at 2 ATA. This is why we call it surface air consumption— because even though the breathing gas is twice as dense at 10 meters depth, the breathing rate is equivalent to 20 L/min at the surface (not 40 L/min at the surface). Of course, the air is twice as dense, so the work of breathing is greater, but SAC does not account for this.
Okay, that’s the math out of the way. In the real world, divers often use the average depth from their dive computers to estimate the average ambient pressure throughout the dive, then divide the volume of gas used by the number of minutes spent underwater and the average pressure. This gives a fairly accurate estimate of the surface equivalent breathing rate. For part of my PhD research, I clipped accurate depth loggers to the chest D-rings of divers and recorded over 1,000 recreational dives. I also used a calibrated pressure gauge to measure the tank pressure before and after each dive, and noted the tank volume stamped on each tank. Then, I asked every diver if they thought the workload during their dive was “resting/light,” “moderate,” or “severe/exhausting.”
Good in the SAC?
In the 1980s, a scientist named Dwyer had divers fin at a certain pace against a set resistance and measured both their SAC and how much oxygen remained in their exhaled gas. This was done at a few set depths, including a series of dives at 10m depth. An equation was generated for each depth to convert SAC into oxygen consumption. The mean depth of my 1,000 recorded dives was 10.7 m, so I used Dwyer’s 10m equation to convert everyone’s SAC into oxygen consumption. I then made one last conversion by dividing everyone’s oxygen consumption by their weight (in kilograms, of course). This standardized the oxygen consumption across the whole range of divers, from small to large and whether male or female.
Interested readers can read my paper, but to make the results meaningful here, I’ll compare the dives by how many metabolic equivalents (METS, i.e., the rate at which a person expends energy relative to the mass or weight of that person) each dive represented. When our oxygen consumption is at its lowest, for example, when we are asleep, we consume around 3.5 ml/kg.min of oxygen, which is by convention considered to be 1 MET. If I consume 35 ml/kg.min of oxygen while running on the treadmill, then I would be running at 10 METS.
In my study, the divers who said their dive was relaxing had an average workload of 5.3 METS. It is important to remember that is an average, because some people had a very low SAC and some people really chewed through their gas, but the average for a resting dive was 5.3 METS, which is about the same as a brisk walk. The dives with a moderate workload averaged 5.8 METS, which is about the same as riding a bicycle at a modest pace (~15 km/hr), and the severe/exhausting dives averaged 6.2 METS, which is about the same workload intensity as an aerobics class.
Dwyer also recorded his divers’ heart rates and tried to generate equations to link SAC with heart rate. Recently I tried something similar and took a research team to Oregon to measure SAC and heart rate in volunteer divers at the Oregon Coast Aquarium. We fitted waterproof EKGs to each diver, plus those sensitive depth/time loggers, and estimated their workload just as I’d described above. But, just like Dwyer, we couldn’t generate a reliable conversion from SAC to heart rate, or vice versa. Therefore, the most reliable estimate of workload that we divers have is, in my opinion, SAC/kg. To give some sort of guide, the “resting/light” divers in my PhD research had an average SAC/kg of 0.21 L/kg.min, the moderate divers 0.23 L/kg.min, and the exhausted divers 0.29 L/kg.min.
As we all know, good trim is essential for reducing workload while diving—as is correct weighting and good buoyancy control. Other factors include finning technique and drag. Using SAC/kg, divers can measure for themselves how much of an effect there is when going from a single tank to a set of doubles, or when adding a stage or multiple stages. Divers can also see just how much of an improvement they make when they perfect their technique over many dives—for example, their DPV technique. [ed: It’s OK to try this at home kids!]
Another advantage of SAC/kg is that it can be compared within a dive team between males and females, between small divers and big divers. In Oregon, the aquarium divers were in drysuits, the water was cold, and the divers were working (cleaning the viewing windows, vacuuming the floor, etc). Their average SAC/kg was 0.26 L/kg.min, which was equivalent to a moderate-to-difficult workload. The full paper was published in the latest issue of Occupational Medicine.
Buzzacott P, Pollock NW, Rosenberg M. Exercise intensity inferred from air consumption during recreational scuba diving. Diving and Hyperbaric Medicine. 2014;44:74-8.
Dwyer J. Estimation of oxygen uptake from heart rate response to undersea work. Undersea Biomedical Research. 1983;10:77-87.
Buzzacott P, Grier JW, Walker J, Bennett CM, Denoble PJ. Estimated workload intensity during volunteer aquarium dives. Occupational Medicine. 2019; https://doi.org/10.1093/occmed/kqz011
Peter Buzzacott, MPH, PhD, is a former recreational and technical diving instructor, now a university researcher with more than 60 published papers on diving injuries. He is a Guest Professor at the Second Military Medical University in Shanghai, in the hyperbaric research laboratory that, in 2017, discovered the first nutritional supplement shown to prevent decompression sickness. Before that, he conducted decompression experiments during a two-year post-doctoral fellowship at a university in northern France. He is an avid cave diver.
Finland’s Newly Established Scientific Diving Academy
by Edd Stockdale
Header image: Antarctic research as part of Science Under the Ice project Photo by @scienceundertheice.
While exploring the aquatic realm, many divers often encounter objects of interest but are unaware of the historical or scientific value to the fields of archaeology, geology, or biology. Even if they suspect their find might be important, they are untrained in how to treat such a find with an investigative approach.
Scientific diving, separate from sport, recreational, or commercial diving, requires occupational training specific to science-led, underwater activities with the purpose of collecting data and/or samples. This type of diving is important both to research, as well as to policy making, because divers with this specific training and background can make the quantitative or qualitative-based assertions necessary to implement the findings. There is a necessary and important distinction between professional scientific divers and the “citizen science” trained divers who are essential in building public awareness, particularly in conservation projects.
The necessary training and the regulation of professional scientific diving varies widely from country to country, both in regulation requirements, as well as in practice. In many countries, scientific work is classified as commercial diving, and regulations are set accordingly. At the opposite extreme, underwater scientific activity can be conducted by anyone certified to dive.
Structured approaches were developed to mitigate the abuses that both of these approaches might create—one such approach was specifically from the American Academy of Underwater Sciences, formed in 1977. AAUS, in 1982, received an exemption from commercial diving standards through self-regulation. In Europe, the process of establishing a recognized training standard was slower because many different European countries had different regulations; however, in 2007, after collaborative efforts by leading researchers, the European Scientific Diving Committee was formed. This agency became the European Scientific Diving Panel (ESDP) in 2008. ESDP established the standards for both Advanced European Scientific Diver (AESD) and European Scientific Diver (ESD) that are recognized by its member countries.
One of the early members in the establishment of ESDP, Finland, has experienced a decrease in scientific dive training options but no decrease in the demand for trained divers because of the increased amount of marine research and monitoring Finland carries out. To fill this void in suitably trained divers and to develop a new generation of marine researchers, a group of leading representatives from various institutions have successfully sought funding to establish a new, centralized training center—the Finnish Scientific Diving Academy (FSDA) at the University of Helsinki Tvarminne Zoological Station. FSDA is located on the shore of the Baltic Sea.
The Academy’s primary objective is to train European standard professional scientific dive training for AESD certification, but this is far from its only goal. In addition to the six-week core program, plans are in place for adding dive training to undergraduate and early career research students to stimulate future generations of field-based marine researchers. Courses for divers who want to gain more experience or to develop skills for citizen-science-based projects with shorter timescales are also in the cards, making the Academy a truly centralized base for all aspects of scientific dive activities, one that can offer expertise across the disciplines.
With its location on the Gulf of Finland, this training will predominantly specialize in cold-water based approaches, though training options in other locations are always a possibility to cover different conditions. Taking advantage of the ice conditions in Finnish winter’s polar research dive training, which, combined with easier access and facilities already established, makes the option to train for polar projects—without the logistical hassle of actually getting to research stations in those regions—a realistic possibility.
Included into the development concept of the FSDA is not only the concentration on classical scientific diving protocols, but also a widening the scope. It is often ironic that all the different areas of diving contain techniques that can overlap to benefit each other but are not taught or communicated; for example, skills used in a cave diving survey could easily benefit an ecological study or archeological field work. Therefore, the coordinator position for the FSDA requires a background in not just scientific, but technical and other areas of diving with the aim to integrate these skills into these areas into the programs.
As a result, in the future, courses will likely be offered for specific evolving technological options, developing techniques, or specialist subjects that research teams need in order to carry out projects. Training may also be offered for more advanced diving, including mixed gas and rebreathers, to expand the ranges and environments to carry out scientific work.
At the other end of the spectrum, driven by the growing need for more studies of aquatic regions combined with reduced funds for research, citizen science or the involvement of non-professional volunteers becomes more relevant all the time.
Training options for divers looking to develop these skills vary dramatically, and they may not be familiar with research institutions where expertise is highly appreciated.
Due to the need for scientific consistency in work carried out, divers not only need high levels of diving ability, but also an understanding of the project goals that are important for the results to be valid. Such training is specialized, but done and implemented correctly, provides scientists with the resources of capable dive teams, which is one of the long term goals of the FSDA. These programs will also aim to cover more specialized fields of study or the application of different diving procedures, both from the requirements perspective of project leaders looking for teams of “citizen scientists,” as well as from the divers themselves.
Overall, the creation of the Finnish Scientific Diving Academy is exciting for both the scientific and regular diving communities, as it aims to address reduced access to specialized training while developing newer techniques and raising awareness of the importance of how research into the marine world is carried out, whether it is surveying a 400-year-old shipwreck or the ecology of a reef.
The FSDA has been initially funded by the Antero and Merja Parma Foundation and Weisell Foundation for three years with aims to secure more funding to remain long term and is coordinated by Edd Stockdale. The first courses will begin in April 2022. Queries should be sent to Edd Stockdale.
Edd Stockdale has worked in scientific and technical diving for over a decade and joined as Badewanne team member in 2019. He is the coordinator of the newly established Finnish Scientific Diving Academy at the University of Helsinki, which was established to develop scientific diving training to further research abilities and develop new approaches to data collection in cold water based science. When not working on research diving, Edd can be found exploring the mines and wrecks in the Nordic region or planning the next adventure. He is supported by Divesoft as well as Santi, Halcyon, and REEL Diving in Scandinavia.
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