Decompression Dive Training Environments – Cave vs. Ocean vs. Inland
While some may think that decompression training is the same regardless of where the dives are conducted, that isn’t the case. It’s true that the theory is much the same. Advanced Nitrox/Decompression Procedures introduces divers to the basic principles of decompression. Basic (Normoxic) Trimix introduces divers to the basic principles of diving while breathing helium. And Advanced Trimix expands on these basic principles and prepares divers to go to deeper depths. There are different decompression models available for use. There are different methods of determining Equivalent Narcosis Depth. The physiology is the same. However, dive planning and execution can be quite varied dependent on where the dives are to take place.
Unless a diver is planning on “flying the computer”, something I don’t subscribe to, conducting decompression dives in a cave environment requires knowledge of the profile of the cave. It’s not as simple as descending to the maximum depth, staying at that depth for a designated period of time, then beginning the ascent with the planned decompression schedule. The hard floor and ceiling of the cave often dictates the dive profile. A direct descent and ascent may not be possible. There may be an extended period of time during the decompression schedule where you must stay at a specified depth because the ceiling prevents you from making an ascent. Sometimes the ceiling may even require you to descend 10-20 ffw after you have already started your decompression schedule! Planning decompression dives in a cave environment requires quite a bit of attention to detail. Respiratory minute volume must be known otherwise you may not even have enough gas to get to your planned destination. Swim pace must be known otherwise you may not get to your planned destination in the time you allotted. It’s not as simple the square profile diving typically done in ocean and inland bodies of open water.
However, in the ocean, there are other considerations that must be accounted for. While planning the dive may not be as involved as for a cave dive, environmental factors must be considered. What are ocean conditions like? Is the surface choppy, making entry into and exit from the water an issue? Is there a current that could blow you off the line and/or the dive site. Will the dive boat tie into the dive site or do a live drop and pick up? The dive can be done as a square profile, which is fairly easy to plan. However, the decompression portion of the dive my require a jon line to hang comfortably off the line, or a surface marker buoy to mark your location as you do a drifting decompression. Also, unlike in cave diving, you must keep your decompression cylinders with you rather than being able to drop them off at the beginning of your dive. While it’s always a good thing to be familiar with respiratory minute volume so that you know if you have enough gas to stay down for your planned time, it may not be necessary to effectively execute the dive. Once you get to your turn pressure, you simply being your ascent. There is no hard ceiling to prevent this. Also, if something goes wrong during the dive causing you to have to abort early, you can simply begin your ascent. In a cave environment, you must make your way back to open water before you can begin your ascent. None of these issues is seen in inland bodies of water.
Inland bodies of water, such as lakes (with the exception of the Great Lakes), quarries, and sink holes, are fairly neutral environments. While there may be entanglement hazards, there are typically no currents, no rough surface conditions, no drifting decompression stops, no hard overheads. Dive planning involves planning for a square profile, heading out to the dive site, and executing the dive. Surface marker buoys will be deployed because all agencies require this skill, but it’s not necessary for the dive, just for the standards. The biggest issue with inland bodies of water is the decreased visibility, which actually makes the instructor’s job much more difficult because it’s not as easy to keep track of all the students. For the student, it’s an easy environment.
So where should decompression dive training take place? While the initial dives should take place in a neutral environment to introduce skills and ensure students are able to perform the skills, final dives during the various courses should be conducted in the environment the student will be doing most or all of their diving once training is completed. If the student will be diving in both cave and ocean environments, then dives should be conducted in both. However, to take a student through this type of training and only conduct the training dives in neutral inland environments is only doing a disservice to them. Remember, training prepares divers to dive in similar conditions as what they experienced during their courses. Therefore, training in a lake or quarry does not prepare a diver to dive in a cave or the ocean. When you prepare to do your decompression dive training, make sure your instructor is going to take you to dive sites that are similar to where you plan on diving. If you have to travel for your training, then do so. Don’t settle for mediocre training in a lake or quarry.
We offer technical dive training from Intro to Tech through Advanced Trimix. Our courses are conducted in caves for cave trained and certified divers and/or on the Oriskany or in South Florida.