Theory and in-water time: these are the two main components of many diving courses. Ask any student diver, technical or recreational, and they will inevitably be more excited about the in-water time, especially open-water dives. But dive theory is more than an afterthought—and here’s why.
Laying a foundation
Far from being ‘the boring part in the classroom,’ dive theory lays the foundation for progressing in your training later. True, the same can be said for skills and practice in the pool and in open water, but without understanding dive theory you will soon hit a ceiling, especially if technical diving is your goal. The key to successful application of dive theory is to really understand the concepts underlying it, rather than simply ticking the correct box in a multiple-choice exam.
From the very first time an open-water student picks up their course manual or logs into their eLearning, they are studying the same concepts of physics and physiology that they’ll need to understand decompression dive plans and rebreather diving. Really? Yes, really.
Many divers may remember seeing a drawing of a balloon being taken underwater and decreasing in size as pressure and depth increase. The same drawing mentions increasing air density at depth. So, chapter one of many agencies’ open-water diver program introduces the inverse relationship of pressure and volume as well as gas density. Technical divers use both these concepts to calculate gas consumption and the most suitable gas for a certain depth.
Physiology is another example. From the first time divers don a tank of air and start exploring the underwater world, they learn that it’s important to control ascent and descent rates. Descend too fast and you may be unable to equalize your ears quickly enough or exceed your planned depth. So far, so simple. As you are moving deeper into technical diving, however, making the most of your limited bottom time becomes crucial and you must balance a safe descent rate with maximized time underwater. What does that have to do with dive theory? Understanding what’s happening in your ears and sinus cavities when you descend and when you equalize will help when it comes to practicing different equalization techniques. Most of those are best practiced on land initially with someone talking you through it, before attempting them underwater.
Decompression and dive theory
Another concept students learn during initial certification courses is the fact that divers’ tissues absorb nitrogen during the dive. The longer you stay at depth, the more nitrogen your tissues absorb, eventually leading to saturation. Granted, most recreational and technical diving stops far short of saturation, but the basic concept remains in place. The longer you stay, the more care you need to take on ascent. In that sense, every dive is a decompression dive — the main difference being that if divers stay within no-stop limits, a slow ascent and a safety stop are enough to fulfill their decompression obligation.
Stepping into technical diving, managing that decompression obligation becomes more complex. While not ideal, a recreational diver could always return directly to the surface. Missing their safety stop means going against strong recommendations and best practice, but, in all likelihood, the diver should still be okay. A technical diver missing mandatory decompression stops has a much higher risk of becoming ill with decompression sickness.
During technical-diving courses, students learn about different decompression algorithms that help them plan and manage their ascent. Their instructor is likely to recommend an algorithm and a degree of conservatism based on their own knowledge and experience, which then becomes the starting point of the new tech diver building their own experience. While this may sound complicated, it’s founded on the basic concept from the open-water diver course: it’s about managing ascent speed.
With that in mind, other considerations follow: how much gas will we need for the decompression stops? Can one diver carry all this gas? What happens if we exceed our planned bottom time? Exceeding the no-stop limit at 100 feet (30 m) for a minute may lead to a one-minute mandatory decompression stop in 10 feet (3 m) and may even have been blown off by the time the diver reaches that depth. However, exceeding planned bottom times by one or two minutes at 328 feet (100 m) will add 10 to 15 minutes to a diver’s decompression obligation, posing serious questions about gas supply and potential exposure if the dive is done in cold water, to name only two considerations.
Planning for those kinds of emergencies all happens on land well before a technical dive. It is not something you do quickly on the boat while gearing up or in the car on the way to the dive site. On the contrary, planning and preparing for big dives can take weeks, if not months, depending on the complexity of the dive. For most standard technical dives (if there is such a thing), planning would at least be done on the day before the dive to allow time to digest and re-read the dive plan, prepare gases, and pack gear. On the day of the dive, a thorough briefing often completes planning.
Studying dive theory and learning more is also a great way of keeping your knowledge fresh. There is much more knowledge out there than what fits into training agency manuals, and the deeper you delve into that, the more you’ll realize that you are only scratching the surface.