~~~ Part 6 ~~~
And that's how Henry had found himself with his laptop on his desk in their study later that night - technically early the next morning - having crawled out of bed after Elizabeth was asleep.
The open water diver certification consisted of three parts: theoretical knowledge, which he could do online, pool sessions to practice and demonstrate skills, and a set of initial supervised open water dives. The dives he figured he could do in Anguilla, but he was determined to do the rest ahead of time. Before he could lose his nerve, he signed up for the next upcoming pool sessions at a nearby dive shop and registered for the online portion of the course. No time like the present to get started with the online material, he thought, giving himself a little pep talk. He could do this. Oorah!
The first e-learning module was about water pressure and air pressure. Water pressure, he began reading, increases linearly with depth, starting at 1 bar at the surface of the water at sea level and increasing 1 bar every 10 meters. The higher pressure affects divers, specifically it affects air spaces: the sinuses, ears, and lungs. The module covered techniques for equalizing the ears - something that was second-nature to Henry from flight training - and stressed the importance of going slowly and equalizing frequently on descent, especially during the first 10 meters, and never equalizing forcefully or descending further if experiencing discomfort. The training advised divers to instead gradually ascend until the discomfort stops, and only then try equalizing and descending again. The training warned that not properly equalizing could lead to a ruptured eardrum.
Rather than this giving Henry something else to worry about, he was actually reassured that recreational scuba training was addressing problems and risks. Sometimes people mistook Henry for a daredevil because he'd been a fighter pilot, but actually it was quite the opposite. As a pilot, he was always simultaneously minimizing risk and preparing for worst-case scenarios. He remembered how much of pilot training covered different, often very rare, failure modes. Being more knowledgeable and prepared for potential dive scenarios would make him a safer and more confident diver.
He read on, reviewing Boyle's gas law: that the pressure of a gas, such as air, is inversely proportional to the volume of the gas; or, more concretely, that when the pressure doubles, the gas compresses to half the volume. Henry recalled having learned this all before, but it felt like it was so long ago. (Because it was; heck, he was flying before he was Stevie's age, talk about feeling old.) He quickly grasped the implication that the deeper the diver is, the more gas the diver will consume. The module explained the correct breathing method: Relaxed breathing, deep breaths, and never holding your breath. Even though he had his reservations about diving, he was confident in his ability to remain calm under pressure - he chuckled to himself at his unintentional pun - he just needed to remember to focus on his breathing. The training covered more possible injuries, this time lung injuries, confirming Henry's claim that humans weren't meant to breathe underwater.
Then there was an explanation of the equipment, which was all new to Henry. And it was sort of fun to be learning in a completely different context than either his academic research or his government work. Planes had fascinated him because somehow, through ingenious engineering, they enabled people to fly. How did scuba equipment allow people to breathe underwater at depth and, correspondingly, at higher pressure?
Henry learned about the hoses and regulators, which regulate the air pressure from the compressed tank to something humans can consume. He was relieved to learn that standard equipment included an alternate backup regulator, so a diver could switch to the backup regulator if the primary failed. While a recreational diver would only carry one tank, divers pair up with a partner or dive buddy, and in the event of a tank failure or a depleted tank, a diver can use one of the regulators on their buddy's tank to share a supply of oxygen. Redundancy and dive buddies were obviously important aspects to diver safety. He learned that standard gear also included a buoyancy control device (BCD), often in the form factor of a vest, that could be inflated or deflated to achieve neutral buoyancy, a pressure gauge to monitor how much air was left in the tank, and of course the tank (cylinder) itself. Henry took a short multiple choice comprehensive quiz, and was surprised to find that he had already completed the first of the seven modules. He pressed on.
The second module opened with the behavior of light underwater: how refraction of light by particles in the water makes everything a diver sees through their mask look both larger and closer, and how water not only absorbs light so that it becomes darker at depth, but how it absorbs some colors of the spectrum more readily than others, beginning with reds and oranges, causing objects underwear to appear bluer. This matched Henry's experience snorkeling. Henry learned why our eyes can't see clearly underwater without a mask, and that just as divers need to equalize their ears, they should equalize the pressure of the air in the mask to avoid squeezing their eyes.
Following the description and explanation of the behavior of light was the behavior of sound. Unlike light which travels much more slowly through water than air, sound travels more quickly underwater than in air. Although we hear very well in the water, the faster speed of sound makes it hard for us to determine the direction a sound is coming from. So it is important to verify location visually, rather than relying solely on hearing, which can be misleading.
Next was temperature and hypothermia, which gave Henry some pause, as hypothermia inevitably brought to mind ice skating with Tommy. Though his memories of the events of that day had blurred with time and his immediate sense of shock had dulled with retellings, he still remembered Tommy's untimely death all too well. He reminded himself that hypothermia, even while ice skating, was rare, and that the Caribbean was a far cry from Pittsburgh winter. He skimmed through the information on dive suits and insulation. Did people even need wetsuits in the Caribbean? Not really, he discovered. They were were used by divers for protection and to maintain body heat and improve performance, especially when doing many repeated dives. But mostly these were thinner and/or shorter wetsuits, and they definitely weren't needed, especially in the summer. Re-focusing on the course, he came to another quiz.
Module three was all about buoyancy and Archimedes' principle. No wonder math-oriented Elizabeth had taken to diving, Henry thought. Fortunately, he wasn't daunted by basic math and physics. Though he saw himself more as a man of the arts, he'd taken some physics courses in pursuit of his dream of becoming a pilot and because he wanted to better understand how planes worked. "A body immersed in a fluid is buoyed up by a force equal to the weight of the displaced fluid," he read. So if an object or a person, weighs more than the fluid it displaces, it will sink; if it weighs less than the fluid it displaces, it will float. Neutral buoyancy, which is the most energy-efficient way to dive, is achieved by having the same weight as the displaced fluid. Saltwater, Henry knew, was heavier than freshwater, which is why it's easier to float in the ocean than in a freshwater lake or swimming pool.
Once divers are wearing their gear, they displace so much water relative to their weight that they are positively buoyant and need to carry weights to achieve neutral buoyancy. Although it was possible to estimate, the exact amount varied from person to person and depended on the gear, so he'd learn how much weight he would need once he was in the water. There was a bit about how to move efficiently underwater: keeping horizontal and streamlined - similar to the design of an aircraft, Henry thought - and pacing yourself, avoiding exertion, and swimming mostly with your legs, using either flutter kick or frog kick and taking advantage of the long dive fins. The rest of the section was about buoyancy equipment: the BCD, which would allow for fine-grained dynamic adjustments of buoyancy by inflation and deflation, dive fins, and the weights themselves. Henry learned that one of the innovations in dive equipment was having quick-release weight pockets integrated into the sides of the BCD vest, rather than wearing all of the weight on a single weight belt around the waist.
Henry thought about stopping there for the night, but he was still plenty awake and on a roll. The next module was on gases: the composition of air (~21% oxygen, and the rest nearly entirely nitrogen) and using Dalton's law - named after chemist John Dalton, not President Conrad Dalton - to find the partial pressure of oxygen at depth (21% of the total pressure, recalling that the total pressure is 1 bar 1/10 the depth in meters). Again, there was a bunch of scary stuff about what could go wrong: nitrogen narcosis, basically becoming intoxicated due to the nitrogen dissolving in nerve cells because of its increased partial pressure, and decompression sickness or "the bends", due to the nitrogen that was stored while at depth subsequently diffusing on fast ascent and forming gas bubbles in the bloodstream. Fortunately, the risk of both conditions was extremely low unless diving more than 30 meters deep, and the entry-level certification Henry was pursuing would allow him to dive down to 18 meters max. Still, in order to avoid decompression sickness, he learned, divers should stay within prescribed no-decompression limits, ascend slowly (no more than 10 meters per minute), and make a safety stop at the end of each dive for 3-5 minutes at a depth of 5 meters (15-20 feet). Henry jotted this last part down on the notepad by his laptop. Nitrogen wasn't the only gas to be concerned about: carbon dioxide, and even oxygen could cause problems too.
Henry wasn't sure he'd sleep well after reading about medical complications, even though he knew rationally that flying - especially as a fighter pilot - had many comparable risks and then some. But it had been over thirty years since he had been starting out as an inexperienced pilot; he was just a kid, and he was so excited to get to fly that he wasn't as worried about the risks as he might be if he were taking up flying now. Not to mention that once he enlisted, he didn't exactly have the option to back out. Diving was different. It wasn't something he had to do. It was something that was supposed to be fun, and he wasn't sure that it would be. Still, now that he had read about it, he had to admit that he was definitely intrigued, even in spite of his fears. He sighed. If he wasn't going to sleep, he might as well keep going and get it done. But first, he put the kettle on to make himself some tea.
Fortunately, module five didn't as easily lend itself to catastrophizing. The topics were hand signals, which Henry was eager to learn so he could communicate underwater; dive planning, which seemed largely analogous to flight planning and pre-flight checklists; and calculating the maximum dive time for a dive at a given depth and the minimum surface interval needed between dives to avoid building up too much nitrogen. A lot of the section was devoted to using dive tables to remain within safe nitrogen levels. In practice, the dive leader would know the limits, and if wearing a dive computer as many divers did nowadays, they'd have far more accurate calculations automatically, so dive tables were mostly a relic of the era when Elizabeth had started diving. Still, looking at the tables gave Henry a rough idea of what length his dives could be, and how long it would take after diving to adjust back to normal nitrogen saturation. He also knew it was important to wait at least 12-24 hours after diving before flying to avoid decompression sickness. Henry took a short break to get his tea.
Next was different kinds of currents, navigation, and a reminder - very much unneeded in Henry's case - to not touch anything. Henry was quite familiar with using a compass of course, so he focused on natural navigation underwater: using the sun, distinctive formations, topography, and the direction of waves and grooves in the sand to navigate. Once again, Henry noted the similarities to flying.
Finally, the last module was about common problems, how to avoid them, and how to deal with them should they occur. Henry read through this module more slowly while sipping his tea. The information mostly seemed like common sense, but he knew that thinking about a problem scenario in the abstract was a lot easier than trying to think clearly while actually experiencing the problem, so it was important to be well-versed in the procedures ahead of time. Henry made a note to himself to come back and review this section in the morning. He'd also review the few notes he'd taken and practice the hand signals.
Henry was quite pleased with himself for having made so much immediate progress. He knew he still had to demonstrate the skills, but having already signed up for the pool sessions, he was sure he'd follow through. He was also quite tired, and for good reason, he confirmed, looking at the time. He closed his laptop, washed his cup, and went back up to the bedroom, where he quietly crawled back in bed next to Elizabeth and almost immediately fell asleep.
The next morning Henry woke after Elizabeth and found her in the kitchen with her coffee. He told her that he'd done the online portion of the course and signed up for pool sessions. She clapped her hands together excitedly before turning serious. "Thank you, Henry. I know this isn't the easiest thing for you, and that you are doing it for me. You've given me so much, and I feel incredibly fortunate to have you alongside me. And I mean that about a lot more than just scuba diving."
"Well, I'm not alongside you yet. Let's just see how the pool thing goes," he downplayed.
Elizabeth swatted him playfully, then pulled him in for a kiss.
"If you were up late, maybe you should go back to bed," she suggested sounding completely innocent, but when Henry looked at her, she was biting her lip, and he caught the twinkle in her eyes. "I," she paused, downing the last of her coffee and heading towards the stairs, "don't have work to go to today, and I'm sure your boss would be understanding about you taking the morning off."
Henry momentarily feigned indecision. "Well, it wasn't washing machine repair, but I guess I do deserve a lie-in," he conceded, eagerly following her upstairs.