Hal Watts was warning divers to: Plan your dive: dive your plan, when a buoyancy control device was an empty bleach bottle with a loop of clothesline tied through the handle. Watts, one of the most colorful, popular and intelligent “pioneers” of technical diving, explained that the most dangerous thing about diving is divers themselves. “We do not belong down there and poor decisions and complacency lead to mistakes,” he says.
“The deeper one dives the more important it is to stick to a well-constructed plan because at depth, even a small mistake can quickly become a very serious accident.” And because of that, Watts has been stressing the need for a dive plan and the requirement to stick with it for decades.
Build your plan from the bottom up
The base structure of a good dive plan deals with the management of five constants: gas, gear, goals, team, and time. The surprise is that whether the dive is a ten-metre bimble on a sunny tropical reef, or a 100 metre wreck dive on a newly discovered shipwreck off Labrador, the basics of a dive plan are the same; the only changes are the details!
Gas management is always the first consideration, and begins with calculations for required volumes – for bottom gas and ascent gases (decompression gases). These volumes are workable quantities of gas based on a known personal surface air consumption (SAC) rate adjusted for depth, workload, environmental conditions, and various physical and mental stressors (dive factors). Armed with figures for projected gas consumption, final adjustments are made for contingencies such as lost gas or a longer ascent schedule, and variable consumption rates among all team members. The rule of thirds for bottom gas (based on the gas volume of the team member starting with the least amount of gas) and doubling ascent gas requirements are a good start and have become the gold standard among the open-circuit community doing staged decompression dives.
Under the gas management umbrella also comes planning for all dive operations to take place at depths where gases deliver acceptable partial pressures of nitrogen and oxygen. This matching process has to consider decompression obligations and narcosis; central nervous system toxicity for single dives and daily limits and – on multiday exposures – pulmonary or whole body oxygen loading.
In order to calculate decompression status divers have their choice of dozens of algorithms. Most teams get comfortable with one and stick with it. Frankly, there are more options for deco tables than watches in the Swatch catalog. A growing segment of the tech community opt to go with a dual-phase model such as one or the other flavor of VPM (Variable Permeability Model), but regardless of this detail, it is important to understand the parameters of the model chosen; most especially the behavior it assumes the diver adopts traveling between waypoints. Other must-knows are how to adjust the chosen algorithm for conservatism, and what changes it demands for contingencies such as longer bottom times, and lost decompression gas.
Narcosis is somewhat easier to plan around, but no less contentious. There are several things that influence narcotic loading besides nitrogen partial pressure and there’s a raft of information and opinions on that score. Cold, dark, current, fitness, work of breathing and a dozen more factors are thought to exacerbate narcosis, but a good place to start is to fix an acceptable partial pressure and work around it. There is no perfect solution but a lot of divers plan around a level somewhere between 3.0 – 3.2 bar. This equates to breathing air at about 30 metres (4 ata).
To help manage CNS and pulmonary oxygen loading, divers have the NOAA tables to fall back on. It’s worth noting that although the limits set out in these tables are almost universally adopted by the technical diving community, and have been interpolated via devices such as the ‘CNS Clock’ there is no real data to tell us that this works or is a valid strategy**.
With this is mind, a sensible tactic is to plan dives around VERY CONSERVATIVE oxygen levels especially on dives where carbon dioxide levels may be elevated due to high workloads, greater depth or shortened dwell times (CCR).
The secrets of gear management boil down to basic common sense moderated with experience. I am a fan of following the minimalist-oriented guidelines that suggest gear be: serviced (good working order); simple (no fancy do-dads); streamlined (zero danglies and configured to be as easy as possible to push through the water); standard (meaning that you and your partners have your kit arranged in a similar configuration that you know and can operate without stress and strain); and suitable (meaning every piece of gear that’s being taken for a swim is needed and unnecessary clutter is left behind).
These guidelines work equally well with open-circuit or closed-circuit gear; back-mounted cylinders or side-mounts, one cylinder or a half dozen; open water or overhead; hot or cold.
Typically, people carry too much tat with them. The habit of swimming with kit that will never be used unless the laws of physics suddenly change denotes laziness not preparedness. The problem is not just the additional weight that must be hauled around, and the corresponding inertia that has to be overcome even when kit is rendered weightless in water, but there are other issues.
Leaving bits and pieces of kit attached to a harness or crammed into pockets smacks of a complacent mindset. A classic example: backup lights. In some cases, these lay strapped to a diver’s harness for weeks without being tested or used or thought about. It’s as though they have become a sort of badge of belonging; to what I am unsure. OK, I know they don’t weigh much and there’s not a lot of inertia to overcome for a couple of flashlights, and they don’t really take up much real estate, but if the dive plan does not call for them, why on earth take them into the water?
Every dive should have an objective, a goal or a purpose; and every dive plan should reflect that objective and translate it into a set of waypoints that can be used to track progress towards completion. A 20-minute dip on a sheltered little reef within a stone’s throw of a beachfront bungalow in Bali by definition is most likely to have a pretty elementary objective and perhaps only a handful of waypoints; but that is not the case with technical dives.
There’s certainly no need to make an objective overly complicated. A reasonable goal for a dive is to see the inside of the wheelhouse on a sunken wreck, take a picture of the telegraph and get you and your buddies home safe and sound. The purpose of the dive could be to test a new strobe, and the objective to add another great underwater photograph to the ‘I love me’ wall in your home office. Easy enough but the whole thing becomes more manageable with a little road map to help get everyone to wonderland and back; those are the waypoints.
Waypoints can be physical landmarks along the way; predetermined marks on the clock; numbers on a depth gauge; pressure drops on an SPG; or a combination of all. Keeping track of waypoints helps everyone to join all the dots and keep up with the dive. Most importantly, it helps divers prepare for what comes next. That may be pulling out a reel, turning on a light, getting ready to switch gas; any one of a number of things. Waypoints help develop situational awareness (SA), and SA makes diving so much safer and more fun than diving with a series of events taking you constantly by surprise!
Always dive with a buddy. That’s something we have drummed into our heads from day one of open water class. What is often overlooked is giving us a glimpse inside the rulebook on how to make sure the buddy we dive with will help make the dive fun and safe rather than hell and dangerous.
Technical diving is sort of self-policing in this regard. Technical divers tend to limit their choice of dive buddy (or better yet buddies since the perfect sized dive team is three people and not two) to people who they know and whose mindset, training, experience and equipment is similar to their own.
The study of team dynamics glossed over, and the vagaries of human nature notwithstanding, the guidelines for putting a good dive team together and diving as a team are straightforward.
Everyone should be capable of doing the planned dive. The team should always stay together, but in the unlikely case of separation or a team member being incapacitated, the remaining member or members should have no problems completing the dives on their own. This is one reason to avoid so called ‘trust-me-dives.’
A trust-me-dive is usually preceded with the proviso: “I know you guys have never done this sort of thing before but I’ve done it a thousand times so just follow me.” It is the diving equivalent of the Darwinian Award Winner’s “Hey, hold my beer and watch this…” Needless to say, they are a bad idea no matter what; and of course are an exceptionally poor choice should anything happen to separate inexperienced team members from the “trust me I’ve done this before” guy.
On the positive side, the safer bet is to always plan a dive around the experience and comfort level of the least experienced diver, and in the water, this person takes on the role of dive leader. Leadership on the surface is usually the task of the most experienced diver, but in the water, this role is taken on by the least experienced. The logic is that the least experienced diver is unlikely to take the rest of the team into a spot that makes them uncomfortable, but will themselves feel comfortable pushing their personal comfort zone a little being in the company of “better” divers.
When a group of divers with comparable experience dive together, leadership duties fall to the “weakest” diver. Weakness in this case is not a pejorative but describes the diver who is carrying a ‘special’ burden. That burden may be a video camera and housing. They may have the least volume of gas, or they may have had a rotten night’s sleep the night before the dive or they may have thrown up on the boat traveling out to the dive site.
Equipment failures can change leadership. Anything that happens to a diver or a diver’s gear that signals “thumbing” the dive (aborting the dive and heading for home) automatically makes that diver the boss; and they lead the team out.
Team roles, the way those roles may changed because of changing circumstances or the dynamics of the dive, and the individual responsibilities of team members on the dive (and before and after) need to be included in a dive plan.
The final set of questions that a dive plan has to answer has to do with time; in effect, how long on the bottom and how long getting back to the surface. As mentioned earlier, there are library shelves filled with an assortment of decompression tables. The odd thing is that most work and lots are applicable to technical diving. And of course step one is actually picking one and then sticking with it.
With the advent of mainstream decompression diving and the whole technical diving thing pulling onto the freeway and joining the mainstream, there are scads of data about successful and unsuccessful ascents from all sorts of depths and durations using a variety of gases. Unfortunately, nobody seems to be collecting and collating it. This makes deciding which decompression model to use as much of a crap shoot as doing decompression itself.
The only constant is that decompression theory is mostly alchemy and very little is black and white; however, there are things a diver can do to beat down the risks to a generally acceptable level. All the old favorites from sports diving still apply; be hydrated, be rested, don’t push limits, control ascent speed, and so on. Technical divers can add to these: use the right gases, follow conservative profiles, and buy good health insurance.
There are no magic solutions or practices that can guarantee divers will not get bent and technical divers have to accept that an element of risk is always present, but there are a couple of things that may help.
First is to understand the way the table works. Most are built around a simple string of mathematical assumptions that attempt to model the vagaries of human physiology. Anyone looking with one eye sort of squinting and their head at a slight angle can look at a decompression schedule (regardless of its flavor) and see that the maths is producing a very distinct curve that describes changes to gas pressure over time. We don’t have to learn the differential calculus to get a handle on this, although it might help. It’s just a pattern. Furthermore, every ascent can be broken into five stages or waypoints and decompression tables dictate how fast or slow a diver can move between those waypoints.
For example, the distance (pressure change actually) between the maximum average depth of a dive and the point in the water column where a diver begins to offgas more than he ongasses, is a fixed point. It is influenced to some extent by the type of gas being used and the time spent on the bottom, but it is a real location. In truth the offgassing ceiling is more a mathematical construct than a physical need, but it is a very important waypoint on any decompression dive.
Knowing where it is in the water column offers a huge advantage to a diver because it tells him the point in his ascent where he will stop racking up decompression obligation and begin paying it off. It is a good strategy never to start a decompression dive without knowing where the offgassing ceiling or gas transition point is. Being armed with this little knowledge nugget is key to understanding the shape of the ascent curve and is the foundation of building a workable contingency decompression schedule in the event of a dive going totally pear-shaped.
Knowing where offgassing starts is also key to managing ascent because it is the point a diver needs to get to as swiftly as practical when the dive is finished. Not a big deal perhaps, but the most common mistake that I see among novice decompression divers is that their initial ascents are too slow and they travel too fast in the final stages.
I am a huge fan of having tables cut and sense-checked before a dive. After all, how can one work out the volume of decompression gases a dive requires without knowing how long the decompression is likely to be?
I am also a huge fan of taking notes before, during and after a dive. Like it or not, we are the guinea pigs in a vast, multi-user decompression experiment. What we do every time we go diving is validate a little piece of voodoo science. In a perfect world and as part of a real experiment, someone would take down the particulars; what we did, for how long, what we breathed and how we felt before, during and after (remembering that for some dives, decompression does not end for a day or so after we surface). These data are invaluable in helping to keep us safe. With notes kept up to date and available, a diver can make decisions about “TIME” that are actually informed by experience; and that is golden.
It is so easy…
I like surprises but not underwater and so I’ve cultivated the habit of trying to avoid them. Because of this, I cannot imagine diving without a good solid dive plan that manages each of the five constants: gas, gear, goals, team, and time. There are folks who think putting together a dive plan is too much of a bother, but the wonderful thing is that once you have developed a plan and used it a couple of times, it becomes part of the fabric of your diving. It becomes so easy that there is no excuse not to follow it. Of course, it helps if the plan is based on good sense because as well as saying “plan your dive: dive your plan,” Hal Watts also warned that a poorly thought out plan melts as soon as it gets wet.
* Doing What Works or DW2 is a catch phrase created by North Florida cave explorer Larry Green to describe a diving philosophy that seeks to keep divers safe and happy following a few simple rules; the most important of which is addressing the problems and challenges of technical diving with an open mind