Lost Diver Gas Protocols -

TDI Lost Diver Gas Protocols

A Discussion on how to train and dive safely

Article by Christine Loew

Have you considered taking a course to become a cave diver? While this information is way beyond helpful in the decision-making process, I think it adds a very helpful point of discussion with your instructor during training. It gives an insight into my development of safe, cave-diving protocols. I believe it is also helpful for seasoned, cave-diving instructors worldwide to rethink their approach to the particular skill I want to talk about while teaching the intro-to-cave course.

I would like to first talk about my experience and expertise. I would then move on to how I find it beneficial to take a new approach to calculate the gas available when a missing diver situation happens. And lastly, I would like to give some scenarios showing how to apply this rule.

So let’s start with my beginnings:

When I started with my cave-diver course back when, I was already a diver and instructor for several years and I have had about 1500 dives under my belt. Teaching cave diving in 2006 was still very much tailored to experienced divers who wanted to venture into a new environment, the caves.

While the goal of becoming a good cave diver has not changed, in today’s world there are more and more divers who do not have a huge amount of dives or experience in a lot of other non-overhead environments. Becoming a cave diver is almost a mainstream goal if you are not only a holiday or occasional diver. The culprit may also be part of the marketing of cenote diving and the beautiful pictures of people in cave-diving environments.

I certainly think that the same rules of teaching a cave course should apply no matter if you are a diver with several hundred dives and already experienced in other technical environments. I also appreciate that TDI standards are not written down to the last step on how to execute a skill. Very often there are differences by region, cave types, equipment configuration, and so on.

Here, I would like to explain and elaborate on my approach to safety for new-cave divers.

The rule for a lost diver search in the overhead is different when compared to open-water diving. In open water, we simply state that when a team gets separated, not to search longer than a minute and then start the ascent. In most of the scenarios you likely find your buddy midwater and after checking that ample gas reserve is still available (mind you – you were freaking out a little bit as you were alone for a moment, so please check your gas) you may proceed to a shallower part of the reef and continue the dive.

In overhead, the rule stated within TDI (and probably pretty much any accredited technical diving organisation) is to reserve at least twice the amount of gas needed to exit and that implied if more gas is still available in your tanks, you may initiate your search if you are mentally prepared for delaying your own exit.

Up to that moment, I was teaching in my cave-diving classes how I have learned the skill in my own course – recalculate your gas underwater, assess your state of mind, start a logic search, exit when new turnaround pressure is reached.

There has been at least one accident in recent years here in the area where a team separation has happened. While the one diver exited being sure the other was ahead, the other diver may have searched and recalculated and searched until the gas in the tank was completely depleted, and the diver perished. While this is not the only factor that led to that fatal accident (and we should know that accidents happen as a chain reaction or an alignment of bad circumstances that, each for itself, would not have that tragic outcome, but brought together, lead to an accident), it was a major contributing factor in my opinion.

I later completed my training as an ANDP instructor and in these courses, it is a mandatory step in pre-dive planning that you calculate for any contingency, being in mixed gas and deco diving namely: too long, too deep and loss of any gas – deco or travel.

So, what happened in cave training with the catchy phrase: Plan your dive and dive your plan when it comes to an emergency? Do we simply abandon this well-established rule?

I would hope not, and I will show you how easy it is to plan for the emergency, as well.

The lost diver search is introduced during the intro-to-cave course. At this time in training, the student has anywhere between 6-8 dives in the overhead and is still diving with the rule of Sixths maximum (assuming backmount or sidemount double cylinders).

When a lost diver situation happens, I do not have to consider where in the dive it happens, whether at the farthest point of penetration, on the way in, or on the way out.

All we have to do pre-dive is to take the total gas amount and calculate two-thirds of it for an emergency, and do the normal dive calculation for a sixth for the normal and uneventful dive.

If then the miscommunication happened and a dive team is separated, the diver initiating the search knows immediately how much gas would be available and when to start to exit to not endanger his life.

So here is the example in metric:

Both divers use the same size of tanks and start both with initially 210 bar.

For intro-to-cave, the planned turn-around pressure is 210 / 6 = 35 bar and 210 – 35 = 175 bar. The emergency turnaround pressure for lost diver is 210 / 3 = 70 bar and 210 – 70 = 140 bar.

So, no matter where and when in the dive the lost diver situation arises, the diver searches until he reaches the 140 bar and then proceeds to exit. If searching while swimming back further into the cave, the search will not go further than the point where the dive was turned initially. Seventy bar is then reserved for the intro-to-cave diver for the exiting part, when he needed 35 bars to get there in normal conditions. We all know that being all of a sudden a solo diver will very likely increase your air consumption, but you are now covered with enough reserve gas. If searching towards the exit, there is even more gas reserve as the diver slowly approaches the exit and can now spend more time to slow down and look around.

When we come to the full cave part of the overhead training, we review and revisit the lost diver drill, as it may have more complexity due to greater distance from the entrance point, complex navigation, or special cave features. At this point, the student has a minimum of 16 cave dives, but does this already mean they are a cave-rescue diver?

I opt for the same approach as before, but it becomes very obvious that if you had planned your dive with the rules of thirds and the lost diver scenario happens at turn-around pressure, there is no gas left to search further into the cave. The diver needs to slowly proceed towards the exit, and of course, leave all previously installed navigation in, and eventually add visual aids for the lost diver.

A couple of more examples:

Both divers use the same size of tanks and start both with initially 210 bar.

The dive plan is with the rules of Fourth, the planned turn-around pressure is 210 / 4 = 50 (Round down) bar and 210 – 50 = 160 bar.

The emergency turnaround pressure for lost diver is 210 / 3 = 70 bar and 210 – 70 = 140 bar.

If it happens at turn point, the diver has 20 bars to search
If it happens on the way in and the team dives at a T intersection in different directions, the diver has until he reaches 140 bar to search the new area
If it happens on the way out and the diver is below 140 bar at time of lost diver, no gas for search but proceed slowly to exit while adding visual aids for the lost diver

A team separation does not happen because one diver did something wrong, but a combination of lack of communication, lack of awareness, overconfidence with own skills and dive conditions different to the ones you trained in. But while you continue cave diving you gain experience and lower these risks and therefore decrease the chance of a lost diver ever happening.

Any firefighter knows that you aren’t supposed to risk your life while rescuing others, but with proper training, the risks they can take are much higher than the usual bystander of a fire. So, unless you have additional training in cave rescue and/or a huge amount of experience in various types of caves and teams, I suggest playing it safe and taking all measures to prevent team separation in the first place.

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