Practical Application of Ratio Deco

By | Knowledge Base

This is a great article giving an example of how ratio deco can be used on any dive. This was written by Brian Wiederspan. Many people either fear ratio deco or completely embrace it. The thing to remember is when using ratio deco and standard gases, the deco curve always looks the same. Therefore, it is much easier to determine “deco on the fly”. I hope you enjoy it.

Dive Safe,
Duane Johnson
Precision Diving

I’d like to take a few moments to illustrate how standard gases and ratio deco have effected my diving recently.

Here, I’d like to talk about the flexibility the standard gases and decompression strategies. Keep in mind that ratio deco isn’t a decompression theory, it’s simply a strategy using existing models and research to help shape an ascent profile.

On our attempt on the SS Governor, we used 15/55 for backgas and EAN50 and O2 for deco. This allowed us a range of depths, generally in the 200’ to 240’ range. That afforded quite a bit of flexibility to explore the wreck, which was especially useful in this case as the wreck is sitting upright where the mudline is at 240’ and the deck is at ~ 200’…quite a variance in depths.

Our plan, however, was to try to keep max depth at 230’, and spend most of our time on the deck at 200’ to keep our average depth at 220’ or shallower, to keep our deco time manageable.

Unfortunately, due to vessel traffic delaying our splash time, we weren’t able to do the Governor. We instead decided to do the Al-Ind-Esk-A-Sea, another large wreck that sank in 1982 after a fire broke out and numerous explosions occurred. Dan Warter has a great article on the Al on his website, DCS Films

Though the profile of the “Al” is similar to the profile of the Governor, it really made me think about what would happen if we were to do another wreck with a completely different profile. In other words, what if we planned to do a wreck that was 240’, but due to conditions, we were forced to do a dive in 200’

Well, for starters, we’d have to make sure our backgas was compatible with the profile of that dive. We had 15/55 in our tanks, which would allow us to go as deep as 240’, and would certainly work for 200’. Now that we know our backgas is ok, we need to figure out our decompression. There’s quite a difference in the deco obligation/profile for a 240’ dive and a 200’ dive. If we simply used the same profile for the 200’ dive as we do for the 240’ dive, our first stop will be much deeper than necessary and our deco time will be much longer than necessary. We could bring out the laptop if we brought it and cut new tables, but we’d also have to print them and laminate them. We could just run our computers as well, which is fine, but if everyone has different computers running different algorithms, that can create some confusion as well.

This is what I like about Ratio Deco…”deco on the fly”, or “tailgate deco” as I sometimes call it, allows me to calculate an entirely new deco schedule in 2 minutes time on scratch paper. Instead of hurrying to pump out a new set of tables, or doing much more deco than necessary because I don’t have any other tables than the ones I made for the original profile, I just grab a pen, a napkin, scroll out my new schedule as a general plan, then relax and prepare mentally for the dive.

How can I do this? Standard gases all have the same deco shape. Sure, we may add extra deco gases, but the shape is the same. No new numbers to remember, no tables to cut every dive. The shape is always the same whether its an mdl dive, Tech 1 dive, Tech 2 dive or a Trimix dive. This makes it very easy to remember and calculate.

How about the reverse? Had we a chosen a mix specific to the depth we planned to go to (or “best mix”), rather than a range and ended up going to a wreck deeper than the one we had originally planned, we wouldn’t be diving at all that day. All that time and effort preparing, the cost of the charter and the gas, and we can’t even dive!

While there’s more benefits to standard gases and ratio deco, these are 2 that I really appreciate and have really positively effected my diving. They allow me to actually explore. We can do our dive, with plenty of flexibility to adjust our profile as needed, then, when our dive is over, we can figure out our deco.

On our dive on the Al-Ind-Esk-A-Sea, we had no tables or deco schedules…nothing written on a wrist slate or in our wetnotes. We did our dive…then, when our dive was done and we were ready to ascend, we figured out our deco. One quick signal of “average depth, 210’” and we both knew what the rest of our profile would look like.

The next 65 minutes we spent decompressing, both of us knowing what the rest of the ascent would look like.

The Value of the Backwards Kick

By | Knowledge Base

Many people have asked me why I put so much effort into showing my students the backwards kick. In this article, I intend to explain why the backwards kick is so important to all levels of diving.

First, let’s look at using the backwards kick in a recreational environment. As we dive, we dive in teams of 2 or 3 divers per team. The backwards kick is essential to maintaining position in the water column. When the team of divers ascends/descends, it is the most critical time of the dive. This is where the majority of problems occur. In order to perform a safe descent/ascent, the team must descend/ascend together. It is critical for the team to stay together. As the team descends, depending on current/conditions, they should descend facing each other. To prevent bumping into each other or swimming around in circles, the backwards kick enables divers to quickly stay in one position, thus focusing on the team members. Same thing holds true for ascents.

These reasons are the same for recreational divers as well as technical divers who must perform decompression stops. By maintaining the team position, the divers can now turn their focus onto more important activities such as the gas switch, shooting a bag, etc.

Now let’s look at using the backwards kick in the technical/overhead environment. When performing tasks such as line tie offs, it is critical for the team keep it’s position. While one person is performing the tie off, another team member should be watching the environment around the team as well as keeping his/her light on the reel/line for the tie off. This requires significant buoyancy and trim control. Thus requiring that the backwards kick be very solid. As the team move through the overhead (either wreck or cave), it is critical that the divers do not bounce off the environment they are moving through. Moving through a wreck or cave requires significant control over your self and equipment. By being able to stay in one spot, divers can turn their attention to handling situations that may potentially creep up.

In this article, we touched on reasons why the backwards kick is an essential skill for divers of all levels. It facilitates control over yourself in the water column. Thus allowing the diver to keep a high level of situational awareness instead of trying to keep their position in the team formation. The backwards kick must be instinctive. That is, that the diver can do it without thinking about it. We are able to walk backwards if the person in front of us. We need to be able to do the same thing while underwater.

Here is an example of what the backwards kick looks like:

Dive Safe,
Duane
Precision Diving

Gas Switching Procedures

By | Knowledge Base

Many folks have asked me about how to perform a gas switch. So I figured I would type up the procedures here. Please keep in mind that these procedures do not replace sound, high quality technical dive training, but act as a supplement to that training. If you are not trained in technical diving, do not try to perform these procedures.

Many people believe that the gas switching process is performed by an individual. That is not correct. Performing a gas switch is a team effort and the focus during the gas switch must be on the team. That way the team deco can be optimized. The gas switch is a time where the awareness of the entire team must be raised to a higher level. As each member of the team switches to a high partial pressure of oxygen, the risk of oxygen toxicity is greatly increased. The team must be focused on each member during the switch to be able to respond to any problems that may occur and to verify that each member of the team is on the right gas.

There are many things that must go on prior to entering the water with a deco bottle. First, the gas inside the bottle must be analyzed. This must happen right before the dive, regardless if the bottle was previously analyzed and marked. Be prudent and re-analyzed just before entering the water or getting on the boat. I always tell my students to analyze the gas just prior to the regulator being put on. Second, after you analyze the bottle, you must mark the bottle with the contents/result of the gas analysis. There are many fancy stickers people use for contents labels. I choose to use the most cost effect method of gray duct tape. On the contents label, I mark the results of the gas analysis, date of analysis, my initials, and the MOD. Deco bottles must have a minimum of four markings on them. 1) Visual inspection sticker, 2) gas contents sticker, 3) clearly identifiable MOD on the outside (facing away from the diver when worn), and 4) clearly identifiable MOD on the inside (facing towards the diver when worn). Item 3 is used by the team to verify the MOD of the bottle being switched to. Item 4 is used by the individual to verify the MOD of the bottle switching to. Deco bottle valves are turned on at the start of the dive and then turned off. This pressurizes the regulator so that it will not come loose during the dive. If the valve was left on, it runs the risk of losing the gas from the bottle without the diver ever knowing it.

To preform a proper gas switch, the steps are as follows:
1) Signal to the team that it you are preforming a gas switch
2) Verify that your at the target depth and not deeper than the planned MOD of the gas switch
3) Verify that the maximum operation depth (MOD) of the deco bottle to switch to and that you are at or above that depth
4) Verify that the regulator is still pressurized and the first stage regulator is seated properly. If the regulator has no pressure, make sure it is seated properly and then partially turn on the valve and re-close it. This pressurizes the regulator.
5) Deploy the second stage regulator from the deco bottle and loop the hose around your neck
6) Re-verify your depth so that you are not violating the MOD of the bottle you are switching to
7) Remove the regulator from your mouth with the left hand.
8.) Insert the deco regulator into your mouth with the right hand.
9) Quickly move the regulator from step 7 to your right hand.
10) As you breath from the deco regulator, watch the SPG on the deco bottle. If the pressure gauge loses pressure greatly, then you are breathing the right bottle. If it doesn’t move, then switch back to the regulator in your right hand and verify the bottle is turned on or you have the correct regulator. To do this, remove the regulator and hose from around your neck and trace the hose back to the bottle. When wearing one deco bottle, this is quite simple, but if you are wearing two deco bottles it must be performed.
11) If step 10 goes smoothly, turn on the valve for the deco bottle completely
12) Re-verify your current depth such that you are not violating the MOD for the bottle breathing
13) Clip off the long hose to the right chest d-ring to keep it out of the way. If you are switching off another deco bottle, remove the deco regulator and hose from around your neck and re-stow it back on the deco bottle.
14) Signal to the team/buddy to verify the MOD of the bottle being breathed and that you are breathing from the right bottle.
15) If the team/buddy signals OK, move to the next team member to perform the gas switch. If you are the last person to switch, then the deco leader will start the deco time for the team. Deco time does not start until the entire team has performed the gas switch. This is why the gas switch procedure must be as efficient as possible so that team members are not sitting on a high PPO2/using up precious deco gas while waiting for others to switch.

If for some reason, you fumble the deco bottle second stage and it falls out of your hand or mouth, quickly go to your bungee backup regulator under your chin. Remove the deco regulator and hose from around your head and trace the hose to the correct deco bottle. Then perform the switch again. We do this so that we do not accidentally grab the wrong second stage (such as our long hose) and breath the wrong gas and not know it. Many people believe that the deco regulator should be deployed prior to arriving at the switch depth in order to make the switch go faster. We don’t do this for the single reason of fumbling the deco regulator and accidentally breathing a gas below it’s MOD. Once you get proficient with the gas switch, the team should be able to switch in less than 2 minutes, assuming a three man team. Two man teams can switch within a minute. Thus removing the need to deploy the deco regulator deeper than the switch depth. Remember, try not to develop bad habits and focus on sound skills.

As you can see, we are always prudent when performing gas switches. Analyze, analyze, analyze your gas and always verify and re-verify your depth so that you do not violate the MOD of the gas being breathed. Always err on the side of caution.

I hope you enjoyed this article and feel free to leave any feedback or ask any questions.

Dive Safe,
Duane
www.precisiondiving.net

The Importance of the TDI Intro to Tech Course

By | Course Reports, Training

When I became a tech instructor, my main focus was on teaching the Advanced Nitrox and Decompression Procedures courses. As time went on, I was finding myself rejecting more potential technical diving students than ones I held classes for. So I decided to find out why. Was it me? Are my standards too high? Do I have unrealistic goals for potential tech students? My curiosity was piqued. As part of my own personal standard, I do an assessment dive with every potential tech student and I video those dives. So I went back to the video of those people I did not accept into my classes. As I watched, one thing became blatantly obvious. These people did not have true mastery of the fundamental skills for diving (i.e. buoyancy & trim control, etc.) and they just did not look that comfortable in the water. Many were OK divers and didn’t kick up the muck or shoot to the surface. But I could just tell they weren’t in full control of their position in the water. [Read more...]

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