One of the most common questions I get from my students is what the progression of courses should be. There are a couple of ways to answer this question depending on where in training someone is and what type of diving someone is most interested in doing. Let's split this up into a couple of categories and approach it from each perspective. We'll look at this from the perspectives of both the open water diver and the overhead diver that are interested in doing some decompression dives.
If an open water diver is interested in pursuing decompression diving but has no real desire to do overhead dives, then the answer may seem obvious. It's just a matter of signing up for an Advanced Nitrox/Decompression Procedures (AN/DP) course and going from there. This isn't necessarily the best way to approach it, though. I'm not an advocate of deep air diving. While AN/DP certifies divers to dive to depths of 140 or 150 feet deep (agency dependent), I don't think this is a good idea in most situations. One of the things I like to do with my students is find out where their personal helium depth begins.
Narcosis is pretty much immediate as soon as we begin our descent. We are affected by the nitrogen even at 20 feet deep. However, the effect is so minimal we don't usually notice it and it won't affect our ability to respond to issues that may arise. This usually doesn't occur until people hit the 60-80 foot depth range. But even at this depth, most divers will insist they are not feeling the effects of narcosis. While, I don't feel it's necessary for a majority of divers to dive trimix at 60-80 feet, I do believe that divers need to recognize they are affected at that depth, even if only slightly. The need to begin using helium in breathing gas usually doesn't start until about 100 feet deep. This number varies with different divers, but most will find that anything deeper than 110-120 has a significant effect on reaction time. It can be pretty easy to find that personal helium depth during a supervised dive and some simple exercises.
If a diver is interested in extending bottom time but remaining relatively shallow (Read: below their personal helium level), then AN/DP is an appropriate course. My AN/DP course trains divers how to plan and conduct dives in the 100-120 foot depth range beyond no decompression limits (NDL) with the appropriate amount of standard and accelerated decompression stops. We focus primarily on learning about the various decompression models available out there and how to implement them into our dive planning. We then go out and do some dives.
If a diver is interested in doing deeper dives, though, then there's a better way to approach this. I offer a course called Advanced Recreational Trimix (ART). This course trains and certifies divers to a depth of 160 feet with minimal decompression. I offer it in conjunction with Decompression Procedures (ART/DP). It's very similar to the AN/DP course with the major difference being additional discussion time about helium as a breathing gas as well as how it affects our decompression. We also conduct deeper dives utilizing helium in our gas mix. AN/DP is not a prerequisite for ART/DP. A diver can sign up directly for ART/DP without any decompression training or experience.
To summarize, if you want to do longer dives in the 100' depth range, AN/DP is the course for you. If you want to do deeper dives, then you should consider ART/DP. Knowing the type of diving you want to do will be helpful in making this decision, but if you're not sure, then save yourself some money and time by taking ART/DP.
Now, let's look at this from the overhead or cave diving perspective. The same discussion applies to the cave diver in regards to longer dives vs. deeper dives. The difference for cave divers is when to sign up for an AN/DP or ART/DP course. My advice has always been to do this mid-way between the cave training. Complete the Cavern and Intro/Basic Cave diver courses, get some experience diving caves, and sign up for a decompression course. This allows us to complete the training in caves as long as we still adhere to the gas management rules of the Intro/Basic Cave diver.
So why not wait until after completing cave diving training? While agencies don't typically require AN/DP before completing the final cave diving course, not having AN/DP will limit what can be done during training. A cave diving course is there to teach divers how to cave dive. Learning how to conduct decompression dives should be left to the decompression diving courses. Some cave instructors won't even accept students into a cave diving course unless they've completed AN/DP first. I don't currently do that, but it's been something I've considered.
I haven't taught anyone at the cave diving level that didn't first complete the AN/DP course, but not having AN/DP would make it necessary to spend a few extra hours discussing decompression theory and how it affects us on the longer dives. It also means we may end up turning dives on time rather than gas pressure in order to minimize our decompression obligation. One of the agencies I teach through also allows me to incorporate the use of stage cylinders during the cave course with students who have completed AN/DP or ART/DP.
So, in summary, the progression of training for cave divers I recommend is 1. Cavern, 2. Intro/Basic Cave, 3. AN/DP or ART/DP, and 4. Cave. This progression allows students to get the full benefit of each course and allows us to conduct a majority of the training in caves. We can also do a mix of open water and cave during the AN/DP or ART/DP courses if the student desires.
Make sure you visit us at Chipola Divers.
Saturday, July 17, 2010
Tuesday, July 6, 2010
Gear Modifications
I was recently asked a question about why I showed one of my students a modification that isn't normally done in backmount. This question came up as a result of a discussion on one of the Internet forums. Here is a slightly modified ( ;-D ) version of my response:
I received an e-mail asking about the reason I have my inflator and dump valve swapped and why I showed one of my students that modification. As my students has already stated, his intention is to transition to sidemount eventually. One of the common modifications in sidemount rigs is swapping the inflator and dump. There are a few reasons for this. In the standard wing, the butt dump is located on what is the underside of the wing when it is mounted properly. Air rises, so when dumping air from here it is necessary to change from a horizontal position to a head down position so the air bubble can rise to the bottom of the wing and release from the exhaust. This change in position isn't always possible when diving some sidemount passages. Also, with the inflator hose on the top of the wing, the only way to get all of the air out of the wing, short of inverting and using the butt dump, is to go into a head up position and raise the inflator hose up. It's physics. Also, in a sidemount rig if the inflator hose is on top, the elbow is exposed and unprotected and subject to damage.
Okay, so with that aside, I also had a student in the course that was in sidemount configuration. When looking over his rig I spoke with him about the two different ways of configuring the inflator and dump valve. I explained to both students the advantages and disadvantages of both and gave them the option of configuring their rigs either way. One thing I never do in my courses is tell my students how they must configure their gear, unless it's a safety issue! I let them know all the different ways I have seen rigs configured and allow them to make the choice.
One of the more important things about overhead diving, both real and virtual overhead, is to build up muscle memory. It's absolutely necessary that divers know where the inflator is, the dump valve, d-rings, cutting tools, etc. I started my cave and tech instructor internships about a year after having gone to sidemount. I hadn't been in my backmount rig in over a year and one of the issues I found I had was reaching for the inflator and dump without thinking about it. They were both in different locations on my backmount wing and I found myself constantly going to the locations where my sidemount inflator and dump are. I teach students in backmount and sidemount. I also feel it's a disservice to my students if I don't demonstrate skills, such as valve drills, in the configuration they are in. So I dive in backmount when I have students in backmount. Somewhere along the line I decided to mount a set of manifolded doubles to my sidemount rig. This left the inflator and dump in the same locations as I'm used to and reinforced the muscle memory I have built up over the years. I also found that dumping from the top was much easier , even in backmount! Because the dump valve is on the back of the wing (or the top when it's on), there is no need to change orientation in the water. There's no need to go head down or head up. Just reach up and dump. The air, as per the law of physics, exhausts up like it's supposed to. Because my student is intending on eventually diving sidemount (before he takes a cavern course), it also made sense to start building that muscle memory now in his current rig. While the inflator and dump may be in slightly different locations, they will be close enough that the transition should be fairly easy. I presented him with the information and he made the decision. While I see some benefit to some of the DIR philosophies, I don't agree that everything needs to be one way. I believe doing what works for one's own diving is the way it should be, as long as safety is not compromised.
And as for technical v. recreational courses... According to many agencies, cavern and intro/basic cave are recreational, but so are cave and advanced nitrox and decompression procedures. IANTD even considers Advanced Recreational Trimix as a recreational sport diver course (max depth of 160'). The technical courses begin with Technical or Extended Range Diver (max depth of 180') and continue with normoxic trimix and above. While some may disagree, the skills learned in ITT are an excellent foundation for cavern. The cavern diving course involves a lot of task loading. There is a lot of line running and doing multiple skills at the same time. Rather than learning to multitask in an overhead environment, it's beneficial to learn how to maintain neutral buoyancy and horizontal trim while task loading prior to that. This is where ITT comes into play.
Don't forget to visit our website - Chipola Divers
I received an e-mail asking about the reason I have my inflator and dump valve swapped and why I showed one of my students that modification. As my students has already stated, his intention is to transition to sidemount eventually. One of the common modifications in sidemount rigs is swapping the inflator and dump. There are a few reasons for this. In the standard wing, the butt dump is located on what is the underside of the wing when it is mounted properly. Air rises, so when dumping air from here it is necessary to change from a horizontal position to a head down position so the air bubble can rise to the bottom of the wing and release from the exhaust. This change in position isn't always possible when diving some sidemount passages. Also, with the inflator hose on the top of the wing, the only way to get all of the air out of the wing, short of inverting and using the butt dump, is to go into a head up position and raise the inflator hose up. It's physics. Also, in a sidemount rig if the inflator hose is on top, the elbow is exposed and unprotected and subject to damage.
Okay, so with that aside, I also had a student in the course that was in sidemount configuration. When looking over his rig I spoke with him about the two different ways of configuring the inflator and dump valve. I explained to both students the advantages and disadvantages of both and gave them the option of configuring their rigs either way. One thing I never do in my courses is tell my students how they must configure their gear, unless it's a safety issue! I let them know all the different ways I have seen rigs configured and allow them to make the choice.
One of the more important things about overhead diving, both real and virtual overhead, is to build up muscle memory. It's absolutely necessary that divers know where the inflator is, the dump valve, d-rings, cutting tools, etc. I started my cave and tech instructor internships about a year after having gone to sidemount. I hadn't been in my backmount rig in over a year and one of the issues I found I had was reaching for the inflator and dump without thinking about it. They were both in different locations on my backmount wing and I found myself constantly going to the locations where my sidemount inflator and dump are. I teach students in backmount and sidemount. I also feel it's a disservice to my students if I don't demonstrate skills, such as valve drills, in the configuration they are in. So I dive in backmount when I have students in backmount. Somewhere along the line I decided to mount a set of manifolded doubles to my sidemount rig. This left the inflator and dump in the same locations as I'm used to and reinforced the muscle memory I have built up over the years. I also found that dumping from the top was much easier , even in backmount! Because the dump valve is on the back of the wing (or the top when it's on), there is no need to change orientation in the water. There's no need to go head down or head up. Just reach up and dump. The air, as per the law of physics, exhausts up like it's supposed to. Because my student is intending on eventually diving sidemount (before he takes a cavern course), it also made sense to start building that muscle memory now in his current rig. While the inflator and dump may be in slightly different locations, they will be close enough that the transition should be fairly easy. I presented him with the information and he made the decision. While I see some benefit to some of the DIR philosophies, I don't agree that everything needs to be one way. I believe doing what works for one's own diving is the way it should be, as long as safety is not compromised.
And as for technical v. recreational courses... According to many agencies, cavern and intro/basic cave are recreational, but so are cave and advanced nitrox and decompression procedures. IANTD even considers Advanced Recreational Trimix as a recreational sport diver course (max depth of 160'). The technical courses begin with Technical or Extended Range Diver (max depth of 180') and continue with normoxic trimix and above. While some may disagree, the skills learned in ITT are an excellent foundation for cavern. The cavern diving course involves a lot of task loading. There is a lot of line running and doing multiple skills at the same time. Rather than learning to multitask in an overhead environment, it's beneficial to learn how to maintain neutral buoyancy and horizontal trim while task loading prior to that. This is where ITT comes into play.
Don't forget to visit our website - Chipola Divers
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