PADI Divemaster vs TDI Extended Range

[Rhone Man]

Decent article on IWR on Wikipedia: In-water recompression - Wikipedia, the free encyclopedia

The original question was posed on the basis of being asymptomatic and being able to get right back down again (good example in Gary Gentile's book on the Andrea Doria when he and Tom Packer had to do exactly that on a blown dive profile).

 

[rjack321]

The original question was posed on the basis of being asymptomatic and being able to get right back down again (good example in Gary Gentile's book on the Andrea Doria when he and Tom Packer had to do exactly that on a blown dive profile).

Are you looking for the DSAT omitted deco recommendation?
Any agency?
Or common sense?

 

[boulderjohn]

Thre is a sure fire procedure to finding the actual answer to this question.

1. Pick up your RDP.
2. Turn it over.
3. Read the third paragraph in the first column, the one titled Emergency Decompression.

 

[boulderjohn]

Explanation:

TDI Extended Range, Deompression Procedures, etc. are classes in which decompression stops are part of the normal procedures. They teach you how to adjust those stops should you overstay your welcome. All its planning assumes you are doing decompression stops from the start.

The PADI RDP is strictly no decompression in its design. Since it includes no decompression stops to begin with, it can't tell you how to adjust them. It can't put you "back on the grid" unless it truly clears you out.

When Spencer, et al did their research to determine the controlling compartment for no decompression diving, they determined that for just about all the dive profiles possible within the range of those tables, the 40 minute compartment controlled the dive. In order to add a conservative measure, they based the tables on the 60 minute compartment.

If you exceed the RDP NDL's, then slower compartments will be controlling your dive, and the RDP is not equipped to handle that.

Thus, if you overstay the NDL's by a brief amount, they require a pretty conservative deco stop followed by a 6 hour surface interval, with 6 hour chosen because it washes out the 60 minute compartment.

If you stay longer, then you get an even more conservative deco stop, followed by a 24 hour SI, which washes out even a 240 minute compartment. By golly, unless you have really gone off the table, your tissues should be in good shape by then.

That is a very conservative approach to decompression. The message I get from it is that if I want to do decompression diving, I should be using a decompression algorithm, and not one that is designed purely for recreational diving.

 

[Rhone Man]

Thanks, Boulderjohn, and whilst I appreciate all that, it still comes back to this for me: if you miss mandatory decompression, PADI are telling you that it is safer to stay on the boat, and TDI are saying that if you can do it quickly, it is safer to go back down. They cannot both be right if they both express it to be a general rule.

I don't think the fact that the RDP calculates surface intervals on a 60 minute compartment affects anything other than length of surface interval. If I find myself at the surface with my computer blaring that I missed a mandatory deco stop (planned or unplanned), the decision as to what to do next will not be based upon which tables I used to plan the dive.

 

[boulderjohn]

PADI's emergency decompression methods require extended stops as well as longer surface intervals.

Controlling compartments also determine stops. The purpose of a an ascent profile, whether it is based on an ascent rate alone or an ascent rate plus deco stops, is to prevent the controlling compartment(s) from exceeding its (their) M-value(s). The ascent profile in the RDP assumes that the controlling compartment (60 minute) will safely off gas on ascent. It further assumes that the slower compartments will not raech their M-values during ascent because they did not get close enough to saturation on the dive itself. If the NDL is exceeded, then there is an assumption that a slower compartment will reach its M-value limit on ascent and thus require a different ascent profile. Thuis will allow the slower compartment to off gas before leaving the water.

BTW, I am not extolling the PADI emergency decompression system. I am just explaining it. I am also TDI trained.

 

[Blackwood]

Does anyone know what PADI teaches on missed decompression at the tec level? Do they change their stance, or stick with the "stay dry" approach?

Thre is a sure fire procedure to finding the actual answer to this question.

1. Pick up your RDP.
2. Turn it over.
3. Read the third paragraph in the first column, the one titled Emergency Decompression.

PADI teaches its "DSAT Tec" courses using the RDP?

 

[Peter Guy]

If I find myself at the surface with my computer blaring that I missed a mandatory deco stop (planned or unplanned), the decision as to what to do next will not be based upon which tables I used to plan the dive.

Is this perhaps a sign of the "Measure with a micrometer, mark with chalk and cut with an ax" problem with decompression "science?" Exactly how "mandatory" IS a "mandatory deco stop" for any particular dive?

And yes, I'd love to hear from a DSAT instructor on this issue -- any of them out here in ScubaBoard Land?

 

[boulderjohn]

PADI teaches its "DSAT Tec" courses using the RDP?

I believe I misread the purpose of the question--thanks for pointing it out. I was reading it as a question about the divemaster certification, which is fully recreational.

 

[rjack321]

Thanks, Boulderjohn, and whilst I appreciate all that, it still comes back to this for me: if you miss mandatory decompression, PADI are telling you that it is safer to stay on the boat, and TDI are saying that if you can do it quickly, it is safer to go back down. They cannot both be right if they both express it to be a general rule.

I don't think the fact that the RDP calculates surface intervals on a 60 minute compartment affects anything other than length of surface interval. If I find myself at the surface with my computer blaring that I missed a mandatory deco stop (planned or unplanned), the decision as to what to do next will not be based upon which tables I used to plan the dive.

Ummm yes they can both be right. You seem to be missing the audience here.

If you miss a few minutes of deco on the RDP you are probably not even going to be bent. Stay on the boat, go on O2, watch for symptoms. Its hard to miss more deco than that as a recreational diver since you should have been on a recreational plan if you were using the RDP. A recreational plan which has run over on time or depth is highly unlikely to have enough gas to complete omitted deco (often expressed as 1.5x the original deco time). Why would you carry enough gas for a tech dive on your recreational dives? Why would you use the RDP to plan deco dives? The deco shown is merely there as a contingency if gas supplies allow. You'll notice its truncated at about 15mins - cause the RDP was never intended as a deco planning tool. Even if you skipped the maximum deco the RDP is guessing at, you are still better off on surface O2 and watching for symptoms since you are assumed to have neither sufficient quantities of backgas nor a deco gas when diving a recreational RDP plan. If you brought all that stuff you are using the wrong tools to plan deco dives. Slightly bent on the boat is fixable, drowned due to OOA is not.

If you plan a deco dive with your TDI training you may miss 5 mins of deco. Or you could miss 50 minutes. If you are asymptomatic and otherwise have the gas and there are no hurricanes on the horizon of course you can go back down and do an omitted deco schedule since you brought enough gas and thermal protection to stay in the water at least this long. If you are symptomatic you still have the option of going back down (which maybe the best option). You planned for a tech dive, you get to chose what to do.