Saw this thread over the weekend & been meaning to contribute...
Hi Mark,
That's an accurate observation...but.. it's really comparing apples with oranges. The key distinction being who the tables were designed to serve. PADI focus on the concept of the NDL because they understand that the scope of their training system needs to be balanced by always permitting their divers to have direct access to the surface. NDL is just a conceptual way of admitting that their training system is limited. Thus, their trained divers are limited. Navy tables were designed for divers who are subjected to a training system of much broader scope.
This is the case today, but we need to be a bit cautious in generalizing, as there had been some versions of the PADI tables over the years that included deco stops too.
Here's mine.
John did an excellent job of concisely summarizing the difference between the Navy tables and the PADI tables.
Agreed. The only thing that I saw that resulted in some confusion was that the NDL's and Residual Nitrogen Group letters for the tables are based upon what "M-values" were selected for the various compartments and which compartment functionally ended up being the "Controlling" one for a particular profile.
There's also a fine art of 'fudging' present within all Tables, since all of their dives (including repetitive dives) are eventually boiled down to a single letter designation that has to try to represent 'all' compartments...both the one that is ultimately controlling a particular profile as well as those that might accumulate enough to be an issue on a subsequent dive - - this is really more of where the 60 vs 120 minute compartment as a factor comes into play.
However, modern technology is throwing a spanner in the works of that well-balanced system. Specifically - the evolution and popularity of diving computers.
True, but in counterpoint, dive computers allow for all compartments in the model to be continuously tracked - - to apply the Tables paradigm, it would be that the computer calculates the 6 (or 16) individual letters for each individual compartment, and then tells you which one is the worst off (eg, "Controlling"). BTW, alluding back to the M-values, it is pretty trivial to make a dive computer more conservative, simply by reducing the max value of all of the M-values by some percentage or fixed value.
For a given ambient pressure, an M-value is defined as the maximum value of inert gas pressure (absolute) that a hypothetical "tissue" compartment can "tolerate" without presenting overt symptoms of decompression sickness (DCS).
However, the limitations of the training remain. The training system assumes that divers will dive short, shallow profiles and not require staged ascents - and that's what it prepares them for. Basic training for basic diving. That diving was named 'recreational'.
That's what it is today.
Agency 'rules' weren't needed before the advent of dive computers - reliance on using the provided tables served to enforce those boundaries. All that PADI can do now is provide recommendations about the limitations that divers should adhere to.
mmmm....this is starting to sound like we are trying to blame dive computers for non-recreational diving.
We can see that there is an obvious 'disconnect' between the principles and concept of training and the potential practices of modern leisure divers. Is it any wonder that some experienced divers criticise that training as being 'inadequate' for the tasks of keeping divers safe?
Is it a failure of the training, or a failure of the divers to understand the limits of that training?
To be honest, I don't think it matters what method a diver uses to calculate their dives; PADI tables, Navy tables, laptop software or dive computers with X, Y or Z algorithm.
WHAT MATTERS is that they recognise the concept of their training and understand what circumstances that training is designed to prepare them for. Training dictates diving boundaries - not the method of calculating nitrogen saturation. The tail shouldn't wag the dog. The tools shouldn't dictate the work.
Some divers argue that people should use their dive computers to exceed the recommended limits of their training program. To me, that's like arguing that motorists should drive their cars to the maximum obtainable speed - that speed limit should be dictated by the capability of the vehicle, not the capability of the driver. Motorists do training that provides capacity to drive under certain -limited- conditions. Their safety is ensured by the imposition of limits. Buying a Ferrari doesn't make you a better driver. Buying a Dive Computer doesn't make you a better scuba diver.
Where the capability of the tool exceeds the capability of the user - then artificial boundaries need to be imposed. This is a situation we now see in recreational scuba diving.
The simple fact is... if a diver wants to do decompression or deep dives... then they need to do appropriate training. PADI and similar agencies don't provide appropriate training for that... they have boundaries. But, they did create the concept of 'technical diving', to allow those boundaries to be extended. The training, standards and demands of that training are, in no way, similar to that provided for recreational diving. It may be provided by the same agency, but it is a totally different concept.
Do we need to define "technical diving"... from a training/limitations perspective..of course we do. It's a totally separate entity to recreational diving. It is based on different concepts, requires different training...and has different limitations. It uses different models for off-gassing. It uses different equipment. It has different procedures. It has different dangers. It has different boundaries.
Diving is diving. You go underwater... you saturate nitrogen, you come up, you de-saturate. Every dive is 'decompression'. Simple. That's an over-arching definition of what we do. However, it can't be an over-arching definition of how we approach it...or how we train to do it. THAT is where the definitions of recreational and technical come into play.
Some good points here; I'll comment on them in aggregate summary later on.
PADI's real goal in making the tables was to reduce the surface intervals between dives so that divers could get in two dives in a dive day without waiting forever. The Navy tables with the 120 minute tissue controlling the surface interval are much longer, leaving divers out of the water sitting on the boat (or wherever) much longer than necessary. Navy divers more frequently do one very long dive and call it a day. PADI intentionally made their first dive limits slightly more conservative than the Navy limits to help reach this goal. Another way to achieve that was to have many more pressure groups in order to decrease the amount of rounding off necessary for calculating the surface interval.
Agreed. And the motivation for them to do this was because recreational diving had become a business, and a longer Surface Interval costs time and time is money, a shorter SI lowered their business expenses and made them more profitable.
As for the original question about defining techincal diving; No, I don't think it serves any usefull purpose.
I'd say that it has limited utility, for several of the reasons you point out:
Some dives will certainly be "tech" and some will certainly be "rec", but there are just too many shaded areas for me to draw a distinct line between them. Limited wreck penetration, cavern diving, throwing on a cf40 of oxygen for a little padding on the last day of your red sea liveaboard. Icediving for example is most certainly overhead diving, but for some reason I have never heard anyone refer to it as "Tech"
I can recall a similar philisophical question many years ago that was discussing what an "Overhead Environment" was. We could easily agree that a 100ft long swim-through was, as was also as a 90ft tunnel ... and 80ft ... and 50ft ... even 10ft ... but if we allowed an interpretation of it being any restriction that prohibited an immediate direct ascent, then even those 1 inch wide hula-hoops that Rec divers were being encouraged to swim through for practicing buoyancy control at some dive resorts ... technically had to count as an "Overhead", which is simultaneouslyl pedantically correct, yet nevertheless utterly absurd. And that's the problems with definitions: we end up with WXY footnotes and the like.
Of course, this also doesn't mean that there's zero value in having a "Not-Rec" tag, be it "Tech" or "Cave" or something else: much of its utility is merely to serve as a warning flag to clearly identify those diving situations that are clearly higher risk than the benign environment - - and all of the simplifying limitations - - appropriate for today's very simple Rec OW-I trained customer.
I'm of two schools of thought on this, though: from a Diving Community perspective, I don't really believe that naming a segment of diving really has all that much value, since risk is risk and it is a continuous gradient. However, there are areas - - cave is the classical example - - where self-regulation for increased training has had a huge impact in reducing dive deaths. But even here, the real observation is that the risks simply ramped up a lot faster - - there isn't necessarily a discontinuity.
Similarly, my OW training many moons ago included the procedures for staged decompression ... as such, I'm quite inclinded to consider deco (particularly "Light" deco) to be well within the recreational realm, at least for what "Rec" meant when I was first introduced to it. For what OW divers are getting taught today, I'm not so sure, though: I can recall diving with an elderly couple a few years ago where the wife nearly flipped out when her computer went into Deco mode towards the end of a dive - - it was first time that she had ever seen it do that.
And the more we learn - - - how about 50 minutes at 100fsw without any deco stops? As per some USN research from a risk-based model from a decade or so ago, that profile only produces DCS symptoms roughly 5% of the time. Frankly, I can see where such knowledge is a double-edged sword because on the one hand there will be those that are risk takers who will abuse the model - - but in counterpoint, if I just did that same profile and was on my deco hang when another diver has a bad emergency, I can be pretty confident that I can abort my deco plans without too much DCS risk and perhaps let that other diver's life be saved ... that's a different trade-off.
Overall, it is simplistically easy to say "Education is the Answer" and suggest that all divers become more knowledgeable as to what's going on inside their bodies. However, such knowledge has overwelmingly been washed out of OW training, presumably on a rationale that it will "scare off" customers, which lets us see where the motivational factors really reside. Diving is an industry afterall, which means that there needs to be viable business models...and one of those business models has indeed been with the identification of "Tech" as a discrete segment and speciality, because the Industry has learned that Tech diver customers spend more money. As such, regardless of what we as divers believe is appropriate for the diving community, there is also this financial incentive within the industry to have the "Tech" label present.
-hh
