Does defining "technical diving" serve any purpose?

[markmud]

Do not expect the letters to cross compare in any meaningful way, the represent partial saturation of completely different compartments.

I completely understand!

markm

 

[DevonDiver]

However, my point was not to bash the PADI methodology, just to point out that no overt distinction is made by the US Navy table regarding NDL and deco. Ascent time was the criterion for the creaton of this table and the so-called "NDL" is treated the same as a staged deco dive. Ascent time whether you are making deco stops or not.

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.

John did an excellent job of concisely summarizing the difference between the Navy tables and the PADI tables. We can see differences in the controlling tissue compartments and how those differences effect the theoretical desaturation of the divers who use them. Understanding this concept, it is easy to see the logical pros and cons of each approach.

The Navy tables permit deeper/longer dives - but also require far more substantial surface intervals to desaturate the slower controlling tissue compartments between those dives. That's appropriate for how the Navy operate. 1 dive - deep and long - get the job done - get back on board.

PADI tables limit the depth and duration of dives - but the shorter controlling compartment permits far shorter surface intervals to desaturate. That is perfect for recreational divers, who typically conduct multiple shallow/short dives per day. 'Fun' divers don't want to be sitting on a boat for hours between dives.

The emphasis of PADI tables is to permit multiple, shallow, dives per day. They do that by using a shorter controlling tissue compartment. PADI focus on a diving 'style' that tries to keep divers away from saturating the slower tissues. In addition to being more suitable for the demands of recreational divers, the added 'benefit' of this 'fast-tissue approach' is that it permits divers to sufficiently de-saturate by only completing a controlled, paced ascent to the surface. No stops are allowed. Ensuring the immediate availability of the surface goes a long way to ensuring the safety of recreational divers. The inherent safety provided by that factor, enables PADI to provide training that is cheaper, quicker and less intensive than that which would be required if slow-tissues/staged ascents were a requirement.

So - if you do a PADI course you have to accept certain limitations with the tables that control the dives. Your dives will be shallower and shorter, but they will always allow direct ascent to the surface and they will allow you to conduct multiple dives per day without excessive surface intervals. The training needed to conduct short and shallow dives, where the surface is always an option, does not need to be as intensive or wide-of-scope - so it's cheaper, quicker, more convenient and less demanding.

However, modern technology is throwing a spanner in the works of that well-balanced system. Specifically - the evolution and popularity of diving computers.

Most divers now use computers to control their dives. Table diving is generally a thing of the past. Divers are now able to dive for as long or as deep as they wish. Dive computers don't provide many limitations - they just calculate based on whatever you choose to do. The limitations of using the tables have been eliminated.

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'. 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.

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.

 

[MauiScubaSteve]

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.

I am wondering if any dive computer manufacturer has been held liable for a bent diver due to following the computer on a decompression dive?

I have read my computer manual and two parts, printed far apart, seem to come together to indicate Suunto was not afraid of divers being bent using the Viper to do decompression dives to 90 meters; as long as you have enough gas to make all the stops.



Edit; Actually the way I read it just now the computer operates every function as long as 99 minutes ASC time is not exceeded, with the deepest ceiling at 328 feet! Has a max "emergency" depth of 492', but the depth gauge has a 262' stated max depth of operation. Not only that, but if you make all the stops, it still allows multiple dives; no error mode if you don't error.

 

[DevonDiver]

I am wondering if any dive computer manufacturer has been held liable for a bent diver due to following the computer on a decompression dive?

I have read my computer manual and two parts, printed far apart, seem to come together to indicate Suunto was not afraid of divers being bent using the Viper to do decompression dives to 90 meters; as long as you have enough gas to make all the stops.

How would they do that? Have dive computers that restricted capability, unless 'unlocked' by punching in your agency training credentials?

Alternatively, just add a disclaimer to their manuals (that reciprocated the advice given by agencies on computers):

i.e. "Users should always dive within the limits recommended by their respective training agencies."

 

[MauiScubaSteve]

WARNING!
READ THIS MANUAL! Carefully read this instruction manual in its entirety,
including section 1.1. "Safety Precautions". Make sure that you fully
understand the use, displays and limitations of the dive computer. Any
confusion resulting from improper use of this device may cause diver to
commit errors that may lead to serious injury or death.

Above is the first Warning.

WARNING!
DECOMPRESSION DIVES ARE NOT RECOMMENDED! DECOMPRESSION
diving limits the divers ability to ascend directly to the surface and may substantially
increase the risk of decompression sickness.

However, if through carelessness or emergency you are forced to exceed the nodecompression
limits on a dive, the dive computer will provide decompression
information required for ascent. After this, the instrument will continue to provide
subsequent interval and repetitive dive information.

Following the above Decompression Dives Warning are 4 pages of how to follow the computer during a Decompression dive.

WARNING!
YOU SHOULD ASCEND AND BEGIN DECOMPRESSION IMMEDIATELY
WHEN THE DIVE COMPUTER SHOWS YOU THAT DECOMPRESSION
IS REQUIRED! Note the blinking ASC TIME symbol and the upward pointing
arrow.
WARNING!
YOUR ACTUAL ASCENT TIME MAY BE LONGER THAN DISPLAYED
BY THE INSTRUMENT. The ascent time will increase if you:
- remain at depth
- ascend slower than 10 m/min [33 ft/min] or
- make your decompression stop deeper than at the ceiling.
These factors will also increase the amount of air required to reach the
surface.
WARNING!
NEVER ASCEND ABOVE THE CEILING! You must not ascend above the
ceiling. In order to avoid doing so by accident, you should stay slightly
below the ceiling.

Below are the warnings for the Nitrox section, but if I enter 1.6 PPO₂ and 25 O₂ % the computer gives a MOD of 178'.

WARNING!
WHEN THE OXYGEN EXPOSURE WARNING (OLF) INDICATES THAT
THE MAXIMUM LIMIT IS REACHED, YOU MUST IMMEDIATELY ASCEND
UNTIL THE WARNING STOPS BLINKING! Failure to take action to
reduce oxygen exposure after the warning is given can rapidly increase the
risk of oxygen toxicity and the risk of injury or death.
WARNING!
SUUNTO STRONGLY RECOMMENDS THAT SPORT DIVERS LIMIT
THEIR MAXIMUM DEPTH TO 40 M [130 FT] OR TO THE DEPTH CALCULATED
BY THE COMPUTER BASED ON THE ENTERED O2 AND PO2
OF 1.4 BAR SETTINGS. Exposure to greater depths increases the risk of
oxygen toxicity and decompression sickness.

 

[Ste Wart]

:cool3:

Hey Wart,

In my simple mind, I may have boiled MY SCUBA diving down to one simple axiom: Decompress appropriately for the dive underway. Forget all of the BS.



markm

Can't argue with that logic

 

[boulderjohn]

The Navy table I have has, for the most part, the same "NDL" limits that the PADI tables have. It is the format that I was comparing.

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.

You may have missed a key part of what I wrote above. Using the 60 minute compartment for shallow dives within limits means that they cannot have the kind of continuity to deeper depths and deco that the Navy tables have.

EDIT: I wrote this before seeing Andy's more compete response.

 

[boulderjohn]

I have never heard of a computer maker being sued and can't believe it would happen--I would think they would have to prove that the algorithm used was unsafe.

That being said...

When I started cave training, my instructor wanted me to carry a multi-gas computer to manage the deco. Having done all my previous tech training with an instructor/agency who thinks computers are the spawn of the devil (and tables not much better), I didn't own one. I went to eBay to find the cheapest used alternative, and I ended up with a Nitek HE. The seller did not have a manual, so I did an Internet search and found a PDF version. It turned out to be a rough draft of the manual that had somehow been made available, I assume mistakenly, on the Internet. It had comments from a reviewer on it. Sections that had warnings on them were highlighted with marginal comments asking if it was wise to include the warnings. The reviewer was concerned that the warnings would imply an imperfection in the product and lead to possible liability. Since I don't have the final draft, I don't know if the warnings were dropped.

 

[DevonDiver]

I have never heard of a computer maker being sued and can't believe it would happen--I would think they would have to prove that the algorithm used was unsafe.

If a motorist died in a car accident due to loss of control via excessive (illegal) speed, then I don't think anyone would consider suing the vehicle manufacturer because their car 'permitted' the driver to exceed the speed limit or reach 'dangerous' velocity. Providing the car hadn't malfunctioned to cause that speed, it's totally driver error... in violation of their 'training' and the rules/laws that govern them.

Likewise, if a diver violated their training and recommendations given with that training, and got bent even though the computer was fully and correctly functioning -then I don't think there'd be any grounds to sue the computer manufacturer. Just because they supplied a device that 'permitted' the diver to exceed their depth or deco capability, wouldn't make it their fault. That'd only be diver error.

However, if the computer failed on a dive...and that caused the 'untrained' diver to get hurt.. there'd be room for legal debate I am sure. That said, the existence and availability of proper training creates a situation where the diver is 'expected' to have the skills and resources to survive such an event. What hurt them wasn't the computer failure - it was the failure to cater for that contingency.

How I'd imagine the legal case proceeding:

Complainant: I am in a wheelchair due to DCS caused by incomplete decompression because my dive computer failed at 200'.

Manufacturer: Every scuba agency trains divers to carry redundant gauges, including computer or depth gauge/timer, to ensure safety in the event of malfunction. This is applicable at depths below 130ft and whenever the diver goes into the decompression mode. Why did you not have a redundant computer/gauges as per that training?

Complainant: I have not done a course that trains me to dive below 130ft or carry out decompression dives. I was not aware of any recommendations to carry redundant computer/gauges for dives to the depth or that entered decompression mode.

Manufacturer: Therefore, we cannot be held liable, as our instruments should only be used in accordance with the appropriate training available for such dives. You had not sought that training, and in doing so had violated the recommendations given to you by your certification agency - showing a lack of prudence and reasonable preparation for the dive. Had you sought and applied appropriate training for the dives, you would not have been injured. Consequently, the equipment failure cannot be determined to be responsible for the injuries that you received.

 

[opperud]

There is a very important difference between the U.S. Navy tables and tables like the PADI Recreational Dive Planner that explains this. Not many people know this. I will try to explain it briefly, but I will warn you that the full details are pretty technical.

Tables are based on the well established theory that different tissues absorb and release nitrogen at different rates. These rates are called halftimes because the rate is not constant. As the tissues get closer and closer to equilibrium, the rate slows down. We approximate that through the concept of half times. A 5 minute tissue will be half way to equilibrium in 5 minutes, and then half way from that level in the next 5 minutes, and then half way from that level in 5 more minutes. A tissue is considered to be at equilibrium in 6 halftimes, so a 5 minute tissue is at equilibrium in 30 minutes.

When a basic table is constructed, it has to use a theoretical tissue that it believes is most critical for planning. This is called the controlling tissue. When the U.S. Navy tables were constructed, its numbers were based on the 120 minute theoretical tissue, because it was believed that this tissue was most appropriate to that kind of diving. That is why the Navy tables "wash out" in 12 hours (6 X 120 minutes).

When PADI did its extensive research leading to the RDP, it reasoned that recreational divers did not dive the kinds of dives that Navy divers do. Recreational divers are frequently more shallow, and they do shorter dives. It tested divers on those kinds of dives. Their research showed that when diving within the limits you see on the the RDP, the 40 minute tissue actually controlled the dive (and subsequent surface interval). To be more conservative, they selected the 60 minute theoretical tissue for the RDP. That is why the PADI tables "wash out" in 6 hours (6 X 60 minutes).

The Navy tables use the 120 minute compartment for the entire tables. PADI did not test below the limits of the RDP and cannot confirm that the 60 minute compartment is a valid choice beyond those limits. In fact, it knows that it is not valid beyond certain limits. That is why the WX and YZ rules demand longer surface intervals for repetitive dives approaching NDLs.

Hmmm... I am pretty sure what you are referring to here is the case for the surface intervals of the those tables...

You must excuse me if I have gotten you wrong, but if all decompression/"no decompression" numbers were to be calculated based on respectively the 60 or 120 min compartment, then there would be no need for any other compartments in that model, and they would produce some odd numbers. it's been a while since I read my PADI rdp stuff, but i'm pretty sure they are both (rdp and us navy) based on a 5 or 6 tissue compartment model.
Saturationdiving is calculated the way you are referring to. Since you are saturated, ie. all compartments are saturated, you only need to consider the slowest compartment since that will obviously be offgassing slowest.
In any other dissolved gas model, the controlling compartment will be whatever compartment reaching it's m-value first. Which compartment this will be will be determined by the profile of the dive and the gas you are breathing.
The faster compartments will have a higher tolerated supersaturationratio (M-value) while the slower compartments will have a lower one.
As such, the faster compartments will typically control deeper dives; the fast compartments will quickly ongass and reach their m-value. As you go shallower, more and more of the compartments can never become the controlling one because the the depth is simply not great enough for them to reach their m-value.
This is also why you get "penalized" harder for long, shallow dives than short deep ones with regards to surface intervals. After a short deep dive, some fast compartment will have reached it's M-value and ended the dive. the slower compartments will not have had time to ongass to any great extent. But, when you reach the surface, the compartment that ended your dive will also offgass as fast as it ongassed, and thus give you great reward for your surface interval.
On a long shallow dive, the faster compartments with their high m-values can never controll the dive, so the controlling compartment will be one of the slower. It will take a long time for these to reach their m-value given their long half-times (aka long ndl times), but when they do, they will also take a long time to offgass. Aka: longer surface intervals.
This is the reason for the all so familiar curve that you see in decompression times, it is also the reason for the x,y,z rule in the padi rdp.

As for the original question about defining techincal diving; No, I don't think it serves any usefull purpose.
A "no decompression dive" is a physical impossibility. When you stick your head under water there will be a compression, and when you pull it back up there will be a decompression.
One can view decompression in two ways. One would be to say: "I'm going to do xyz dive, how much decompression will be necessary?" Aka "deco diving"
The other would be to say: "I'm comfortable with doing xyz decompression, how long can I stay at xyz depth and still get away with it?" Aka "NDL diving"

Now, who is to say what that pre set decompression should be? 9 m/min, 18 m/min, 5...... It would be perfectly possible to create tables with significantly longer NDL times than those that we see in most tables, one would just have to adjust the ascent rate accordingly. Setting them too low would not be so great either, since you would then spend to much time deep while ascending which you would again have to make up for as you got shallower (so they should probably be about where they are ). Decompression is really just another fancy word for an ascent rate that becomes slower as you get closer to the surface.

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"

Now, this may very well just be a result of me finding the word "Tech" a little cheesy, and sorry for all the OT


Best,
Bjørn