Dive computers are untested and unsafe?

[rossh]

It is worth pointing out that there are two tables/models (in general use) actually based on experimental data (and can be called safe): The original Navy Tables, and the RDP.

Those two planning methods are at either end of the spectrum. It's a brave diver indeed, who would follow an original Navy table. Note also that man tested does not automatically equal "safe".

The "man (lady) tested" standard is not as attractive as it sounds. The Navy standard is tested, but its too aggressive for most of us. The Buhlmann standard is also too aggressive for most of us. Many simple computers claim to be ZHL 16, but actually include a lot of extra safety margins padded on. You can use GF to get real Bulhmann with GF 100/100, but that's not a preferred plan either. The DCEIM is a tested method that does give plans with more conservatism, but its not used much in the Tech world. So be careful for what you wish for. Man tested standards do not seem to be a desirable attribute.

Many of today's dives are conducted with planning from models of advanced math and considerations of physical properties of bubble behavior. Yet others use a simplified time / pressure relational method to do the job. Adoption of these methods and planning tools, came from anecdotal observations that they do a better job than anything else.


Indecently, the DCS numbers have remained mostly static over the last decade or more (DAN yearly reports), while tech dive has grown enormously. i.e. the ratio of injury gets lower every year. This would imply that collectively, we are all doing a better job of deco and managing the risks.

Regards

 

[Duke Dive Medicine]

Actually, DAN has done a lot of work in this area during the last 15 years or so through its Project Dive Exploration and has a much better grasp on this than you might think. They don't know the total number of dives worldwide, but they know the total number of dives and the total number of incidents of all kind in their representative study. In the latest released edition (1968), it reports on page 6 that the DCS incident rate is 2 cases for every 10,000 dives.

EDIT: I forgot to mention the source. The results are on page 6 of the annual fatality report (1968). You can examine all the charts and graphs there if you would like.

John,
Are you sure you got that year correct? If this is 1968 it's way past my nap time.

But seriously, if you break the PDE data down even further, the DCS incidence for warm-water liveaboards is about 0.4 cases per 10,000. For cold-water wreck diving, it's more like 6 cases per 10,000. All of these dives were performed using computers. Though beano might be technically correct in saying that there isn't any "experimental data" behind some of the computer algorithms, they are empirically verified on a continuous basis, and the more dives that are performed, the more solid those empirical data become. Granted, the system isn't perfect, but we are actively working to improve it, e.g. by encouraging computer manufacturers to collect data directly from divers.

Best regards,
DDM

 

[boulderjohn]

John,
Are you sure you got that year correct? If this is 1968 it's way past my nap time.

Ooops! 2008.

 

[300bar]

Hmmm let's see.

No computer test subjects, I did 4500 dives over 25 year 99% with computer.
I did (55m Deep) long, day. night, training, deco and non deco,drift, low viz, high viz,cave(sort of) wreck you name it. No DCS as of yet.

Yeah I think the PDC has proven it self.

 

[boulderjohn]

Indecently, the DCS numbers have remained mostly static over the last decade or more (DAN yearly reports), while tech dive has grown enormously. i.e. the ratio of injury gets lower every year. This would imply that collectively, we are all doing a better job of deco and managing the risks.

...and I have no hesitation about using VPM to plan decompression.

 

[boulderjohn]

What appears to me to be the biggest factor in DCS remains unexplained. I attended a presentation from a DAN representative a few years ago, and she said that their studies showed that a huge percentage (over 80% if I recall correctly) of DCS cases came on the first day of a dive trip, and over 80% of those cases came on the first dive of the day. (Actual statistics muddled by memory.)

 

[DiveNav]

......their studies showed that a huge percentage (over 80% if I recall correctly) of DCS cases came on the first day of a dive trip, and over 80% of those cases came on the first dive of the day. ....

THAT's intriguing :confused4:

 

[300bar]

What appears to me to be the biggest factor in DCS remains unexplained. I attended a presentation from a DAN representative a few years ago, and she said that their studies showed that a huge percentage (over 80% if I recall correctly) of DCS cases came on the first day of a dive trip, and over 80% of those cases came on the first dive of the day. (Actual statistics muddled by memory.)

Funny, have seen quite a few DCS cases, but NEVER on the 1st day let alone the 1st dive.
Only one I've seen with DCS symtoms on the 3rd day, was a guy with an inner ear infection, no DCS afterall.

 

[Dr Deco]

Hello Readers:

Non-Tested Tables?

I wish to be very clear - again. There are no non-tested tables or computers on the market. Period. All decompression schemes, one way or another, trace their primary constants – the NDLs – to something that has been derived from tests with humans over past decades. Over the past ten years, I have seen in the Ask Dr Deco forum allegations of non-tested tables. If only for legal reasons, this would never be done.

Pedigree

The US Navy tables are traceable to US Navy tests using Navy divers are test subjects. The PADI RDP is based upon US Navy results [for the NDLs] as modified by the Doppler bubble detection experiments of Merrill Spencer MD [the original Doppler user for diving] in the early 1970s. For the PADI development tests, these new NDLs [slightly modified] were then tested with volunteer divers from the Pacific Northwest region. US Navy tables and PADI tables are not at opposite ends of the spectrum. They actually are “kissing cousins.”

Because the PADI data was published, it was a very convenient source for tested NDLs in recreational divers with a wide age spectrum. Yes, one might make some modifications and “tweak” things to make an appearance of originality. It is possible to allow a reduction in NDLs or ascent supersaturation [e.g., a change in the “gradient factor”] as the user might decide, but all is traceable to tests. This is necessary for legal reasons. If one checks the computers, you will find that many reference the PADI tests. Tests are expensive, and it is not necessary to “reinvent the wheel” as they say.

There are other test data and models available, and none are “voodoo.” Those from Professor Buhlmann [ZHL 16] have been employed as well as the Canadian tables [formerly DCIEM]. We have also the VPM system and BSAC.

Theoretical Tables

No tables are based solely on theories, because there are none that work sufficiently. It is necessary to get the NDLs from human tests. There are “theoretical rationals” given for what is occurring, but much has been found to be wishful thinking. JS Haldane, in 1908, proposed a rational for what was occurring but this was found wanting as far as the physiology went.

In 1908, JS Haldane published his tables for the Royal Navy based on laboratory trials with animals. To study the physiology he used goats as well as a small menagerie of animals such as large and small rats [Haldane wrote, “Details were eaten by a goat”], rabbits, mice, guinea pigs, and hen’s eggs. He found that it was not possible to make tables from goat data, because there was no way to transfer DCS data from animals to humans. His final tables were made with data from human volunteers.

RGBM Tables

There are some tables [e.g. NAUI] that come from Bruce Weinke PhD, and I understand the model is also in a couple of computers. While this model is based on microbubbles for some of the ascent characteristics, this also reverts in the end to ascent criteria as determined from actual dives in the ocean with humans [although they are not technically “test subjects”]. These tables do use “advanced math” but do revert to actual field data for DCS/no DCS.

DCS Rates for Tables and Computers

These appear to be about the same. Even though computers have the possibility of diving constantly to the model limits, most divers either do not or the system makes use of conservative factors.

In actuality, all DCS is unexplained in terms of the gas loading analysis - unless you really mess up! I look at things from the basis of bubble growth, bubble micronuclei concentration, and exercise and the enlargement of nuclei by stress assistance. These are not generally analyzed [and not always possible to analyze]. Scientists for several decades have looked at biochemical mechanisms for DCS without success. No one has looked at why some divers are resistant and work from that starting point! I tried at NASA but the studies were not funded [NASA is always short of money].

It is difficult to determine the actual statistics since DCS might be known but not the total number of dives. There was one attempt to determine dive number from the number of tank fills. Most divers do use dive computers but it is recommended that someone has a table topside in case a computer fails. There are other methods of fixing those problems, however.

Thanks for reading.

Dr Deco :doctor:

 

[Jax]

What appears to me to be the biggest factor in DCS remains unexplained. I attended a presentation from a DAN representative a few years ago, and she said that their studies showed that a huge percentage (over 80% if I recall correctly) of DCS cases came on the first day of a dive trip, and over 80% of those cases came on the first dive of the day. (Actual statistics muddled by memory.)

Just a muddled SWAG: can that not be directly attributed to vacation divers who forget and come up too quickly? I don't remember where on this board I heard it, but it was stated that people come up the last 15' after their safety stop in about 15 or so seconds! I've observed a lot of that on my vacation dives.