Decompression Tables

[NJDiver07866]

I love you guys...I'm a smart @ss so don't get angry when I say this...

I checked the bubble model software, it does not take into account me barfing up my breakfast, my spastic colon that flairs up and dehydrates me, the 10MG of paxil that I take or the pint of blood I donated 3 days ago.

I respect the fact that hard working people are trying to accurately collect data, and I bet ya they are hand grenade close in accurate numbers, but not exact.

I think of it as a lottery, every time I go diving I buy a ticket… one day I’m going to win the great big bubble prize…

 

[Gene_Hobbs]

That is only an abstract at this point and not a full paper. After it is presented in October, you might be able to get a copy of the poster to fill in some of the holes.

As for methods of data collection... The dives and reports are from DAN's Project Dive Exploration so the methods are easy to find. There are several publications available from the previous analysis done with this data set.

As for the probabilistic models... The development of these models is VERY well documented in a series of technical reports from the US Navy entitled "Statistically Based Decompression Tables". (list here) The particular model used for the abstract above is the BVM(3) model developed by Dr's Gerth and Vann:

Gerth, WA; Vann, RD. Probabilistic gas and bubble dynamics models of decompression sickness occurrence in air and nitrogen-oxygen diving. Undersea Hyperb Med. 1997 Winter;24(4):275-92. RRR ID: 2258 (More detail available in the full NOAA report on BVM(3) here)

Although the Navy tables have been around a long time, they were updated this year to use oxygen from 20 feet up.

Bruce, minor correction, new O2 depth for the USN Rev.6 tables is 30fsw.

The USN is using VPM.

Nope, sorry... The only thing the Navy has done with VPM was the risk analysis Keith Gault ran for the UHMS abstract we put together this year (we did our risk calculations with BVM(3), USN93, and NMRI98). All current modeling efforts are on the VVAL-18M parameter set as mention in Keith's post here.

If the USN Tables are pushed to the limits... yes - 5% bend rate. That includes the following caveat. If you are not ascending at 1 foot per second. You are off the table.

You make this sound like the USN57 model is an iso-risk table. Saying a percentage means nothing without qualifying the exact profile and model used to analyze that risk. NONE of the "no stop" dives will result in a 5% bend rate if the table is used as prescribed. If you go with the "extreme exposure" or longer decompression time allowable with USN57, the percentage is sometimes higher than 5%. (These are risks calculated with all three of the models we used in our analysis above).

...and the full paper with abstract quoted earlier in the thread is here:

Dunford RG, Vann RD, Gerth WA, Pieper CF, Huggins K, Wacholtz C, Bennett PB. The incidence of venous gas emboli in recreational diving. Undersea Hyperb Med. 2002 Winter;29(4):247-59. RRR ID: 3773

 

[boulderjohn]

John,

Anyway you look at it, 52,168 dives were made that resulted in 23 DCS hits. ALL dives were undertaken with dive computers.

Perhaps all 23 hits were attributable to a few divers, who decided that their computers didn't require batteries, or maybe just didn't turn them on...

Personally however, I'm willing to assume that Dr Richard Vann, Director of Applied Research at the Duke University Medical Center for Hyperbaric Medicine and Environmental Physiology, as well as the Research Director for DAN, would insure (in his opinion) that these statistics represented the recreational diving public at-large and not solely a few people who were just trying to commit suicide.

If that is what you got out of what I wrote, then my communication skills are even more horrible than normal.

As I understood your original post, you said that if 1 dive out of every 2,200 results in DCS, then everyone will get DCS eventually because everyone dives 2,200 dives. If I misunderstood you, please correct me.

I first disputed the belief that every diver will complete 2,200 dives in a lifetime. If you have evidence that this figure is a correct average, please correct me.

I then pointed out that you cannot distribute probability evenly across a population unless all other factors are equal. For example:

• This winter a certain percentage of Americans will get frostbite. That does not mean the people living in Hawaii have the same statistical chance of getting frostbite as the people in Minnesota.
• A certain percentage of Americans will be attacked by sharks this year. The probability that the people swimming off Florida beaches will be attacked is greater than it is for the people spending the entire year in Kansas City.
• Next weekend I will do a number of extended dives in the 150 foot range using trimix. At the same time, hundreds of divers will be diving in the 25-35 foot range in John Pennecamp State Park in Florida. The odds that I will get DCS are better than the odds that any of the Key Largo divers will get DCS.

Or do you disagree with those examples?

 

[GrandpaScuba]

If you want the Navy tables you can get them from the manual which is available free here... US Navy Diving Manual Revision 6 NEW [BK-USN-Rev6] - It's Free! : Tech Diving Limited, a subsidiary of Scuba Training and Technology Inc.

This is a 20MB PDF file.

 

[HowardE]

If you go with the "extreme exposure" or longer decompression time allowable with USN57, the percentage is sometimes higher than 5%. (These are risks calculated with all three of the models we used in our analysis above).

well...there you go.

 

[Puffer Fish]

Please to meet you Richard. Now you can't repeat what you wrote; I've had DCS (Type I after adhering to the decompression profile).

Including you, I've known 6 people (one of those had 2 hits...so it is 7 events)

 

[HowardE]

Nope, sorry... The only thing the Navy has done with VPM was the risk analysis Keith Gault ran for the UHMS abstract we put together this year (we did our risk calculations with BVM(3), USN93, and NMRI98). All current modeling efforts are on the VVAL-18M parameter set as mention in Keith's post here.

E-mailing contact at NEDU for confirmation one way or the other.

The post you reference is over a year old.

 

[Puffer Fish]

John...your point is valid, if the only factor associated with DCS is time and depth. But we know there are people with a huge tendency to get DCS... as there are individuals with a tendency not to get DCS...
Note: That assumes that every PFO event is removed from the list of DCS hits.. which may or may not be the case.


So what percent of the population is hypersensitive to DCS? It is possible that it is 1 in 2,200...in which case neither you nor the shallow divers are at any greater risk.

We also know there are several other factors that greatly increase your risk...going from cold water to a hot tub, for example. Dehydration is another one... What we don't know, is how many of those hits were due to something besides the time and depth they were at.

As someone with over that magic 2,200 number, I can only assume at this time that:

1. I am on borrowed time, and my hit is just around the corner, or

2. Someone else has been nice enough to take a hit in my place.

I like to think it is the later.

If that is what you got out of what I wrote, then my communication skills are even more horrible than normal.

As I understood your original post, you said that if 1 dive out of every 2,200 results in DCS, then everyone will get DCS eventually because everyone dives 2,200 dives. If I misunderstood you, please correct me.

I first disputed the belief that every diver will complete 2,200 dives in a lifetime. If you have evidence that this figure is a correct average, please correct me.

I then pointed out that you cannot distribute probability evenly across a population unless all other factors are equal. For example:

• This winter a certain percentage of Americans will get frostbite. That does not mean the people living in Hawaii have the same statistical chance of getting frostbite as the people in Minnesota.
• A certain percentage of Americans will be attacked by sharks this year. The probability that the people swimming off Florida beaches will be attacked is greater than it is for the people spending the entire year in Kansas City.
• Next weekend I will do a number of extended dives in the 150 foot range using trimix. At the same time, hundreds of divers will be diving in the 25-35 foot range in John Pennecamp State Park in Florida. The odds that I will get DCS are better than the odds that any of the Key Largo divers will get DCS.

Or do you disagree with those examples?

 

[Meng_Tze]

It also begs the question, how many DCS Type I cases were not reported. I believe quite a few more than were.

I know of a few.............:blinking:

 

[LeadTurn_SD]

I also personally know of 2 "for sure" hits (from the 70's), both VERY well deserved, both unreported.... sadly, one still spends most of his time in a wheelchair (lost about 90% of motor function in both legs); the other was mild and made a full recovery.

I've never taken a hit, nor has anyone on a dive I've led or been on (we stayed within table protocols, plus "buffered" it.... the guys I knew who got bent took a big excursion outside the tables...).

So the 1 in 2,220 rate reported in the study may actually be as good a "ballpark" figure as any other. I have not read the study yet, but it would be interested to know how many cases were "un-deserved" hits....

Best wishes.