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derek

By derek •

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New DCI Modelling

     " Researchers have created a new model for predicting decompression sickness after deep-sea dives that not only estimates the risk, but how severe the symptoms are likely to be.

      The US Navy Diving Manual may incorporate the model into its next update, as will commercial products intended to help recreational divers plan their ascents to avoid "the bends."

      The results appear online on March 15, 2017, in the journal PLOS ONE.

    "The current guidelines only give you a probability as to whether or not decompression sickness is likely to happen after a given dive," said Laurens Howle, professor of mechanical engineering and materials science at Duke, who has been working on these models with the Navy for a decade. "This is the first time we've been able to also address the likely severity of the potential sickness, helping divers determine acceptable risk."

      All risks have two components -- the likelihood of something bad happening and just how bad that something is likely to be. Having a model that accurately provides both aspects will allow divers to better plan safe depths and ascents to help their bodies adjust -- preventing painful and potentially fatal results."


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EXNDDIVING

John,

i don't understand this article. You can't predict where a bubble will end up and how painful it will be. Each dive and diver are different. Hence a neurological exam.

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tim

Hi Derek - fascinating  (And NO, I did not follow the maths!).

 

Basically used records of over 3,000 actual dives and applied a three state model to predict no DCI, mild DCI (Pain only) and Serious DCI (Cardio/neurological DCI)

 

They used the 2008 (Rev 6) USN tables 'no decompression limit' to compare the US Navy's 'standard' of accepting up to a 2% risk of mild DCI and 0.1 % risk of serious DCI (I'm not sure many commercial diving people will accept a hit rate of 'one serious DCI per 1000 dives as normal)

 

They concluded that the USN 2008 'no decompression limits' was conservative for mild DCI - ie you could - theoretically!!! - dive longer for the before you reach the 2% risk of mild DCS

 

BUT they also noted that you had to 'vastly reduce' bottom times to keep within the 0.1 % risk of serious DCS

 

To meet the 0.1% risk of serious DCI, the table they quoted was the French Navy NM90 table.

 

Which kind of supports a lot of people's gut feeling that the old USN air tables are a tadge risky when used straight out of the box  - even the US Navy concluded they produced an unacceptably high rate of DCS in the deep air range - That's why they upgraded from Rev 6 to Rev 7 last yea (And why they upped from Rev 5 to Rev 6 in 2008).

 

I believe - but am open to being corrected! - that the French Navy tables are based on a Haldanian model (derived from extrapolating data from actual dives) as opposed to Algorythms (bubble modelling maths) which kind of pushes one to think that science is good, but actual experience is better.

 

It would be interesting if they re-ran the modelling using the NDL limits from USN Rev 7 to see if the new version is any safer.

 

Thanks for posting the link!

 

 

 

 

 

 

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