Diving inverted profiles?

[drichman]

With todays modern computers, what is your opinion on diving inverted profiles (i.e. a deeper dive following a shallower dive). I got certified over 20 years ago and then took a long break from diving. What is the current teaching recommend assuming you are using a modern dive computer?

 

[Blackwood]

Most current teaching is still 'deeper dive first.'

 

[Garrobo]

Dunno about the rules but I did an inverted dive last week. Did a 46', 29 minute dive, followed by 45 minutes SI and finally a 105', 21 minute dive. Flew home the next morning after an 19 hour 15 minute wait. Still alive and no bends.

 

[jeckyll]

Garrobo: That's like saying you drove with no seat belt and lived. So what?

There is nothing inherently dangerous about a reverse dive profile providing that
the decompression algorithm adequately takes into account excess dissolved gas (gas
loading), unresolved free gas (gas bubbles), and changes in the underlying size
distribution of bubble formation nuclei (gas nuclei). Only the first of these effects is
accounted for in conventional dissolved gas algorithms. All three can be addressed
within the context of the Varying Permeability Model.

From: http://www.peter-rachow.de/vpm-rdpw.pdf

IMO, tables and current computer programs for NDL dives are based on doing the deepest dive first. If you were to do a deep dive second, compress the bubbles and then have a quick ascent... well, lets just say I wouldn't want to do that.

As always, YMMV, but I personally don't feel I know enough about decompression and how reverse profiles may affect my body to feel comfortable doing them. Especially if there are large variances in the dives (i.e. I think doing a 40 foot dive followed by a 50 foot dive is much less risky than doing a 40 foot dive followed by a 100+ foot dive).

In any case, if a dive does turn into a reverse profile due to ___ (insert something you think is a good reason), I would spend more time shallow, specifically at 20 and 10 feet to ensure I give my body a chance to deal with offgassing in that situation.

 

[tc]

For an interesting example check the dives garrobo lists on the tables, after working it through now check it again but switch the order of the two dives and see what a difference it makes.

 

[TheHobster]

a few years ago the industry brought a few folks together and discussed a number of topics, this being one - it was decided from a safety standpoint there was no difference, however, the reverse profile did result in less bottom time

 

[Nomad]

Always remember, dive tables, whether they are on a chart or in a dive computer, are entirely theoretical. You can fallow a table perfectly and *still* get bent. Conversely, you can blow your tables out the wazoo and *not* get bent.

Although an inverted profile may not kill you, diving conservatively increases your chances of feeling good at the end of the day.

 

[spectrum]

a few years ago the industry brought a few folks together and discussed a number of topics, this being one - it was decided from a safety standpoint there was no difference, however, the reverse profile did result in less bottom time

I have read the same but cannot cite it.

Having less allowable BT may or may not have an effect on the actual dive since NDL is often not the reason to turn a dive.

 

[jeckyll]

Well, the paper I quoted from and referenced above was presented at the "Reverse dive profile workshop" in 1999 at the Smithsonian Institute... maybe that was the one?

 

[rawls]

I read somewhere...again, like spectrum, I cannot recall where I read it, but it basically stated that a reason why reverse profiles were not recommended is because the majority of research on dive profiling is based on deepest dive first and consequently there was not as much research on dive profiling utilizing reverse profiles...