Shallower dive then deeper dive?

[Hal]

Have always tried to comply with the rule re. deeper dives followed by shallower dives. On an dive trip I'll be doing in February, it appears that the deeper wreck dive I want to do (around 100 ft) will be in the afternoon. Divers offered in the morning are shallower reef dives. Anticipate using nitox (32%). So, increased risk of decompression sickness if do shallower dives followed by deeper ones?

Thanks,

Hal

 

[SDAnderson]

Do a search using the phrase "reverse profiles." You'll find that reverse profiles, within limits, are no longer considered to be the bugaboo that they once were.

DAN has stuff about it on their website, but it came out of a workshop sponsored by the Smithsonian several years ago and attended by a veritable who's who from the dive and hyperbaric medical community.

Steven

 

[Cave Diver]

Have always tried to comply with the rule re. deeper dives followed by shallower dives. On an dive trip I'll be doing in February, it appears that the deeper wreck dive I want to do (around 100 ft) will be in the afternoon. Divers offered in the morning are shallower reef dives. Anticipate using nitox (32%). So, increased risk of decompression sickness if do shallower dives followed by deeper ones?

Thanks,

Hal

I've seen several debates arguing whether a reverse profile actually put you at that much more risk of DCI. Ultimately, it will be your call, but some things to consider include nitrox (which you already mentioned).

Trying to allow a longer surface interval.

Making sure you stay well hydrated.

Stay within your tables or computer NDL's.

Do a deep stop for a minute on your ascent, and make your ascent as slow and controlled as possible.

Spend a few extra minutes doing your safety stop.

 

[Bob3]

it came out of a workshop sponsored by the Smithsonian several years ago and attended by a veritable who's who from the dive and hyperbaric medical community

I've got that on tape, (its around here someplace).
I'll have to ask them for permission to rip it to MP3 format, if I can figure out who to ask ...

 

[Capt Jim Wyatt]

I do reverse profiles very often..never had a problem. It is quite common for me to do do 2 shallow reef dives (25fsw)in the morning and then 2 deeper (100fsw) dives in the afternoon.

 

[Genesis]

I don't think they do a thing to your DCI risk.

However, they DO have an ugly impact on the no-required-stop limits for the later, deeper dives. Of course if you are intentionally willing to do mandatory decompression, then its (mostly) irrelavent; if you do the deco properly then you don't pay all that much of a penalty on the next one in terms of ITS decompression.

What I try to avoid is SIs under an hour if I'm diving beyond 60' or thereabouts.

 

[Capt Jim Wyatt]

What I try to avoid is SIs under an hour if I'm diving beyond 60' or thereabouts.

Agreed...I always have about 2.5-3 hours SI between the 2nd shallow & the first deep. Then 60 mins between 1st & 2nd deep.

 

[Diver0001]

Have always tried to comply with the rule re. deeper dives followed by shallower dives. On an dive trip I'll be doing in February, it appears that the deeper wreck dive I want to do (around 100 ft) will be in the afternoon. Divers offered in the morning are shallower reef dives. Anticipate using nitox (32%). So, increased risk of decompression sickness if do shallower dives followed by deeper ones?

Thanks,

Hal

There is actually some information about this out there. IIRC Dr. Wienke says that reverse profiles with a difference in depth of over 40ft carry an increased risk of DCS. Do a search for the username "BRW" and read what he has to say about it.

R..

 

[Genesis]

There is actually some information about this out there. IIRC Dr. Wienke says that reverse profiles with a difference in depth of over 40ft carry an increased risk of DCS. Do a search for the username "BRW" and read what he has to say about it.

R..

Yes, Bruce has said that, BUT....where's the evidence?

DAN is "the source" for statistics on DCI, at least in the states. They have recently reversed their former position on reverse-profiles, saying that they cannot find statistically-significant increases in risk with them.

 

[H2Andy]

Dr. Wienke says that reverse profiles with a difference in depth of over 40ft carry an increased risk of DCS.

yes, much like bounce diving can increase your risk of DCS (i think of
reverse profiles as a "slow motion" bounce dive).

i think the keys are (a) don't dive even close to the maxes and
(b) have nice and long surface intervals.

when i do reverse profiles, i do everything else about the dives with
extra safety margins, just to be safe. i've never had a problem.