Are multiple dives more risky for DCS than just 1 dive?

[Chavodel8en]

The reason I pose this question. The vast majority of my diving is shallow local shore dives - basically zero DCS risk. But when I go on vacation, I often schedule one deep wreck dive. Since my wife doesnt dive, I dont do alot of diving - just the 2 tank morning trip - maybe one the next day - never more than 4 dives in 48 hours (or even the whole trip).

I was in Oahu diving the Sea Tiger - I basically let the NDL get to 1 before I headed up. (I extended my safety stop to ~ 5 minutes). I would never push the NDL like this if I did a bunch of dives in a short time period. But I feel there is less risk for me doing this one deep dive (and the subsequent shallow reef dive).

And I understand DCS doesnt strictly follow any rules. But generally, would you say the risks are much greater if you a doing a bunch of dives?

 

[gamon]

What exactly is an NDL of 1?

Yes generally speaking multiple dives of depths greater than say around 30 feet carry a greater risk of DCS than a single dive over a 24 hour period.

 

[Johnoly]

But generally, would you say the risks are much greater if you a doing a bunch of dives?

Yes.
The Sea Tiger is 120ft to the sand and is an advanced dive. Depending a bunch of factors (too many to list) you can get DCS on this dive and doing "a bunch of dives".

 

[GreggS]

When we were at Anthony's Key Resort in Roatan two years ago, we could do 3 dives a day + 2 night dives. We opted out of 2 of the dives during the week but still did 18 in 6 days. And this was on air with some dives over 100 fsw. We pushed our NDL close a couple of times but never got into deco. We're going back to AKR in June for the SB Invasion and plan on doing nitrox this time.

So as @gamon said, yes, multiple dives increases the chance for DCS. But just pay attention to your computer and you should be fine. But anything can happen.

And @gamon, I took it to mean he was showing an NDL of 1 minute remaining.

 

[boulderjohn]

I am reporting this from memory from a DAN presentation I saw about 13 years ago..

A dive study showed that an overwhelming percentage of DCS cases occurred on the first dive of a vacation, and an overwhelming percentage of those occurred on the first dive that day.

 

[Brett Hatch]

John, that is a very interesting finding. If it is true, it would suggest that the primary cause of DCS in rec dives is not the dive profiles per se (or related things like gas choice or equipment failure), but basically rustiness. Spacing out, forgetting how to use your equipment correctly, struggling to control your ascents with new or unfamiliar gear, struggling with poor weighting, etc. Do you interpret it along these lines as well?

In any case, if you have a link to that DAN presentation or it underlaying research, I would be eager to see it.

 

[Juels4488]

Yes, multiple dives even no decompression dives build up the residual N2 in your body. Unless you wait to off gas you’ll have residual N2. Diving is not a natural occurrence for the human body. If conducting multiple dives things like temperature, exhaustion, among other things increases the likely hood of DCS. Although it increases the likely hood using approved decompression techniques, ascent rate and proper surface interval will reduce the chances.

 

[boulderjohn]

Yes, multiple dives even no decompression dives build up the residual N2 in your body.

As much as this makes sense, I am having inner vibes telling me I read a study to the contrary. I will have to search. I am just cautioning about making too many assumptions.

 

[shurite7]

Dr. Neal Pollock, formerly with DAN Americas, noted repetitive dives have not been a clear contributor to DCS and many divers experienced the malady on the first dive. He also mentioned there are documented cases of caisson workers who experienced the bends on Monday more so than the rest of the week, supporting the idea human physiology can build some resistance against getting bent.

What I’ve learned over the years is to understand what a dive profile really means (time depth relationship, sawtooth vs square vs multilevel vs bounce vs spikes, ascent rates, stops) to manage the dive, note your physiological state to know if you can push it a little or simply back off, and be aware of workload throughout and shortly after a dive to avoid unnecessary stress. Also, learn how to use the computer you are using in order to understand the information it is displaying in order to manage the dive profile and note that it does not represent your physiological state.

The only way to prevent any possibility of getting bent is not to dive, otherwise except the risk and learn as much as you can to manage it.

 

[Kendall Raine]

For what it's worth, I've found doppler bubble scores went down across multiple days and dives per day on similar profiles. This was true doing two a days to 230-250 using 15/55 on the Wilkes Barre and two months ago doing 4-5 dives a day to 100-140 in Truk using 30%. Those were all generally square profile swimming dives-although lots of penetration so low exertion. This was also true of the guys I was diving with too so it's not just a quirk of my physiology.