Breathing O2 during surface interval

[Brett Hatch]

It is true that everybody's physiology is different, and varies day-to-day as you say. In much the same way, the models we use to try to avoid DCS vary, so different models will produce different results. There are a few different types of models, and within a given type there are parameters which can be tuned to one's preference. And no matter who you are, how you dive, which model you choose, and whether you follow its guidance or not, there is always a non-zero chance of a DCS hit, always. Now with that in mind, let's look at a few different models.

Day 2 / Dive 1 on air was to 105'. My PADI RDP table suggests a maximum NDL time of 16 minutes. Punching this into my Shearwater's dive plan mode (in default recreational settings), I get just 11 minutes. It's a little hard to read the photos of your dive profile, but it looks like the 105' was a brief dip, and most of the bottom time was more like 100'. Using 100' instead, I get 20 minutes and 13 minutes, respectively. From the picture I can't say what your bottom was, but I betcha these two models would put you in mandatory deco for the first dive alone.

Assuming that you just baaaarely made it out in time, the PADI RDP would make you in pressure group O; after surface interval of 58 minutes, you are in pressure group E. An E diver on air going to 100' has an NDL of just 10 minutes. Again, it's a little hard to read the profile, but there was a good amount of time spent near the bottom, and the whole dive was 32 minutes -- almost certainly in mandatory deco range. Some other posters calculated things using different tools, but reached the same conclusion.

So, what do we make of this? Well, maybe some of the other posters are correct, and in some way you misused your computer. In that case, easy solution: you've got some homework to do to figure out the mistake and how to avoid it next time. Or maybe they're wrong, the computer was used as intended, but its results are quite different from what I have calculated here, and from what others calculated. That could totally be the case, and I would interpret it as the computer is not conservative enough. I mean, several other calculations put you in mandatory deco here, your computer said you were fine, and guess what, you got bent. If the computer was not misused in any way, then the only reasonable conclusion in my humble opinion, is that the computer is an unsafe piece of s***. Would you mind using the computer's planner mode to plan these dives, and see what it spits out?

Anyway, I am sorry to hear that you got bent while doing your best to avoid it, and am glad that it was minor and that you're OK. I'm not trying to be argumentative here. It's just that the results of that computer are strikingly different from other results. I want to know where the massive discrepancy came from, because it just doesn't seem right.

By the way, if you would like to learn more about diving physiology, decompression sickness, and how all of these models work, Mark Powell wrote a great book on this topic. It's called Deco for Divers, and it's available online for around $30 to $40. The book draws on decades of real studies of decompression illness, and compiles it all into a very layperson-readable format. There's not much math in the actual text of the book, which keeps it readable, but there are appendixes in the back for the gigantic nerds among us, if you're into that kind of thing. And the whole book is pretty short. I managed to read it about a month during my half-hour subway commutes to work (in the before-times when commuting via subway was a thing).

 

[Hortondon]

It is true that everybody's physiology is different, and varies day-to-day as you say. In much the same way, the models we use to try to avoid DCS vary, so different models will produce different results. There are a few different types of models, and within a given type there are parameters which can be tuned to one's preference. And no matter who you are, how you dive, which model you choose, and whether you follow its guidance or not, there is always a non-zero chance of a DCS hit, always. Now with that in mind, let's look at a few different models.

Day 2 / Dive 1 on air was to 105'. My PADI RDP table suggests a maximum NDL time of 16 minutes. Punching this into my Shearwater's dive plan mode (in default recreational settings), I get just 11 minutes. It's a little hard to read the photos of your dive profile, but it looks like the 105' was a brief dip, and most of the bottom time was more like 100'. Using 100' instead, I get 20 minutes and 13 minutes, respectively. From the picture I can't say what your bottom was, but I betcha these two models would put you in mandatory deco for the first dive alone.

Assuming that you just baaaarely made it out in time, the PADI RDP would make you in pressure group O; after surface interval of 58 minutes, you are in pressure group E. An E diver on air going to 100' has an NDL of just 10 minutes. Again, it's a little hard to read the profile, but there was a good amount of time spent near the bottom, and the whole dive was 32 minutes -- almost certainly in mandatory deco range. Some other posters calculated things using different tools, but reached the same conclusion.

So, what do we make of this? Well, maybe some of the other posters are correct, and in some way you misused your computer. In that case, easy solution: you've got some homework to do to figure out the mistake and how to avoid it next time. Or maybe they're wrong, the computer was used as intended, but its results are quite different from what I have calculated here, and from what others calculated. That could totally be the case, and I would interpret it as the computer is not conservative enough. I mean, several other calculations put you in mandatory deco here, your computer said you were fine, and guess what, you got bent. If the computer was not misused in any way, then the only reasonable conclusion in my humble opinion, is that the computer is an unsafe piece of s***. Would you mind using the computer's planner mode to plan these dives, and see what it spits out?

Anyway, I am sorry to hear that you got bent while doing your best to avoid it, and am glad that it was minor and that you're OK. I'm not trying to be argumentative here. It's just that the results of that computer are strikingly different from other results. I want to know where the massive discrepancy came from, because it just doesn't seem right.

By the way, if you would like to learn more about diving physiology, decompression sickness, and how all of these models work, Mark Powell wrote a great book on this topic. It's called Deco for Divers, and it's available online for around $30 to $40. The book draws on decades of real studies of decompression illness, and compiles it all into a very layperson-readable format. There's not much math in the actual text of the book, which keeps it readable, but there are appendixes in the back for the gigantic nerds among us, if you're into that kind of thing. And the whole book is pretty short. I managed to read it about a month during my half-hour subway commutes to work (in the before-times when commuting via subway was a thing).

yep. I know that the tables show I was in deco but tables don’t measure variable depth. I also knew before entering the water that I’d be in the edge. The computer I use is a Galileo Luna. The risk setting was set on L3 and if you miss a deco stop if freezes for 24 hours. The computer also drops a risk level during the dive if your profile warrants. In this case it did drop a level, did not go into deco and did not freeze. There were two others on the dive and they didn’t go into deco either.

I’m currently reading “Scuba Physiology: Thing you know all about Scuba medicine? think again?” While I’m not finished reading it I have found it to be very informative.

I’ve also taken the time to learn more about my computer. There is a setting called PDIS (Profile Dependent Intermediate Stop). It’s not a deco stop but an optional stop that kicks in when your body starts off-gassing. I have now turned this on to add another layer of caution. The formula used to determine time of off-gassing is depth, time at depth, and breathing consumption.

I am kind of a nerd looking into this but more interested in learning more about how to prevent it (no guarantee I know) than what caused it. Everyone on here has been helpful including those that keep saying I was in deco because it makes me think about the conditions and how I can be more aware.

 

[ontdiver]

The computer I use is a Galileo Luna. There is a setting called PDIS (Profile Dependent Intermediate Stop). It’s not a deco stop but an optional stop that kicks in when your body starts off-gassing. I have now turned this on to add another layer of caution. .

I have a Luna as well and have been using the PDIS function for several years. I let my DB know about the anticipated stop before we start the dive. This helps in eliminating confusion.

 

[rick00001967]

Im hardly an expert on this.....but couldnt you potential run into CNS oxygen exposure limit issues?

if you do a few substantial dives pushing 1.4...then hop back up to the surface where you sit at a 1.0..then hop back down pushing a 1.4 again?....thats a lot of time with a high PO2

i am surpried no one mentioned this. unless i missed it.
i have never heard of anyone using O2 at the surface (unless it was used for medical treatment). i have never even heard it suggested until reading this.
obviously breathing O2 at depth has a greater partial pressure so it should have a more eficient effect for decommpressing compared to breathing it on the surface.
i hope anyone doing this is tracking the O2 exposure. especially if you are doing more dives that day.

 

[jale]

Hi
Using O2 at surface other than for medical reason was (is?) done in some circles and tables are available to determinate your position.

 

[dmaziuk]

obviously breathing O2 at depth has a greater partial pressure so it should have a more eficient effect for decommpressing compared to breathing it on the surface.

Why? You're breathing 0% N2, what's driving the decompression is PPN2insp, not PPO2 -- depth or no depth.

(Obviously, IRL PPN2insp will be greater at depth so in practice depth matters. Just not for the reason stated.)

 

[boulderjohn]

i have never heard of anyone using O2 at the surface (unless it was used for medical treatment). i have never even heard it suggested until reading this.

Well, I missed the initial thread because I was totally engaged in something else, so I am just reacting to the last posts.

The use of surface oxygen as a treatment is well known; the use of surface oxygen as a prophylactic measure is less well known, and it is not well documented. It does, however exist, and it exists with some frequency.

To understand the concept, think about both NASA astronauts and U2 pilots. Both risk DCS because of incredibly rapid ascents to extremely low pressures. Both try to mitigate this risk through breathing oxygen for hours before their flights. They want to eliminate nitrogen in their bodies to the greatest degree possible prior to their coming ascent.

In theory, the same would work for scuba diving. If you breathe oxygen prior to an ascent, especially after a previous dive, you should be be better prepared for the next dive. This is not a new idea. The US Navy and NOAA have studied this sort of thing for decades. A little over a decade ago, the then hyperbaric physician in Denver provided our high altitude diving group a NOAA table outlining the use of oxygen for this purpose. It provided a table defining the effects of surface oxygen in reducing pressure groups using the US Navy/NOAA dive tables. (I would like to provide that, but the NOAA web site no longer has it available--or at least I can't find it.) Standard tables show you how pressure groups change over time while breathing air; these tables showed how they changed breathing oxygen. The effect was very significant.

As a technical diver in the midwest, I do technical dives at fairly high altitude (4,600 feet) and then drive home, climbing to 7,800 feet. That includes one unknown already--how do you decompress on a 2.5 hour drive, shaped like a surface decompression ascent, that gradually takes you to a 3,200 foot ascent? We add a second unknown--how does breathing oxygen along the way impact decompression? What at least some of us do is take our oxygen decompression bottle into the front seat with us and breathe it as we drive, for at least an hour. Maybe more.

We wish it were more scientific, but we have failed to get Shearwater to take the one simple software step that would help. As we ascend under water, we tell the computer what gas we are breathing, and it calculates decompression accordingly. On the surface, it assumes we are breathing air, measures the atmospheric pressure, and calculates decompression accordingly. If Shearwater allowed us to tell our computers that we are breathing oxygen instead of air, everything would be hunky dory. We could check our tissue saturations as we drove, but it won't do it, obviously because there is no science behind it.

 

[Scuba Client]

Good point. I should have been more specific. I’m referring to non-deco dives of 100-130’ depth. Diving Nitrox. No more than 32% at 100’ and less than 32% on dives greater than a depth of 110’.

At those depths you should at least have a 3-hour interval, and maybe stop diving for 12-hours if you feel fatigued.

 

[Scuba Client]

Well, I missed the initial thread because I was totally engaged in something else, so I am just reacting to the last posts.

The use of surface oxygen as a treatment is well known; the use of surface oxygen as a prophylactic measure is less well known, and it is not well documented. It does, however exist, and it exists with some frequency.

To understand the concept, think about both NASA astronauts and U2 pilots. Both risk DCS because of incredibly rapid ascents to extremely low pressures. Both try to mitigate this risk through breathing oxygen for hours before their flights. They want to eliminate nitrogen in their bodies to the greatest degree possible prior to their coming ascent.

In theory, the same would work for scuba diving. If you breathe oxygen prior to an ascent, especially after a previous dive, you should be be better prepared for the next dive. This is not a new idea. The US Navy and NOAA have studied this sort of thing for decades. A little over a decade ago, the then hyperbaric physician in Denver provided our high altitude diving group a NOAA table outlining the use of oxygen for this purpose. It provided a table defining the effects of surface oxygen in reducing pressure groups using the US Navy/NOAA dive tables. (I would like to provide that, but the NOAA web site no longer has it available--or at least I can't find it.) Standard tables show you how pressure groups change over time while breathing air; these tables showed how they changed breathing oxygen. The effect was very significant.

As a technical diver in the midwest, I do technical dives at fairly high altitude (4,600 feet) and then drive home, climbing to 7,800 feet. That includes one unknown already--how do you decompress on a 2.5 hour drive, shaped like a surface decompression ascent, that gradually takes you to a 3,200 foot ascent? We add a second unknown--how does breathing oxygen along the way impact decompression? What at least some of us do is take our oxygen decompression bottle into the front seat with us and breathe it as we drive, for at least an hour. Maybe more.

We wish it were more scientific, but we have failed to get Shearwater to take the one simple software step that would help. As we ascend under water, we tell the computer what gas we are breathing, and it calculates decompression accordingly. On the surface, it assumes we are breathing air, measures the atmospheric pressure, and calculates decompression accordingly. If Shearwater allowed us to tell our computers that we are breathing oxygen instead of air, everything would be hunky dory. We could check our tissue saturations as we drove, but it won't do it, obviously because there is no science behind it.

Wouldn't you already be acclimatized?

 

[living4experiences]

These are very interesting posts and I have a basic question, so pardon my ignorance. Where are you getting supplemental oxygen to breathe on a surface interval or at the end of the dive day? Is this something you get a prescription from a doctor and bring it on the boat with you? Do you buy it at a medical supply store? I've heard about the recreational oxygen, like Oxygen Plus and Boost, that comes in a can, but I don't know if that is helpful for diving. All of my diving requires travel by plane, so how would I obtain an oxygen bottle at my destination? I've been hit with skin bends and it's been suggested to me that having pure oxygen on hand would help move the bubbles along, so to speak, so I can off-gas faster on a multi-dive, multi-day trip. I will dive with Nitrox 32% whenever possible to aid in prevention of future hits of skin bends, but I'd love to get ahold of some oxygen to reduce any risk.