What went wrong on your dive today/recently? And what did you learn?

[UofMI_Divegeek]

From my article:

Calculating Gas Density

www-personal.umich.edu

Using ideal gas approximation at STP (standard temperature and pressure)

For 32% O2

Oxygen mass in 1 liter of mix: 0.32 (1.428 g/L) (1 L) = 0.4569 g Nitrogen mass in 1 liter of mix:: 0.68 (1.251 g/L) (1 L) = 0.8507 g ______________________________________________________ Mass of NOAA I mix occupying 1 liter at STP: 1.3076 g Density of dry air at STP = 1.2960 g/L (from CRC Handbook of Chemistry and Physics)

This is a very small difference (0.0116 g/L at STP) which is why I was surprised to hear it might be a factor in our dive.
and
need enough significant figures to see the difference 'cause with 2 significant figures they are the same.

 

[scubadada]

Hi @UofMI_Divegeek

I'm not arguing about your personal experience.

I have had a small number of dives with great exertion in which CO2 retention may have contributed to my perception of shortness of breath. I did as you did, I stopped, rested, and did some deep breathing until I felt better.

 

[UofMI_Divegeek]

For small differences, need more than 2 significant figures to visualize the values.

 

[johndiver999]

From my article:

Calculating Gas Density

www-personal.umich.edu

Using ideal gas approximation at STP (standard temperature and pressure)

For 32% O2

Oxygen mass in 1 liter of mix: 0.32 (1.428 g/L) (1 L) = 0.4569 g Nitrogen mass in 1 liter of mix:: 0.68 (1.251 g/L) (1 L) = 0.8507 g ______________________________________________________ Mass of NOAA I mix occupying 1 liter at STP: 1.3076 g Density of dry air at STP = 1.2960 g/L (from CRC Handbook of Chemistry and Physics)

This is a very small difference (0.0116 g/L at STP) which is why I was surprised to hear it might be a factor in our dive.
and
need enough significant figures to see the difference 'cause with 2 significant figures they are the same.

Thanks, so the difference is less than one foot of equivalent depth.

In other words, the nitrox at 60 feet is lighter than air at 61 feet, correct? So you would have us believe that you observed huge differences in performance with an equivalent depth differential of 8 inches?

Obviously this is silly, you could not replicate the actual depth profiles between two drift dives to that degree of precision. How can you do the math without throwing out your conclusion?

Note, I didn't check your calculations, just assumed you were correct.

 

[CJS]

Not recent, but had a lovely dive at around 35m/115ft and noticed something dangling from my chest D-ring.. My car keys and garage remote control. I’d hung them there when carrying the twinset down to the boat.

Damn and blast. The keys are now trashed and I’ll have to get the wife to drive a spare set over,,, grrrr. May as well complete the dive as there’s nothing I can do.

Had a lovely dive, about 90 mins with deco.

When back in port walked back to the car and without thinking pressed the unlock button on the car key. Well, knock me down with a feather…. The car unlocked!

Somehow the key had lasted over an hour at depth and the deco. That’s a massive hat-tip to Subaru!

The garage remote didn’t work, so I undid it, threw out the battery and rinsed the electronics under the tap. Dried it and left it in the airing cupboard for a few days. Inserted a new battery and voila, it worked!


Wonder what the max depth is for the car keys? No, not going to try it again.

Apart from the resurrection of the garage remote; I have the same story!

 

[UofMI_Divegeek]

Thanks, so the difference is less than one foot of equivalent depth.

In other words, the nitrox at 60 feet is lighter than air at 61 feet, correct? So you would have us believe that you observed huge differences in performance with an equivalent depth differential of 8 inches?

Obviously this is silly, you could not replicate the actual depth profiles between two drift dives to that degree of precision. How can you do the math without throwing out your conclusion?

Note, I didn't check your calculations, just assumed you were correct.

Consider:

The point of my original post (a "war story" from my web site) here was to alert divers to the possibility of CO2 issues WHILE DOING WORK (activities that generate much increased metabolic CO2). Typical recreational diving does not involve (or shouldn't (g) intense physical labor.

The 0.0116 g/L value was at STP, i.e at one atmosphere

Using the ideal gas assumption that density is directly proportional to pressure, the density difference between NOAA I and dry compressed air at 60 ffw can be approximated:

(0.0116 g/L/atm) x (60ffw/34 ffw/atm + 1 atm) = 0.0205 g/L

This density difference is indeed small, but it is not zero.

The fact remains that 2 divers on 2 separate dives while doing intense aerobic exercise in extreme current exhibited symptoms consistent with a CO2 overload while using NOAA I as a breathing mix. The same divers doing a repetition of this dive (using same equipment and same dive plan) did not experience any CO2 issues while using a compressed air breathing mix.

There must be a physiological explanation for this difference in observed fatigue and perceived air starvation.

If the CO2 retention cannot be explained by increased respiratory workload while breathing a slightly more dense gas while doing an intense aerobic activity in extreme current, then what explanation is there?

I should add that this particular dive profile is the only time I have experienced such a profound air starvation event while breathing oxygen enriched air (values from 31 to 38% O2). This event was downright scary ... only time my sense of air starvation was so extreme that I felt a growing urge to spit out the regulator. A sense that went away during rest stops.

Oxygen enriched air (using proper MOD and O2 toxicity constraints) is a wonderful recreational breathing mix. But I believe, based on experience, that oxygen enriched air should not be used in dives with anticipated physical labor or intense aerobic activity.

BTW: river flow under the Blue Water Bridge is ~ 85 million gallons / min with current velocity often exceeding 10 knots (11.5 mph, 18.5 km /hr). So, this is not the typical recreational dive site.

A recent weather channel special on flooding stated that water flow of 10 mph exerts the same pressure as a wind speed of 270 mph.

As I have told my river diving students, "Things are different when you play in a world where exhaled bubbles do move straight up!

 

[Rollin Bonz]

@UofMI_Divegeek

Isn't your position kind of the definition of anecdotal evidence?

Just because it happened to you once, does that mean it's "an issue", especially since it doesn't make much sense, based on the math and experience of others?? CO2 buildup is a known issue, but an increased risk with 32%?? What about all us rebreather divers breathing a mix giving us a constant PO2 of 1.2??

 

[inquis]

If the CO2 retention cannot be explained by increased respiratory workload while breathing a slightly more dense gas while doing an intense aerobic activity in extreme current, then what explanation is there?

Anxiety comes to mind. The density difference is insignificant.

 

[johndiver999]

Consider:

The point of my original post (a "war story" from my web site) here was to alert divers to the possibility of CO2 issues WHILE DOING WORK (activities that generate much increased metabolic CO2). Typical recreational diving does not involve (or shouldn't (g) intense physical labor.

The 0.0116 g/L value was at STP, i.e at one atmosphere

Using the ideal gas assumption that density is directly proportional to pressure, the density difference between NOAA I and dry compressed air at 60 ffw can be approximated:

(0.0116 g/L/atm) x (60ffw/34 ffw/atm + 1 atm) = 0.0205 g/L

This density difference is indeed small, but it is not zero.

The fact remains that 2 divers on 2 separate dives while doing intense aerobic exercise in extreme current exhibited symptoms consistent with a CO2 overload while using NOAA I as a breathing mix. The same divers doing a repetition of this dive (using same equipment and same dive plan) did not experience any CO2 issues while using a compressed air breathing mix.

There must be a physiological explanation for this difference in observed fatigue and perceived air starvation.

If the CO2 retention cannot be explained by increased respiratory workload while breathing a slightly more dense gas while doing an intense aerobic activity in extreme current, then what explanation is there?

I should add that this particular dive profile is the only time I have experienced such a profound air starvation event while breathing oxygen enriched air (values from 31 to 38% O2). This event was downright scary ... only time my sense of air starvation was so extreme that I felt a growing urge to spit out the regulator. A sense that went away during rest stops.

Oxygen enriched air (using proper MOD and O2 toxicity constraints) is a wonderful recreational breathing mix. But I believe, based on experience, that oxygen enriched air should not be used in dives with anticipated physical labor or intense aerobic activity.

BTW: river flow under the Blue Water Bridge is ~ 85 million gallons / min with current velocity often exceeding 10 knots (11.5 mph, 18.5 km /hr). So, this is not the typical recreational dive site.

A recent weather channel special on flooding stated that water flow of 10 mph exerts the same pressure as a wind speed of 270 mph.

As I have told my river diving students, "Things are different when you play in a world where exhaled bubbles do move straight up!

Thanks for the detailed response. I have no good reason to doubt your observations of the differences between two dives. However, I can't get aboard the gas density train as the explanation for this, particularly when we know it would be impossible to control the depths of the comparison dives to the accuracy necessary to potentially elicit a difference.

So what reasons?

• Maybe the later dives, the divers were more accustomed to the current and didn't do the same unwise activities (to the same intensity anyway) of the earlier dive with nitrox.
• Perhaps there was a contaminant in the nitrox gas.
• Perhaps the current velocity on the different days was not identical
• Perhaps, and I wonder about this...that the higher oxygen level (of nitrox) PROMOTES co2 retention because the body does monitors both oxygen and co2 levels. Even though we know co2 monitoring (via blood gas ph maybe?, I forget) is the primary stimulant for breathing, perhaps the higher pp of oxygen reduces this stimulus to a small degree and allows the body to initially withstand a higher co2 level for a short period of time with a reduction in the stimulus to breathe, and this delays the need to "keep up" and eventually results in a problem? I have felt something like this when freediving and when in shape - once I get down to 60 feet or so, it often feels like I can stay for a while with less urgency to ascend or breathe, compared to a 25 ft dive. I always wonder if this (subjective perception) was due to the high pp of oxygen at greater depth. Anyway, that idea is something I have wondered about from a lot more anecdotal information than you have seemingly relied upon.

I have no doubt that you and your buddy screwed up, over exerted yourselves (possibly by trying to stay together) and then had a co2 build up. I just see no plausible reason to claim that the difference was associated with miniscule differences in gas density associated with oxygen content. I'm pretty familiar with drift diving, so I know how it can be strenuous.

 

[L13]

Thanks, so the difference is less than one foot of equivalent depth.

In other words, the nitrox at 60 feet is lighter than air at 61 feet, correct? So you would have us believe that you observed huge differences in performance with an equivalent depth differential of 8 inches?

Obviously this is silly, you could not replicate the actual depth profiles between two drift dives to that degree of precision. How can you do the math without throwing out your conclusion?

Note, I didn't check your calculations, just assumed you were correct.

/s
Always swim 8" shallower than you otherwise would on every dive, and you will never have a CO2 hit.
/s

@UofMI_Divegeek how did you ensure that your dive profile on the air dive stayed withing 8" of your nitrox dive?

If you didn't, then that is at least as likely an explanation as the gas change to one less dense by the equivalent of 8" depth.