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

[UofMI_Divegeek]

/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.

The expressed concern was breathing oxygen enriched air while doing physical labor.

Under normal swimming conditions, the small density difference between air and oxygen enriched air is of no significance. But, under work load, the body is producing abundant CO2. This increases the need to ventilate the increasing amount of CO2.

A denser gas is more difficult to exhale, and the presumed mechanism is decreased ventilation promotes CO2 retention.

 

[inquis]

The camel's back did not break from that straw.

 

[Wibble]

Isn't denser gas harder to inhale -- the chest muscles / diaphragm put pressure on the lungs to blow the gas out; inhaling is more difficult than exhaling.

Or is it just me that can blow a balloon up and not suck as hard?

 

[L13]

The expressed concern was breathing oxygen enriched air while doing physical labor.

Under normal swimming conditions, the small density difference between air and oxygen enriched air is of no significance. But, under work load, the body is producing abundant CO2. This increases the need to ventilate the increasing amount of CO2.

A denser gas is more difficult to exhale, and the presumed mechanism is decreased ventilation promotes CO2 retention.

So, swim 8" shallower any time you are doing physical labor. Problem fixed!

 

[UofMI_Divegeek]

When using a regulator,, inhalation is assisted by the intermediate pressure driving the second stage. Exhalation through the regulator is a tad more difficult
and
the produced CO2 is not inhaled, it needs to be exhaled.

 

[Wibble]

When using a regulator,, inhalation is assisted by the intermediate pressure driving the second stage. Exhalation through the regulator is a tad more difficult

Sorry, not trying being difficult here...

Exhalation is very easy. It's just blowing just hard enough to "pop" the exhale valve on the second stage.

On a rebreather it's just the mushroom valve and "pumping" the gas through the scrubber.

 

[L13]

Along with the fatigue was massive sweating and a mild headache ... the sense of air starvation was extreme.
...
we were doing extreme aerobic exercise which was generating lots of metabolic CO2.
and
the same dive on compressed air did not create the problems we encountered on NOAA I, so the only apparent difference in observed symptoms was the breathing gas.

If the statement that the dives were "the same dive", with the only difference being nitrox/air, is to be taken at face value, and if the reason is accepted as density, then doing "almost the same dive" just 8" deeper on air would have produce the same extreme effects as the original dive on nitrox.

An 8" difference in usable depth due to density between the gasses for any given level of exertion seems trivial. The idea that the difference between a dive with no observed CO2 effects and a dive with extreme CO2 effects is 8" of depth is not credible.

 

[Rollin Bonz]

If the statement that the dives were "the same dive", with the only difference being nitrox/air, is to be taken at face value, and if the reason is accepted as density, then doing "almost the same dive" just 8" deeper on air would have produce the same extreme effects as the original dive on nitrox.

An 8" difference in usable depth due to density between the gasses for any given level of exertion seems trivial. The idea that the difference between a dive with no observed CO2 effects and a dive with extreme CO2 effects is 8" of depth is not credible.

And it would follow that, if such a small change in gas density had such a marked effect, that doing a dive with ANY physical exertion breathing a gas with a density of even 5.2 (air at 110ft) with no observed CO2 effects would seem to be an impossibility

 

[Belzelbub]

And it would follow that, if such a small change in gas density had such a marked effect, that doing a dive with ANY physical exertion breathing a gas with a density of even 5.2 (air at 110ft) with no observed CO2 effects would seem to be an impossibility

Exactly. I vary rarely dive without some level of exertion. I can count on one hand the number of times I've had an air starved feeling. Only need one finger for when using EAN. If the tiny change would be enough to trigger it on a dive with some level of exertion, I'd expect it to happen to me a lot more frequently.

 

[scubadada]

Isn't denser gas harder to inhale -- the chest muscles / diaphragm put pressure on the lungs to blow the gas out; inhaling is more difficult than exhaling.

Or is it just me that can blow a balloon up and not suck as hard?

The work of breathing is greater on exhalation than on inhalation. Here is a flow loop from a breathing simulator. The work of inhalation is 0.33 J/l, the work of exhaling is 0.85 J/l, for a total of 1.18 J/l. The work of breathing goes up at depth and higher flow rates.

Testing is often performed at a range of depths from 132-198 ft/40-60 m and a range of volumes from 1.32-2.65 cu ft/min/37.5-75 l/min.

Latest ScubaLabs reg test - huh?

Is "DACOR" back in business? This is news to me. News to me too. It said the company was West Marine which runs retail stores selling boating items here in the US. They must have bought the name from Mares. From what I remember Dacor was supposed to be Mares budget brand but they really didn't...

scubaboard.com

@tbone1004 has posted a nice way to display this, I couldn't easily find it