Riding out a storm, sealed up tight down below. Watch out for CO2.

[Cpt Pat]

Originally Posted by StuM

So it's very much a situation of dangerous levels of both CO2 and O2 go hand in hand.

As a pilot who flew skydivers to 12,500 feet several times a day in an unpressurized airplane, I became very familiar with hypoxia. The insidious thing about hypoxia is - the symptoms are actually pleasant: mild euphoria, a feeling of relaxation and comfort, and becoming detached (gee, flying sure is fun - I wonder who's flying the plane?).

Fly a little higher, and your color vision is diminished to the point that it appears you're flying in a black-and-white movie. Thinking becomes extremely labored. I'd do simple math, like fuel consumption calculations, and when I could no longer do simple multiplication and division, it was time to put on the O2 mask and open the tank valve. (Provided you weren't hypoxic for very long, recovery is nearly immediate.) Individual symptoms vary, but mine are fairly typical.

My point is: you can't count on any unpleasant symptoms to detect hypoxia. As others have pointed out here, there are unpleasant symptoms such as anxiety and hyperventilation that accompany too much CO2, but if there are major distractions - like getting bounced against the cabin walls and overhead - you may not recognize those symptoms for what they are. Wanting to open a hatch may be mistaken by crew members as a panicked desire to escape the cabin. It's important to understand what's going on.

On a separate topic: I don't know how climate change got into this thread. I suspect some posters are attempting to politicize the discussion. It's a vitally important but very separate topic. The ambient CO2 level today was a little over 400 PPM (it'll only go higher as time goes on), but that level is nowhere near being toxic or causing any known cognitive effects.

[john61ct]

Yes and I certainly avoided any mention of CO2 toxicity being an issue. Getting that idea from the excess greenhouse gasses issue is just silly, and never imagined anyone here would conflate CO2 with CO or anything else.

Just that if someone as clued in as Cpt Pat was concerned about low O2 levels - in and of itself whatever the cause - in that context, I would not just dismiss that concern out of hand, nor discourage installing a sensor, assuming the other more common sensors were already deployed or planned anyway.

[Singularity]

Originally Posted by Cpt Pat

As a pilot who flew skydivers to 12,500 feet several times a day in an unpressurized airplane, I became very familiar with hypoxia. The insidious thing about hypoxia is - the symptoms are actually pleasant: mild euphoria, a feeling of relaxation and comfort, and becoming detached (gee, flying sure is fun - I wonder who's flying the plane?).

Fly a little higher, and your color vision is diminished to the point that it appears you're flying in a black-and-white movie. Thinking becomes extremely labored. I'd do simple math, like fuel consumption calculations, and when I could no longer do simple multiplication and division, it was time to put on the O2 mask and open the tank valve. (Provided you weren't hypoxic for very long, recovery is nearly immediate.) Individual symptoms vary, but mine are fairly typical.

My point is: you can't count on any unpleasant symptoms to detect hypoxia. As others have pointed out here, there are unpleasant symptoms such as anxiety and hyperventilation that accompany too much CO2, but if there are major distractions - like getting bounced against the cabin walls and overhead - you may not recognize those symptoms for what they are. Wanting to open a hatch may be mistaken by crew members as a panicked desire to escape the cabin. It's important to understand what's going on.

I'm sincerely grateful to your posts...many/most have taught me something useful. I'll try to reciprocate, but you have to meet me half way. I don't mean to denigrate, be superlative, whatever. We've both experienced hypoxia at altitude while piloting, presumably both have taken chamber flights, and perhaps both have gone through PROTE (sea-level/normobaric hypoxia simulation in a tent) training.

What you do not seem to appreciate, and what I am apparently unable to adequately explain, is that what causes the somnolence, poor decision making, stupor, incapacitation process in an airplane cabin at altitude will not occur in a boat. The physiologic processes involved are different such that you cannot extrapolate one experience to another. Just like I can't sit on a couch breathing ambient air at 40k feet and survive, you cant extrapolate your aviation hypoxia concern with sea-level gas concerns.

For purposes of teaching symptoms of the hypoxia associated with flight, PROTE does a good job. But let's review how it works.

In a PROTE tent...the tent (say at sea level) has gas concentrations just like outside the tent. The students then go into the tent, have a seat, oxygen masks nearby. The operator then starts pumping in extra nitrogen into the tent, effectively lowering the % of air that is oxygen. The operator does nothing per se with C02, so C02 levels ~basically stay the same during the test (save for what the students have produced in the tent...minuscule production during the duration of the demonstration).

As the oxygen level in the tent decreases...because of too much (benign) nitrogen added by the operator...oxygen uptake in the blood of the student begins to fall off. Cognitive function begins to decline. There is no onboard/natural signal to the student that there is a problem. Without intervention, the student will pass out. QUITE analogous to the "free diver pass-out" thing where there isn't sufficient C02 onboard to say "hey dummy, we've got a problem here" before oxygen is too low to stay awake. The free diver will pass out. If you left them alone at watched them....you'd see in a few seconds/minutes them starting to gasp underwater. The gasping (~~agonal breaths) created by the elevated C02. Same at 22,000 feet...no elevated C02 to let you know there's a problem...you pass out...teaching the lesson of PROTE training.

But what if we ran PROTE differently. Let's say that we simulate your boat cabin in a storm scenario. First, we have to agree that the only dominant gasses in the cabin are nitrogen, oxygen, CO2. Next, we have to agree that really, the only thing that changes while in the cabin, is the conversion of 02 into CO2 and H20. No other funny gasses, and really nitrogen sort of stays stable. So if THIS TIME in the tent...we start with normal concentrations of all gasses, but instead of displacing oxygen with nitrogen...if instead we use CO2....this is what happens. In short order, the place smells like an azz factory. Very quickly. You get nauseated, feel pukey, anxious, feel like you are smothering, and you will start gasping for air even if you don't want to (it's an automatic nervous system thing). This is over a few minutes in a PROTE theoretical experiment.

In real life in a boat, the picture would look like the average "submariners suck on the bottom" scenario. No one going ape$hit within minutes because of gasses. Just a long, slow, painful, miserable suffering death. After 12-100s of hours (depending on the size of the compartment) people getting more and more anxious, sweaty, pukey, headache, psychotic, despirate, gasping, more gasping, bloodied hands, Lord of the Flies type picture.

The evolution of this situation is in no way analagous to having your cannula pinched at 18k while flying your turbo Senaca. It's just not.

In most simple terms...the CO2 'get fresh air now' drive is the most primal/strongest urge known to man. In a boat, you would have to resist this for a day or more before things reached a critical level. It stands to reason that if you somehow have the ability to willfully ignore the urge to breath for 36 hours that an alarm saying "hey, open a window" isn't going to help.

What should be said, not in a context of sensors, is that stale air exacerbates seasickness, could contribute to people's migraine frequency, etc, etc, etc. But the "sensor" and "asyphyxiation because of consumption" aspects of things are just not science-based at sea-level and serve no other function than to reinforce fear of something lethal where non exists.

[Buzzman]

Air-Only Dorade – Air-Only deck ventilators

[Don C L]

Originally Posted by Buzzman

Air-Only Dorade – Air-Only deck ventilators

Hey, for a second I thought someone had stolen my idea! They may be ok, but they won't seal up when inverted, in fact the opposite.

[Franziska]

For a practical approach, see what Sven Lundin did on his micro cruisers for this.

Very small volume, two people on board. Very seaworthy despite the size. Surely he has a clever solution.
Just Google him.

[Cpt Pat]

Originally Posted by Buzzman

Air-Only Dorade – Air-Only deck ventilators

Great idea... as long as you don't think about it. The balls will float in the open position if the boat is inverted or heeled past 90 degrees - gravity being what it is.

This is a really old issue with dorade vents. The problem is described well in: "Desirable and Undesirable Characteristics of Offshore Yachts," page 108, published in 1987.

Here's a science experiment: Take an empty water bottle with its cap removed, and plunge it inverted into water, cap end down. Very little water enters. This simulates a well-sealed boat that is perfectly inverted (in the real world, one hopes the boat doesn't stay in that popsition). Now, while keeping the cap end immersed, rotate the bottle 90 degrees so it sits sideways in the water (simulating a knockdown or entry/recovery from being inverted). What does the water do now?

That's the problem with dorde vents. The 32-year-old book sited above recommends having a threaded cap to seal dorades from below. In my case, all we had was a towel to stuff in the opening from below, which is better than nothing.

Dordes are great at keeping spray out, and even water out from boarding seas. They are not great at keeping water out when immersed on a boat heeled past 90 degrees. The whole air/water separation scheme depends on a normal orientation of gravity, i.e., the boat being right-side-up.

In my opinion, from a storm survival standpoint, and ordinary cowl vent is safer, provided the cowl can be removed and replaced with a tight fitting cap. Of course, it's far safer yet to not find yourself in a storm in the first place.

[john61ct]

https://beta.washingtonpost.com/business/2019/06/06/why-crowded-meetings-conference-rooms-make-you-so-so-tired

[hellosailor]

This is how the Vikings became such great sailors. In open longboats with no closed cabins, they never had a CO2 buildup problem.

I wonder if the good doctor ever used his meter while on a commercial aircraft?

[john61ct]

https://inspectapedia.com/indoor_air...ide-Levels.php

https://journals.sagepub.com/doi/abs...20326X18793997

[hellosailor]

Don't tell the airlines about that! They'll charge an extra $44.95 for supplying a tank of OSHA-compliant breathable air from now on. (Free of charge in business deluxe class.)

[GordMay]

10 Tips for Home Indoor Air Quality - ASHRAE ➥ https://www.ashrae.org/File%20Librar...op10forIAQ.pdf

[Checkswrecks]

Originally Posted by john61ct

https://inspectapedia.com/indoor_air...ide-Levels.php

The conclusions with my underlining about airlines were:
"Carbon dioxide levels measured in-flight in the aircraft cabin ranged between 0.04% or 400 ppm and 0.1% or 1000 ppm to date in our studies and were measured at close to 0.5% or 5,000 ppm in earlier studies."

"As indicated at CO2 HEALTH EFFECTS, occupants are unlikely to be affected or to notice CO2 levels under 2% or 20,000 ppm - a far higher number than in-flight aircraft cabin carbon dioxide levels."

Airlines sure don't have CO2 as a problem and these conclusions just verify what are well documented and known in the airline industry. The cabin air is completely changed every third minute or more so there's no chance for CO2 build-up or even the dreaded sharing of farts. [A phrase used to tease newbie flight attendants.]


and

"Opinion: Perhaps to investigate or reduce air traveler complaints of dizziness or fainting we should look more closely at altitude and cabin pressures as well as other factors such as passenger hydration (drink plenty of fluids), anxiety, physical stresses before the flight (rushing, carrying bags), passenger movement & stretching during flight (avoid blood clots), the increasingly cramped seat space limitations and cramping, and aircraft cabin ozone levels."

Also well known is that the real problems are dry air, cabin altitude, and lack of movement. It's so well documented that it's the reason why the 787 and A350 designs were changed to provide passengers with lower cabin altitudes and higher humidity.

So unless they are trapped at the bottom of the ocean like in the 1970s movie, let's just leave aviation out of the discussion.

[Cpt Pat]

Follow up: After a month of having a CO2 monitor on board my 26 foot sloop: the CO2 reading when I enter the cabin is 440 PPM, which is very close to the CO2 concentration measured in Hawaii (https://www.co2.earth/daily-co2) and well within the stated accuracy of the meter. The CO2 level begins to rise immediately when I'm in the cabin. With the companionway hatch open but no air movement in the cabin, it rises rapidly to 800 PPM if I'm just lounging around, and peaks around 1,300 PPM if I'm doing anything active.

When I experimentally sealed up all the hatches and vents and just sat still, it rose to 3,300 PPM in 120 minutes before I became uncomfortable and stopped the experiment. (I turned the meter around so I couldn't see it during the experiment.) With normal ventilation, the C02 reads 600-650 PPM when I first wake up, and then rises to 800 PPM once I'm up and awake.

This is with only myself aboard. Presumably, the CO2 concentration would rise to twice those levels (minus the 440 PPM ambient) with two people on board.

In a storm, with the hatches and vents sealed, I presume the space could not support more than four very anxious - and cognitively impaired - people in the cabin for any length of time without some form of ventilation.

[GordMay]

At the activity levels found in typical office buildings, steady-state CO2 concentrations of about 700 ppm above outdoor air levels indicate an outdoor air ventilation rate of about 7.5 L/s/person (15 cfm/person). Laboratory and field studies have shown that this rate of ventilation will dilute odors from human bioeffluents to levels that will satisfy a substantial majority (about 80%) of unadapted persons (visitors) in a space. CO2 concentrations in outdoor air typically range from 300 to 500 ppm.
Thus indoor CO2 concentrations of 1000 to 1200 ppm, in spaces housing sedentary people, is an indicator that a substantial majority of visitors entering the space will be satisfied with respect to human bioeffluents (body odor/farts).
Note however that CO2concentration is not a good indicator of the concentration and occupant acceptance of other indoor contaminants, such as volatile organic compounds off-gassing from furnishings and building materials. Thus CO2concentration is not a reliable indicator of overall building air quality.