Oxygen Candles: Providing Emergency Air | Hacker News Reader

Oxygen Candles: Providing Emergency Air

minearc.com

323 pointsthunderbong138 comments

This website has claims falsely that oxygen tanks need co2 scrubbers and candles don’t. That is not true and can get people hurt!

You need co2 scrubbers for any oxygen producing solution, since co2 kills faster than o2 scarcity.

Having a candle, and just a candle alone in a hermetically sealed room will result in suffocation as fast as without it.

I reported the post as it contains false and dangerous info.

Is there such a thing as a portable c02 scrubber - other than a plant?

Yeah -- soda lime, etc. e.g. https://minearc.com/remove-co-co2-in-refuge-chamber-chemical...

Are there solutions for CO2 scrubbing that use electricity and can run indefinitely, rather than chemical substrates that get used up and require replenishing?

Yes, but the context of this post was emergency systems which are purely chemical.

For routine operations on e.g. a submarine, https://www.naval-technology.com/contractors/materials/atmos...

As other people have mentioned, this is a great introduction to the topic: https://www.youtube.com/watch?v=g3Ud6mHdhlQ

While probably not as applicable on Earth, the ISS CO2 scrubbers use a chemical substrate that is then exposed to space where the CO2 is sent off.

https://www.eni.com/en-IT/scientific-research/space-free-co2...

It looks like Monoethanolamine (MEA) can be reused after a regeneration cycle. Of course, you will need somewhere to dump the CO2.

https://en.wikipedia.org/wiki/Ethanolamine#Gas_stream_scrubb...

Soda lime can also be used after a regeneration cycle. If you heat it sufficiently it releases the CO2 again.

Sure. The trick is that there are regenerative chemical substrates. The material absorbes co2, gets saturated, cycled to a different part where it is heated and releases the co2 and can be used to capture again. If you use electricity to do the heating and cycling you have exactly what you asked for.

On the other hand these units are usually not small or portable. Here is a press release from a manufacturer: https://www.naval-technology.com/contractors/materials/atmos...

One method if you have enough electricity is to capture some amount of air from the room, compress and/or refrigerate it until the various gasses liquefy (they each liquefy at a different temperature/pressure), and drain off each liquefied gas that you want to separate into its own container.

At least, that's how the CO2-filtering device described in The Martian worked. I'm not sure if anyone uses that system in real life. Apparently on the ISS they use filters made of zeolite[1]. From that article though it didn't say if the filters were reusable. If they are, maybe just using filters is good enough for quite a long time.

[1] https://www.syfy.com/syfy-wire/nasa-launched-an-upgraded-co2...

The zeolite filters are regenerated by heating them, which causes them to release the captured CO2. This is obviously done in a sealed chamber so that the CO2 can be captured or vented overboard.

Remember the talks about DIY Oxygen concentrators during COVID emergency days, using two pipes filled with zeolite beads alternatingly pressurized from pumps and valves so to separate Nitrogen in the air and leaving Oxygen in the gas? Apparently the same Pressure Swing Adsorption principle is used to extract couple other gases as well, and CO2 is one of them.

Yes. There is a soda lime canister integrated into the design of anesthesia machines.

And plants are not viable as CO2 scrubbers on small scales. It takes a lot of plants to scrub the CO2 exhaled by a single human - somewhere on the order of 10 full-size trees!

This would make for a lovely mine if you had 10 full size trees inside it.

minecraft intensifies

Single human produces around 1kg of CO2 per day: https://www.sciencefocus.com/planet-earth/how-much-does-huma...

Seems that algae are up to 400x more efficient at CO2 scrubbing than terrestrial plants. See: https://newatlas.com/environment/algae-fueled-bioreactor-car...

No idea though if such bio-tanks are a viable solution in a rather devoid of solar light shelters.

Plants are generally net neutral in CO2 consumption. They consume CO2 during the day, but when not producing energy through photosynthesis, they consume O2 and produce CO2 for their cellular respiration.

The net effect is generally, plants release similar amounts of CO2 at night as they consume during the day. The exception here would be plants that use Crassulacean acid metabolism for photosynthesis, which would be a lot of your arid native plants.

I would expect plants to be CO2 negative while growing since they're using the carbon to add to their dry mass. Once fully grown I'd expect the plants to be roughly neutral.

Yes, e.g. if you look at "rebreather" diving equipment, it's essentially a backpack life support system, including CO2 scrubber.

Wasn't that one of the things Apollo 13 had to figure out how to rig up in order to survive?

I don't see where it claims that.

They point out that piped air is one option (which is basically continuous open circuit in these settings; exhausting to outside.). The alternative is oxygen cylinders mounted on the chamber (or inside the chamber), which (generally) require scrubbers.

Oxygen candles are then mentioned; they are essentially a nearly direct replacement for oxygen cylinders, but with somewhat better storability. It is silent on whether co2 scrubbing is needed, but obviously would in the same settings oxygen cylinders would.

"A candle is an entirely independent source of oxygen from within the refuge chamber. In this way, it’s isolated from common faults found in the other sources:

Compressed Air: The feed can often be compromised during an emergency due to damage to the circuit or carbon monoxide contamination requiring the chamber to be isolated."

The candle is not isolated from the common fault of carbon monoxide contamination. Both Oxygen candles and oxygen cylinders will generally require scrubbers.

I think you are mixing up carbon monoxide contamination and carbon dioxide build up.

They mean that with oxygen candles you don't risk having your very oxygen reserve introduce carbon monoxide in the air you breathe, as it could happen of you have a contamination at the source of compressed air.

Okay, ignoring carbon monoxide contamination. The site also states: "Oxygen cylinders are used in the event compressed air fails and generally require the support of a scrubbing system to remove carbon dioxide and carbon monoxide from the air."

If Oxygen cylinders generally require a scrubber I think it's safe to assume that a Oxygen candle will also need a scrubber.

They list issues with other systems but don't acknowledge the same problems that exist with their own.

Oxygen candles smell bad. I would never want to use one except in an emergency situation. No scrubber necessary if I’m just evacuation.

> in a hermetically sealed room

I thought these chambers have pressure-triggered relief valves and rely on elevated pressure in the chamber to force air out? Basically dumping some of the existing air/gas in the chamber which carries away some CO2 with it.

Yeah, unless you need to stay silent for detection reasons or warfare, my guess would be that in a fixed facility, it would be way cheaper and reliable to have a positive pressure or flow of air going outward. I've seen windows and buildings do this completely passive, so a modern design would only have this as an absolute emergency, as they are dangerous and doesn't solve the Co2 problem.

Don't see how this is relevant for civil use though, but hey, maybe some paranoia can sell some candles.

I disagree, for contextual reasons. Oxygen candles are an emergency safety supplies item for people who get serious training in industry- and facility-specific safety procedures. Notice the slant to the headings, language, photos, etc. on the page. This is very clearly not a consumer product, and phrases such as "Used as the last means of breathable air within a refuge chamber..." really don't suggest "try this at home, kids!".

But there is also an oxygen candle above every seat in passenger airplanes, right? Then it would be a consumer product ...

I think that's stretching the definition of consumer product to the point of losing its usefulness. A lot of (semi-)automated emergency tech contains seriously dangerous stuff, like explosives or highly toxic materials, and these devices are usually very carefully engineered to keep the risks from using that tech acceptable even under emergency circumstances, and risk tolerance tends to be a lot higher for a device meant to be used in a decompressing plane in the first place. You can't use that oxygen candle outside such a situation, and you can only use it through the extremely constrained user interfaces provided by the yank switch and mask.

Ok fair. I just thought that it proved that they could be made safe. I now realize that emergency situations have very different tolerances for safety.

This.

Similar - a residential electrical service panel. It's generally okay for even a little kid to flip a wall-mounted light switch. Touching the circuit breaker handles on the service panel is a "competent adults, paying close attention, only at need" activity. And digging inside that service panel should only be done by professionals.

>Touching the circuit breaker handles on the service panel is a "competent adults, paying close attention, only at need" activity.

Kindly screw off with the FUD peddling.

You should be able to flip breakers all you want without doing anything more than annoying people by interrupting whatever those breakers were powering.

A breaker panel is designed so that you need to get out a screwdriver and remove fasteners to get near anything that might hurt you.

Unless someone is actively working on a circuit <insert a bunch of low effort comments about the virtues of lock out tag out here> you shouldn't be able to hurt anyone or anything by flipping a breaker on or off. Breakers protect the wires. Devices are responsible for their own protection. Incomplete circuits get capped to prevent shorts to ground or elsewhere.

At small scale, either living alone or with a few other responsible adults, you're pretty much correct.

But you've never had grandkids who got interested in playing with the breaker panel, have you? Nor almost gotten yourself electrocuted, when you trusted a "not quite so sharp as they once were" older relative to turn off the specific 20A circuit that you were working on?

Also worth noting - residential circuit breakers, even new (vs. decades-old plastic that's getting kinda brittle) are often rated for vastly fewer on/off cycles than even the crappiest old wall-mounted light switch.

I agree, kids and senile seniors should be kept away from the breaker panel.

But that wasn't your original assertion, stop moving the goal posts.

Well, if you're working on the wires, lightswitches can be just as dangerous as breaker panels.

Don't ask incompetent electricians to help you with electrical work. Check!

> lightswitches can be just as dangerous as breaker panels

That's very much not the case. A light switch, at least in the US, is just 120V. Sure, it could kill you, but 99.999% of the time it'll just annoy you if you touch the hot wire inadvertently. You can easily get 240V inside the panel, however, and on top of that you can easily get it at 200A. I'm a lot more careful when I've got the panel cover off for any reason.

There isn't 240V to ground, which is the usual path for shocks. To get 240V through your body, you'd need to touch two hot wires at the same time. And you feel it when you touch the first one, so I think this is rare. You should be working with one hand most of the time.

The 200A is a danger. A direct short from a bus bar to ground can peak at 1000s of amps before the main breaker blows.

True, and of course it only takes a small fraction of one amp to cause harm to a human, if the path of the current crosses your heart or lungs.

240V at 200A would burn you crispy, but it's a bit challenging to get to.

120V at a fraction of 1A can disrupt/stop your heart, and it's easy to get inside a service panel.

OK, but no one is talking about working on the inside of panels.

It's been clear throughout the thread, but yes -- don't open breaker panels and work on them casually.

Flipping a breaker in a closed, code-compliant panel is exactly as safe as flipping a lightswitch in a closed, code-compliant wall box.

> OK, but no one is talking about working on the inside of panels.

I must have misunderstood, then -- you said light switch wiring is as dangerous as breakers, and breaker wiring can only be found inside the panel.

It won't be particularly rewarding, but if you go back through the history you will see the full context.

It involves the safety of requesting an inexperienced person to flip breakers.

Sure, I get that. But the wiring in a panel is just as hidden as the wiring of a light switch.

This was exactly my point. :)

>A breaker panel is designed so that you need to get out a screwdriver and remove fasteners to get near anything that might hurt you.

you hope.

zinsco breaker panel boxes are still commonplace in the united states on older properties; they require no fasteners to open up and are (mostly) bussed in such a way that they're extraordinarily dangerous when open.

Still, I agree with the spirit of your message -- but let's be clear, household electrics are dangerous, and not every breaker panel is going to be designed with safety in mind.

Some Zinsco panels do require fasteners.

The faultiness of Zinsco panels are not a special concern with flipping the breakers. They're just faulty. And you don't even need to open them to be dangerous, they have corrosion and heating problems.

> not every breaker panel is going to be designed with safety in mind.

Well, to be fair -- of course they were designed with safety in mind. They just failed.

But yes, replace any Zinsco panels! Also some Federal Pacific and Challenger/GTE-Sylvania panels. This should be caught in a home inspect, and most home insurance companies will make it a requirement of coverage.

Two of the last three houses I've lived in had front panels that no longer fit, so you needed to take care when operating the breakers. In the older one, we tripped a breaker and about half the lights in the house went out. I went hunting for it and eventually went to flip off the main to start a more thorough check, only to find that is what had tripped, leaving half the house on... About half my 120 and all my 240 breakers were wired direct to the bus bypassing main. I'd love to hear a pro's stories. I bet they see really weird and terrible stuff.

FWIW: Poorly-fitting panel covers would never pass an inspection and are inherently dangerous. It's really important for the panel to be enclosed. Humidity, dust, vermin, and fingers get in. Sparks get out. Your home insurance would be worthless in case of a fire. Never mind the risk to irreplaceables.

But re: tripping the main -- this is likely a fault in the breaker itself. It's not likely that a faulty line breaker allowed enough current to trip the mains breaker (though it does happen, but see below). Of course several overloaded lines can trip the mains, but this is exceedingly rare. A fault in the mains breaker is a serious problem for sure. However, unless you inspected the wiring yourself, I'd hesitate to assume that it was miswired as you describe.

In standard US residential service, you get two 120V lines ("legs"). If the mains breaker failed, it's possible to lose one of those legs to the buss that supplies the line breakers (and the house fixtures), while the other leg stays up and powering the "other half" of the house. In this case, 240V appliances will appear to be "out" because they are only getting partial power (240V is really just two 120V services, 180degrees out of phase).

So I'd guess the cause was a failed/fatigued mains breaker. That's a job for an electrician, regardless, who would surely notice miswiring if present, and the other code violations that you definitely had.

The inspector did fail it, and has failed every house I've ever had inspected. The inspectors for my buyers also failed it. People just kind of live with it on old houses. Never thought about it making an insurance claim fail. So the main breaker only turns off one leg? Why wouldn't you have one for each.

The mains breaker controls both legs, but they are separately protected. So if a protection sensor fails, it might only interrupt one leg. The switch controls both legs though.

I've done a lot of electrical work in old houses, but only in big cities where a failing inspection is just not tolerated. I've seen old country homes where regulation is ... less strict. This might not be an urban/rural divide, but that's my experience having lived in both.

I'm amazed that you were able to buy or sell a house that did not pass inspection. If the buyer was financing, the mortgage would require insurance, which would require inspection. In a cash sale, the buyer should be sophisticated enough to take responsibility for the repairs.

I think (in my high-regulation states) it's actually not legal to sell a house that does not pass a safety inspection. At least not without surrendering the certificate of occupancy until repairs are completed and inspected.

These houses have all been in the DFW metroplex, so low regulation TX. The people that bought the terrifying breakerbox had a first time homeowner loan and the lender complained about some of the vegetation being too close to the house, but somehow the box was ok. I turned the main breaker on and back off, and half the lights were still in. Weird one. All the outlets that had a ground hole were actually grounded, most of my friends have houses with fake grounds, knob and tube or worse, aluminum wiring. Regulations are sometimes a good thing. Its probably why our houses are cheaper though.

Couldn't it also be a really old style of panel without a singular main breaker, either falling under the "rule of 6" or perhaps dating from before it?

> Touching the circuit breaker handles on the service panel is a "competent adults, paying close attention, only at need" activity.

This is not accurate.

Circuit breakers are just lightswitches with the ability to switch themselves OFF.

The larger breakers (you mention "handles" instead of "switches") are the same, although rated for higher current than typical household lightswitches.

The breaker panel is just a grounded metal box. It is not dangerous to touch, except in fault cases where the whole building has dangerous power.

And just like you should not unscrew a lightswitch cover unless you know what you're doing, you should not unscrew a breaker panel cover.

Same rules -- but if you break them, the difference becomes important: Inside the breaker panel, it's possible to come into contact with higher current sources than inside a lightswitch box.

A breaker has bare live metal exposed inside that will shock you if you touch it. Maybe newer designs don't, but mine does.

Right, just like a lightswitch. But in both cases, only if you open the protective enclosure with a screwdriver.

Mine has no such enclosure, just a door that takes no tools to open.

That might be a 1960s-70s-era Zinsco.

If so, you should get it replaced right away. Easy access to the internals is the least of your concerns -- these panels are unsafe as designed, and responsible for much fire and death.

Yikes! Did this pass an inspection like that? I'd highly suggest moving this higher up on the TODO list. Whether its a panel that needs replacing or just a cover needs to be replaced, it should be corrected. Please, don't become a statistic! </randoInternetNanny>

I have no idea when's the last time an inspector saw this place. It's a mobile home manufactured in the 60s so a lot of lax code is probably grandfathered in. The panel is too high and out of the way for a child to reach and I'm smart enough not to touch it. I imagine whoever I sell the house to is going to demolish it anyway.

In other words, contemporaneous with the Chevy Corvair, and pre-dating most modern safety regulations.

Hey! I liked my Corvair. I learned how to drive in a Corvair. It was also the car father/son project where I learned I had no interest in being a grease monkey.

You're right, but given that some people subject their breaker boxes to amateur fiddling, leaving loose or missing covers and poorly done wiring, I sympathize with his point. I wouldn't send a kid to flip a breaker unless it was my own house and I knew the breaker box was safe. I realize that in theory a light switch can be unsafe just like a breaker box, but in practice, I would never worry about sending a kid to flip a light switch.

Fair enough. I would never live in a house that had sketchy service panels, and in an unknown/presumed-dangerous environment, I'd never send an inexperienced person to mess with service panels (or lightswitches) I hadn't inspected myself.

The oxygen generators in an aircraft are only designed to provide emergency oxygen if cabin presurization is lost, until the pilots can descend to breathable atmosphere (under 10,000 ft). I.e. maybe 10 minutes or so. There will be no dangerous accumulation of CO2 in that time, hence no need for scrubbers.

If cabin presurization is lost, there will be no dangerous accumulation of CO2 period, because it leaks out through the non-airtight seal between the oxygen mask and your face. The emergency oxygen is more about providing a breathable partial pressure of oxygen (~0.2 atmosphere IIRC) when the total pressure is much lower than sea level, by greatly increasing the concentration.

People get surgery every day, does that make the surgical instruments that are used, consumer products?

No. Sorry I was wrong.

Jesus, I swear I haven't heard anyone say that on the internet in over a decade. Unironically, thanks.

See https://en.m.wikipedia.org/wiki/Emergency_oxygen_system for details on the two types of systems used (not an expert, just duck-ducked it out of curiousity). Yes - there is (sometimes) an oxygen candle above each seat. Does that make it a consumer product? I'm not sure and no opinion on that aspect, I mainly included the link for those interested in how they work. To coin a phrase 'Now I know'.

By that reasoning the chemical explosive inside a car's airbag is also a consumer product. Same for toxic carcinogenic rhodium found in catalytic converters. I could go on.

Just because something in a consumer product does not mean that thing, by itself, is a consumer product. Or at least us using the term "consumer product" is stretched near the breaking point if you look at things that way.

Yes. Sorry I was wrong.

The page doesn't technically say that candles don't require scrubbing. Candles also require scrubbing. But the disadvantage is omitted from candles, while explicitly presented for cylinders:

"Oxygen cylinders are used in the event compressed air fails and generally require the support of a scrubbing system to remove carbon dioxide [...]"

Oxygen cylinders are also used as an emergency non-consumer product. The comparison is a misleading one.

This is correct. A person in a hermetically sealed suit will die of CO2 poisoning a long time before Oxygen deprivation. However in most mines, they will engineer gas permeability so that CO2 and other poisonous gasses can seep to areas with lower concentrations and out of the mine. Coal mines seem to be particularly bad with regards to permeability.

In this case, an Oxygen candle _MAY_ be enough to keep people alive. However, why O2 tanks would need scrubbers and candles wouldn't doesn't make any sense.

https://www.hindawi.com/journals/ace/2018/3976505/

https://www.cdc.gov/niosh/mining/works/coversheet1621.html

Just so we're all perfectly clear, this one poster got upset about this website and reported it for misleading information and this is now the top comment.

The company sells an air scrubber: https://minearc.com/products/air-quality-management/life-sup...

I love this place.

False and dangerous to whom?

Anyone in a position to be using oxygen candles or bottled oxygen in a survival shelter setting is likely to have had safety training in how to use them, and if it is a situation where CO2 concentration is likely, that should have been accommodated in the construction of the refuge or shelter.

> You need co2 scrubbers for any oxygen producing solution, since co2 kills faster than o2 scarcity.

Given their uses are the space station, planes and submarines, cant you just vent some of the atmosphere out since you're in a pressurized tube of some kind to lower the CO2?

It's far too expensive to launch new material up to do that. It's much better to scrub out the CO2 specifically than to throw out mixed gases. If you're just removing CO2 you only need to replace it with new oxygen which can be electrolicized from water stores but if you're tossing out cabin air in bulk there's stuff like nitrogen that's harder to replace. The ISS is basically sea level air with 21% O2 and the rest nitrogen plus trace CO2 and other gasses, that nitrogen would be much harder to replace.

With hydrolysis you just have waste Hydrogen to toss which could in the future be combined with CO2 from the scrubbers to create methane fuel (probably not in significant quantities but it closes the cycle on O2 as the Sabatier reaction also creates H2O which could feed back into electrolysis or drinking.

Smarter Every Day did an interesting series of videos about nuclear submarines.

They use these candles to help replenish the oxygen in them: https://www.youtube.com/watch?v=g3Ud6mHdhlQ

I just watched that today! Super interesting set of videos. I highly recommend watching them.

Most interesting part for me was the basically continuous education aspect for everyone on board, as well as the very frequent drills. I guess a combination of keeping people educated/trained and avoiding idleness in such an environment for months at a time.

I'm kinda torn on this. On one hand it's super interesting, on the other it's state-sponsored army propaganda series, luring in young Americans, painting everyone in service as a hero.

Oh no, a clearly labelled piece of entertaining advertisement, how awful.

Also... even these show how difficult life on a submarine is (and the ultra-wide angle used most of the time shows how extremely claustrophobic everything is). Not exactly appealing. It takes some very special people to do this kind of job, and I doubt a lot of people are cut out for it...

You underestimate how big a role the "cool factor" plays in recruitment. Note how propaganda always focuses on jets and tanks and submarines and aircraft carriers and futuristic gadgets, and when they do feature an soldier it's always a badass tier-one operator who gets to flaunt the uniform code. Seventeen-year-olds don't get so excited about the prospect of burning literal shit in a hole behind some godforsaken checkpoint in Afghanistan until one day an IED takes their leg off.

I was in a different branch but I feel like the series was probably a remarkably balanced portrayal of Navy/submarine life. There's a lot of cool stuff to talk about but clearly it's a demanding job and most of those sailors looked worn right out.

As mentioned in the video, candles are a backup/supplemental form of oxygen generation. Older platforms will have an AEOG (Automated Electrolytic Oxygen Generator), popularly known as "the bomb", and newer platforms will have the substantially safer LPE (Low-Pressure Electrolyzer).

Burning candles is a hassle and creates a big mess, to the consternation of junior enlisted who have to haul clinkers around and clean up the constant dust storm they leave behind. That said, huffing that good O2 straight out the spout will keep you awake, especially if your boat has been below 18% for awhile.

I remember A gang telling me how explosive the whole AEOG process was when I checked in. It literally is a potential bomb.

They used to be worse! The original 6L16 EOG didn't have the "A". It was neither Automated nor Advanced, the only "A" it had was operated by A-gangers!

3k-lbs of pure O2 combined with a reputation for fires, rapid depressurizations, and hydraulic leaks. More than one auxiliaryman got blasted to bits by those things back in the '60s. Every submariner thinks theirs is a unique and special hell, but I don't envy those who went underway with the old O2 plants.

At the end of the movie about the Kursk, someone drops one in water accidentally and it seems the air ignites afterwards. Are these candles the same thing?

That was a potassium or alkali metal oxide that reacted with the salt water and exploded

Potassium superoxide which acts as an CO2 scrubber, oxygen generator and dehumidifier in one. It reacts violently with water, and since it produce massive amount of heat and oxygen, it will also cause an explosive fire if the reaction occur near a fuel.

In Kursk it is suspected that it got dropped into water that had a lot of oil floating on top.

Hollywood has always perpetuated the myth that when you are in an air tight room you'll die as you run out of oxygen. The CO2 poisoning will kill you before you run out of oxygen.

So, if you're sitting in a nuclear shelter, remember to get the CO2 scrubbers working first, then worry about the low oxygen.

Huh? How is Hollywood at fault?

I think the myth is older than Hollywood and it is ingrained in our languages - when people begin to suffocate they say „I meed more air”, not „The air is to stuffy”. And this leads to a mental model of bringing more oxygen in as helpful instead of letting co2 helpful.

Hollywood at least got it right in Apollo 13!

For decades the US Navy used the OBA[1], or Oxygen Breathing Apparatus, for fire-fighting, which also worked using a sodium chlorate candle. I had only ever used them in boot camp, as when I got to the fleet they were starting to switch over to SCBAs — what actual fire-fighters use on land. I was always terrified of the thought of having to use one in because I vaguely recall something about them potentially exploding if they got too wet which seemed almost guaranteed being on a ship in the ocean.

A few years ago, maybe 2015 or so, I was walking through base on my way home and saw a moored tugboat was on fire. The two guys on board were in OBAs trying to put it out while waiting for the base FD to show up, so I suppose they’re still used in some places.

[1] https://en.m.wikipedia.org/wiki/Oxygen_breathing_apparatus

It's notable that humans cannot detect low oxygen levels.

Tasks become harder and you make worse decisions, but at no point will you think "I need more oxygen, better light the candle".

On the other hand, high CO2 is pretty detectable. You'll start to find the air 'stuffy' and it will be immediately obvious there is something wrong with the air.

Even high CO2 - which your brain does detect - won't be detected fast enough by your brain to do anything useful about changes that arise very suddenly, because the sensor is measuring your blood, and high blood CO2 can mean you're seconds away from unconsciousness but with impaired cognition. You're screwed.

Humans will clamber down into a space that's been flooded with CO2 (to fight fires or by mistake), go, huh, that's not... er... bonk, and lose consciousness. Then others up top are likely to climb down to "save" the people who just fell over for no reason and suffer the same fate.

This happened on a log carrying frieghter near here, a few years ago.

The unprocessed logs in the holds are slowly rotting, so the air in the holds can be depleted of oxygen.

A crewman went into the hold to check on something, and collapsed. Another crewman went in to rescue the first, also collapsed. I don't recall how many went in, but eventually someone grabbed an oxygen tank and managed to save the last one. The rest died.

I've watched a presentation on this problem that showed surveillance footage of this exact kind of situation happening and costing the lives of at least two people (I think the fourth one realized what was going on and got geared up before saving the last one to go in before him). You could watch them simply drop like flies, it was obvious they didn't realize what was happening to them before they fainted.

Are you sure those cases are CO2 and not CO? Iirc CO is the truly fucked up one because it binds to hemoglobin much more readily than CO2 thus displacing both CO2 and O2 in the blood.

With CO the issue is that it binds to haemoglobin and stays bound to it permanently. Only a small proportion of CO2 in the blood is bound to haemoglobin (~10% [0]) so the real issue is that the O2 carrying capacity is reduced. As red blood cells are constantly being replaced limited exposure is not a long term issue, but this is a process that takes weeks. This means that someone with acute exposure cannot be helped with supplemental oxygen (or just being taken outside) unlike with CO2.

CO2 in high concentrations causes issues through various mechanisms with a major one being that it impairs your ability to absorb O2 and other cellular disruption through increasing the pH of your blood [1]. This can cause unconsciousness in seconds at high concentrations and other potentially fatal impairments even at lower levels.

So CO poisoning is worse as there's no (easy) therapy for it but it is still very possible to have fatal exposure to CO2 if you are not able to receive fresh air in a immediate time frame (minutes).

There is also the general issue that confined spaces might be low on O2 as well, as described in this video on confined spaces in ships [2].

[0] https://www.ncbi.nlm.nih.gov/books/NBK532988/

[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5380556/

[2] https://www.youtube.com/watch?v=uNVj_JpZia8

With Carbon Monoxide there's a big risk of gradual poisoning. For example if you run a stove in a sealed compartment to keep warm, well, the Carbon Monoxide released can't escape and will gradually poison you over even several hours. If your body had a CO sensor, you'd realise there was a problem in plenty of time to flee, because it's so gradual, but it doesn't and so you might feel a little sleepy and that's it, you're probably never going to wake up.

With Carbon Dioxide that gradual risk doesn't exist, you would realise there's a problem. You will probably even be woken if CO2 gradually rises, you'll become conscious, discover the air seems "stuffy" and go somewhere with fresh air.

The problem in the drastic CO2 scenarios is it's too sudden. It's understandable (more so than with Carbon Monoxide) that we didn't evolve to cope with that. Prehistoric man did not use CO2 fire extinguishers.

Is this because we don't feel out of breath by lack of blood oxygen, but by an excess of blood CO2? Also related to hyperventilating causing fainting because you scrub out CO2 and hence think you have plenty of oxygen, and the use of a paper-bag to re-circulate some of the CO2 to keep blood levels of CO2 high enough.

Yes. If you try to hold your breath, the pain you feel is from CO2 buildup, not because of a lack of oxygen. If you lie still, the oxygen would last for many many minutes, but most people will be in such a pain after a minute or two that the body refuse to keep holding the breath.

Consequently, that's why hyperventilating is absolutely a no-go when freediving. It tricks your body, by not triggering the CO2 feeling. So then you can suddenly pass out without feeling you were close to running out of air.

Is, at the same time, hyperventilating an effective (but very dangerous) way for people to get better at freediving? It seems like it would help people get deeper, especially when they are no where near their limits. That also sounds like it would make things even more dangerous, because when you get better and do get near your limits, you don't notice.

For most people, I think the increased heart-rate of doing the big breathing motions would nullify the theoretical gain. So it feels easier, but you can't really hold any longer, you just pass out unexpectedly.

The best way to get better is to do "co2 tables", just slouch in your couch and do the intervals of breathing/holding, and learn to control your body. When actually diving, we never push our limits, compared to what we know we can handle on land. Like, I can hold my breath for 5 minutes, but would seldom be more than a minute underwater.

Co2 tables are actually very meditative. After the first convulsions, if you manage to calm your body down, it's quite a weird headspace to be in for the next minutes.

A dropping level of CO2 from hyper ventialtion also disturbs the acid-base balance in the blood which in itself can cause dizziness, impaired mental function and tingling fingers as if you have a lack of oxygen.

At high altitude it's easy to mistake this for hypoxia (due to loss of pressure), because the feeling and visible symptoms can be very similar.

The distinguishing symptom is seeing blue lips/fingers, that doesn't happen with hyperventilation. But if you've taken hypoxia that far you're in a lot of trouble.

Recommended approach for flight crews is to not bother figuring out whether it's hypoxia or hyperventilation but instead for everyone to put on oxygen masks, verify each other's masks and focus on breathing normally. It will fix both issues and ensures that the rest of the crew is fine in case it was hypoxia.

"A dropping level of CO2 from hyper ventialtion also disturbs the acid-base balance in the blood which in itself can cause dizziness, impaired mental function and tingling fingers as if you have a lack of oxygen."

Hyperventilation is also at the core of Holotropic Breathwork, which people deliberately do to get psychedelic effects:

https://www.holotropicbreathworkla.com/how-to-do-holotropic-...

   The candles can enter a state of elevated oxygen (maximum 32%), classified as oxygen-enriched. However, the same fire ignition risks remain at these percentages, and no additional ignition risk is present.

i do not think this is accurate, considering the candle produces pure oxygen, this risk would be highly dependent on the environment and amount of air

If memory serves, the incorrect storage of oxygen candles on Valujet Flight 592 was the cause of its crash.

Good memory! Well, kind of ... here is the NTSB Report on the crash (PDF): https://www.ntsb.gov/investigations/AccidentReports/Reports/... - its interesting: Planes back then had an emergency oxygen system that worked on the same principles like the candles mentioned above, but these were much smaller. The crashed plane transported discarded / expired oxy generators in loose cardboard boxes since they were not labled as hazardous materials. One of theses generators was probably the cause for a chain reaction and the crash.

Older Admiral Cloudberg write-up on that crash:

https://imgur.com/a/vodAg

This is blowing my mind, probably envisioning the wrong size of the candle for this kind of output:

> The candle supplied by MineARC Systems burns for approximately 60-90 minutes, producing 2600L of oxygen. This amount can provide approximately 20 hours of breathable air for four people. An oxygen candle cannot have its oxygen production regulated or halted and once ignited; it produces oxygen at a rate of approximately 28 Litres per minute until it is exhausted.

Oh I see now, it's that big metal cylinder on the floor, they are going to pour the powder into it and ignite?

https://minearc.com/wp-content/uploads/2021/01/cristel-train...

I'm also struggling to get an idea of the size of the candle; the article gives no information and it's unclear if the photos of the demo are using the same product as described in the text. Surely something that can produce 2600L of oxygen must be pretty big? It's a shame that the page gives no clue as to the size and weight.

Another page details a 'rugged oxygen generator' - https://minearc.com/products/emergency-response-products/rug... that produces 90L of oxygen over 15 minutes, and that is 115mm x 284mm, weighing 2.3kg. Confusingly, the PDF of the product specs shows that it comes with a mask - so 90L of oxygen is for one person, for just 15 minutes here? And if used with a mask, is it actually pure oxygen being produced, or breathable air (where does the nitrogen come from?) I'd love to know more, but the website doesn't tell us.

Average human: breathes approximately 7 liters per minute of air, give or take @ 21% oxygen. Maybe 22L of oxygen under normal respiratory demand. More if under stress of course.

At 100% oxygen that’s 105L of O2? So guesstimating almost 100% O2?

Source: am paramedic, not doctor or respiratory therapist.

Breathed air is diluted right, to some lower % of oxygen content, but it needs to be in the calculation.

Exhaled air is about 17% oxygen, 4% carbon dioxide. So, as previous poster noted, scrubbing the CO2 is your first priority. You can't breathe air with greater than about 4% CO2 indefinitely. Oxygen levels lower than 15% are also bad.

Diving rebreathers are an interesting implementation of these rules in that they are lethal if you get it wrong.

It's not ignited, this is how airplane oxygen systems work. A phosphorus match provides the activation energy (as heat), which causes the decomposition of Sodium Chlorate (NaClO3) to Sodium Chloride (NaCl, table salt) and free oxygens. The oxygens combine to form atmospheric oxygen (O2).

At standard conditions, a single mole of oxygen occupies 22.4L. The conversion rate from NaClO3 to O2 is 2-to-3, so for every two moles of sodium chlorate you burn, you get three moles of Oxygen, or 67.2L.

The molar mass of NaClO3 is 106.44g.

So some quick math, to fill 2600L we need 116 moles of oxygen, which we can produce with 77 moles of sodium chlorate. Multiply by the molar mass and we get ~8kg.

Sodium chlorate has a density of 2.49 g/cm^3, so an 8kg slug will fit in a 3.2L bucket.

3L of powder gets you 2600L of oxygen, not bad!

Thanks, I attempted to do the calc in my head... and it's been to long, that I learned Chemistry in school apparently.

What this boils down to is "salt is a couple orders of magnitude more dense than air, so we can fit a lot of air in very little salt". Which is a sentiment I think most people can feel is correct even if they don't know their ideal gas law or whatever.

He did the math, what a legend.

I believe these are the same candles used on submarines to make oxygen: https://www.youtube.com/watch?v=g3Ud6mHdhlQ

For fun, I went looking to see if you can buy one. In theory, you can buy them here: https://www.oclugo.com/our-products/chlorate-candles/)

I'm guessing the best place to find them would be a military surplus dealer.

I remember these critters, from the 1970s: https://en.m.wikipedia.org/wiki/SolidOx_(welding)

In 1997, a chemical oxygen generator failed aboard the Mir space station, and caused a pretty nasty fire:

https://en.m.wikipedia.org/wiki/Vika_oxygen_generator

https://www.nasa.gov/pdf/602090main_44s_international_life_s...

I’m missing something, it says these burn at 1100 degrees. There is no oxygen but enough space for me to be ok burning something at 1100 degrees next to me?

That really depends on the density/surface area of the item. I mean, a standard light blub filament burns at like 3000F, but you don't really feel that.

It sounds like a lot but it is about the same temperature as that of a regular wax candle flame.

> these burn at 1100 degrees

Would be cool if something else could be done with the heat to get rid of the CO2, like a Sabatier reaction (sorry, a bit handwavy).

https://www.oclugo.com/our-products/chlorate-candles/

This provides accurate info on specifications and the details about these candles/devices from a different manufacturer. Including % of particulates.

I wish they had a video demo or at least an image of one burning.

Still doesn't show the burning, but shows the setup, inserting a red phosphorous igniter, etc: https://youtu.be/h7Jonu6cXoY?t=396

I don't know why but that was incredibly satisfying to watch as well as educational.

from the video: > if carbon dioxide level exceeds 25ppm

The global average atmospheric carbon dioxide in 2020 was 412.5ppm. We're so screwed, aren't we?

> the oxygen-producing chemical is sodium chlorate

Stupid question: How is it the sodium chlorate and not the barium peroxide that produces the oxygen?

They have these "candles" in submarines for emergencies, I was told on a submarine tour some years back.

Nice summary of the process.

Mars

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