M.S.A. ChemOx: Better Breathing Through Chemistry

[00:00:12]Hello everyone and welcome to another video on our own devices. I'm Jin Messier and today we're having a look at a really cool piece of rescue breathing equipment. This is a Chemox breathing set manufactured by the Mine Safety Appliances Company, today MSA Safety of Pittsburgh, Pennsylvania, and designed for use by firefighters, mine rescue teams, and other emergency personnel in toxic, smoky, or otherwise unbreathable environments. Now, you'll recall that a few years ago, we looked at the all-ervice gas mask made by the same company. Link in the description.

[00:00:41]However, this can only filter out smoke and toxic gases like carbon monoxide and doesn't supply the user with any additional oxygen, meaning it can't be used in atmospheres where the oxygen concentration is dropped below around 19.5%.

[00:00:54]The Chemox, by contrast, is far more similar to the Taetto submarine escape set we also looked at in another video, but with one important and very cool difference. Now, before we get started, I do need to give a huge shout out to the Fallaren Museum in Pontage Prei for lending me this unit to show you today.

[00:01:10]Right, let's dive right in. So like the taetto, the chemox is a form of rebreather or closedcircuit breathing set. And these rely on the fact that exhaled breath actually contains a surprising concentration of residual oxygen. So while ordinary air contains around 21% oxygen, exhaled breath contains between 15 and 16% oxygen. So theoretically, you could keep rebreathing the same lung full of air several times before completely running out of oxygen. Problem is, of course, that that breath becomes increasingly concentrated with carbon dioxide, which will quickly poison you. But if you could somehow filter out that carbon dioxide and replenish the oxygen level so it stays around 21%, you could get a lot of mileage out of the same volume of breathing gas. And that is exactly how rebreathers work. Classic rebreathers such as that patented in 1878 by Henry Floyce, master diver for Seb Gorman and Company of London, incorporate a cylinder of pure oxygen breathing gas in a scrubber canister containing carbon dioxide absorbing material such as sodium, potassium or lithium hydroxide.

[00:02:17]When the user breathes out, the exhaled air passes through the scrubber canister which filters or scrubs out the car dioxide. The scrubbed air is then enriched with a small amount of oxygen from the cylinder before being rebreathed, hence the name. These devices allowed miners, mine rescuers, firefighters, and other workers to achieve several hours of useful breathing time with a very compact breathing set. As covered in my Tauret video, the system was adopted by several navies in the 1920s and 30s to help sailors escape sinking submarines and for use by combat frogmen, in which application it had the added advantage of not leaving a telltale trail of bubbles. However, despite their many advantages, oxygen rebreathers suffered from one major shortcoming. They could not be used at depths below 4 m or 13 ft. since at these higher pressures pure oxygen becomes toxic to breathe. Other major shortcomings of traditional rebreathers included the weight and bulk of the oxygen cylinders and scrubber canisters and the tendency of the cylinders to leak in storage. However, in the early 1940s, the MSA company introduced the Chem Ox which dispensed entirely with the gas cylinder and instead incorporated a canister of potassium superoxide or KO2 which reacts with water to produce potassium hydroxide, hydrogen peroxide and oxygen.

[00:03:26]and with carbon dioxide to produce potassium carbonate, potassium bicarbonate, and even more oxygen. So, not only does potassium super oxide absorb carbon dioxide and moisture from the user's breath, but actually uses them to generate oxygen, neatly combining the functions of oxygen source and CO2 scrubber into one compact, lightweight package, which I think is really, really neat. In 1946, the Chemox was certified by the United States Bureau of Mines as a 1-hour auxiliary breathing apparatus, while soon after it was officially adopted by the US Navy for shipboard firefighting as the oxygen breathing apparatus or OBA. Now, while extremely light and handy, the original Chem Ox suffered from a fundamental flaw in that it took up to 15 full breaths to sufficiently charge the system with gas volume, carbon dioxide, and moisture to make the reaction self- sustaining.

[00:04:15]meaning that you couldn't really use it in an emergency when the atmosphere suddenly became unbreathable. So in 1948, MSA introduced a new type of canister incorporating what is known as a chemical oxygen generator, an oxygen candle, or a chlorate candle. This is a canister containing a mixture of sodium chloride and either iron powder or berium peroxide and potassium perchloride. When set off by lead stiff and tetrazine percussion cap, this mixture under goes a highly exothermic reaction that burns at 260 degrees C or 500 degrees Fahrenheit and decomposes the sodium chlorate into sodium chloride and oxygen. Interestingly, this is the exact same system that feeds the emergency oxygen mass in airliners.

[00:04:54]Indeed, the reason you were instructed to pull the mask down before putting it on is that this action pulls a lanyard that fires the percussion cap and ignites the oxygen generator canister.

[00:05:03]The systems generate oxygen for around 15 minutes, which is more than enough time to get the aircraft down to a safe altitude following a depressurization event. Now, as you can imagine, the extreme heat produced by these cartridges can be very hazardous. And indeed, the accidental activation of expired oxygen generator canisters led to the crash of Value Jet Flight 592 in the Florida Everglades on May 11th, 1996, killing all 110 people aboard.

[00:05:28]Oxygen generators have also been used aboard man spacecraft with the Russian Vika lithium chloridebased system being responsible for a serious fire aboard the mere space station on February 24th, 1997. Anyway, getting back to the subject of the video, the integration of an oxygen candle into the Chem Ox cartridge allowed it to start producing oxygen right away, meaning it could be used in emergency situations. Right. So, I think that's enough preamble for now.

[00:05:53]Let's actually have a closer look at this unit and let me show you how it works. Right. Right. So, this would originally have come in a metal reinforced cardboard case with compartments for the unit itself, several spare breathing canisters, a disassembly wrench and other accessories, and detailed instructions on the inside of the lid. The breathing mask on this example is unfortunately missing, but it would have been very similar to the one on the allervice gas mask, save for the inclusion of an inhalation valve on the front, but more on that later. There were also two breathing hoses and one-way valves to allow circular gas flow as opposed to two-way pendulum breathing.

[00:06:24]Interestingly, MSA offered and still offers a special spring wire bracket to allow the fitting of corrective eyeglasses inside the mask. Now, the breathing hoses connect the mask to the main body of the unit, which incorporates a padded chest plate, shoulder and waist straps to secure the unit to the chest, a D-ring at the back for attaching a lifeline, a breathing manifold body, an enclosed housing for the breather canister, a hinged bail and jack screw for securing the canister in place, and a breathing bag. The ladder cools the generated oxygen which emerges from the canister at high temperature and stores it until it is needed. This uses replaceable single-use breathing canisters which come in two versions.

[00:07:00]Type A or standard type containing only potassium superoxide and type B or quick starting type incorporating an oxygen candle. Now there are a number of different versions of this basic system produced over the years differing in the configuration of the breathing bags, the canister attachment system and other components. For example, the US Navy used three different versions designated the type A, the type A1, and the patrol type. The type A had a double front-mounted breathing bag and a swing down lash to secure the breathing canister to the manifold. The patrol type had a single vest style breathing bag and a swing out bail and jack screw canister mounting mechanism, while the type A1 was a hybrid of the previous two, featuring the breathing bags of the type A and the canister mounting mechanism of the patrol type. To install a canister, you remove the plastic safety cap from the top, swing out this bail, insert the canister as so, swing back the bail, and tighten this jack screw to force the canister up into the manifold. This breaks the metal foil seal on the neck, which protects the active chemicals from moisture and CO2 ingress in storage and presses the canister against the internal seals.

[00:08:02]Now, this system allows the canister to be held in reserve position below the manifold, preventing the chemicals from being depleted until you tighten the jack screw and activate the canister.

[00:08:11]Some versions also featured a swingway stop to prevent the canister from being raised and activated prematurely. The bail can also easily be swung out of the way to jettison a spent canister. Very handy since said canister will likely be very hot. Type A or standard canisters must be activated prior to entering a hazardous environment. This is done by using one hand to pinch shut the breathing tubes and the other to open the air intake valve on the front of the mask. You then breathe in, release the valve and tubes, and breathe out, discharging carbon dioxide and water vapor into the canister. You then repeat this process 15 times to fully charge the system. By contrast, to activate a type B or quick activation canister, you slide off these covers on the bottom, revealing a pair of short lanyards. You then yank these out sharply perpendicularly to your body, pulling out a pair of cotter pins, firing percussion caps, and igniting the oxygen candles. The one-way valves cause exhaled breath to flow through the right-hand breathing hose and down a central channel to the bottom of the canister from where it diffuses upwards through the potassium superoxide granules which absorb moisture and carbon dioxide and generate oxygen. The scrubbed and enriched breathing gas exits out the top of the canister and enters the breathing bag from where it is drawn out via the left-h hand breathing tube. Now, a really interesting detail on this unit is this little gauge on top, which is a one-hour mechanical timer with an alarm bell that lets you know how much breathing time is left in the canister. Now, of course, this only provides a rough estimate since canister life is entirely dependent on breather demand. So, it will last a lot longer if you take infrequent shallow breaths as opposed to frequent deep breaths. And for this reason, it was standard practice to set this to 30 or 45 minutes to give you an adequate reserve. Compare this to the equivalent gauge on the MSA gas mask, which is not a timer at all, but a sort of breathing odometer that tracks the total volume of air breathed by the user. Some versions of the Chemox also featured either a manual or automatic pressure release valve on the breathing bag. If we go back to the chemical reactions taking place inside the canister, we can see that more oxygen is generated than carbon dioxide is consumed, meaning that the unit produces an excess of oxygen that must be continuously vented. This valve also allows the user to purge excess nitrogen and saliva from the system, though this particular example seems to be missing that feature. Now, as I mentioned, the used canisters will be extremely hot and must be either handled with the gloves or released using the swingway bail system. And to dispose of the canisters, the instructions on the canisters themselves recommend punching a number of holes in the outer casing and dunking the entire canister in water in order to react away any remaining potassium super oxide. Then the canister and the water can be disposed of. Though, as I mentioned before, the reaction generates potassium hydroxide and hydrogen peroxide, which are highly toxic and corrosive. Even more worryingly, potassium super oxide can combust violently when exposed to oil and other hydrocarbons, which are likely to be encountered in many firefighting scenarios, especially aboard a ship. And indeed, the cartridges feature a very prominent warning sticker reading, "Caution, never allow any substance to enter the neck of the canister." These hazards are among the reasons the Chemox eventually fell out of favor, being largely replaced in firefighting service by simpler self-contained breathing apparatus, or SCBA gear with compressed air tanks. And while the Chemox generates oxygen at ambient pressure, SCBAs can produce positive pressure, helping to keep smoke and toxic gases out of the face mask. Modern SCBAs can also incorporate more advanced communications gear, heads-up displays, and other technology. Now, one of the very last users of the Chemox was the US Navy, though starting in 2001, even they started replacing their units with more modern SCBAs. And that, dear viewers, is a brief overview of the Chem Oxford breather set. I've actually been wanting to cover one of these for quite a while and actually ordered one on eBay, but eBay decided that the cartridges were too hazardous to ship and cancelled and refunded my order. So, when I saw this unit at the Fallen Museum, I knew that I had to cover it and they were kind enough to loan it to me for a couple of days to make this video. So, again, huge shout out to that museum. If you're ever in Portage Pre or Manitoba as a whole, well worth checking out. It's a neat little outdoor museum. Anyway, that's all I have for you today. Thank you so much for watching. I'll see you next time, another video. We'll look at more breathing gear and other fascinating devices just like these. Until then, I'm Jin Messi from Our Devices. Have a great day.