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Everything you ever wanted to know about CO2 (but never thought to ask)

By Lennard Zinn

A clear and present danger? Some folks think so.

A clear and present danger? Some folks think so.


Dear Lennard,
You may want to do a little better research when answering these questions next time because both of your CO2 answers were completely wrong.

1) Flying with CO2: CO2 cartridges are banned from all aircraft because they are listed as hazardous materials by the Federal government Department of transportation and FAA. The reason for this is that the containers are un-regulated and can and do have the ability to fail with out warning. The department of transportation does not allow these to be transported in any way by air, which means they cannot be shipped via FedEx, UPS or any air service.

They must be ground shipped and they even fall under the same hazardous materials rule that they cannot be driven inside of certain tunnels.

They are classified this way because they are imported and not regulated by the U.S. EPA and Hazardous materials standards. They also do not meet the safety standards of containers under pressure for the U.S. because they do not have a safety valve to relieve pressure slowly if a problem arises. You can see this kind of basic safety valve on a can of shaving cream … the little rubber plug on the bottom would pop out as well as the release valve in the thumb switch simultaneously to render that container pressure-less if it reaches a specific external or internal pressure.

What you also do not understand is that if the cabin pressure of an airplane changes drastically (say like a 30,000 feet breach) then there is a very good chance those CO2 containers would breach as well, which could (with a very low chance) cause catastrophic problems if they detonate near key aircraft components.

2) What is in that cartridge? Stayfill contains a completely inert gas that is a byproduct of a process they use for transporting highly toxic gases, it would be very comparable to Argon gas … it is not flammable.

Innovations “bigair“does not contain propane. They use the byproduct of propane gas that is used for transporting liquid propane it is almost exactly the same as CO2, but instead of lying to consumers by saying their CO2 is from “natural sources” or “volcanic sources” they follow the Federal guidelines and list it as a Propane like gas. By the way there is no way to get CO2 from “natural sources” or “volcanic sources” CO2 in these cartridges are completely man made/ manufactured and are pretty harmful to the environment, that is why no one manufactures CO2 in the US because they would not be able to meet EPA standards.

Dear Mark,
This is a forum for all of us to learn from each other, and as y’all have probably noticed, I have a thick skin for people telling me I’m wrong, so please continue to bring it on. I got a lot of mail on this issue.

Here is what Northwest Airlines has to say about it: As you can see, CO2 cartridges are allowed in both checked and unchecked baggage as long as they are part of mechanical limbs or life vests. American Airlines doesn’t mention mechanical limbs but it does allow two spare cartridges in addition to two in a life vest.

The question is whether there is any significant difference between your average CO2 cartridge and one in a self-inflating life vest (or spares for said vest). Perhaps I’m making a wild assumption, but I doubt it.

It may be that some of those respondents who accused me of making dangerous statements misinterpreted my comment about the airline regulation. Don’t get me wrong; I advise adhering to any and all airline restrictions.

Sometimes people refer to the 1996 ValuJet crash in the Everglades when they talk about CO2 cartridges, and just to nip that in the bud, let me point out that those were oxygen-generating canisters, which produce heat when triggered (CO2 cartridges are much smaller and get cold) and of course oxygen would fuel a fire (CO2 does not). In this article about that accident and a similar incident on a parked plane in 1986.

I find this to be an interesting quote: “The canisters are used in many Boeing jets, the DC-10, the L-1011 and some Airbus models to provide emergency oxygen. Ironically, the ValuJet DC-9 used a conventional stored oxygen system; the plane was simply transporting the canisters.”

I’m sure we all feel safer knowing that little CO2 cartridges are regulated. I appreciate your explanation of regulations, but with regard to your statement that a 30,000-foot breach would be likely to breach a CO2 cartridge, surely you jest. Say the cabin were pressurized to sea level (1 bar = 14.5psi), which it is not; usually it is at 7,000 feet equivalent, or around 0.8 bar = 11.6psi. (You know this because even taking off from Denver at 5,000 feet, the water bottle you topped off in the airport lets out air when you open it at cruising altitude. The low cabin pressure can even explode a Mylar balloon (veering off the subject, I’ve got a funny story about this I’ve attached at the bottom of this column if you’re interested.) The hold is also pressurized and temperature controlled; pets are carried in there after all.

The top of Mount Everest is at almost 30,000 feet, and the air pressure there is around 0.3 bar = 4.3psi. So the breach would suddenly decrease the air pressure against the outside of the CO2 cartridge by 10psi at the most, and probably more like 7psi, less than one percent of the canister’s 853psi at 70 degrees(F). That is why airplane manufacturers do not worry about having CO2 cartridges installed on every life jacket under every seat in the plane.

A pressure change of 7-10psi may be enough to burst some shampoo containers, but it’s not enough to burst most road bike tires inflated to riding pressure, and I wonder whether it is even enough to burst a can of soda or beer carried in the hostess’s cart, much less a CO2 cartridge.

Furthermore, the cartridge would be contained inside somebody’s luggage. While you could get a CO2 cartridge to go shooting around the room by pounding a nail in the end of it and letting it go, and you could use one to propel a toy car or a paintball, you know from experience with bike tires that they do not push back very hard on your hand when you screw one up and blow the cartridge without inflating the tire. It’s hard to imagine one getting out of a closed piece of luggage on its own.

As for heat in the cargo hold in case of a delay on the ground causing problems with CO2 cartridges, I’ve left my bike with CO2 cartridges in the seat bag in the hot sun for extended periods while I was on river trips with nary a burst cartridge. In fact, I’ve left cans of beer in a car in 100-degree-plus heat at Lee’s Ferry, Arizona, at the put-in of the Grand Canyon and was glad to find on my return that they were intact. I realize this is anecdotal evidence, but I doubt I’m the only one. Please write me if you’ve had one burst from heat in a car (or from flying).

I do understand about regulations and labeling, and I’ll take this opportunity to thank the many of you who wrote me about those.

Again, obey all airline regulations. Below is an explanation of them by somebody in the business.

As for your second point, below are more explanations of the contents of StayFill and other tire-inflation cartridges. I did not get a response back from Innovations in Cycling to my email asking about the contents of BigAir.

From an airfreight shipper
Dear Lennard,
I’ve just been reading your article replying to a question about transporting CO2; I’m a UK based airfreight shipper and I’m qualified to ship dangerous goods by air; this is governed by both IATA regulations that apply globally and also 49CFR regulations that America applies to their airspace, which is a nightmare.

These rules are part of a bigger picture dictated by legislation (which I’m sure you know makes for some amazingly non-nonsensical rules!). If you’re interested the life jackets you mention (along with avalanche rescue backpacks and mechanically operated limbs using non-flammable, non-toxic gas cylinders along with barometers you’ll be please to know) are permitted as checked or carry-on baggage as they are specifically mentioned in the IATA regulations. Items that aren’t specifically mentioned in the IATA regulations are subject to the full rules which in the case of CO2 inflators means they would need to be packed in a specially approved outer packaging, have pressure relief devices fitted, a shippers declaration formed filled out by someone as geeky as me who has the proper training, etc, etc. These rules also apply to things like magnets, lithium ion batteries, fish scrap and so on.

Camping stoves also used to fall under these rules, but due to the frequency of gas stoves being found in luggage and because of some pressure put upon IATA by a group formed to change these rules; this has been included in the list of exemptions. So I presume you could form your own pressure group to change the rules for CO2 inflators on board aircraft.

From a former Vittoria/Geax engineer
A mix of methane and propane is used inside most inflate and repair cartridges (those spraying latex foams, like Geax Pit-Stop): this gas does escape through butyl tubes quite fast (from 8 to almost 0 bar overnight), much faster through latex tubes.

I don’t know about compatibility issues between these gases and material used for tyres or tubes: they just don’t stay in contact long enough to create problems in bicycle applications.
Alberto De Gioannini
Effetto Mariposa

From Vittoria/Geax
The content in Pit Stop is butane, propane and isobutene gas.

I’ve asked for the documentation that proves that our Pit Stop doesn’t create corroding problems.
Samuele Bressan
Product Manager & Designer
Vittoria Group

The gas in the Stayfill cylinders is inert so not flammable, toxic, or corrosive; StayFill is a alternative to inflating tires with air, N2, or CO2. It’s a gas mixture we came up with some time ago for a fire sensor system that would hold 120-150 pound-force per square inch gauge (psig) in a plastic line for five years or more. After further thinking, we discovered it worked quite well in bicycle tires. I filled my mountain bike tires up about five years ago to 50 psig and it is still at 50 psig. Finally, we found a vendor to package it up in those cartridges.

We used the standard size cartridges used for CO2 because there are a lot of dispensers already out there.

It will probably take 2.5-3 of our 25-gram cartridges to fill a 26-inch by 2.1-inch mountain bike tire. You can top off the pressure with air. Using 12psig of air in conjunction with the StayFill will actually put the tire in equilibrium. Our new design that should be available in March and will be a larger cartridge with 115 grams of product. This will fill up to a 29-inch mountain bike tire or three road tires to 115psig.

We have one customer that is using it with the tire sealant Slime in New Mexico and the sealant is not drying out like it used to using air. This customer thinks they now have the ultimate tire.

With respect to the first part of that article, using propane (big air) in your rubber/latex based tires is like using Vaseline with your condoms; they don’t last long. Petroleum based products decompose organic substances like rubbers or latex material so I am not sure how long it would take for the propane to begin showing signs of decomposing the inner tire wall.

Here is the link to the material safety data sheet for propane by Air Liquide. Down near the bottom they discuss propane’s use with hydrocarbon lubricants and say, “Non recommended, significant loss of mass by extraction or chemical reaction.”

Propane may not be a lubricant per se, but it is definitely a hydrocarbon. Special rubber compounds can be made to be compatible with hydrocarbons, but it does not strike me as a specification a tire manufacturer would have chosen when they selected the tire materials. We have a division that makes compressed natural gas transports and they ran into a major problem a while back using a rubberized hose with natural gas, which typically has about 8-10 percent propane. The hose began disintegrating after a few months of use under pressure.
Michael Koonce
IGX Group, Inc.

“Proprietary?” Oh really?
Dear Lennard,
Regarding your VeloNews.com article on tire gas that mentioned Stayfill and it being proprietary. The mention of large molecules and special tire gas reminded me of the Ferrari claims of a “proprietary” gas fill used in their F1 car tires and which was part of the McLaren spying saga in 2007. The real story there is that the “secret” gas “formula”, which contains three different hydrofluorocarbon molecules, is in fact identical to a readily available off-the shelf DuPont refrigerant called SUVA 404A (HP62), see DuPont for info and a Materials Safety Data Sheet.

If not the same stuff, Stayfill has to be a similar refrigerant gas mix — there are a very limited number of (ambient temperature) gases with large molecules. Ferrari, for their purpose (lower tire contact temperatures), found that a mixture of Suva 404A and CO2 was best (sorry don’t recall the exact proportions but I recall 80/20 being tried). Of course Stayfill’s real marketing coup is in the packaging, though it’s always possible they’ve mixed two different SUVA product mixtures just to be able to say “proprietary.”

I’ve also been told that Suva 404A had been used in MotoGP and Daytona Superbike racing at least 2 years before Ferrari got the umm, idea.

A quick tale about Mylar balloons on airplanes
In 1998, the World Master’s cross-country ski championships were held in Lake Placid, New York, and I participated along with a number of my ski buddies. The final celebratory dinner, held on the rink where the “Miracle on Ice” hockey victory by the young college players of Team USA over the experienced Soviet team occurred at the 1980 Winter Olympics, had a “western” theme and included hundreds of large aluminized Mylar balloons shaped like red cowboy boots floating above the tables. My daughters were young at the time, we had horses at home, and horse-loving girls also love red cowboy boots, so I grabbed a few of the balloons to bring back to them.

This being pre-9/11, nobody said a word as I passed through security at the Burlington, Vermont, airport boarding the flight to Washington with the large, shiny balloons floating behind me. Being seated in the back of the plane and concerned about storage space back there being filled by the time I reached my seat, I stuck the balloons in various overhead bins as I walked down the aisle. Some time after the pilot had allowed us to lean our seats back, I was awakened from a light slumber by a large “bang” emanating from one of the overhead bins in which I’d placed balloons. I shrunk down in my seat behind a copy of VeloNews as passengers looked around with wide eyes. Nobody figured it out, and I cringed the whole flight in fear of the others going off, which they did not. As I exited the plane with two whole balloons and one limp one, the flight attendants, as usual, thanked me for flying with them.

Figuring that it must have been a defective balloon, I boarded the plane to Denver with the two intact balloons. What was I thinking?

I remember this time looking straight at the welcoming flight attendants with the balloons held in front of me as I boarded, thinking they might warn me if it was an issue, but they did not. I shrugged and stuck them in overhead bins where there was space as I made my way back to my seat in steerage.

As you might imagine, another one exploded on that flight, passengers once again looked around wide-eyed, and I once again sat in fear of the last one blowing up the rest of the flight. I arrived home with one cowboy-boot balloon (just enough for the girls to fight over, so I gave it to my wife) — and a good story. I wonder if any of the foreign skiers also tried to fly home overseas with those balloons.

Technical writer Lennard Zinn is a frame builder (www.zinncycles.com), a former U.S. national team rider and author of numerous books on bikes and bike maintenance including the pair of successful maintenance guides “Zinn and the Art of Mountain Bike Maintenance” – now available also on DVD, and “Zinn and the Art of Road Bike Maintenance,” as well as “Zinn and the Art of Triathlon Bikes” and “Zinn’s Cycling Primer: Maintenance Tips and Skill Building for Cyclists.”

Zinn’s regular column is devoted to addressing readers’ technical questions about bikes, their care and feeding and how we as riders can use them as comfortably and efficiently as possible. Readers can send brief technical questions directly to Zinn. Zinn’s column appears here each Tuesday.