Some of the most common questions surrounding localized cryotherapy (such as with the Subzero from America Cryo) are about the gas required for the treatment, CO2. Lets dive into some of the most common questions, shall we?
Why CO2?
People often think that Localized Cryotherapy uses liquid Nitrogen, and while certain older systems as well as full body Cryotherapy Chambers do use Nitrogen, liquid CO2 is much more commonly used in Localized Cryotherapy. Lets compare the two:
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CO2 condenses (turns from gas to liquid) at a higher temperature than Nitrogen. This means that, while both are sufficiently cold enough to induce a Thermal Shock, the risks such as causing a frost bite with CO2 are lower than with Nitrogen. CO2 can also be kept liquid in a pressurized tank, while Nitrogen must be cooled to stay liquid. This makes the logistics surrounding CO2 much simpler than Nitrogen.
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CO2 is often more affordable and readily available than Nitrogen. Even just using think about it logic, any fast food joint, gas station, or restaurant with a soda fountain needs CO2 to carbonate those sodas. CO2 is also widely used in welding and other industries, making it very easy to source in most cases.
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Both CO2 and Nitrogen are relatively inert gasses, meaning they are non reactive with other materials. Nitrogen has a slight advantage as it has a lower risk of causing asphyxiation in confined spaces (this is why it is used in full body Cryotherapy Chambers, and in fact molecular Nitrogen), but both gasses are not flammable, and don’t pose major health risks. CO2 does take back the lead in terms of handling safety. There is a much lower risk of complications with an improperly stored CO2 tank than an improperly stored Nitrogen tank.
What exactly do I need?
So, lets get specific. What exactly do you need to (other than the device, of course!) for Localized Cryotherapy?
Grade of CO2.
There are three different grades of CO2 that are typically available:
- Commercial / Industrial Grade This is typically the least expensive grade of CO2, is targeted for industrial use, and is normally available from a welding supply store.
- Food Grade This is typically a bit more expensive and more pure than industrial CO2, and is available from suppliers that deal with restaurants or breweries. It can sometimes also be available from Industrial Gas Suppliers.
- Medical Grade This is the highest grade, most pure CO2 available. It is normally used in surgical applications, requires a license to purchase, is the most expensive, and comes from a medical gas supplier.
While all three grades of CO2 are appropriate for use with localized cryotherapy machines, I recommend looking for Commercial Grade CO2 first. It is normally the easiest to source and least expensive, though in some locations Food Grade CO2 may be more readily available. Praxaire and Linde are common distributors where you can source CO2.
Tanks.
The next thing to consider is what size of tank will work best for you. While there are multiple options, 20 pound and 50 pound tanks tend be best in most circumstances. 20 pound tanks are roughly the size of a scuba tank, and are better if you have to take the treatment to the horse. 50 pound tanks are larger and heavier, and typically better if you can have a treatment area and can bring the horse to the setup. CO2 tanks should normally come with a label clearly showing that they contain CO2.
One last consideration, your CO2 tank will need a Siphon Tube. Also referred to as a Dip or Eductor Tube. This is essentially a straw that is essentially a straw from the valve on the top of the tank down into the liquid CO2 resting at the bottom of the tank. The liquid CO2 is what allows Localized Cryotherapy to achieve the rapid temperature drop required for the therapy to be effective. Thankfully, getting a tank with a Siphon is just a request you need to make with the supplier when picking up a tank. Tanks with Siphons will typically have a label specifying they are intended for liquid withdrawal.
Is it safe?
Generally speaking, handling and use of Compressed CO2 is safe to handle under most circumstances. That being said, there are a few items to keep in mind:
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Because we use tanks designed for liquid withdrawal, an uncontrolled release (such as opening the valve with nothing connected) will vent extremely cold liquid CO2, which does pose a risk of frost bite if it contacts the skin. The valve on the tank should never be opened with nothing connected and should be closed immediately if a leak is observed. Tanks with Siphons should also only be opened when they are oriented with the valve at the top (with one exception noted in the next section).
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While generally speaking we work on horses in large spaces or outdoors, CO2 is a colorless, odorless, tasteless gas that is heavier than air and can accumulate with improper ventilation. It is worth being aware of the symptoms associated with an accumulation of CO2. These can include: increased respiratory or heart rate, impaired decision making, dizziness, headache and nausea. The risk of this happening is highest when working for extended periods in smaller spaces, or during transport in an enclosed vehicle. If you start noticing any of these symptoms in yourself or the people around you, you should immediately stop treatment, turn on a fan, open a door or window, and leave the area while the CO2 dissipates.
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While it is not strictly necessary to remove the Cryotherapy device from the tank when not in use, make sure that the hose is wrapped in a way that it can’t be tripped over and that the valve on the tank is closed when not being used. Tanks should be stored against a wall or in a corner, and especially with larger tanks should be tied or strapped to the wall so they can’t be knocked over. For long term storage, tanks should be kept in a cool, dry place away from excessive direct sunlight.
Help! I think I’m out of CO2!
There are a few reasons your CO2 tank may be empty, but lets start with the obvious:
You are actually out of CO2!
Of course, the Liquid CO2 in the tank is a limited resource. That being said, there is a little bit of nuance in understanding when a tank is empty. A functionally empty tank will still have pressure, so you can judge based on gas venting from the device. A tank that still has useful Liquid CO2 will discharge a foggy cloud, and a tank that is out of Liquid CO2 will have a primarily clear discharge. The cloud density will vary based on the relative humidity, but it will always be visible.
In most circumstances, you will get slightly less useable CO2 than the, for example, 20 pounds advertised. There are a few reasons for this:
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The tanks are not always filled precisely, and may be slightly overfilled or under filled.
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There are always small losses, for example when venting the hose prior to disconnecting or when purging the line after first connecting the device to the tank.
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The siphon tube does not reach all the way to the bottom of the tank, meaning there will always be a few drops of Liquid CO2 at the bottom of the tank that the siphon can’t reach.
You can keep track of how much CO2 you are getting out of a tank by weighing the tank when its fresh, and again once it presents as empty. The difference between the fresh and empty weight will match the amount of CO2 used. Based on my experience with the Subzero, you will use about a pound of CO2 per minute of discharge with the middle size nozzle.
A fresh tank immediately appears empty.
There are two reasons a fresh tank can appear empty. Sometimes, the gas supplier will accidentally give you a tank that does not have a siphon tube, or the siphon may be damaged/disconnected and the supplier is not aware. In either case, there is a simple way to validate if there is an issue with the siphon:
The Tip Test!
With either a damaged or missing Siphon, the Liquid CO2 will not be accessible. If you have a second person (carefully) hold the tank upside down and then check the discharge from the device, you should see the expected foggy spray. By turning the tank upside down, you are forcing the Liquid CO2 in the tank to sit directly on the valve, allowing it to be directly extracted. If the Tip Test produces the expected discharge, in most cases the supplier will just swap the tank out for you.
If the Tip test doesn’t produce the expected discharge, there is one last possible cause…
Dry Ice Formation.
Under certain, uncommon, conditions the Liquid CO2 in the tank can flash freeze into dry ice. In the rare event this happens, typically you will be dispensing gas from the device and suddenly the stream will slow or stop completely. It can also present with the bottom of the tank feeling especially cold to the touch, or forming frost of condensation. If this happens, stop dispensing gas and close the tank valve. Normally, letting the tank sit in a warm room for a couple of hours will resolve this, however you may need to return it to the supplier for a fresh tank.
Conclusion
I hope this has helped demystify why CO2 is used for Localized Cryotherapy, and helped understand some of the nuance around CO2! If you have any questions I would love to hear from you!