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CO2 Cylinder CO2 Tank Frequently Asked Questions

Liquid CO2 storage tanks

The use of bulk storage of carbon dioxide in cylinders or outdoor tanks has grown exponentially over the last several years. Every restaurant, brewery, welding supplier, indoor grower as well as many manufacturers rely on bulk CO2 as part of their business.

Because we offer CO2 storage safety alarms, we get asked questions about CO2 storage tanks and cylinders. Here are some of the most common questions with links to additional resources.

How are CO2 tanks and cylinders delivered?

Carbon dioxide has become a global commodity used by both business and industry. To ensure a constant supply of the gas, a supply chain of many different businesses are involved.

It starts off with collecting the gas. CO2 is a natural byproduct of many different chemical processes. One of the most common is by capturing it from the production of ammonia used as plant fertilizer for the farming industry worldwide. In addition, CO2 is captured in the exhaust streams of industrial burners or energy plants. While not as common, CO2 can also be captured during industrial fermentation, cement production or even removed from the air, although these processes are not yet scalable to meet the world demand.

Once the CO2 is collected it is scrubbed to get to the proper purity, then compressed into a liquid and transported via ocean cargo ships, rail tanker or truck to a regional or local CO2 distributor. The distributor is responsible for certifying the purity of the gas, then transporting it either by portable cylinder or by tanker truck to the end user.

What color are CO2 cylinders?

There are 2 color standards for CO2 cylinders: the United States, and the rest of the world. In addition, the color standards in the US are a recommendation and not law. Therefore, you should never rely on the color of the CO2 cylinder to tell you what gas is inside. Instead, you should rely on the label on the side of the cylinder, which is required.

With all those caveats, large CO2 cylinders typically have a gray shoulder at the top of the tank and below the valve stem worldwide. CO2 tanks are typically stainless steel. Small CO2 cylinders or cartridges could be any color.

Is CO2 dangerous?

While carbon dioxide is a naturally occurring gas, too much of it in the air can cause at the least headaches, drowsiness and at the worst, suffocation. Fresh air contains 0.04% CO2 (400 parts per million) CO2. However a leaking tank or cylinder nipple, or a leaking hose or manifold can quickly raise the CO2 level in an enclosed area up to 3% or more very quickly. This is because liquid CO2 under pressure expands to 535 times its volume as a gas.

While CO2 tank or cylinder leaks are rare, leaking components in the system can and do happen. Learn more about the dangers of CO2.

What’s the difference between CO2 at the welding store and CO2 in a restaurant?

Most bulk CO2 isn’t processed from fresh air, but is collected as a byproduct of other industrial processes like ethanol production. Once the CO2 is collected it is rated according to its purity. For example the industrial CO2 in a welding shop is rated at 99.5% purse, while beverage grade CO2 used in restaurants must be at least 99.9% pure. Learn more about CO2 purity levels here.

Does the quality of CO2 in the cylinder affect the taste of beer?

Absolutely. While food grade CO2 is rated as 99.9% pure, that means there are 0.1% of other gases in the tank. At CO2Meter we like to measure gases in parts-per-million. This means there are up to 1,000ppm of other gases in the tank or cylinder that could impact the overall taste, especially in beer. For this reason, it is important to both periodically clean bulk tanks and to verify the CO2 quality with your CO2 distributor. Learn more about CO2 quality for brewers.

How big a CO2 tank can I use without a safety alarm?

The National Boiler Inspection Code recommends that any business that stores more than 100lbs. of CO2 indoors use a CO2 Storage Safety Alarm. A 100lb. cylinder is 62” tall and 10.5” wide. This size is used in venues who want to reduce the number of tank changes each day. While the old-style cylinders are smaller, if the total weight of CO2 is over 100lbs. an alarm must also be used.

Where can I get my CO2 tank filled?

Small CO2 cylinders can be refilled at many local hardware stores. Larger cylinders can be refilled or exchanged at welding supply stores. For businesses that use lots of CO2, the best solution is to contact a local CO2 distributor like Airgas NuCO2 that will schedule a truck to bring you CO2 cylinders or refill an outdoor tank.

Note that transporting CO2 cylinders is dangerous. While CO2 cylinders are virtually indestructible, if the neck is broken it can become a virtual missile. This is why it is illegal to ship CO2 without proper safeguards and registration.

How do I know how much CO2 is in my tank?

You have 2 options: if your tank has a dual gauge regulator, you can read the amount of pressure on the dial. The pressure will go down as the tank empties. The downside of this method is that once the pressure begins to drop it will run out fairly quickly. For portable CO2 cylinders, the most accurate way to determine the amount of remaining CO2 is to weigh it. The empty cylinder’s weight should be printed on the side, or you can google it. Subtract the cylinder weight from the actual weight, and you know how many pounds or kilos of CO2 you have remaining.

Can my CO2 tanks be filled with other gases besides CO2?

While putting other gases in a CO2 tank or cylinder is possible it is inadvisable, dangerous, and in some situations could be illegal. Tanks are marked with the gas that is in them for safety. A grey shoulder around the nipple on a CO2 cylinder is the universal code for CO2. See a chart here (pdf). In addition, a sticker on the side of a larger cylinder or tank has hazard warning pictograms. On CO2, it is a green triangle that says “non flammable gas” If you were to fill this tank with a flammable gas, it would be dangerous to others in the future.

How can I prevent CO2 leaks from occurring?

With their sturdy Department of Transportation DOT-3AL rated design, a new CO2 tank or cylinder will not leak for decades. By law, refillable tanks must be retested using a hydrostatic (water pressure) cylinder wall expansion test or ultrasonic wall thickness test and a visual inspection every 5 years before refilling. The date of each test must be stamped on the cylinder.

The possibility of leaks is much more likely via the valves and fittings used to route the CO2 from the tank or cylinder to the place the gas is dispensed. If you’ve ever had a water leak at home, you know that they can be difficult to find and fix. The same goes with CO2 leaks.

While there is no way to prevent all leaks, you can reduce the likelihood by having a CO2 delivery system installed by a qualified technician and inspected regularly. If the CO2 valves and fittings are in an enclosed area in a business, by regulation you should also have a CO2 safety alarm to warn occupants if a leak occurs. Read more about CO2 leak training here.


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