CO₂ Grades Explained

A CO₂ grade is a certified minimum purity level with capped limits on specific impurities, set by a governing standard and matched to how the gas will be used. The grade tells you what’s guaranteed to be in the cylinder and, just as importantly, what’s guaranteed to be kept out.

Why Does Using the Right CO₂ Grade Matter?

Using the wrong grade can contaminate your product, fail an inspection, or waste your money, depending on which direction you get it wrong. The stakes climb as the CO₂ gets closer to a person.

Go too low, and impurities meant for a welding bay end up somewhere they shouldn’t. Trace benzene or heavy hydrocarbons in the gas carbonating a sparkling water is a real problem, not a rounding error.

Go too high, and you’re paying a premium you don’t need. A fabrication shop buying beverage-certified CO₂ to shield mild steel welds is lighting money on fire.

The right grade is the one that matches the job. That sounds obvious until you realize how many buyers order by habit and never check what they’re actually getting.

How Are CO₂ Grades Measured and Set?

A CO₂ grade is defined by two things: a minimum purity percentage and a list of maximum impurity limits, both written into a published standard. The purity percentage is the number everyone quotes, but the impurity limits are what actually set the grades apart.

Several bodies set those standards. In the U.S., the Compressed Gas Association publishes CGA G-6.2, the commodity specification for carbon dioxide. Beverage makers lean on the International Society of Beverage Technologists (ISBT), medical CO₂ follows a U.S. Pharmacopeia (USP) monograph, food grade ties to the Food Chemicals Codex and FDA rules, and Europe works from European Industrial Gases Association (EIGA) standards.

A higher purity number doesn’t automatically mean a higher grade, and that catches a lot of people off guard. What separates the tiers is which specific impurities are capped, how tightly, and who’s enforcing it. A specification typically controls:

• Purity floor: the minimum percentage of actual CO₂
• Moisture: water content, often held to single-digit or low double-digit ppm
• Oxygen and carbon monoxide: capped in the low ppm range for consumable grades
• Hydrocarbons: including benzene and acetaldehyde, capped tightly where taste and safety matter
• Sulfur compounds: carry odor and health concerns even in trace amounts

Impurity limits are measured in parts per million (ppm), and for the strictest grades, parts per billion (ppb). The proof that a batch actually hit those numbers is the Certificate of Analysis, which we’ll come back to.

What Is Industrial Grade CO₂?

Industrial grade CO₂ is the baseline utility tier, generally 99% pure or better, with looser impurity limits because nothing here is meant to be eaten, drunk, or inhaled. It’s the workhorse grade for jobs where trace contaminants don’t change the outcome.

You’ll find it shielding metal inert gas (MIG) welds, where purities around 99.5% are common, along with water treatment, foundry work, and general manufacturing.

Industrial CO₂ isn’t certified against the tighter impurity limits that food, beverage, or medical use demand, so it has no place in a soda line or an operating room.

That doesn’t make the gas dirty. Industrial CO₂ often comes off the same source streams as higher grades, but it isn’t tested and certified to the stricter limits, so you can’t bank on what’s in any given batch.

Where the job doesn’t hinge on those limits, industrial is the economical choice.

What Is Food Grade CO₂?

Food grade CO₂ is carbon dioxide certified safe for contact with food, generally at least 99.9% pure with hard caps on impurities like benzene, carbon monoxide, and heavy hydrocarbons. The jump from industrial to food grade is less about the purity number and more about the guaranteed limits on what could contaminate a product.

In the U.S., that certification runs through FDA requirements and the Food Chemicals Codex. Suppliers have to document testing and quality control, and a food safety risk assessment is standard practice at plants producing CO₂ for consumables.

The line between regular and food grade is where a lot of operations run into problems, and it’s worth understanding the specific differences between regular and food grade CO₂ before you assume your supply qualifies. Food grade covers a wide range of uses, from freezing and chilling to modified atmosphere packaging, each with its own considerations worth a closer look.

What Is Beverage Grade CO₂?

Beverage grade CO₂ is the consumable tier tuned for carbonation, meeting ISBT guidelines that cap more than 30 individual impurities, many at ppm and some at ppb levels. It shares the roughly 99.9% purity floor with food grade, but it’s the most exhaustively specified consumable grade because of everything it controls beyond that number.

The reason is taste. Carbonated drinks are brutally sensitive to trace contamination, and impurities like sulfur compounds, acetaldehyde, or benzene can taint flavor and aroma at concentrations most processes would ignore. Think about how a single drop of something can change a whole glass of water.

That’s why the ISBT specification reads like a laundry list of named compounds with individual limits, rather than a single purity target.

What Is Medical Grade CO₂?

Medical grade CO₂ is carbon dioxide regulated as a drug, produced under a USP monograph that sets a purity floor of 99.0% and caps specific impurities like carbon monoxide and hydrogen sulfide. It’s used for procedures like insufflation in laparoscopic surgery, where CO₂ inflates the abdominal cavity, and in certain respiratory applications.

That 99.0% floor might have jumped out at you as lower than beverage grade’s 99.9%, which makes medical grade look weaker on paper. It isn’t.

Medical grade earns its standing through drug-level oversight, not a bigger purity number. Every batch is produced under pharmaceutical regulation with documentation to match, and the impurities that matter for the human body are the ones held in check. It’s an example of why grade ranking is about scrutiny and fit, not just counting nines.

What About Research and Specialty High-Purity CO₂?

Research and specialty grades have purity requirements of 99.99% and 99.999%, which the industry calls four nines and five nines, for jobs where even trace contamination skews a result or damages equipment. These are the highest raw purities in the CO₂ lineup.

The applications are precision work: laboratory analysis and instrument calibration, gas chromatography, CO₂ lasers that are sensitive to moisture and hydrocarbon buildup, and supercritical extraction where leftover residue can’t be tolerated.

You’re not putting this in a keg. It costs more and exists for a narrow set of uses, but when the work demands it, nothing lower will do.

How Do You Know You’re Getting the Right Grade?

Ask your supplier for documentation that ties the gas to its spec, and know which document you’re getting. A grade name printed on an invoice doesn’t count for much.

For consumable and high-purity grades, a Certificate of Analysis is the standard. It’s a batch-level report showing the actual measured results for that specific lot, and reputable suppliers provide one for food, beverage, medical, and specialty CO₂.

For basic industrial grades, many suppliers issue a Certificate of Conformance instead, which states the gas meets a spec without listing lot-specific test numbers. That’s usually fine for industrial work, and you can still request a batch analysis when the job calls for it.

The Cost of Guessing

Getting the CO₂ grade wrong can mean you overpay for purity you don’t need, or under-buy and put a product, a process, or a person at risk. Match it to the job up front and then it’s smooth sailing.

Lawrence Haynes

Lawrence is the Marketing Director at WestAir Gases & Equipment in San Diego, CA