Carbon dioxide

At 15°C and 1.013 bar absolute, Air Liquide gives gaseous CO₂ density of 1.8714 kg/m³. 10 kg is therefore about 5.34 m³ of equivalent gas at those conditions. Compare the phase, reference conditions, withdrawal arrangement and grade separately when sizing a supply. Air Liquide property data

Identity and phase behavior

CO₂ (CAS 124-38-9) is supplied in several phases and grades. Welding, liquid cooling and laser resonators use different delivery arrangements and impurity specifications. Airgas CO₂ catalog, Linde laser-gas guidance

Reference conditions matter when comparing quantities. Air Liquide's gas encyclopedia gives approximately 1.8714 kg/m³ at 15°C and 1.013 bar, versus 1.9763 kg/m³ at 0°C and 1.013 bar. These describe gaseous CO₂, not the density of cylinder liquid. Its phase data place the triple point near −56.6°C and 5.19 bar absolute, the critical point near 31.1°C and 73.8 bar absolute, and atmospheric-pressure sublimation near −78.5°C. Thus dry ice sublimes at atmospheric pressure; liquid CO₂ requires suitable pressure and temperature. A room-temperature cylinder is not simply a compressed permanent-gas bottle. Air Liquide gas encyclopedia, CO₂ properties

For the stated 15°C condition, the conversion is 10 kg ÷ 1.8714 kg/m³ ≈ 5.34 m³. Size cylinder capacity and withdrawal separately. Air Liquide property data

Cylinder pressure is not a contents gauge

CO₂ cylinders commonly contain liquid with vapor above it. The British Compressed Gases Association's dispense-gas guidance explains that pressure does not indicate the quantity remaining: use weight to determine contents. It distinguishes gas-use cylinders, which withdraw vapor from above the liquid, from liquid-use cylinders with a dip tube reaching the liquid. Its instructions are written for drinks systems, but the distinction explains why the outlet phase must be specified rather than inferred from the chemical name. BCGA L10 dispense-gas guidance

Vapor withdrawal cools the contents through evaporation. Delivery pressure can fall when heat transfer cannot support demand, even with CO₂ remaining. EIGA warns against heating cylinders to increase discharge. EIGA Doc 67/20, sections 7.5 and 8.4

Keep three records separate: container water capacity, net CO₂ mass, and working delivery pressure. Select replacement timing from the supplier's contents method and process continuity needs, rather than treating a falling gauge reading as a calibrated percentage-full indication. Confirm the withdrawal type from the label and supplier documentation; appearance alone is insufficient. BCGA L10

Welding and cutting roles

CO₂ is an active shielding gas, particularly for steel GMAW/MAG. Its suitability depends on the filler, base metal, transfer mode, and qualified welding procedure. In its automotive MIG guidance, Miller compares 100% CO₂ with 75% argon/25% CO₂: pure CO₂ provides deeper penetration but more spatter and a rougher bead. That comparison is a process tradeoff, not a guarantee of adequate fusion or acceptable properties on every joint. Voltage, current, wire size/feed, thickness, position, and joint geometry remain relevant. Miller automotive MIG guidance

Changing from an argon-rich blend to pure CO₂ is consequently a procedure change, not just a cost substitution. Miller's pulsed-MIG guidance says carbon-steel pulse and spray modes typically require at least 80% argon, and explicitly excludes CO₂ blends from aluminum welding. Confirm the actual power-source program and consumable recommendation before changing gas; do not extrapolate a steel short-circuit setup to aluminum or a pulsed process. Miller pulsed-MIG guidance

A CO₂ laser introduces a different gas function. Linde distinguishes resonator gases used to generate laser light from assist gases delivered to the cutting process. Its LASERLINE offering lists CO₂ at 99.995% (4.5) for resonator service, either supplied separately to integrated mixers or within an OEM-specific LASERMIX blend. Common cutting assist gases in that program include nitrogen, oxygen, argon, and helium. The machine name does not establish that ordinary welding CO₂ is an acceptable resonator refill or cutting assist gas. Linde LASERLINE and LASERMIX

Other documented roles include refrigeration, chilling/freezing, snow cleaning, pH control, and supercritical extraction. These require application-specific systems; a liquid injection or extraction specification should not be reduced to a welding gas flow setting. Messer CO₂ applications

Grades and impurity specifications

Read individual limits as well as the headline assay. Airgas lists Bone Dry CO₂ at 99.9% purity with 10 ppm water, and Research CO₂ at 99.999% with 3 ppm water, alongside additional impurity limits and a table footnote governing total indicated components. Concentrations are ppm by volume unless otherwise specified. Its catalog also distinguishes certificates included with particular products from certificates available on request. These are supplier-specific grades, not universal definitions of “dry” or “research.” Airgas CO₂ grade table and notes

Specify the sensitive contaminants, test basis, certificate, phase of sampling where relevant, and intended application. Food/beverage, pharmaceutical, semiconductor, refrigerant, and industrial uses have different quality contexts. Messer offers these categories separately; a purity number alone does not establish food or medical suitability. Match the current local product specification and applicable process requirements rather than choosing the largest number in a catalog. Messer CO₂ specifications and applications

Delivery and hazards

EIGA distinguishes vertical vapor-withdrawal cylinders without dip tubes from liquid-withdrawal cylinders with dip tubes. It prohibits direct connection of the latter to gas-use systems or ordinary regulators: liquid can damage regulator internals. Liquid-to-gas service requires an appropriately sized vaporizer. Match equipment to phase, pressure, and sustained demand with the supplier. EIGA Doc 67/20, sections 8–9 and 12.3

The Linde Austria SDS, version 2.6, revision 8 September 2025, classifies CO₂ as liquefied gas under pressure and warns that heating can cause container explosion. It also identifies cold burns/frostbite from liquid contact and, critically, rapid circulatory insufficiency at high CO₂ concentrations even at normal oxygen concentrations. Oxygen displacement is therefore only part of the inhalation hazard. Use the supplied product's current jurisdiction-specific SDS and site exposure controls; nonflammability does not make an enclosed release safe. Linde CO₂ SDS, sections 2 and 4

EIGA says oxygen-depletion devices are unsuitable as CO₂ alarms; its guidance addresses CO₂ detection and ventilation. It also warns of dry-ice plugs and trapped pressure after liquid depressurization. Follow supplier procedures for obstructed equipment. EIGA Doc 67/20, sections 5.3 and 11.2

Related reference

Welding methods