IS 307: the Indian Standard for carbon dioxide and its black cylinder

IS 307 splits carbon dioxide into two grades, and the choice between them catches people out because the higher-purity grade is not the drier one.

• Grade 1 is specified for reagent and welding use. It is the drier of the two by two orders of magnitude, because moisture in a shielding gas ruins the weld and moisture in a reagent gas ruins the analysis.
• Grade 2 is specified for beverages, fire extinguishers, refrigeration and general commercial use. It carries the higher assay, because a beverage gas has to taste of nothing, but it tolerates far more moisture.

Neither grade is simply "better". Asking a supplier for "the purer one" without saying what it is for is how a welding shop ends up with a wetter gas than it needed.

A caution on the word "beverage". IS 307 describing a grade as suitable for beverages is a statement about the chemistry of the gas. It is not a food-safety certification and it is not the same as a food-grade supply chain. Food and beverage contact in India engages FSSAI, and beverage carbon dioxide is normally held to an industry beverage specification on top of the chemical one. If you are buying CO₂ for carbonation, ask for the certification, not just the grade.

For the actual limits, work from IS 307 itself — we use it to set our specification, we do not republish it.

IS 307, Carbon Dioxide, is the Indian Standard specifying carbon dioxide as a product. It is one of the older standards in this cluster and has been reaffirmed rather than revised — normal for a gas whose specification has not needed to move.

If you are writing a tender clause, check the BIS catalogue on the day rather than trusting a reaffirmation date printed on a supplier’s brochure. That advice applies to every standard on this site, but it applies most to the old ones.

This is the part that matters more than the specification.

Under IS 4379, carbon dioxide and oxygen are both black cylinders. The only thing separating them on the paintwork is a white or aluminium neck band on the carbon dioxide.

That band is not a robust signal:

• it fades in sunlight and weather
• it gets overpainted during refurbishment
• it disappears entirely under a coat of workshop grime

So the rule in every plant we supply is the same, and it is worth putting on a wall: colour tells you where to look, the stamping tells you what it is. IS 4379 requires the cylinder to be marked with the gas name and chemical formula, and every cylinder carries stamped identification on the shoulder. Read it, then read the label. Colour is the third check.

Carbon dioxide is liquefied in the cylinder, not merely compressed. What the valve gauge reads is the vapour pressure above the liquid, and that stays roughly constant while any liquid remains — so a gauge showing healthy pressure tells you almost nothing about how much gas is left.

Content is established by weight, against the tare stamped on the cylinder. A CO₂ cylinder that feels light is nearly empty whatever the gauge says.

Carbon dioxide is filled to IS 307 at the Guwahati works, into cylinders built and requalified to the standards above, painted and marked so the contents can be identified before anyone connects anything.

One thing to raise when you enquire: if your use is food, beverage or anything ingested, say so. Those applications carry purity and impurity requirements beyond the industrial specification, and industrial grade should never be assumed suitable for them. See carbon dioxide for supply detail.