What are industrial gases? The four families the five ways they are supplied, and the Indian standard for each

An industrial gas is a gas made in quantity and sold for what it does in a process: oxygen to burn hotter, nitrogen to keep air out, argon to shield a weld, acetylene to cut steel, carbon dioxide to carbonate a drink. Most are separated from air or recovered from another process, purified to a stated grade, and delivered in a cylinder, a tank, a pipe or a plant on the customer's own site. In India each major gas has its own Bureau of Indian Standards specification and its own cylinder colour.

Three things: it is produced in bulk rather than in a laboratory, it is sold to a purity specification, and it is delivered under pressure or as a cryogenic liquid. The Gas Cylinders Rules 2016 give the legal threshold. Rule 2(v) treats any gas exerting more than 2.5 kgf/cm² absolute at 15 °C, or more than 3 kgf/cm² absolute at 50 °C, as a compressed gas, and expressly includes cryogenic liquids. Once a gas crosses that line, its cylinder, valve, filling, storage and transport are regulated by PESO.

The Rules then sort gases by what they do in a cylinder, using critical temperature, the temperature above which a gas cannot be liquefied by pressure alone. A permanent gas has a critical temperature below −10 °C and stays gaseous in the cylinder at any pressure; oxygen, nitrogen, argon, hydrogen and helium are permanent gases. A high-pressure liquefiable gas has its critical temperature between −10 °C and +70 °C, which is where carbon dioxide and nitrous oxide sit. A low-pressure liquefiable gas, such as LPG or ammonia, has one above +70 °C. Acetylene is a fourth case, a dissolved gas held in acetone inside a porous mass, for reasons explained on why acetylene is dissolved in acetone.

The atmospheric gases dominate by volume because their raw material is free. The U.S. Standard Atmosphere 1976 gives dry air as 78.08 % nitrogen, 20.95 % oxygen and 0.93 % argon by volume, with every other component together under 0.05 %. Separating air is therefore the largest single activity in the industry; the routes are compared on types of industrial gas plants.

The Gas Cylinders Rules also define the hazard classes that decide how a gas is stored and moved. Rule 2(xxvi) calls a gas flammable if it forms a flammable mixture at 13 % or less in air, or if its flammable range is wider than 12 percentage points; acetylene, at 2.5 to 82 % in air under IS 14814:2023, qualifies on both counts. Rule 2(xlv) calls a gas toxic if its maximum allowable concentration for breathing does not exceed 100 mg/m³. The full hazard picture gas by gas is on which industrial gases are flammable.

One gap is worth knowing before a tender asks for it. The BIS committee that writes the gas specifications, CHD 06, publishes no standard for an air separation or PSA plant; it covers the product gases and, through the IS/ISO 8573 series, the purity classes of compressed air. A claim that a PSA plant is built "as per IS" therefore has no plant standard behind it. The trade-offs between cylinder supply and a plant are set out on cylinder supply or on-site generation.

Two cautions apply to that table. First, the specifications set limits that buyers often misquote. IS 308:2024 sets no minimum acetylene purity at all, only four impurity limits, including phosphorus compounds at 0.01 % v/v and sulphur compounds at 0.02 % v/v. IS 309:2023 now has three oxygen grades at 99.95, 99.5 and 99.0 % minimum, so "99.5 % to IS 309" names Grade 2 and should say so. IS 1747:2023 abolished the old "technical" and "pure" nitrogen grades. Second, the colours are law, not decoration: Rule 8(1) of the Gas Cylinders Rules 2016 applies IS 4379 to industrial cylinders and IS 3933 to medical ones, and the warning label that Rule 9 requires on every cylinder says that its colour must not be changed. The full scheme is on cylinder colour codes.

The welding column is the one most buyers meet first; welding gases explained gives the gas for each process. The physical data behind every row, such as boiling point, density and flammable range, are collected on the industrial gas properties table.

Kamrup Industrial Gases Limited, founded in 1947, fills dissolved acetylene, industrial and medical oxygen, nitrogen, argon, carbon dioxide, compressed air, calibration mixtures and ultra-high-purity acetylene in DMF at its own PESO-approved works at Noonmati, Guwahati and at Howrah, Kolkata. KIGL operates an air separation plant and supplies liquid oxygen and liquid nitrogen. Helium, hydrogen and nitrous oxide are supplied from licensed producers; helium is not produced in India at all. KIGL also builds acetylene plants, PSA oxygen and nitrogen plants, gas pipelines and medical gas pipeline systems.