IS 308:2024 explained what the Indian specification for dissolved acetylene actually limits, how it is tested, and what changed in the fourth revision

IS 308:2024 is the Indian Standard that defines what a cylinder of dissolved acetylene must contain, and — just as importantly — what it must not. It is a short document with four numerical limits, a sampling scheme and a set of laboratory methods, and it is widely misquoted: the "99 percent purity" that Indian suppliers attach to it is not in it at all. This page explains the four limits, how each is tested, where the 2024 fourth revision differs from the 1988 third revision, and how the Indian specification sits against the European grade codes.

IS 308 was first published in 1953 and revised in 1962, 1977 and 1988; the fourth revision was issued in July 2024 by the Industrial Gases Sectional Committee, CHD 06, under the Chemical Division Council. Its scope is the requirements and methods of sampling and test for dissolved acetylene gas. Clause 4.1 describes the product: acetylene dissolved in acetone to IS 170, or another solvent, held in a homogeneous porous substance packed in a cylinder so that it is not deemed an explosive under the Explosives Act 1884. That last phrase matters, because Government of India notification GSR 625(E) of 7 August 1983 declares acetylene an explosive when liquid, under pressure or mixed with air or oxygen; the porous mass and solvent are what take the product out of that definition. The cylinder side of the specification is on the dissolved acetylene standards page.

There is no row for acetylene content. The standard limits what may be present besides acetylene, and leaves the balance implied. A fifth requirement applies only to acetylene for navigational illuminants: clause 4.4 caps chloro-compounds at 0.001 percent by volume, tested by Annex B-7, a survival from the era of acetylene-lit buoys and lighthouses.

Table 3 of the 1987 edition of IS 1040, the calcium carbide standard, requires the gas evolved from carbide in the laboratory to contain at least 99.0 percent acetylene by volume, with up to 0.15 percent H₂S, 0.06 to 0.08 percent PH₃ depending on quality, 0.001 percent arsine and 0.10 percent ammonia. That is a description of raw generator gas from compliant carbide. IS 308 describes the gas after purification, in the cylinder. The two are written by different committees — IS 1040 by the inorganic chemicals committee, IS 308 by the industrial gases committee — on unrelated revision cycles, and they are structured differently: IS 1040 has a positive assay and IS 308 does not. Read together, they define the purification duty: compliant carbide may legally deliver 0.15 percent H₂S and up to 0.08 percent PH₃, and the cylinder may contain 0.02 and 0.01 percent respectively, so the purifier train has to bring both impurities down by a large factor. Phosphine is the harder of the two, because the lime slurry in the generator holds back most of the sulphur but very little of the phosphorus, leaving the purifier to remove it. Indian carbide is at the high end of the world phosphine range, which is the subject of the phosphine in Indian carbide page, and the equipment that does the removing is described under acetylene purification systems.

Clause 6.1 allows samples to be drawn from the filling rack during filling, or from 5 percent of the cylinders after blowing off about 15 percent of the gas in them. Clause 6.2 requires two separate samples from the rack, and clause 7 declares the lot conforming only if both samples satisfy every requirement. Before the laboratory tests, Annex B-2.2 purges the sample cylinder through a regulator at 0.2 kgf/cm², venting about one sixth of the contents, so that the gas analysed represents the bulk and not the vapour space, where insoluble gases concentrate above the solvent.

The four Table 1 limits are the same figures as in the 1988 third revision. The revision restyles the document, incorporates the two amendments issued to the 1988 edition, and updates the referenced standards: acetone to IS 170:2020, nitric and hydrochloric acids to IS 264:2005 and IS 265:2021, rectified spirit to IS 323:2009, reagent water to IS 1070:2023, rounding to IS 2:2022, dangerous-goods marking to IS 1260 (Part 1) and classification to IS 1446:2002. It carries the ICS code 71.100.20 and may be marked with the Standard Mark under the BIS Act 2016.

Two things did not change and are worth knowing. Clause 5.1 still refers the cylinder design to Government of India Notification M-1268(1) of 9 January 1939, with modifications ordered by the Chief Inspector of Explosives, whereas IS 309:2023, IS 1747:2023 and IS 307:2024 cite the Gas Cylinders Rules 2016 and the SMPV Rules 2016. The governing cylinder instrument in India is Rule 37 of the Gas Cylinders Rules 2016 and IS 7312:2018, whatever IS 308's packing clause says. And the standard still cites the 1973 edition of the gas-industry glossary IS 7062, which BIS revised in 2024.

EIGA Doc 240 codes grade by the count of leading nines and the next digit, and warns that words such as "industrial" and "high purity" have no legal definition. It also records that purified acetylene in European practice is typically below 10 ppmv phosphine and 10 ppmv H₂S, and that targets of 1 ppmv are not uncommon. IS 308's limits are therefore a floor, not a description of good practice; a filler whose purifier is working will be well inside them. KIGL's ultra-high-purity acetylene is specified against an impurity table (PH₃ and H₂S each not more than 10 ppm, a KIGL specification) for that reason, and the grade vocabulary is set out under acetylene grades explained.