User Guide to Thresholds and Classification - Environmental ...

42User Guide for Thresholds and ClassificationsMeasuring the flammability of gasesThe ISO 10156:1996 test involves introducing a known concentration of a gas and air mixture, in a reactiontube fitted with an ignition spark plug with 5 mm gap, connected to a 15 kV spark generator, and observingwhether a spark results in a flame rising up the tube.The procedure involves beginning with a low concentration of gas, and repeating the test several times, eachtime gradually increasing the concentration of gas until a spark results in a flame rising up the tube.The calculation methods in the ISO standard appear to apply only to certain applications such as special gasmixtures produced to order (in small quantities).Alternative test methodsFor alternative test methods see:‗Limits of flammability of gases and vapours‘ (Coward and Jones, 1952);‗Flammability characteristics of combustible gases and vapours‘ (Zabetakis, 1965);Flammability of Mixed Gases (Burgess et al, 1982);Code of Practice for Selection, Installation and Maintenance of Electrical Apparatus for Use in PotentiallyExplosive Atmospheres (Other Than in Mining Applications or Explosives Processing and Manufacture),BS 5345 Part 1: 1989 (British Standards, 1989); andDetermining Limits of Flammability of Chemicals at Elevated Temperature and Pressure, ASTMStandard E918-83: 1988 (ASTM, 1988).Comparison with previous Dangerous Goods Act 1974 criteriaThe Dangerous Goods Act 1974 (which was repealed by the Hazardous Substances and New OrganismsAct 1996 (HSNO Act)) scheduled flammable gases into the four categories.Class 2(b): ethane, ethylene, hydrogen, methane, and any other flammable gas (other than that coveredby the following bullets) included under any succeeding paragraph of this class).Class 2(c): acetylene, compressed or dissolved, and contained within a porous substance.Class 2(d): liquefied petroleum gas and any other liquefied flammable gas.Class 2(f): anhydrous ammonia.The Dangerous Goods (Class 2 – Gases) Regulations 1980 classified gases in many cases by their intendeduse, for example, ammonia. In other cases, the regulations subdivided the gases into groups such aspermanent flammable gases and liquefied flammable gases. By comparison, the HSNO Act has only twoclasses, which relate to the level of the flammable effect.Relationship to the Gas Act 1992The regulations made under the HSNO Act do not apply to any gas distribution and transmission system,which comes under the provisions of the Gas Act 1992. While substances such as natural gas are clearlyflammable, the Gas Act generally provides up-to-date and effective control in these circumstances.Consequently, specific provisions are included in the Hazardous Substances (Classes 1 to 5 Controls)January 2012 EPA0109