Chemical vapour classification

Classification of gases, chemical vapour and volatile liquids... 

Chemical Vapour Deposition Precursors and Their Classification... 

In a sense this subdivision of the composition of the atmosphere is arbitrary since some of the so-called contaminants are derived partly or wholly from natural sources. However, in that their concentrations vary appreciably within very narrow geographical limits, they may be distinguished from the contents of Table 2.8 (with the possible exception of water vapour). Table 2.6 lists those contaminants which are important from a corrosion standpoint. Excluded are contaminants found only in very specific locations, e.g. in the vicinity of a chemical works. The concentrations given are intended only to indicate general levels in the usual classification of environments and not to define a particular environment. 

Following the historical development of electrical engineering and explosion protection, zone classification was the objective of national standards and installation rules. Most of the leading industrial countries established an installation practice for chemical plants and the oil and gas industry with two or three zones for areas hazardous due to gas- or vapour-air mixtures and two zones for areas with hazardous dust-air mixtures. Apart from this philosophy, the coal mining industry in most countries tends to avoid an area classification and defines only one category of explosion protection ( firedamp-proof ). More recent standards or directives present a three-zone concept for areas endangered by combustible gas- (vapour-, mist-) air mixtures and dust-air mixtures in industrial plants (other than coal mines). 

Flammability classifications of solvents (and other chemicals) are based on flash point (fl.p.) measurements. Flash point is the lowest temperature at which a liquid has sufficient vapour pressure to form an ignitable mixture with air near the surface of the liquid. The following criteria currently apply (CHIP Regulations 2009) ... 

Vapour inhalation values are intended for use in classification of acute toxicity for all sectors. It is also recognized that the saturated vapour concentration of a chemical is used by the transport sector as an additional element in classifying chemicals for packing groups. 

Olsen, E. and Nielsen, F. (2001) Predicting vapour pressures of organic compounds from their chemical structure for classification according to the VOC-directive and risk assessment in general. Molecules, 6, 370-389. 

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