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Reciprocal Calculation Procedure (RCP)
Setting occupational exposure limits (OEL) for hydrocarbon solvents is challenging since this type of solvents have complex and variable hydrocarbon compositions . This means that the worker will inhale not only one but many types of hydrocarbons from the solvent at the same time. Some of these hydrocarbons are well characterized and have their own OELs, but for others, information may be limited. Therefore, it is vital to define an OEL that takes into account all the relevant types of hydrocarbons and provides consistent occupational advice.
An approach that enables to calculate a unique OEL for each hydrocarbon solvent, based on relatively simple compositional information is needed. Furthermore, it is not always possible to identify all of the components of hydrocarbon solvents, and most of the existing toxicology data relates to representative hydrocarbon solvents rather than their individual components.
Therefore, the RCP-approach was developed by hydrocarbon solvent manufacturers in the United States and Europe, which groups all hydrocarbons of similar physical, chemical and toxicological properties and assigns them a group guidance value (GGV), which covers existing OELs of representative hydrocarbons within a group. Using these GGV values in the RCP calculation ensures that the hydrocarbons in that group do not exceed their own individual OELs. In practice this means measuring a single OEL that reflects the solvent’s hydrocarbon composition.
Each GGV is supported by a series of toxicological studies including acute central nervous system effects that confirm that certain hydrocarbon constituents can be grouped together under three GGV and distinguish them from the Substance Specific Values or SSV.