Reciprocal Calculation Procedure (RCP) part 1: what hydrocarbon solvents and RCP are

This video explains what are hydrocarbon solvents and how to calculate their occupational exposure levels thanks to the Reciprocal Calculation Procedure in order to protect workers from adverse health effects.
What are hydrocarbon solvents?
Hydrocarbon solvents are products that are widely used in commerce.
Some of these substances are volatile, and exposure to vapor is likely to occur during use.
In some situations, exposure levels may be relatively high, characterized by effects ranging from dizziness to drowsiness,
that can be prevented by recommending occupational exposure limits, commonly known as OELs.
An OEL is the maximum air concentration of a substance, at which workers can be exposed throughout their working lifetime, without developing adverse health effects.
However, setting occupational exposure limits 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, the information may be limited, so action must be taken towards setting an OEL that considers all relevant types of hydrocarbons and that provides consistent occupational advice.
Therefore, an approach that permits the calculation of a unique occupational exposure limit for each hydrocarbon solvent, based on relatively simple compositional information is proposed by hydrocarbon solvent manufacturers in the United States and Europe.
The desired method for setting an OEL should:
1. be applicable to all hydrocarbon solvents
2. be based on sound scientific principles
3. take all hydrocarbon types into account
4. take special note of any hydrocarbon of unusual toxicity (e.g., n-hexane, naphthalene)
5. produce changes in OELs that are proportional to the variability in composition
6. ensure that the specific OEL of an individual hydrocarbon is not exceeded
7. be readily adaptable to advances in understanding of the toxicity of the individual hydrocarbons.
However, it is not always possible to identify all of the components of hydrocarbon solvents, and most of the toxicology data is on representative hydrocarbon solvents rather than their individual components.
Therefore, the Reciprocal Calculation Procedure - RCP- approach was developed, which groups all hydrocarbons of similar physical, chemical and toxicological properties and assigns them a group guidance value or GGV, which covers existing OELs of representative hydrocarbons for the entire group.
When these GGV values are used in the RCP calculation, it is ensured that 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.
These GGV are:
C5-C8 aliphatic constituents
C9-C15 aliphatic hydrocarbon constituents
And C9-C15 aromatic constituents