Volatile Organic Compounds, or VOC’s, are those ingredients in a paint that evaporate during or after the application of said paint. The VOC content is often expressed numerically as “grams per litre”.
Broadly speaking, we can generally think of VOC’s as “solvents”, but the legislative definition of VOC includes many chemicals that are not solvents, such as ammonia, as well as exempting some solvents from VOC classification, such as acetone.
As you might infer, the definition of what is and isn’t a VOC is as much a legislative issue as a scientific one, and it differs between countries (or even between states such as in the USA).
In Australia, VOC restrictions for paints are essentially voluntary.
APAS, the Australian Paint Approval Scheme, sets VOC limits for certain types of paints being used by government departments.
It’s voluntary in the sense that it only applies if you want to sell paint to the government (whereby it must be “APAS-approved”), but if you don’t, then these VOC limits are not relevant or applicable to you.
Even so, APAS currently only concerns itself with setting VOC limits for waterborne paints – not solvent-based ones. Why? It acknowledges that using solvent based paints is essential for industrial purposes, and their VOC levels are all so high that it is kind of meaningless to set limits.
Outside of these APAS VOC limits, there are no legislative restrictions on the VOC content of paints used in Australia.
Out of interest, APAS uses the following descriptions for VOC level.
< 5 grams per litre: “very low”
5 – 49 grams per litre: “low”
50-99 grams per litre: “moderate”
100-249 grams per litre: “high”
250 grams per litre: “very high”
A typical two-pack, solvent-based polyurethane coating has a VOC level of around 600 grams per litre, which would clearly be rated as “very high” by this definition, although it is typical for a solvent-based product.
Outside of APAS, these definitions are at best simply a guide, with various non-government parties coming up with their own terms and limits.