In the alphabet-soup world of finishing, the acronyms VOC and HAP stand for Volatile Organic Compound and Hazardous Air Pollutant respectively.The term ”organic” in the chemical world means that it is based on tetravalent carbon. For finishing, organic solvents are those that contain carbon, which is just about everything other than water.Volatile simply means they will evaporate at standard temperature and pressure.
Since not all VOCs are hazardous, and since not all hazardous materials are VOCs, the term HAP picks up those things that fall in that murky area. As far as finishing materials are concerned, the two are typically measured together, and with only a few exceptions, are one and the same.
Why are They a Concern?
Specifically,VOCs were found to be ozone generators.When exposed to sunlight,VOCs in the air form ozone, which is an ingredient of smog. The problem is that not all VOCs are ozone generators. Some are not, and even among those that are, some are very slow or weak ozone formers while some are very fast or strong ones.Thus, not all VOCs are created equal.
Because of that, some volatile organic compounds which do not generate ozone have been declared exempt. That means that even though they are VOCs by definition, they are not legally regarded as VOCs as far as coatings and strippers are concerned. Acetone, methylene chloride, methyl acetate and parachlorobenzotrifluoride (PCBTF), which was originally marketed under the trade name Oxsol 100, are all examples of exempt VOCs.Thus, you can buy zero VOC lacquer that is 75 percent volatile organic compound solvent, yet is legally free of VOCs. In this case, the solvent is usually a mixture of acetone and PCBTF.
How are They Different?
The issue with VOCs, as far as the EPA is concerned, has to do with whether or not they generate ozone. It’s that simple and that specific. HAPs, on the other hand, focus on hazard to both humans and the environment. As you can see, it is a much broader term.
That said, there are VOCs which may be hazardous to the environment as ozone generators, but not hazardous to humans, and vice versa. For example, methylene chloride, the main ingredient in many paint removers, is not considered a VOC because it is not an ozone generator.Thus, the EPA allows it in formulations without penalty. However, it is harmful to humans, and if you use it, you must take the appropriate safety precautions.Thus, it is a HAP but not a VOC.
Acetone, on the other hand, is not an ozone generator either, nor is it considered by the EPA to be particularly harmful. It is neither carcinogenic nor does it appear to cause any other serious illness. For that reason, the EPA sees it as neither a VOC nor a HAP.
That does not mean there is no danger connected to it. Acetone, like many other ketones, is very flammable, so it is a fire hazard. In contrast, methylene chloride is nonflammable — so nonflammable, in fact, that you can add it to flammable compounds to make them nonflammable.
Isoparaffins, the ingredients in “odorless” mineral spirits, are a good example of a third category. They are ozone generators, but are not particularly hazardous to humans.Thus, they are restricted by the EPA, but generally do not require extreme handling cautions.