VOCs include both man-made and naturally occurring chemical compounds that are released into the atmosphere as a gas. They are found in oil-based paints, adhesives, and cleaning supplies and may trigger respiratory irritation, headaches, or other health concerns. VOCs also react with nitrogen oxides and sunlight to form smog. Both federal and state regulators have imposed limits on VOC emissions, primarily at the manufacturer level. A number of products, from paint to engine degreasers and windshield washer fluids, have been reformulated to reduce their VOC levels. Additionally, there has been an effort to switch the public from oil-based paints and cleaning solvents (enamel, lacquer, mineral spirits, etc.) to water-based paints like latex. The paint industry has expanded the range of water-based finishes that are available to assist in the conversion. Sometimes it is not a voluntary switch. A number of states or urban areas have banned retail sales of certain oil-based products in an effort to combat smog.

Aerosol can spray paints are frequently used for smaller jobs and touch-up painting. They rely on VOC-emitting propellants, gasses used to which expand and force out the paint when the valve is opened. The propellants have changed over the years. Chlorofluorocarbons were banned in 1978 since they deplete the upper ozone layer. Butane and propane were then widely used until they were identified as significant smog contributors. The paint industry has more recently relied on a variety of hydrofluorocarbons to serve as propellants. To address VOCs in aerosol paints, both the U.S. Environmental Protection Agency (EPA) and California have limited the amount of propellants that can be used in spray paint. As with paints purchased in cans, the issue is largely being addressed at the manufacturer level through product reformulation.

HAPs pose a separate concern. They are hazardous metal compounds-cadmium, chromium, nickel, etc.-that become airborne during paint stripping operations or surface coating and autobody refinishing operations. The EPA now regulates most activities except low-volume operations such as when hobbyists restore or customize one or two personal vehicles (or the equivalent in pieces) per year. The EPA rule establishes "best practices" (spray booth, spray gun cleaning, etc.) for minimizing HAP emissions during surface coating operations. All shops are effectively required to have a filtered spray booth or prep station and use high-volume low-pressure (HVLP) or equivalent spray equipment. Spray guns are required to be cleaned manually or with an enclosed spray gun washer. According to the EPA, if new equipment is required to meet the requirements, the costs should be recouped through a more efficient use of labor and materials. (It should be noted that the Occupational Safety and Health Administration requires commercial spray finishing operations to be performed in a booth or similar enclosure.) The HAP rule does not apply to painting done with an airbrush or hand-held non-refillable aerosol cans.

Engine Swapping
Hobbyists frequently ask us about the rules governing engine switching in project vehicles. First of all, those engaged in engine switching activities are bound by specific state laws that may vary from state to state. Having said that, there are some general guidelines one may consider. This article will cover the rules for switching the engine in production-type vehicles (but not specially constructed vehicles, street rods, kit cars, and the like). The basic rule of engine switching (as opposed to installing a "replacement" engine) is that the change must do no harm. This means that the engine being installed must theoretically be at least as "clean" as the one taken out. Several requirements may define "clean" for the purposes of engine switching: