Dust absorbs moisture, which also plays a role in failure. Periodically spraying air through the heat sink fan is a good PM measure. However, although discharging compressed air into a VFD is a viable option in some environments, typical plant air contains oil and water. To use compressed air for cooling, you must use dry, oil-free air or you're likely to do more harm than good. This, in turn, requires a specialized, dedicated, and expensive air supply.
Common plastics are prime generators of static electricity.
Keep It Dry Figure 2 shows a control board that was periodically subjected to a moist environment. Initially, this VFD was wall mounted in a clean, dry area of a mechanical room, and moisture wasn't a problem. However, as is often the case, a well-meaning modification led to problems. An area of the building required a dehumidifier close to the mechanical room. Because wall space was available above the VFD, this is where the dehumidifier went.