[billbo911]

I doubt FIRST would rule it's use illegal because it modifies performance of the item being sprayed.
That said, I definately believe they might ban it's use for health reasons.

Dust Off is difluoroethane, a refrigerant.

Here is the "Safety" text from Wikipedia on difluoroethane.

The practice of deliberately inhaling or “huffing” canned air can be extremely dangerous or fatal. The intentional inhalation of 1,1-difluoroethane contributed to the death of actress Skye McCole Bartusiak, and caused a fatal cardiac arrhythmia in a 42 year-old man.[4] Several reports of fatal car crashes have been linked to drivers huffing 1,1-difluoroethane.[5][6][7] Due to inhalant abuse, a bitterant is added to consumer canned air products.

In a Du Pont study, rats were exposed to up to 25,000 ppm (67,485 mg m−3) for six hours daily, five days a week for two years. This has become the no-observed-adverse-effect level for this substance. Prolonged exposure to 1,1-difluoroethane has been linked in humans to the development of coronary heart-disease and angina.[8]

Though not extremely flammable in gaseous form, 1,1-difluoroethane can burn under some conditions. As such, there is also a warning label present on some gas dusters. When inverted to spray liquid, the boiling fluorocarbon aerosol is easily ignitable, producing a very large blast of flame and extremely toxic gases such as hydrogen fluoride and carbonyl fluoride as combustion products.