I know there are several that do offer the classess. I personally went through TDI/SDI as my LDS just got 5 star certified through them. The classes are very informative. I am actually building my own tank tumbler as a DIY project and my LDS will use it once it is complete to make our job easier when we get in those paintball tanks that always seem to have fair to heavy oxidation in them. PSI is considered one of the top of the line classes for tank inspection if I remember correcty.