Trucking: ICC/MC number requirement?, kellogg community college, cdl license

Question
I manage a training program that trains airport fire fighters with a mobile aircraft trainer. This trainer is 50' long owned by the State of Michigan with a exempt state plate on it. The trailer is the aircraft unit. It isn't carried on a flat bed it is the trailer. The tractor is owned by Kellogg Community College and it also has an exempt state plate. Total weight is 68,800 lb. Unit was built with a FAA grant and given to the State of Michigan to train the Great Lakes and Eastern FAA region. We have been training  South Dakota, Utah, Connecticut, Tennessee, New York, Pennsylvania and Wisconsin. Basically anywhere an airport wants the training. So, my question is do I need a ICC or MC number on the tractor and trailer? We have a fuel sticker. We have been asked asked a couple of times at the scale house if we had a ICC number I told them we were exempt. They seem to buy that but, I don't know if I am legal or not. we have been operating since 1995 (mostly around the Great Lake states but, have been going out more and more as people hear about the mobile trainer. If you look at our website you will see the unit.  www.kellogg.edu/arff  Please let me know what you think. Thanks

Answer
Hi Joe, Sorry for delay giving you an answer. The Regulations exempt from CDL license firefighters and driver responding to emergencies. You will need to pnone the DOT in Washington at 703-280-4001 for a clearification on the operation of your vehicle.  I an glad to know you are doing such a great service for our firefighters,etc.  Good Luck. J P Long