Any person possessing a valid commercial driver's license authorizing the operation of a Class A combination vehicle may lawfully operate a Class A, B, or C commercial motor vehicle without a hazardous materials endorsement if such person:

(1) Is acting within the scope of his or her employment as an employee of a custom harvester operation, agrichemical business, farm retail outlet and supplier, or livestock feeder; and

(2) Is operating a service vehicle that is:

(a) Transporting diesel fuel in a quantity of one thousand gallons or less; and

(b) Clearly marked with a “flammable” or “combustible” placard, as appropriate.