Tenn. Code Ann. § 4-4-109

Whenever, in the carrying on of the work of any department, the services of any expert, or the use of any special apparatus shall be desired, or any work needs to be done for which the department is not equipped, the commissioner thereof may request the assistance of any other department that may have the needed experts or apparatus. It is lawful for the department so called upon to cooperate in meeting the need so far as it can be done without detriment to the work of that department, and the actual costs, as determined by the commissioner of finance and administration, shall be the proper charge, unless otherwise approved by the commissioner of finance and administration, and filed with the comptroller of the treasury.