Tennessee Code Title 40. Criminal Procedure § 40-23-110

If, by any attempt to rescue a convict on the way or by any other unforeseen danger, it becomes essentially necessary for the safe conveyance of the convict to summon a stronger guard than the sheriff conducting the prisoner may have been authorized to summon, it is lawful for the sheriff to summon an additional guard or guards as shall be necessary for that purpose. The additional guard or guards shall be paid as other guards, on the oath of the sheriff that the additional guard or guards were essentially necessary, and the officer making the payment being satisfied with the truth of the oath.