Except as provided in this Code section, no state official or employee, when traveling by commercial air carrier on a first-class basis, shall be reimbursed for that portion of the first-class air fare which exceeds the amount of the fare of the next lowest fare for the flight on which such official or employee is traveling. This shall not prohibit the reimbursement for the entire cost of first-class air fare under any of the following conditions:

(1) Space is not otherwise available;

(2) A licensed medical practitioner certifies that because of a person's mental or physical condition specific air travel arrangements are required; or

(3) The commissioner of public safety certifies that specific air travel arrangements are necessary for security reasons.