Tenn. Code § 8-3506
After the time mentioned in § 8-3452, any class B or class C member who has five (5) or more years of creditable service, and any class A member who has ten (10) or more years of creditable service of which at least five (5) years are consecutive years of service immediately preceding termination of service on account of disability, upon the application of the head of the department, institution, commission, board or agency in which said employee is employed, or upon his own application, with the approval of the head of such department, institution, commission, board or agency, within not less than thirty (30) nor more than ninety (90) days next following the date of filing such application, may retire on a disability retirement allowance, provided that the medical panel, after a medical examination of such member, shall certify that such member is mentally or physically incapacitated for further performance of duty, and that such incapacity is likely to be permanent, and that such member should be retired.
Any political subdivision which participates in this system may elect, by ordinance or resolution, to provide that the number of years of creditable service required for disability retirement of its firemen and policemen may be reduced from ten (10) to five (5) and that the required number of years of consecutive service immediately preceding termination of service on account of disability may be reduced from five (5) to two (2). Any political subdivision making such an election shall make a special accrued liability contribution in an amount as determined by an actuarial valuation in the same manner and form as prescribed for initial contributions in § 8-3604.
Until such time as this section becomes effective as provided in § 8-3452, § 8-3506 of the Tennessee Code as enacted by chapter 6 of Public Acts of 1955, prior to amendment, shall remain in full force and effect.
T.C.A. § 8-3506