Upon application of a member in service of the employer, any member who has had not less than five (5) years nor more than twenty (20) years’ service with the employer and who has become totally and permanently incapacitated for duty, as a result of causes occurring other than in the performance of his duty, shall be retired by the board not less than thirty (30) nor more than ninety (90) days next following the date of filing such application, on a non-duty disability retirement allowance. Any such disability shall be certified to the board in the same manner as provided in Section 21-29-35.