Section 13(2)(b) in The Chennai Corporation (Superior) Service Pension Rules, 1970
(b)If a member of the service has been declared by the Medical Board to be completely and permanently incapacitated for further service, in special cases, leave or an extension of leave may be granted to him as debited against the leave account, if such leave is due to him provided that the amount of leave so granted, together with any period of duty beyond the date on which the Medical Board signed their report, shall not exceed six months.