Section 13-624. Pension for service

a. Any member who has or shall have
  performed duty in the department of health, for a period of twenty years
  or upwards, upon his or her own written application to  and  filed  with
  the  board of trustees, setting forth at what time, not less than thirty
  days subsequent to the execution and filing thereof, he or  she  desires
  to  be  retired,  or  upon  a  certificate  and  report  of  a  board of
  physicians, appointed by the  board  of  health,  certifying  that  such
  member  is  permanently  disabled  so as to be unfit for further duty in
  such department, or upon attaining the age of seventy  years,  shall  be
  retired  from  active service by resolution of the board of estimate, as
  of the date specified in  said  application,  or  certificate,  or  upon
  attaining  such  seventieth  year,  and  shall be placed upon the health
  department pension roll, provided that at the time so specified for  his
  or  her  retirement,  his  or her term or tenure of office or employment
  shall not have terminated or have been forfeited, and  provided  further
  that  upon  his  or her request in writing the member shall be granted a
  leave of absence from the date of filing said application until the date
  the retirement becomes effective. A member in city-service, however, who
  has or shall have attained the age of seventy years, upon  the  approval
  of  the  commissioner of health, may request the board of estimate to be
  continued in the public service for a  period  of  two  years  and  such
  board,  where advantageous to the public service, may grant such request
  for such period, not exceeding two years as such board may determine. At
  the termination of such additional period of service, such board in like
  manner may permit such employee to continue in the  public  service  for
  successive  two  year  periods  or any portion thereof. In no case shall
  public service be continued after a member shall have attained  the  age
  of  eighty  years.  Any member placed upon the health department pension
  roll under the provisions of this section shall be awarded, granted  and
  paid  from such fund by the trustees thereof an annual sum during his or
  her lifetime equal to one-half of the annual  salary  received  by  such
  member at the time of retirement plus one and one-half per centum of the
  annual  salary  received  by  him  or  her  each  year subsequent to the
  completion of his or  her  thirtieth  year  of  service,  provided  that
  paid-for  service before October first, nineteen hundred twenty shall be
  credited whether in the department  of  health  or  in  any  other  city
  department.
    b. Pensions granted under this section shall be for the life of person
  receiving the same, and shall not be revoked, repealed or diminished.
    c.  When  a  member has been awarded and granted a pension pursuant to
  the provisions of this section and shall die prior to receiving payments
  from such pension fund equal to the compensation earned by him or her in
  the city service while a member during  the  twelve  months  immediately
  preceding  his or her retirement, there shall be paid by the trustees of
  the pension fund to his or her estate, or to such person as  he  or  she
  has nominated or shall nominate by written designation duly executed and
  filed  with  the  board of trustees during his or her lifetime, a sum of
  money equal to the difference between the compensation earned by him  or
  her  in  the  city  service  while  a  member  during  the twelve months
  immediately preceding his or  her  retirement  and  the  total  payments
  received by him or her from such pension fund.