No person otherwise properly admitted to the fund shall be excluded from continuing membership therein solely because the member's employment by or service with a fire department is not in the capacity of a firefighter or volunteer firefighter, but no credit shall be given for service rendered in any month by any member of the fund unless such service is rendered as a firefighter or volunteer firefighter and no benefits payable by the terms of this chapter to a firefighter or volunteer firefighter shall be payable to any member unless such member is serving as a firefighter or volunteer firefighter at the time such benefits are earned or become payable. For any period during which any member provides service which is not creditable, the member shall be deemed to be on leave of absence from the fund.