Sec. 6.01. INITIAL ELIGIBILITY FOR DISABILITY RETIREMENT. A firefighter is eligible to retire and receive a disability retirement annuity if:

(1) application for retirement is made by the member or the member's legal representative or if the board of trustees determines that, although no application has been filed, retirement is for the good of the fire department;

(2) the medical board certifies that the member is unable to perform the duties of the member's occupation as a firefighter and sends the member's application to the board of trustees; and

(3) the board of trustees approves the disability retirement.