Any member of the relief association who is unable, because of physical or mental disability, to perform the duties of a firefighter shall receive monthly a disability pension equal to fifty percent of the monthly salary of a first-class firefighter on January first of the year that the pension is being paid, unless that member is eligible for a larger service pension in which case the member shall draw an amount equal to the member’s service pension. No member shall receive a disability pension unless the member is disabled for a period of at least seven consecutive days, at which time the member must be paid from the time of disability. However, a member may not receive a disability pension for the days the member was reimbursed by the city for accumulated sick leave.