(a) If any employee who has served less than twenty years and who remains in the active service of the agency has, in the opinion of the board, become permanently partially or totally disabled to the extent that the employee cannot adequately perform the duties required of an employee of the agency from any cause other than those set forth in the preceding section and not due to vicious habits, intemperance or willful misconduct on his or her part, the employee shall be retired by the board. The employee is entitled to receive annually and shall be paid from the fund in equal monthly installments during a period equal to one-half the time he or she served as an employee of the agency or until the disability eligibility sooner terminates, a sum equal to five and one-half percent of the total salary which would have been earned during twenty-five years of service. At the end of the one-half time period of service, the benefit payable for the remainder of the retirant's life is an annual sum paid in monthly installments equal to one-half the base salary received by the retirant from the agency in the preceding twelve-month period immediately prior to the disability award: Provided, That if the retirant was not employed with the agency for twelve months immediately prior to the disability award, the amount of monthly salary shall be annualized for the purpose of determining the benefit.

(b) If the employee, at the time of retirement under the terms of this section, has served twenty years or longer as an employee of the agency, the employee is entitled to receive annually and shall be paid from the fund in equal monthly installments, commencing on the date the employee is retired and continuing during his or her lifetime while in status of retirement or until the disability eligibility sooner terminates, a sum equal to five and one-half percent of the aggregate of salary paid to the retirant through the day immediately preceding his or her disability award, to be determined in the manner provided by subsection (c), section twenty-seven of this article.

(c) An employee awarded a disability benefit under the provisions of this section may receive retirement disability annuity payments on the day following the board's approval of his or her disability application. Upon termination of employment and receipt of properly executed forms from the agency and the employee, the board shall process the disability retirement benefit and commence annuity payments as soon as administratively feasible.

(d) For the purposes of this section, the term "salary" does not include any compensation paid for overtime service.