(a) If the revenue from a building or structure described by Section 1504.102 is encumbered under this subchapter, each expense of operation and maintenance, including all salaries, labor, materials, interest, repairs and additions necessary to provide efficient service, and each proper item of expense, is a first lien against that revenue.
(b) An expense for a repair or addition is a first lien only if, in the judgment of the governing body of the municipality, the repair or addition is necessary to:
(1) keep the building or structure in operation and provide adequate service to the municipality and its residents; or
(2) respond to a physical accident or condition that would otherwise impair the original security.