In case of any great public calamity, such as an extraordinary fire, flood, storm, epidemic, or other disaster, the board may, by resolution passed by a four-fifths vote of all its members declare and determine that public interest and necessity demand the immediate expenditure of public money to safeguard life, health, or property, and thereupon proceed to expend or enter into a contract involving the expenditure of any sum needed in such emergency without observance of the provisions requiring contracts, bids, or notice.