Regular meetings of the Board shall be held at least once in each calendar month, the time and place of such meetings to be fixed by the Board. Special meetings may be called by the chairman or by any 3 members of the Board by giving notice thereof in writing, stating the time, place and purpose of the meeting. Such notice shall be served by special delivery mail deposited in the mails at least 48 hours before such meeting. Four members of the Board constitute a quorum for the transaction of business. All action of the Board shall be by ordinance or resolution and, except as otherwise provided in this Act, the affirmative vote of at least 4 members is necessary for the adoption of any ordinance or resolution. The chairman is entitled to vote on any and all matters coming before the Board. All ordinances, resolutions and all proceedings of the District and all documents and records in its possession are public records and open to public inspection, except such documents and records as are kept or prepared by the Board for use in negotiations, legal actions or proceedings to which the District is a party.