The provisions of Sections 63.168-63.169 of this code do not apply to:
(1) improvements carried out and performed by the United States;
(2) calamities or emergencies which make it necessary to act at once to preserve the property of the district;
(3) unforeseen damage to district property, machinery, or equipment or necessary emergency repairs to them; or
(4) contracts for personal or professional services or work done by the district and paid for by the day as the work progresses.