(a) This subchapter applies only to a district that is located wholly in a county:
(1) that borders the United Mexican States;
(2) that contains a municipality with a population of more than 500,000; and
(3) for which the commissioners court appoints a board of emergency services commissioners under § 775.034.
(b) This subchapter controls over a provision of this chapter or other law to the extent of a conflict.