(1) School officials shall design ventilation equipment and other mechanical noise sources in classrooms to provide background sound which conforms to a noise criterion curve or equivalent not to exceed NC-35. School officials shall certify, or hire the appropriate person to certify, that ventilation equipment and other mechanical noise sources that have been installed meet the NC-35 noise criterion design standard.

(2) Portable classrooms constructed before January 1, 1990, moved within the same school property or within the same school district, are exempt from the requirements of this section if the portable classrooms meet all of the following criteria:

(a) Noise abating or noise generating features are not altered in a manner that may increase noise levels;

(b) The portable classrooms were previously in use for instruction;

(c) Ownership of the portable classrooms remains the same; and

(d) The new site meets the noise standard in WAC 246-366A-030 (3)(c).