Or. Rev. Stat. § 468.959
(2) For purposes of this section:
(b) “Upset” includes an exceptional and unexpected occurrence in which there is unintentional and temporary violation of the requirements of ORS 824.050 to 824.110 or ORS chapter 465, 466, 468, 468A, 468B or 825 or of any rule adopted or permit or order issued under ORS 824.050 to 824.110 or ORS chapter 465, 466, 468, 468A, 468B, or 825 because of factors beyond the reasonable control of the regulated person or entity. “Upset” does not include a violation caused by:
(3) To establish the affirmative defense of upset or bypass, the defendant must prove the occurrence of an upset or bypass and that the defendant:
(4) It is an affirmative defense to an offense under ORS 468.922 to 468.946 that the defendant:
[1993 c.422 §17]