Cooper/T. Smith Corporation d/b/a Blakeley Boatworks, Inc. (Blakeley) repairs ships at its shipyard in Mobile, Alabama. OSHA issued Blakeley a single-item citation following an accident involving one of its employees working on a barge. The citation alleges a serious violation of 29 C.F.R. § 1915.77(c) for Blakeley’s failure to ensure employees were using fall protection while exposed to a fall hazard of more than 5 feet. The Secretary proposed a penalty of $4,900. Because the parties stipulated that the Secretary established his prima facie case, the only issue before Administrative Law Judge John B. Gatto was Blakeley’s affirmative defense of unpreventable employee misconduct (UEM). After a hearing, the judge found that Blakeley had established the defense and vacated the citation. For the reasons discussed below, we reverse the judge’s decision and affirm the citation.