Suncor Energy (U.S.A.) Inc. operates a refinery in Commerce City, Colorado. The Occupational Safety and Health Administration inspected the refinery in response to a complaint that an employee had fallen and was seriously injured. As a result of the inspection, OSHA issued Suncor a citation alleging two serious violations and one other-than-serious violation of various provisions of the general industry permit-required confined spaces standard, 29 C.F.R. § 1910.146, with a total proposed penalty of $12,000. The Secretary subsequently amended Item 2 of the serious citation—which alleged a violation of 29 C.F.R. § 1910.146(d)(4)(iv) (addressing the provision of personal protective equipment)—to allege in the alternative a violation of 29 C.F.R. § 1926.451(g)(1), a construction standard requiring fall protection on scaffolds over 10 feet high, with a proposed penalty of $7,000.