Aerospace Testing Alliance, an aerospace engineering company, contracts with the U.S. Air Force to operate a sheet metal shop at Arnold Air Force Base in Tullahoma, Tennessee. In May 2016, the tip of an ATA employee’s finger was crushed while operating a power shear in the metal shop. Following the accident, the Occupational Safety and Health Administration conducted an inspection and issued ATA a one-item serious citation alleging a violation of 29 C.F.R. § 1910.212(a)(1) for failing to properly guard the power shear’s hold-down pistons. Following a hearing, Administrative Law Judge Heather A. Joys affirmed the citation and assessed the proposed $6,300 penalty. For the reasons discussed below, we reverse the judge and vacate the citation.