Abstract: At 1:30 p.m. on June 25, 2020, an employee was working as an installer for a general contractor specializing in cleanroom construction. The employee was installing I-beams to a new addition "Shasta Cleanroom" inside the existing building. According to coworkers the employee was working with Coworker #1 and Coworker #2 installing a 17-foot-long by 4-inch-deep by 6-inch-wide I-beam. The employee was positioned on one end of the beam while Coworker #1 was positioned in the middle and Coworker #2 was positioned at the other end. The employee and Coworker #2 were using a Genie Aerial Lift while Coworker #1 was using a Genie Hoist while lifting the beam to the desired height of approximately 15 feet. Coworker #2, the Lead for the job, stated that they take turns connecting the beam to the respective posts with nuts and bolts. After Coworker #2 secured one of the two holes with a nut and bolt using a spud wrench, it was the employee's turn to connect the beam on his side. While in the process of connecting the beam, the beam slid unexpectantly, and the employee caught his left thumb between the metal parts. The employee partially amputated his thumb and was transported to the hospital where he was admitted and required surgery.