Abstract: On October 10, 2002, an accident took place at the Metropolitan Water District of Southern California site at the Jensen Treatment Plant in Granada Hills, California. The Jensen Treatment Plant is a very large water treatment plant and water storage area where water from the California Aqueduct is treated and distributed to other agencies from this site. The area also is the site from which the Metropolitan Water District stores and maintains its construction equipment and materials. On the day of the accident, two maintenance mechanics were dispatched to the northwest section of the plant to recover a John Deere 410D backhoe that was in need of repair for transport to the Lake Matthews site. The mechanics fixed a flat on the backhoe first before trying to load the backhoe onto a trailer for the ride up to the garage. As standard practice, any equipment that is going to be transferred to another site is inspected and repaired before it is transported. The 410D backhoe is equipped with a cable-operated boom lock, which keeps the boom from moving during transport. The boom lock was broken and was on the list to be repaired. A coworker was operating the backhoe, checking it out to see how it was operating and raised the boom but did not realize that Employee #1 was trying to lock the boom in the upright position. Employee #1 misjudged the operating speed of the boom and did not move his hand away from the pin and boom. Employee #1 got his right thumb caught between the lock pin and boom, pinching his thumb and causing the amputation of the thumb. The coworker saw Employee #1 crouching below the cab and quickly stopped the operation of the backhoe. When he got out of the backhoe to ask Employee #1 what he was doing, Employee #1 explained what had just happened to his thumb. The accident happened at 9:30 a.m. and Employee #1 was rushed to Granada Hills Hospital. The thumb was reattached and Employee #1 was at home resting at 2:00 p.m. the same day.