UNITED STATES
DEPARTMENT OF LABOR

Abstract: At approximately 11:00 a.m. on June 26, 2007, Employee #1, a heavy equipment operator, began operating an excavator after first inspecting the machine. He had been mining and mucking for about an hour when he noticed a slow drip coming from the right front port plug. Employee #1 pulled back and raised the boom slightly to investigate it. At this time, Employee #1 did not notice any significant damage to the plug, and the drip stopped when pressure was applied to the cylinder. He called on the mine phone and spoke to his coworker, a contractor at the site, who was at the bottom of an exit shaft, about 2,400 ft back. He told Employee #1 that he would get a new plug. Employee #1 resumed his work, moved the boom forward, and then was moving the boom either up or down when the plug blew out. It struck Employee #1's left hand with sufficient force to break off the left joystick and cause significant trauma. He was evacuated from the tunnel and taken to the hospital, where he underwent the surgical amputation of his left middle finger back to the wrist and the relocation of his index finger to the middle position. After the accident,the plug was found to have been damaged, probably by rocks and boulders while mining or mucking. The damage to the head caused the threaded portion to take on an oval shape that was approximately 1/8 in. out of round. The full depth of the threads on the ends of the oval were damaged consistent with the plug being ejected. The threads on the sides of the oval were undamaged, indicating that these were not engaged due to the shape of the plug after it was damaged. While mining prior to the accident, the pressure in the hydraulic system reached approximately 3,000 psi. The computer logs were not entirely clear but showed that just before the accident the pressure was no more than about 1,600 psi. Why the plug did not fail during mining, and how a plug with most of its threads not engaged only dripped slowly when under pressure both remain undetermined. The accident occured during the excavation of an 11 mi long by approximately 12 ft diameter tunnel. Excavation had been completed from the portal to about 8,900 ft using a conventional rotary boring machine and drill and blast methods. A digger shield-type tunnel boring machine was then launched and had evacuated approximately 525 additional feet. The digger shield TBM, built by CTS, Inc., specifically for this project, utilizes an excavator arm with a tooth attachment on its end to dig at the tunnel face. Underneath the tooth is a flat shovel attachment or paddle that the operator uses to pull muck onto the lower steel apron of the shield and onto the conveyor belt. On each side of the arm are hydraulics that provide vertical motion for the boom. On the upper part of each cylinder, angled outwards about 45 degrees are two ports for the hydraulic connections, one on each end. Mirroring these ports, facing downward and outward, are unused threaded ports that are plugged with 1.5 in. hex-head screws in steel plugs. When the operator is mucking, the boom is pulled back toward him so that at the end of the pull, the cylinder on his side is approximately 1 ft to his left. In the fully down position, the front plug is about even with the operators left joystick, both in height and position. There were no witnesses to the accident and no citations were issued as a result of this investigation,