EE had repaired a leak in the suction hose on a co-worker's boom. EE got on the bolter so EE could listen for leaks around the cyclone, troubleshooting. EE told co-worker to drill a test hole so EE could see if there were any leaks. Co-worker swung the boom in pinning EE's foot between the L Arm and the bolter frame. Co-worker was on knees and could not see where EE was.