Fall Through Deck Plate at Bldg 983 Z-Machine High Bay NA—SS-SNL-1000-2007-0021 hinge Trapezoidal deck plate. Veronica Martinez Sandia Site Office What happened? Monday, December 3, 2007 A worker stepped on one of the trapezoidal deck plates to reach for a damaged rod nearby.... the trapezoidal deck plate flipped and fell into the tank…… the worker then fell into the opening. Luckily he was able to grab onto a nearby flexible cord and fell approximately 4 feet……though the potential fall distance was 10 feet to the first platform. What is Z-Machine? Z-Machine is a radially configured pulsed power accelerator consisting of 36 modules arranged around a central experiment vacuum chamber. Center Water Section Section/Vacuum Oil Section 20 ft 108 ft diameter Background…… July 27, 2006 - late September 2007 Z-Machine was refurbished. The old equipment and components within the tank were completely removed from the tank! Background/History July 27, 2006 - late September 2007 Z-Machine was refurbished. The oil/water barrier wall starting to be installed! Background/History July 27, 2006 - late September 2007 Z-Machine was refurbished. The water section and the platforms starting to be installed. Notice the trapezoidal plates! Critical Decision 4 was granted on September 24, 2007. Normal operations commenced. The top of the machine is covered by deck plates for walking and working. In 18 areas, around the center of the machine, are trapezoidal deck plates that are hinged for access to the water tank for component removal if necessary Normal operation of the trapezoidal plate being lifted open by its’ hinge. 33.1” Dimensions: The hinged plates were originally designed to facilitate removal of large components from the water section. 49.5” 6 of the 18 trapezoidal plates had their hinges removed where structure or utilities prevented them from being completely raised. 15.5” Z-Machine – Water Section On the day of the incident, the water had been drained from the tank. Worker sustained minor injuries, a small laceration on the wrist and some minor swelling Categorized Significant Category 3 10(3) Near miss Injuries could have been much more significant !!!! Series of events…. Sept 20, 2007 a worker noticed that one of the plates did not fit properly. The A/E firm was contacted about the problem. There was not a recognition that other plates could become loose. Nov 21, 2007 manager inspected the other deck plates and they appeared to be in place and holding up well. Nov 30, 2007 the hinge pin material was received from the A/E. Nov 30,2007 Z-Machine fired a shot. Nov 30, 2007 The suspect plate was seen loose by a person walking through the area. The person was not part of the Operations crew and assumed they would address the issue. December 3, 2007 11:45 am Worker fell into tank! Root Cause Removal of the hinge pins. The decision was made during the installation of the deck with the intent of improving the safety of dive operation. The decision did not take into account system issues with the potential for the plates to fall due to movement of the deck was not recognized. Contributing Cause The workmanship of the decking appears to be less than adequate. The decking is showing gaps both vertical and horizontal that were not evident after initial installation. After each shot there is a post-shot assessment of the area performed for emergency conditions. However, there is no systematic walk-down of the walking/working surfaces looking for worker hazards. Lessons Learned: • Prior to CD-4, numerous readiness activities took place. A Pulsed Power Class III review was performed. Four hazard focus areas were selected to be reviewed/walked-down. One of focus areas was dive operations. • The focus was testing each of the sub-systems, interfaces between the various systems of the machine and the associated hazards. • Focus was given to the diving hazard. Divers were expected to dive within the water tank. The focus was to minimize that hazard. The design of the floor structure (trapezoidal deck plates) was changed. One hazard was minimized while another hazard was introduced. The End Questions?
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