A criticality accident occurred on December 30, 1958, at the Los Alamos National Laboratory in Los Alamos, New Mexico, in the United States. It is one of 60 known criticality events that have occurred globally outside the controlled conditions of a nuclear reactor or test, though it was the third such event that took place in 1958 after events on June 16 at the Y-12 Plant in Oak Ridge, Tennessee, and on October 15 at the Vinča Nuclear Institute in Vinča, Yugoslavia. The accident involved plutonium compounds dissolved in liquid chemical reagents; within 35 hours, it killed chemical operator Cecil Kelley by severe radiation poisoning.