Following the accident, the control room of the Fukushima Daiichi plant was the scene of a terrible tragedy. It was a clear case of operator error, in this case, a major mistake in the evaluation and interpretation of control-room monitoring data, which had caused the reactor operators to do nothing to prevent a meltdown. The operators waited for an electrical circuit to open the relief valve, and for some reason they did not do so. It was a tragic event that contributed to the containment of the Fukushima Daiichi power plant, but it could have been avoided with good communications between the control room and the operator monitoring the plant.
In the aftermath of the accident, the plant and the control-room operator were heavily criticized, with some citing the mismanagement of the plant at Three Mile Island as the sole cause of the accident at the Fukushima Daiichi nuclear power plant. However, a detailed study published in 2010 (Radwan et al. 2010278) concluded that the control-room personnel had taken the proper actions in the minutes after the emergency arose. The control room operator (who did not provide additional comments to the press at the time) was not involved in the design of the control system that was ultimately responsible for the situation at Three Mile Island. The reactor operator had taken the appropriate action of opening the relief valve, but had no way of verifying that the valve was in the desired position. Pressured by the situation, the operator may have intended to apply sufficient voltage to move the valve in a direction to close it, but may have forgotten to do so. The temperature rose because of the high velocity of coolant, and the valve was stuck open. The temperature reached a few degrees above the boiling point of sodium-coolant coolant, which was usually around 300° C. In a fraction of a second, the pressure rose to 6 times normal values. The operator correctly realized that something was wrong and tried to turn the valve off. During the process, coolant temperature continued to rise, but could not rise any further because of the heat capacities of the vessel and the pressure-relief valve. Even though the temperature of the sodium coolant rose to around 400° C, the emergency cooling systems were never activated, because the operators did not realize that they were required to operate these systems. Moreover, if the operators had activated the emergency cooling systems, there would have been further meltdown of the reactor core.
In the early morning hours of November 8, 1905, four workers who were asleep in a shed adjacent to a gas-fired stoves manufacturing facility in Brownsville, New York, were killed when an explosion occurred. The cause of the fire was determined to be a poorly designed grate that had not been properly welded. When this grate was improperly assembled, the flame would not travel through the grate and could ignite the gas that was trapped in a confined space behind the grate. A second source of ignition was the electric arc that occurred as the metal melted and copper and zinc melted into one another. Although the improperly designed grates were used in gas-fired stoves for several years, the design flaw and weld problems were not discovered until the accident. The investigators concluded that the fire had been caused by the ignition of a spark or electrical arc that had been caused by the melting of the metal and by the incomplete welding of the two halves of the grate. 827ec27edc