A catastrophic failure is a sudden and total failure from which recovery is impossible. Catastrophic failures often lead to cascading systems failure. The term is most commonly used for structural failures, but has often been extended to many other disciplines in which total and irrecoverable loss occurs, such as a head crash occurrence on a hard disk drive. Such failures are investigated using the methods of forensic engineering, which aims to isolate the cause or causes of failure. For example, catastrophic failure can be observed in steam turbine rotor failure, which can occur due to peak stress on the rotor; stress concentration increases up to a point at which it is excessive, leading ultimately to the failure of the disc. In firearms, catastrophic failure usually refers to a rupture or disintegration of the barrel or receiver of the gun when firing it. Some possible causes of this are an out-of-battery gun, an inadequate headspace, the use of incorrect ammunition, the use of ammunition with an incorrect propellant charge, a partially or fully obstructed barrel, or weakened metal in the barrel or receiver. A failure of this type, known colloquially as a "kaboom", or "kB" failure, can pose a threat not only to the user(s) but even many bystanders. In chemical engineering, thermal runaway can cause catastrophic failure. Examples Examples of catastrophic failure of engineered structures include: The Tay Rail Bridge disaster of 1879, where the center of the bridge was completely destroyed while a train was crossing in a storm. The bridge was badly designed and its replacement was built as a separate structure upstream of the old. The failure of the South Fork Dam in 1889 released 4.8 billion US gallons (18 billion litres) of water and killed over 2,200 people (popularly known as the Johnstown Flood). The collapse of the St. Francis Dam in 1928 released 12.4 billion US gallons (47 billion litres) of water, resulting in a death toll of nearly 600 people. The collapse of the first Tacoma Narrows Bridge of 1940, where the main deck of the road bridge was totally destroyed by dynamic oscillations in a wind. The De Havilland Comet disasters of 1954, later determined to be structural failures due to metal fatigue that had not been anticipated at the corners of square windows used by the Comet 1. The 62 Banqiao Dams failure event in China in 1975, due to Typhoon Nina.