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A cascading failure is a condition of interconnected systems when the failure of one part or component can lead to a failure in related areas of the system that propagates itself to the point of an overall systems failure. There are many types of cascading failure events that can occur in natural and man-made systems, from electrical and computer systems to political, economic, and ecological systems. The field of research known as complexity science attempts to define the root causes for such failures so as to build in safeguards that may be able to prevent them in the future.
A common yet hard-to-predict type of cascading failure event is a single point of failure, where one component fails and inexplicably leads to a domino effect, triggering a rapid spread of the condition to other parts of the system. An example of this took place in 1996 in the United States, when a power line in the state of Oregon failed and triggered a massive failure of the electrical grid throughout the western US states and Canada, affecting between 4,000,000 and 10,000,000 customers. When the transmission line failed, it caused the regional electrical grid to break up into separate transmission islands which were not able to handle the increased load, and then also failed, leading to the collapse of the entire system. A similar cascading failure occurred in the mid-western US state of Ohio in 2003, which led to the largest electrical blackout in US history.
Often, a cascading failure involves multiple systems that fail due to the butterfly effect, where a seemingly very small event ripples out to produce a much larger one. An example of this is the crash of a DC-10 aircraft over Paris, France, in 1974, killing everyone on board. A later investigation into the cause of the crash revealed that a cargo bay door had not been fastened properly. The man most directly responsible for this reputedly could not read English and therefore was not able to read the instructions for how to properly fasten the door.
The technical design for the cargo door allowed it to be closed without the latches being fully engaged. As the aircraft climbed to 13,000 feet (3,962 meters), internal pressure caused the door to give way, and the explosive decompression around the door as it blew off damaged hydraulic controls in the area, which caused the pilots to eventually lose complete control of the aircraft. The root cause of such a cascading failure is difficult to determine. It spans the regions of education, governmental policies for the hiring of immigrants, engineering designs for hydraulics and avionics, and informal social support systems within the work environment.
The power grids of high voltage systems are the most notable example of large cascading failure events, but failures in large systems are not rare. From traffic jams to market crashes, or forest fires that start with a single spark, large system crashes are often a direct result of what is known as a Byzantine failure event, where an element of a system fails in an unusual way, often continuing to function and corrupting its environment before it completely shuts down. Such events reveal an underlying condition of all complex systems described by chaos theory, which is that of sensitive dependence. Each part of a system is expected to behave within a certain range of parameters, and, when it strays outside of that range, it can start a chain reaction that alters the behavior of the entire system.
The Kessler syndrome is one example among many where science is trying to get ahead of the curve and predict a cascading failure before it occurs. Based on the theories of Donald Kessler in 1978, a US scientist working for the National Aeronautics and Space Administration (NASA), it charts the effects of the collision of objects in low Earth orbit (LEO). Such collisions over time will fuel an exponential increase in the number of small particles in LEO, known as a debris belt, making trips into space much riskier than before. Over 500,000 pieces of debris in orbit traveling at up to 17,500 miles per hour (28,164 kilometers per hour) are tracked as of 2011 on a continuous basis to avoid future catastrophic collisions. A particle as small as a marble could do irreparable damage to a military or scientific spacecraft upon impact, resulting in possible deaths or political and ecological impacts of unforeseen proportions.