## A brief history of reliability

 The first edition of System Reliability Theory: Models and Statistics Methods, by Arnljot Høyland and Marvin Rausand was published in 1994. We present here the first section on the Brief History of Reliability:

A brief history.

Reliability, as a human attribute, has been praised for a very long time. For technical systems, however, the reliability concept has not been applied for more than some 60 years. It emerged with a technological meaning just after World War I and was then used in connection with comparing operational safety of one-, two-, and four-engine airplanes. The reliability was measured as the number of accidents per hour of flight time.

At the beginning of the 1930s, Walter Shewhart, Harold F Dodge, and Harry G Romig laid down the theoretical basis for utilizing statistical methods in quality control of industrial products. Such methods were, however, not brought into use to any great extent until the beginning of World War II. Products that were composed of a large number of parts often did not function, despite the fact that they were made up of individual high-quality components.

During World War II a group in Germany was working under Wernher von Braun developing the V-1 missile. After the war, it was reported that the first 10 V-1 missiles were all fiascos. In spite of attempts to provide high-quality parts and careful attention to details, all the first missiles either exploded on the launching pad or landed "too soon" (in the English Channel). Robert Lusser, a mathematician, was called in as a consultant. His task was to analyze the missile system, and he quickly derived the product probability law of series components. This theorem concerns systems functioning only if all the components are functioning and is valid under special assumptions. It says that the reliability of such a system is equal to the product of the reliabilities of the individual components which make up the system. If the system comprises a large number of components, the system reliability may therefore be rather low, even though the individual components have high reliabilities.

In the United States, attempts were made to compensate a low system reliability by improving the quality of the individual components. Better raw materials and better designs for the products were demanded. A higher system reliability was obtained, but extensive systematic analysis of the problem was probably not carried out at that time.

After World War II, the development continued throughout the world as increasingly more complicated products were produced, composed of an ever-increasing number of components (television sets, electronic computers, etc.). With automation, the need for complicated control and safety systems also became steadily more pressing.

Toward the end of the 1950s and the beginning of the 1960s, interest in the United States was concentrated on intercontinental ballistic missiles and space research, especially connected to the Mercury and Gemini programs. In the race with the Russians to be the first nation to put men on the moon, it was very important that the launching of a manned spacecraft be a success. An association for engineers working with reliability questions was soon established. The first journal on the subject, 'IEEE Transactions on reliability' came out in 1963, and a number of textbooks on the subject were published in the 1960s.

In the 1970s interest increased, in the United States as well as in other parts of the world, in risk and safety aspects connected to the building and operation of nuclear power plants. In the United States, a large research commission, led by Professor Norman Rasmussen was set up to analyze the problem. The multimillion dollar project resulted in the so-called Rasmussen report, WASH-1400 (NUREG-75/014). Despite its weaknesses, this report represents the first serious safety analysis of so complicated a system as a nuclear power plant.

Similar work has also been carried out in Europe and Asia. In the majority of industries a lot of effort is presently put on the analysis of risk and reliability problems. The same is true in Norway, particularly within the offshore oil industry. The offshore oil and gas development in the North Sea is presently progressing into deeper and more hostile waters, and an increasing number of remotely operated subsea production systems are put into operation. The importance of the reliability of subsea systems is in many respects parallel to the reliability of spacecrafts. A low reliability cannot be compensated by extensive maintenance.

JOC/EFR February 2017