Reliability in equipment depends upon the quality of the initial research, its design, the quality of the materials used, the quality of the parts used in its construction, the external influences upon its operation, and the frequency and quality of maintenance. The continuing increase in the complexity of mechanical and electromechanical systems increases the probability of equipment failure.
Equipment and machinery are more reliable than their human operators. Industrial accident figures indicate this. The continuing increase in the complexity of industrial systems increases the probability of human failure.