This may happen in three ways: First, redundant safety devices result in a more complex system, more prone to errors and accidents.
Third, redundancy may lead to increased production pressures, resulting in a system that operates at higher speeds, but less safely.
Defence in depth consists in a hierarchical deployment of different levels of equipment and procedures in order to maintain the effectiveness of physical barriers placed between radioactive materials and workers, the public or the environment, in normal operation, anticipated operational occurrences and, for some barriers, in accidents at the plant.
Defence in depth is implemented through design and operation to provide a graded protection against a wide variety of transients, incidents and accidents, including equipment failures and human errors within the plant and events initiated outside the plan.
Different security products from multiple vendors may be deployed to defend different potential vectors within the network, helping prevent a shortfall in any one defence leading to a wider failure; also known as a "layered approach".