Читать книгу Risk Assessment - Marvin Rausand - Страница 59

The termination of the ability of an item to perform as required.

A failure is always linked to an item function and occurs when the item is no longer able to perform the function according to the specified performance criteria. Failure is an event that takes place at a certain time . Item failures can be recorded, and we can estimate the frequency of failures in a certain population of similar items. This frequency is called the failure rate of the item.

The occurrence of some failures can be observed immediately when they occur, and these failures are called evident failures. For other failures, it is not possible to observe the failure without testing the item. These failures are called hidden failures. Hidden failures are a particular problem for many safety systems, such as fire or gas detection systems, and airbag systems in cars.

After a failure, the item enters a failed state or a fault and remains in this state for a shorter or longer time. Many failures require a repair action to be brought back to a functioning state. Some items – especially software items – may spend a negligible time in failed state.

A fault of a technical item is defined as follows: