Mean Time Between Failures (MTBF)

Definition - What does Mean Time Between Failures (MTBF) mean?

Mean time between failures (MTBF) is a value that describes the average amount of time for which a given machine or electronic system will be able to operate before experiencing a failure.

Specifically, it describes the time between inherent failures—those caused by the stress created by a system’s normal operations. The term refers solely to repairable failures. The average time until a non-repairable failure occurs is referred to as “mean time to failure.”

Safeopedia explains Mean Time Between Failures (MTBF)

When used to describe the general reliability of a machine or system based on its design, the MTBF describes the time to failure for a system that is being used in an intended context—operated properly, undamaged, and in an environment it is designed for. If necessary, the reliability of a specific system that is being used in unideal conditions may be monitored by examining whether its time between failures shows significant deviation from its expected MTBF.

Since the MTBF is a value that provides a quantification of the reliability of a given system, it is used during the design stage of a product’s development to ensure that the design is reasonably robust. It is also used as a benchmark for monitoring the ongoing reliability of a machine or system that has been deployed in the workplace.

The MTBF can be calculated by dividing the time period that a particular asset has been active by the number of failures that have occurred during that period. When a system is being designed, it is usually impractical to operate it until it has accrued enough failures to produce a reasonable mean value. As an alternative, an engineer will follow a recognized standard, such as IEC 61709, which describes how to conduct reliability testing to generate the MTBF as a predicted value.

The MTBF is an important consideration for safety equipment and safety-critical processes. A safety control with a short MTBF and one that takes a significant amount of time to repair could cause considerable disruptions if its use is necessary for a certain activity to safely proceed. Frequent failures may raise workplace safety risk if a worker or project manager erroneously believes that it is worth the risk to move ahead with a project without the failed safety control in operation or if the failure creates an immediate risk of a safety incident.

A higher failure rate than predicted by a system’s MTBF may signal that something about the system’s operation is being performed incorrectly. As most occupational health and safety standards require proper use of equipment for compliance, a deviation from the MTBF can act as a signal that the equipment is potentially being used in a noncompliant manner.

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