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Probabilistic Safety Analysis (PSA)

A classical application of the probabilistic analysis is the probabilistic safety analysis (PSA).

Probabilistic Safety Analysis –  MSE Inc. – Management-System-Experts

Risk Control by PSA

Accidents and events, respectively, cannot completely be prevented, but the probability of occurrence and the extent of damage can effectively be influenced. A proven method for this is the

probabilistic safety analysis (PSA).

The PSA allows the numerical quantification of risk variables in the industry and is, besides the deterministic analysis, an indispensable part of safety management.

Probabilistic Assessment

Probabilistic assessments assume that the occurrence of an undesired event is only a matter of time.

Therefore, there is always a certain probability for the occurrence of an event.

How great this probability is can be calculated with a PSA as well as which contributing factors, e.g.,

  • the reliability of personnel actions and
  • the reliability of technical equipment,

decisively influence this reliability.

PSA Model Principles

An event tree model represents the possible courses of events from the initiating event to the corresponding accident consequences. Event trees show the phenomenological, time-dependent mitigation functions of the safety barriers during the accident development. An event tree starts with an initiating event.

The fault tree model represents error combinations that can cause a safety system to fail to perform its functions when requested. The fault tree model takes into account technical failure mechanisms and human errors.

Event trees and fault trees are linked together.

After completion of the basic PSA, an update is made at regular intervals, in which all changes in the boundary conditions are considered (living PSA).

Importance Analysis

By means of the importance analysis it is determined which contributing factors have an outstanding influence on the error frequency.

Knowing the dominant contributing factors enables targeted countermeasures to reduce the probability of error occurrence or to reduce the error consequences, respectively.

Living PSA

After the basic analysis, an update is carried out at regular intervals.

Thereby it is examined whether risk-relevant boundary conditions have changed:

  • Changes in processes
  • Changes in the technical equipment
  • Changes in the regulatory framework
  • Changes in reliability data

If there are any changes, they are included in the recalculation.

Effect of the PSA Application

The PSA used in nuclear technology as an international standard for the safety assessment of the operation of nuclear facilities has led to an extensive optimization of safety technology in Germany and has, thus, contributed significantly to the high safety level in German plants.

The PSA methodology can be transferred analogously to other sectors with elevated risk potential and leads to a significant increase in the safety level, if applied systematically.

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