Safety barriers prevent accidents or limit the consequences of accidents. A safety barrier responds to some adverse condition or an event that, without the barrier, is likely to lead to an accident.
Safety barriers can be purely technical systems, or whole or in part involve the actions of humans.
We differentiate between passive safety barriers, such as guard rails and fire walls, and active barriers. We emphasize that active barriers shall be complete, that means that they are able to perform all three actions: Detect the hazardous situation, Diagnose/Decide on the proper response and Act accordingly. Typical examples of incomplete barriers are alarms, where the response of the operator is not clearly considered.
All safety barriers are risk reducing measures, but not all risk reducing measures are safety barriers. We like to call safety measures only for safety barriers if those measures respond “at the sharp edge” to incidents. That is, the action of a safety barrier is unplanned and unexpected, because the incident comes at unexpected times. All other risk reducing measures, such as maintenance, inspection, providing procedures, training and proper design, are planned activities. These risk reducing measures are important for the success of the safety barrier, but they are normally not included in safety-barrier diagrams. The present software is able to include these risk reducing measures and also present them in the diagrams as secondary safeguards.
We distinguish different types of barriers. A recommended set of barrier types is described in the note “Types of safety barriers“. For a scientific discussion and definition of safety barriers we refer the list of other publications included on the documentation page.
The barrier is pictured as follows in a barrier diagram. If the barrier fails, we get the condition on failure (normally the unwanted outcome). If the barrier functions we get the condition on success – this may be a normal condition that for us – as risk analysts – has little interest, and we may choose not show it. But functioning barriers can have side effects which we want to analyse as well.
Presentation of a safety barrier in a safety-barrier diagram