´A barrier system is a system that has been designed and implemented to perform one or more barrier functions´
This definition by Sklet , defines barrier systems as the means to implement a barrier function. For example. A fire extinguisher is a barrier system that is there to implement a mitigation function. The type of barrier system is inherent to the barrier itself, unlike the barrier function, which is a relative property. There are different ways to categorise barrier systems as well. ARAMIS, a European project to implement the Seveso II Directive, has 11 different types . In this article we’ll talk about a simpler categorisation with 5 types.
A barrier system can first be divided into active or passive. A passive barrier is for instance a fence or dyke. Active hardware can be further divided using the Detect-Decide-Act (DDA) principle. A complete active barrier system includes all three. Depending on whether these three elements are performed by people or technology determines what kind of active hardware it is.
If the DDA system is completely represented by people, we call it a Behavioural Barrier. If the whole cycle is hardware based, we call it Active hardware. If the DDA cycle is a mix between people and hardware, we call it a Socio-Technical (or Man-Machine) barrier system. The last type is one where there is no detection, but a continuous action (like for instance a ventilation system). This is called Continuous hardware.