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Robert Lawson

The Classification of Barriers in Safety Functions

Robert Lawson

The term barrier is often used in the description of safety characteristics in a system. The difference between barrier functions and a barrier is that the barrier function represents a function that is planned to prevent, control and mitigate any undesired events or accidents whereas the safety barriers refers to the physical and non-physical means by which it is achieved. The nature of the barriers is independent of their origin, purpose and location. In terms of their nature, barrier systems are classified into the following four categories,

Material / Physical barrier

It consists of the physical obstacles that do not break or fracture easily that can act as a hindrance for an unwanted action or event. Though it cannot always prevent it under all the circumstances, it will at least slow it down or delay it. It can withstand forces up to a certain maximum beyond which is no longer effective. A material barrier does not have to be interpreted by the acting agent in order to work. The best example for this type of barrier is the k rails along the road that restrains vehicles from going off their path. Valves, Seat belts, walls and air bags also fall under the same category.

Functional barrier

It prevents any unwanted action to be carried out by establishing an interlock that is either logical or temporal. Functional barriers set up one or more preconditions that have to be met before an action can be carried out. An example for this is a lock, whether it is a physical lock that requires the use of a key or a logical lock that needs some kind of password or identification.

Symbolic barrier

Unlike a physical barrier, symbolic barriers have to be perceived or interpreted by the acting agent for achieving its purpose. All kinds of signs and signals are symbolic barriers, specifically visual and auditory signals. Whereas concrete barrier along the road acts as both material and symbolic barrier by indicating the edge of the road and preventing a car from going off the road at the same time, reflective posts and markers are only symbolic barriers.

Immaterial barriers

This final class of barriers is not physically present during the action but was previously imposed functionally in the form of rules, regulations, and safety principles.

The classification of barriers is not simple. They are often complemented by one another.

The author of this content has volunteered to create awareness on safety for the Department of public safety for many years. He has written various articles on highway concrete barriers and traffic control. He recommends DCC for buying concrete barriers. For more details, visit here,

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