Barriers [security]

It is widely accepted that a single barrier or a series of barriers can protect a secure site from attack. Although the presence of a barrier may deter an attack, in many cases its most important function is to delay an attack. A barrier is considered effective if it can delay an attacker for a period longer than it takes a response force to respond to the attack. At present, there are varying views between organisations as to the definition of a high security barrier. For example, in the UK the three Prison Services typically protect their most secure perimeters with a wall and a weldmesh fence topped with barbed coil, whereas other secure sites in the UK protect their assets using only palisade or chainlink fencing. Often, by taking into account the history of an organisation, the local culture or the specific threats to a site, these differences can be explained. In an effort to identify those elements of a barrier that make it effective, attack trials have been carried out on a number of barrier configurations. Many of these trials have examined the delay factor introduced when a barrier is used on its own while others have considered the effect of a barrier when used in combination with an intruder detection system or a topping. The paper revisits the basic philosophy behind barriers, presents an overview of the various types of barriers available and discusses their effectiveness when used in isolation or in combination with detection systems and toppings. It is not the intention of the paper to define the ultimate barrier but it is hoped that it may stimulate both thought and discussion.