One of the building blocks of the guideline is the concept of Consequence Class. It is a qualitative rating of the consequences resulting from the failure of mitigation measures with regards to the degree of loss of life, and economic, social or environmental impacts. These classes are borrowed from the European Norm EN 1990:2003 “Eurocode: Basis of structural design”. There are three levels of consequences defined as low, medium or high (as shown below), which consider both the effects on the area of protection and the mitigation system’s integrity.
In the guideline, these classes are used to determine the required level of safety of components and characteristics of planned mitigation structures. For example, they determine the factor of safety applied to forces used during design, geometric coefficients applied to bounce heights, or the allowable opening of gaps after an impact event. As the consequence class increases, so does the level of safety applied.
Consequence Class 1
Provides the least conservative case for protection. It should only be used where there is a low impact on human life with small or negligible economic, social and environmental affects.
Examples may include the protection of agricultural buildings with low frequency of occupation such as barns, green houses, forest roads and freight roads with low traffic frequencies.
Consequence Class 2
Provides a modest case for protection. Normally applied where there is a medium impact on human life with possibly considerable economic, social and environmental affects.
Examples may include the protection of residential buildings, public buildings with medium consequences of failure, such as office buildings, regional and national traffic routes with Daily Traffic Volumes < 50,000 vehicles.
Consequence Class 3
Provides the most conservative case for protection. It is applied where there is a high impact on human life with very large economic, social and environmental affects.
Examples may include the protection of grandstands, public buildings with high consequences of failure, such as concert halls, regional and national traffic routes with Daily Traffic Volumes > 50,000 vehicles
CEN (2005) EN 1990:2002, Eurocode – Basis of structural design. European Committee for Standardization, Brussels, Belgium.
What level of risk is there?
How is the design block selected?
What system capacity is sufficient?
What system height is required?
How is an anchor verified?
What other performance criteria are there?
How can the system be safely adapted to a site?
What recommended maintenance protocols exist?