Like an airplane crash, an explosion pressure wave is rated as an extremely rare event (safety level 4), and thus qualifies as beyond design system status. An explosion pressure wave is a chemical explosion in the form of a deflagration (pressure rising relatively quickly, building up reflected pressure). It may be caused by using explosives or if a high-energy container bursts, so that an explosion pressure wave must be accepted as a design basis when carrying hazardous cargos by rail, water or road and when storing containers with high energy content.

A chemical explosion causes pressures on the building concerned and induced vibrations in that building. The external explosive loads due to air pressure waves give an explosion pressure which can be expressed in time and place terms

as follows:

P = Ps + c • q where

ps is the compression pressure, including reflected increase q is the velocity pressure (dynamic pressure) c is a coefficient of form

With box-shaped buildings (non-slender structures), the c • q component may be ignored; with slender structural sections, the explosion pressure can be treated as a static wind load c • q as defined in DIN 1055-4 [49]. For more details of using this function for explosion pressure see DIN 25 449 [15].

As a general rule, if no more precise local studies are available, possible explosion pressure waves can be established using the pressure wave in the BMI guidelines [50]. This function, as shown in Figure 5.8, is specified in the RSK guidelines for PWRs, and represents a conservative assessment of potential explosion pressure waves. This approach assumes that the pressure wave can come from any given direction and that there is a level pressure front.