For persons side-onto the approachingblast wave, the dynamic pressure and incident pressure are additive (Figure 7-9). In the region of short - duration blast waves (a positive phase of 3 msec or less), there is a twofold difference in magnitude between the curves for the end-on and side -on orientations.
Individuals positioned against a large reflecting surface and normal to the incident shock would have the peak reflected pressure as their effective blast dose (Figure 7-10).
For example, the threshold (that is, the lowest overpressure at which trivial lesions are first detected) for lung injury is about 12psi for blast waves of greater than 20-30 msec duration; scattered pleural petechiae are the threshold injury. Subjects end-on to the blast would require an incident shock of 12 psi static pressure to cause this lesion. If the subjects are oriented side-on,an incident shock of 10 psi (with an associated dynamic pressure of 2psi) would cause equal damage. If the subject is against a reflector, an incident shock of just over 5 psi (reflecting to 12 psi) would cause the same injury. Although all three examples have different incident blast waves, the biologically effective blast loading is the same.