7" when discussing effects of air blast it is customary to distinguish betveendlrect and indirect damage. Direct damage is, for instance, collapse of waffs androofs due to the fact that one side of these surfaces e:cperiences a tremendousincrease in the static overpressure whereas the other does not. Direct dalxage toobjects such as trees in a forest, telephone poles and. metal sheet constructions ismainly caused by the strong winds. Direct damage to hurans coul-d. consist of eardrunrupture at moderate overpressu?e and in addition hemorrhage of the l-ungs at higireroverpressures. stil1 higher overpressures would cause air to be forced into theveins through the l-ungs resulting in death vithin a few minutes. Generally speaking,a hruan being can withstand much higher pressu."es without fatal direct injuries thanthose requiTed to severely damage even very sol-id. buildings. Ind.irect damage, caused by collapsing buildings, glass fragnents and other debris flying in the airor high vinds dragging peopre into solid objects is a much nore likeiy mechanismfor producing blast injuries and fata-lities, sinee this can occur at distances fromground zero vhen the direct bl-ast damage is negrigible for hurnans. As little as0.0f5-0.02 MPa (0.15-0.20 atm or 2-3 psr) could be expected to blov people out ofmodern office buildings, for instance. B. consid.ering the fact that an attacked area .srill- in general contain objects ofvarious resistance to blast such as buirttings more or less solidl,y constructed., g/ It is of interest to note here that subsurface bursts are rnore efficientthan surface bursts in crater crea.ting and underground d.amage. Hence earth-penetrating devices of very high precision can be quite danaging to fortifiedund-erground structures even with yielcls as ttsma.lltt as of the order of s. few kt.Al 35 /92 Annex f&ge rou Height of burst (m) 3000 2000 I 0005000 4000 I 000 3000 Fig. A:1 The "optimum height of burst" concep! Due to shock reflection at the ground, the area covered by at least a given overpressure depends on height of burst as well as on weaPon yie1d, This is itlustrated for two different overpressures and two
**Analysis**
This text appears to be discussing the effects of air blasts on humans and buildings, specifically the distinction between direct and indirect damage, and the factors that influence blast injuries and fatalities. The text assumes a level of technical knowledge and uses specialized terminology, suggesting a focus on a specific area of study. The language and content also imply a focus on a specific type of disaster or emergency response.

**Category**
Science and technology, Health