A primary injury is caused by a direct effect of blast overpressure on tissue. Primary blast injury affects air-filled structures such as the lungs, ears, and GI tract the following mechanisms: spalling (e.g., from lung parenchyma to alveolar space, causing tissue surfaces to explode geyser-like); shearing, due to differential ineia (e.g., pulmonary vessels and air spaces), resulting in ruptured vascular and bronchial pedicles; and implosion of flexible air spaces, which rebound to greater than original size, resembling miniexplosions. Ref: Halpern P. (2011). Chapter 8. Bomb, Blast, and Crush Injuries. In J.E. Tintinalli, J.S. Stapczynski, D.M. Cline, O.J. Ma, R.K. Cydulka, G.D. Meckler (Eds), Tintinalli's Emergency Medicine: A Comprehensive Study Guide, 7e.