Primary blast injury is caused by which physical factor?

• A. The blast overpressure or wave from an explosion
• B. Shrapnel penetration
• C. Thermal burns
• D. Toxic inhalation

Answer: (A)

The initiating factor in primary blast injury is the blast overpressure—the sudden, high-pressure shock wave produced by an explosion. This rapid pressure rise and fall damages air-filled organs and structures most sensitive to pressure changes, such as the ears and lungs, and can lead to things like tympanic membrane rupture or pulmonary injuries. This mechanism is distinct from other injury types: shrapnel or debris cause secondary injuries, extreme heat causes burns, and inhaled toxins or gases cause toxic inhalation injuries. So, the primary blast injury is driven by the overpressure wave itself, not by fragments, heat, or inhaled substances.