Hydrostatic Shock - Inferences From Blast Pressure Wave Observations

Inferences From Blast Pressure Wave Observations

A shock wave can be created when fluid is rapidly displaced by an explosive or projectile. Tissue behaves similarly enough to water that a sonic pressure wave can be created by a bullet impact, generating pressures in excess of 1,500 psi (10,000 kPa).

Duncan McPherson, a former member of the International Wound Ballistics Association and author of the book, Bullet Penetration, claimed that shock waves cannot result from bullet impacts with tissue. In contrast, Brad Sturtevant, a leading researcher in shock wave physics at Caltech for many decades, found that shock waves can result from handgun bullet impacts in tissue. Other sources indicate that ballistic impacts can create shock waves in tissue.

Blast and ballistic pressure waves have physical similarities. Prior to wave reflection, they both are characterized by a steep wave front followed by a nearly exponential decay at close distances. They have similarities in how they cause neural effects in the brain. In tissue, both types of pressure waves have similar magnitudes, duration, and frequency characteristics. Both have been shown to cause damage in the hippocampus. It has been hypothesized that both reach the brain from the thoracic cavity via major blood vessels.

For example, Ibolja Cernak, a leading researcher in blast wave injury at the Applied Physics Laboratory at Johns Hopkins University, hypothesized, "alterations in brain function following blast exposure are induced by kinetic energy transfer of blast overpressure via great blood vessels in abdomen and thorax to the central nervous system." This hypothesis is supported by observations of neural effects in the brain from localized blast exposure focused on the lungs in experiments in animals.

“Hydrostatic shock” expresses the idea that organs can be damaged by the pressure wave in addition to damage from direct contact with the penetrating projectile. If one interprets the "shock" in the term "hydrostatic shock" to refer to the physiological effects rather than the physical wave characteristics, the question of whether the pressure waves satisfy the definition of “shock wave” is unimportant, and one can consider the weight of scientific evidence and various claims regarding the possibility of a ballistic pressure wave to create tissue damage and incapacitation in living targets.