Premier Date: October 14, 2012

A battlefield trench built with sharp 90-degree corners can help stop a shock wave and save a soldier’s life.

plausible

This myth supposedly arose from the German army’s careful construction of its trenches during World War I. Adam and Jamie started by building small-scale trenches filled with water and colored oil to help visualize wave movement. Three trenches were built: one straight, one with two sharp corners, and one with two soft (curvy) corners. A motorized mechanism generated waves at one end of each trench and the amplitude of the waves was measured at the opposite end. The amplitude for the straight trench was 0.75 inches (19 mm), for the sharp cornered trench it was 0.125 inches (3 mm), and for the soft-cornered trench it was 0.25 inches (6 mm), lending credibility to the premise.

For full scale testing, three 50 foot (15 m) trenches were dug in the same shapes and lined with plywood to ensure straight edges (the soft corners were not lined). A 25 lbs (11 kg) charge of TNT was used for each explosion and force sensors were placed at 10 foot (3 m) increments from the charge. The following table summarizes the findings.

Trench Shape Pressure at 20 ft Pressure at 30 ft Pressure at 40 ft Pressure at 50 ft Open-air (control) 39 psi (269 kPa) 12 psi (83 kPa) 7 psi (48 kPa) 5 psi (34 kPa) Straight 397 psi (2737 kPa) 65 psi (448 kPa) 38 psi (262 kPa) 21 psi (145 kPa) Sharp corners 60 psi (414 kPa) 19 psi (131 kPa) 12 psi (83 kPa) 7 psi (48 kPa) Soft corners 76 psi (524 kPa) 21 psi (145 kPa) 13 psi (90 kPa) 8 psi (55 kPa)

Because the intensity of the blast was lower with sharp corners than with soft corners or no corners, the myth was deemed plausible.