Jamie and Adam prepare to detonate a charge. [1]
- The Myth - A person can increase his chances of surviving an underwater explosion by floating on his back at the surface.
- Verdict - Confirmed
- Notes - Adam and Jamie built a 15 ft (5 m) deep cylindrical tank, fitted it with pressure sensors at four depths, and filled it with water. Firing an underwater .357 Magnum revolver loaded with blanks to generate shock waves, they found that the sensor nearest the surface gave the lowest readings.
For full-scale tests, they used a mast fitted with sensors at depths of 6 in (15 cm) and 2.5, 15 and 25 ft (0.76, 4.6 and 7.6 m), with a fifth at the surface. The first two depths were intended to represent the depth at which a swimmer's torso would be submerged if he were floating or treading water. A 10 lb (5 kg) charge of TNT was set off at a depth of 15 ft (5 m) and a set distance from the sensors (30, 70 or 150 ft (9.1, 21 or 46 m)).
Using a pressure threshold of 87 psi (corresponding to a 50% mortality rate from the shock wave), Adam and Jamie found that a floating person would survive at 30 ft (9 m), while greater depths led to pressures likely to cause death. At longer distances, the readings fell below 87 psi. Based on the 30-foot results, they declared the myth confirmed. Jamie attributed these results to the fact that much of the energy from the underwater pressure wave dissipated into transverse waves when it reached the surface.
This myth was featured in the 2011 episode Paper Armour