The MythBusters The MythBusters

MythBusters Episode 239: Tanker Crush

Premier Date: January 16, 2016

A railroad tank car can implode if filled with steam and sealed, due to a partial vacuum being generated inside as the steam condenses.


For a demonstration, Adam added a small amount of boiling water to a 1 gallon (3.8 L) metal can, screwed on the cap. As he allowed it to cool, the can slowly buckled. Adam and Jamie then repeated the test with a 55 gallon (210 L) drum; after a tense wait of more than 20 minutes, the container’s side walls suddenly collapsed. They performed a third test, fitting the drum with a vacuum gauge and temperature sensor, and recorded a time to failure of 8 minutes, a peak vacuum of 16 inches of mercury (54 kPa), and a temperature drop from 195 °F (91 °C) to 170 °F (77 °C). When another drum was steam-cleaned to heat it to 203 °F (95 °C), it took 16 minutes to fail; the peak vacuum was 17.5 inches of mercury (59 kPa), and the buckling was more pronounced. Adam and Jamie then built a small-scale tank car out of four drums welded together, and reproduced a similar implosion.

The full-scale tests began at a railroad depot in Boardman, Oregon. They set up a decommissioned tank car measuring 67 feet (20 m) in length and 10 feet (3.0 m) in diameter and with 0.5 inch (13 mm) steel walls, making it the largest prop ever used on MythBusters. After Adam inspected the interior to verify that it was in good condition, they sealed the release valves and attached a vacuum gauge and temperature sensors. The car was steam-cleaned for 3 hours, reaching 209 °F (98 °C), after which the steam was shut off, the hatch was sealed, and a fire hose began to spray water over the car to simulate rain and more quickly cool the car. The vacuum readings peaked at 27 inches of mercury (91 kPa) as the car cooled to 100 °F (38 °C), but no collapse had occurred after 60 minutes and they ended the test at that point.

Theorizing that internal damage or corrosion could make collapse more likely, Adam and Jamie obtained a second, older car. For this test, they used an industrial vacuum pump to achieve the same negative pressures, but much more quickly. Again, the car remained intact after 60 minutes, so they ended the test and vented it to the atmosphere. Finally, to investigate the effect of physical damage, they dropped a 3,200 pound (1,500 kg) concrete block onto the tank car from a height of 30 feet (9.1 m), resulting in a significant dent. When the pressure was pumped down again, the car collapsed at 23 inches of mercury (78 kPa). Adam and Jamie declared the myth-as-stated busted, but noted that it could happen if the tank car is already badly damaged.