MythBusters Episode 225: A-Team Special

An explosion inside a sewer can launch a manhole cover up into a car, disabling it without severely injuring anyone.

plausible

At an abandoned quarry, and Adam and Jamie began a control test by setting up a stationary car and placing nine sticks of dynamite on the ground beneath the engine bay. They put Buster in the driver’s seat and wired him with sensors to measure the blast. Plywood cutouts were placed nearby to gauge shrapnel injuries to bystanders. The explosion destroyed the car, and Buster’s sensors gave a peak of 26 psi (180 kPa). This was considered survivable, but with multiple severe injuries. The bystanders received a lethal pressure of 90 psi (620 kPa) as the blast wave spread out from under the car.

Next, they dug a large trench, covered it with metal plates and dirt, and installed a manhole. One end of this simulated sewer was left open in order to replicate an actual sewer system with plenty of space for gases to expand. The dynamite was placed just below the manhole cover and a second car was placed directly above it, with Buster and the bystanders positioned as before. This time, the blast briefly lifted the front of the car into the air and caused much less damage than in the control test. Buster experienced a pressure of 9 psi (62 kPa) and the bystanders experienced 11 psi (76 kPa) – both survivable with minor injuries. Adam and Jamie decided that the myth was plausible.

An improvised cannon made from a log and fueled by propane can effectively fire wooden planks at an adversary.

busted

To imitate a scene from The A-Team, Adam made a cannon barrel by cutting a log to a length of 40 inches (100 cm) and drilling out its center. Jamie connected the breech to a propane tank and added a spark generator as the ignition system.

After their first attempts to fire the cannon, Adam and Jamie realized they were using too much propane and there wasn’t enough air in the mixture. After adjusting the ratio, the mixture ignited but the wooden projectile remained in place because it did not fit tightly in the barrel, allowing the combustion gases to escape. Adam added a plastic plug to make a tighter seal, but the next test still barely pushed the plank out of the cannon.

Jamie decided to pump pure oxygen into the breech along with the propane to enhance the combustion. This idea was so effective the cannon split into two pieces along its length on the first attempt. After repairing the cannon, they tried several different propane/oxygen ratios but were unable to get a satisfactory launch. The myth was declared busted at this point.

Adam and Jamie wanted to see if they could build something better under similar circumstances to the scene. They visited an abandoned lumber yard and gave themselves one hour to build a working board launcher from the tools and supplies on hand. Their machine used an industrial torque wrench to spin a trailer wheel at high speed and hurl boards from an ammunition hopper (similar to a baseball pitching machine). With this machine on a swiveling mount, they were able to launch small wooden boards at nearly 60 miles per hour (97 km/h) and successfully hit a group of targets.