Explosive Energy of Dry Ice Bombs
Thursday, October 17, 2013
|Christopher from Salem, OR, USA via Wikimedia Commons|
Last Tuesday, officials arrested the alleged dry-ice bomber of LAX airport. Dicarlo Bennett, a 28-year-old who handled baggage and ramp service at LAX, had created four dry ice bombs, two of which exploded within the airport facility. The other two were found and discarded before exploding.
Thankfully, no one was injured and in light of the coming holiday and LAX upset we’ve provided some calculations that indicate just how dangerous dry ice bombs can be and how to safely enjoy the misty aura of dry ice.
Carbon dioxide vapor, or gas, is what comprises the mist. The solid, ice form of carbon dioxide sublimates – or phases changes from a solid to a gas - at pressures lower than 5.3 atmospheres. So, when you expose dry ice to air at sea level, which is about one atmosphere, it begins producing carbon dioxide vapor, which expands, consuming increasingly more space.
What Bennett did, and what no one should do at home, was place dry ice in a container and then seal it. As the ice sublimated, the resulting gas expanded building pressure within the bottle. Once the pressure inside matched the ultimate tensile strength (the maximum breaking resistance of a material under pressure) of the bottle, then that’s when the bottle went boom.
Exactly how much boom are we talking? About the equivalent of 7.8 grams, or 0.27 ounces, of TNT.
Suppose that the 20 fluid ounce bottles that Bennett used were your standard, run-of-the-mill water or soda bottles made from polyethylene terephthalate plastic. PET plastics have a tensile strength of about 55 Megapascals. Since pressure is equivalent to energy density, we simply calculate the volume of the bottle to determine the explosive energy of Bennett’s dry ice bombs.
One gram of TNT is equivalent to 4,184 Joules of energy, so this tells us that the dry ice bombs that exploded at LAX created the same energy as if Bennett had used TNT amounting to 7.8 grams, or about the amount of one, medium-sized pitted green olive. For comparison, the average pipe bomb detonates with an explosive energy equivalent to about 5 pounds of TNT – almost 300 times more energy.
Although the energy released is relatively small, the shock wave of a dry ice bomb can be loud enough to cause hearing damage. Moreover, the explosion sends bits of plastic and residual dry ice flying in all directions, which can cut and burn the skin. Lastly, dry ice bombs can be unstable and explode unexpectedly, making them dangerous to approach once sealed.
Some reports are saying that Bennett planted the dry ice bombs as a prank - a dangerous, illegal prank that has landed him behind bars with a $1 million bail. In fact, building dry ice bombs is illegal in many parts of the country. So, if using dry ice this Halloween, please make sure to handle with gloves and place in a well ventilated space.