Boom! Dry ice as a new type of bomb?

Last tuesday night, Disneyland California had to be partly evacuated after a trash can exploded near Mickey’s Toontown. A terrorist attack in the middle of an amusement park? Or just a prank that got out of hand?

Police quickly found out that the origin of the explosion was a plastic bottle filled with dry ice, which is the solid form of carbon dioxide. It’s a lot colder than normal ice (about -56°C) and doesn’t make everything wet, since it goes directly from the solid form (ice) to its gaseous form. That makes it perfectly suited to package ice cream, for example. It’s also known to produce a lot of white smoke during the sublimation process, a property used to create fog effects in theater, or to make your drink at the cocktail bar smoke ominously. Scientists use it a lot for their experiments, and I remember it succesfully kept our beer cool for several days at a hot summer festival.

But what happens when you put it into a plastic bottle and seal it? Since the surroundings of the bottle are usually a lot warmer than -56°C, the dry ice will start to turn into gas rather quickly. As this process evolves, the pressure in the bottle increases dramatically, until the bottle finally breaks and explodes with an enormous bang. It also has quite some force, as has been tested by Mythbusters (who else?). Tons of youtube videos exist where people blow up bottles in their backyard (a more dramatic version of the Mentos+Coke experiment). Want an example?

At Disneyland, fortunately, nobody got hurt. The police claims that the bottle of dry ice was tossed into the trash can ‘by accident’. Well, when was the last time you were carrying a bottle of dry ice with you at amusement park? Exactly what I was thinking… Someone just wanted to have some fun and make a loud bang.

It could have been a lot worse, though, since these kind of ‘bombs’ are not always as fun and harmless as they may seem at first sight. When filled with nails or sharp objects, or when a glass bottle is used in stead of a plastic one, it becomes a grenade which can cause serious injuries or death. Even a normal plastic bomb that takes longer than usual to explode can be a serious risk, when someone approaches it or picks it up. And this is more common than you might think. That’s why dry ice bombs are forbidden by law in many places, including California. Let’s hope Mickey Mouse doesn’t end up in jail for his innocent prank…

PS: Don’t try this at home!
PPS: It works even better with liquid nitrogen, if you have that. Wait, what? Please forget what I just said! I’d never encourage people to do dangerous physics experiments!

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