There's a simple way to make liquid nitrogen cause an explosion. To be clear, this is something you shouldn't do. But there are tons of people doing it! Some of them in pools. Find out the easy way to do it, and why you should always set a liquid nitrogen bomb off where there is plenty of space and air flow.
It seems like liquid nitrogen should be a very safe element to work with. Yes, it's cold, but most people who have spilled it on their hands or fingers know that a splash won't hurt anyone. The liquid rolls off the skin like water, or boils and jumps off the skin as gas, making the sensation less intense than the solid cold weight of an ice cube. Nitrogen is chemically safe, as well. All humans live in a constant atmospheric bath of nitrogen, which makes up almost eighty percent of the air.
Liquid nitrogen can't poison or freeze people, but it has hidden dangers. One of these is simple asphyxiation. Nitrogen as liquid is a great deal more dense than nitrogen as gas. A small amount of nitrogen boiling and turning into gas, as it does quickly at room temperature, will expand and greatly change the chemical composition of the atmosphere in the room. Suddenly someone is breathing much more nitrogen and less oxygen. Often, they don't even know it. Nitrogen suffocation has been proposed as a humane method of execution. People breathe out carbon dioxide, preventing the pain that happens when too much carbon dioxide builds up in the body, but unknowingly take in nitrogen instead of oxygen when they breathe in. Many people in labs have died of this kind of suffocation when liquid nitrogen spilled, boiled quickly, and displaced their oxygen supply. So when playing with liquid nitrogen, even a small amount, always keep windows and doors open, and if possible stay outside.
Especially if making a 'bomb.' Many readers pricked up their ears when reading about the massive change in density that happens when liquid nitrogen goes from liquid to gas. The gas will fill a volume about six hundred times the size of the liquid. If that gas is in a sealed container, and the container is of just the right strength, it will blow apart violently. A weak container, or a container with a weak spot, will just blow a hole through that spot and leak gas steadily. A container that's too strong will force the gas into liquid form, giving off heat as it does. But one that's just right will hold until the pressure builds up on all sides and then - boom.
How are labs getting their supply of liquid nitrogen? Most lab assistants will have seen liquid nitrogen being stored in a massive metal thermos-like container. This container both keeps the pressure on the nitrogen and has large spaces between its inner and outer walls. Usually they create a vacuum between these walls, insulating the inner nitrogen from the temperature of the room. Anyone who needs some liquid nitrogen gets a mini version of this giant thermos to transport their small amount.
Via The Naked Scientists.