Liquid nitrogen is a form of liquefied atmospheric gas that is used in cryogenics, the freezing of foods for transport, and by auto racers to burn more fuel and air in their cars' internal combustion engines. Racing enthusiasts commonly refer to liquid nitrogen as NOS. Liquid nitrogen is transported in pressurised tanks called Dewars. Because of the large gas expansion ratio, the gas can be extremely harmful if vaporised or exposed quickly, causing possibly fatal explosions. Before purchasing or handling liquid nitrogen, it's important to know how to take the proper safety precautions.
Read about liquid nitrogen safety before purchasing a tank (See the Resources section). Understand what to use and what not use around liquid nitrogen. For example, you should not wear a watch or jewellery when handling liquid nitrogen. Set up a plan for what to do in any possible worst-case scenario, such as a pressurised Dewar tank venting spontaneously.
Search online to determine the amount of liquid nitrogen you need in case you need to purchase more than one Dewar.
Call your local welding supply company or gas supplier store ahead of time to let them know how much liquid nitrogen you need. This is the best option if you are purchasing a large amount. Other stores which may sell smaller quantities of liquid nitrogen include hardware and paintball stores.
Go into the store to purchase one or more 5-gallon (25-liter) Dewars of liquid nitrogen. Make sure to purchase a Dewar with a loose cork. Also, while at the store purchase all other equipment that you need for handling the liquid nitrogen. For example, you can store some of the liquid nitrogen in a metal Thermos for up to two days.
Show your safety knowledge and be ready to give a reason for purchasing the liquid nitrogen. Depending on the store's policy of selling liquid nitrogen, you may be required to sign an agreement of purchase and use for the store's legal protection in case the liquid nitrogen is used for illegal purposes.