Liquid nitrogen (LN2) is nitrogen in its liquid state, existing at the extremely cold temperature of approximately \(-196^\circ\text{C}\) (\(-320.5^\circ\text{F}\)) at atmospheric pressure. As a cryogenic liquid, it is produced industrially by the fractional distillation of liquid air. This colorless, odorless substance is in high demand across numerous industries due to its powerful cooling capabilities. While purchasing LN2 is generally possible, the transaction depends heavily on specific logistical requirements and strict adherence to safety protocols.
Accessibility and Purchasing Requirements
Purchasing liquid nitrogen is typically straightforward, provided you engage with the correct suppliers. Primary sources include industrial gas companies, such as Airgas or Praxair, which operate extensive distribution networks. Local welding supply shops, specialized scientific distributors, and farm supply centers may also sell it to individuals.
A significant hurdle for consumers is the requirement to possess a proper cryogenic container, known as a Dewar flask, before a supplier will complete a sale. Suppliers often require customers to bring their own container, as they will not dispense the product into an unapproved vessel due to safety concerns. While some industrial suppliers may have minimum purchase requirements, smaller capacity dewars down to 5 liters are readily available for private purchase.
Certain vendors may require a safety review or a signed waiver to ensure the consumer understands the risks associated with handling cryogenic liquids. It is advisable to call ahead to confirm the supplier’s specific policies, including any age restrictions or required documentation. The cost of the liquid itself is relatively low, but the initial investment in a certified Dewar and appropriate safety gear is the main financial barrier to entry.
Essential Safety Precautions
The extreme cold of liquid nitrogen presents an immediate hazard of cold burns or frostbite upon contact with skin or tissue. This effect can happen almost instantaneously and is similar to a severe thermal burn, potentially causing extensive tissue damage. To prevent this, appropriate Personal Protective Equipment (PPE) is necessary, including insulated cryogenic gloves and a full-face shield or unvented safety goggles. Gloves should be loose-fitting so they can be quickly removed if LN2 is accidentally spilled inside them.
The most significant environmental danger is the risk of asphyxiation, as liquid nitrogen rapidly vaporizes, expanding by a factor of nearly 700 times into gaseous nitrogen. Since nitrogen gas is odorless and colorless, it can quickly displace oxygen in a confined space without warning. This reduction in oxygen concentration below the safe level of 19.5% can cause dizziness, unconsciousness, and death. Therefore, all handling and use of liquid nitrogen must occur in areas with strong, active ventilation to prevent the accumulation of this heavy, cold gas.
Storage and Transportation Equipment
The prolonged storage of liquid nitrogen requires a specialized container called a Dewar flask, which is a highly efficient vacuum-insulated vessel. The Dewar functions much like a large thermos, using a vacuum layer to minimize heat transfer from the environment. This design reduces the rate at which the LN2 “boils off” and evaporates.
A defining feature of these cryogenic storage tanks is the loose-fitting stopper or vented lid, which is an important safety mechanism. Liquid nitrogen is constantly boiling, and if it were sealed in a non-vented container, the rapid pressure buildup from the expanding gas would cause the container to rupture or explode. For transportation, the Dewar must be secured upright in a vehicle, ideally in an open bed or trunk, or in the main cabin with windows rolled down to ensure continuous ventilation and mitigate the asphyxiation risk.
Common Practical Applications
Liquid nitrogen’s extreme cold and inert properties make it valuable for various applications beyond industrial use. In culinary arts, it is used for flash-freezing food, such as making ultra-smooth ice cream or creating dramatic, smoky effects in molecular gastronomy. The rapid freezing preserves the cellular structure of food better than conventional methods, maintaining superior quality and texture upon thawing.
Technologically, LN2 is used by computer enthusiasts to cool central processing units (CPUs) and graphics cards to extremely low temperatures, a process known as overclocking. This practice allows hardware to run at much higher speeds than normal without overheating. In medical and cosmetic fields, professionals use LN2 for cryotherapy to freeze and remove unwanted skin lesions, such as warts and benign growths, and for the long-term cryopreservation of biological samples.