Use of liquid nitrogen (LN2) has grown rapidly the last several years, due in part to the growth in stem cell research and other medical uses. Unfortunately, so have the number of serious accidents and injuries. These incidents have occurred not only during use, but also during transport and storage.

A wide variety of laboratories use LN2. Most common are chemistry and physics labs, nanotechnology, computer chip design, and production and cryotube research. There is also growing use in the healthcare arena in the rising need for dermatology and skin cancer treatment and as research and development with stem cells advances.

LN2 is classed as a cryogenic fluid, being a liquefied gas that must be kept at extremely low temperature. Boiling points for cryogens are defined as below -150°C (-238°F). LN2 boils at -196°C (-320°F). This fact presents the primary hazard: contact will produce severe burns and more serious injuries due to instant freezing.

As most of you probably know, nitrogen is also an inert gas. Due to LN2’s physical properties, a very small amount of the liquid can expand into very large volumes of gas. This presents the second most important hazard: displacement of oxygen and possibility of asphyxiation.

In addition to the physiological hazards above, physical hazards abound with LN2. Handling and using LN2 can be done safely, if we recognize the hazards and strive to control them. If we become cavalier and things go wrong, serious injury and/or death is usually the end result. Here is one recent example:

As mentioned above, the hazards fall into two categories: physiological and physical. Physiological hazards produce bodily harm and fall into two main categories, those that damage tissue from direct contact and those that can cause asphyxiation.

LN2 flows freely as a liquid and, as a result, may splash and spill. Accidental splashes or contact with an extremely cold cryogen freezes and kills tissue instantaneously. Therefore, direct contact must be prevented at all costs.

Cryogenic liquids contain a tremendous amount of potential gas volume. For example, one unit volume of LN2 will expand to produce 700 times the volume of gas when vaporized. This rapid and extreme expansion can lead to oxygen displacement. A leak or vessel breakage can result in an oxygen deficient atmosphere very quickly, especially in small enclosed areas with poor ventilation. Due to LN2’s odorless and colorless properties, this situation is very hard to recognize.

Physical hazards from LN2 include explosion risks from pressure buildup. As mentioned above, the gas volume generated from the vaporization of the liquid phase is very large and happens rapidly. If this phase change occurs in a vessel unable to contain the pressures exerted, it can fail catastrophically from over-pressurization.

Anyone who handles or uses cryogenic liquids must have adequate knowledge of the particular material’s properties and the safe handling practices. Specific understanding acquired through proper training must include:

Ensure all employees handling and using LN2 read and understand the safety data sheet. In addition, develop and follow standard operating procedures (SOPs) whenever handling or using LN2. To jump-start your training and SOPs, here are some quick tips:

Tags: Cold Storage Cryogenics nitrogen Product Resource: Resources

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