Cryogenic materials are used in a wide variety of laboratories. They are common in chemistry, healthcare, and physics labs, and are becoming more prevalent as stem cell, nanotechnology, computer chip design, and cryotube research advance.
Cryogenic fluids are liquefied gases that must be kept at extremely low temperatures. Boiling points for these gases are usually below -150°C (-238°F). For this article, we will consider materials with boiling points below -75°C as cryogenic (so as to include dry ice).1 Due to its physical properties, a very small amount of the liquid can expand into a very large volume of gas.
The most common cryogens include helium, hydrogen, nitrogen, and oxygen. You will encounter them on a daily basis if you receive shipments packed with dry ice, preserve samples with liquid nitrogen, remove impurities with cold traps or baths, or keep equipment cooled. All these tasks can be done safely if we recognize the hazards and endeavor to control them. Should we become cavalier, things can go very wrong. Here are a few examples:
Generally, cryogens present similar hazards as compressed gases. The primary hazards fall into two categories: physiological and physical.
Physiological hazards produce bodily harm and are divided into two main categories—those that damage tissue from direct contact and those that can cause asphyxiation.
Cryogenic materials flow freely just as other liquids do and, as a result, may splash and spill. The effect produced from accidental splashes or contact with extremely cold cryogens is similar to liquid nitrogen used by your dermatologist. Direct contact with liquid nitrogen or other cryogens freezes and kills tissue rapidly.
Cryogenic liquids contain a tremendous amount of potential gas volume. One-unit volume of liquid nitrogen, for example, will expand to produce almost 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 rather quickly, especially in small areas with poor ventilation.
Physical hazards include explosion risks from pressure buildup and those from chemical reactions or combustion.
As mentioned above, the gas volume generated from the vaporization of the liquid phase is very large. If this phase change occurs in a vessel unable to contain the pressure exerted, it can fail catastrophically from over-pressurization.
Related Article: Safe Handling of Liquid Nitrogen
Cryogenic fluids with a boiling point below that of liquid oxygen, such as nitrogen, are able to condense and accumulate oxygen from the atmosphere. Violent reactions—for example, rapid combustion or explosion— may occur if incompatible materials, such as most common organic compounds, come in contact with the oxygen.
Anyone who handles or uses cryogenic liquids must have adequate knowledge of the particular material’s properties and safe handling practices.4 Specific understanding acquired through proper training should include:
Ensure all employees handling and using cryogens read and understand the safety data sheet. In addition, develop and follow standard operating procedures (SOPs) whenever handling or using cryogenic materials. To jumpstart your training and SOPs, here are some quick tips:
1. Prudent Practice in the Laboratory: Handling and Disposal of Chemicals, National Academies Press, National Resource Council, Washington, DC. 1995. http://www.nap.edu/catalog/4911/prudent-practices-in-the-laboratory-handling-and-disposal-of-chemicals
2. “Inquiry after man dies in chemical leak,” BBC Online News, Monday, October 25, 1999. http://news.bbc.co.uk/1/hi/scotland/484813.stm
3. “Lab Safety Cryogens Incidents,” American Industrial Hygiene Association, Laboratory Health and Safety Committee. 2015. https://www.aiha.org/get-involved/VolunteerGroups/LabHSCommittee/Incident%20Pages/Lab-Safety-Cryogens-Incidents.aspx
4. “How Do I Work Safely with Cryogenic Liquids?,” Canadian Center for Occupational Health and Safety, Hamilton, ON, Canada. 2015. http://www.ccohs.ca/oshanswers/prevention/cryogens.html
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