Q&A column

Megan O. Nakashima, MD
Assistant Professor of Pathology
Cleveland Clinic Lerner College of Medicine
Staff Hematopathologist, Cleveland Clinic
Member, CAP Hematology/Clinical
Microscopy Committee

Q. Can you please provide guidance on revised checklist requirements GEN.77500 Liquid Nitrogen and Dry Ice and GEN.77550 Liquid Nitrogen Safety?

A. Liquid nitrogen poses a significant safety risk to laboratory personnel and others entering the laboratory. At room temperature, it is converted to nitrogen gas at an expansion ratio of approximately 1:700 (1 L LN2/700 L nitrogen gas). Because nitrogen gas has a higher density than oxygen, it displaces oxygen starting at floor level and can create an oxygen-deficient atmosphere, potentially resulting in asphyxiation. The risk of asphyxiation is dependent on the amount and rate of nitrogen gas release, the proximity of personnel, and the ventilation in the area. Nitrogen gas is odorless and colorless, so unless an alert system is used, laboratory personnel may not be aware of an unsafe condition, such as a leak or spill.

To demonstrate compliance with the revised GEN.77550 in the Sept. 17, 2019 checklist edition, laboratories must place oxygen sensors with a low oxygen alarm in appropriate locations where LN2 is used or stored if the gas poses an asphyxiation risk. The sensor must be placed at or below typical breathing height and near where a leak would most likely occur. For example, if personnel in the work area sit at a microscope bench, the sensor must be mounted lower to the ground than it would be for personnel who perform their duties while standing. The laboratory must evaluate its LN2 usage and work environment (e.g. size of room, ventilation) to determine the appropriate number, type, and location of sensors needed.

If a laboratory is using a small volume of LN2 (e.g. no more than 1 L) and decides not to monitor an area using or storing LN2, it must have records to show that it assessed the use of LN2 in the laboratory (amount used, rate of nitrogen gas release, proximity of personnel, and ventilation in the area) and the risk of asphyxiation (based on a worst-case scenario) and determined there is no risk of asphyxiation.

Requirement GEN.77500 on LN2 and dry ice, in the 2019 checklist edition, includes the following safety provisions:

• mandatory use of skin and eye protection (e.g. gloves, goggles, and face shields) when decanting LN2 and handling dry ice.
• storage and use of LN2 and dry ice only in well-ventilated areas.
• training of all personnel on the safe handling of LN2 and dry ice.
• posting of appropriate signage in areas where LN2 is used and/or stored.
• availability of a safety data sheet.
• development of a plan for immediate treatment of individuals overcome by toxic or oxygen-displacing fumes.

For more information on this topic, the CAP recommends that laboratories visit the OSHA website for the OSHA QuickFacts “Laboratory Safety: Cryogens and Dry Ice” and the OSHA booklet “Laboratory Safety Guidance.”

Occupational Safety and Health Administration. Laboratory safety guidance. 2011:24–25. OSHA website. https://osha.gov/Publications/laboratory/OSHA3404laboratory-safety-guidance.pdf.

Occupational Safety and Health Administration. OSHA QuickFacts. Laboratory Safety: Cryogens and Dry Ice. OSHA website. https://www.osha.gov/Publications/laboratory/OSHAquickfacts-lab-safety-cryogens-dryice.pdf.

Lyn Wielgos, MT(ASCP)
Checklist Editor
CAP Accreditation Programs
College of American Pathologists
Northfield, Ill.