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Student Sustains Cold Burns When Retrieving Vial from Liquid Nitrogen

What Happened?

A principal investigator (PI) was instructing an undergraduate student in their laboratory on how to transfer cryovials from a liquid nitrogen storage dewar to a –80 °C freezer. During the procedure, one of the cryovials dislodged from the rack and fell into the liquid nitrogen. The PI placed the remaining cryovials into the –80 °C freezer and asked the student to retrieve the dislodged vial, which was floating in the liquid nitrogen. The student, wearing cryogenic gloves over nitrile gloves, reached into the liquid nitrogen and grasped the vial directly. They reported a burning sensation to the PI at the time, but observed no visible cold burn.

Several hours later, the student noticed blistering on their fingers and sought medical attention. They reported the incident to their PI, who directed them to the Occupational Health Facility for further evaluation.

What Was The Cause?

  • Immediate cause: The student's gloved hand entered liquid nitrogen to retrieve a cryovial, exposing the gloves and, through glove wetting or ingress, the skin to LN₂ temperatures beyond the PPE's rated performance. Tissue freezing occurred, producing a delayed-onset cold burn that blistered several hours later.
  • Underlying causes:
    • No retrieval tool (tongs, forceps, scoop) was used or available for manual retrieval from the LN₂ dewar.
    • Cryogenic gloves were relied upon for a task outside their rated performance (submersion rather than incidental contact).
    • The PI directed the retrieval without specifying a safe technique or providing a tool.
    • The PI's and student's hazard model for cryogenic burns did not incorporate the delayed presentation of cold-burn injury, leading to a wait-and-see response to immediate symptoms.
  • Root causes:
    1. Training / hazard-recognition gap at the supervisor level. The PI's understanding of cryogenic glove ratings, safe retrieval techniques for dropped items in LN₂, and cold-burn presentation was incomplete. This affects not only this incident but all LN₂ training the PI has previously delivered or will deliver.
    2. Absence of a retrieval tool requirement and availability. The lab did not have a standard expectation, and likely did not have the equipment visibly staged at the dewar, that retrieval of dropped items from LN₂ requires a dedicated tool. This is both an engineering control gap (tool not present) and an administrative control gap (rule not written).
    3. Absence of a "dropped item" SOP for LN₂ storage. The lab had no defined procedure for what to do when a cryovial falls into the dewar — the single most common accident in cryogenic storage work. Without a defined procedure, the response defaults to improvisation under supervisor direction, which is exactly what happened.
    4. Gap in post-symptom response guidance. The lab had no clear rule stating that any reported burning, tingling, or numbness following LN₂ contact would trigger an immediate medical evaluation, regardless of visible findings. Deferring until visible injury appears is medically inappropriate for cold burns.

How Can Incidents Like This Be Prevented?

  • Never reach into liquid nitrogen. Dropped items are always retrieved with tongs, forceps, or a cryogenic scoop. Hands never enter the dewar.
  • Stage the tool at the dewar. Place tongs, forceps, and a scoop on a hook next to every LN₂ storage unit. If the tool isn't there, the retrieval doesn't happen.
  • Cryogenic gloves are not submersion gloves. They protect against brief, incidental contact with cold surfaces and vapor. Submersion in LN₂ is outside their designed purpose.
  • Wear a face shield, not just safety glasses. LN₂ splash reaches the face during routine handling. Face shield, long-sleeve coat, closed-toe shoes, long pants — no exposed skin at wrist, neck, or lower leg.
  • Cold burns are delayed. Burning, tingling, or numbness after LN₂ contact should trigger an immediate visit to Occupational Health, regardless of visible injury. Do not wait for blisters.
  • Supervisors: stop and fetch. When something goes wrong during training, model the correct response — stop, fetch the tool, then proceed. Students replicate what they see.
  • Consider vapor-phase storage. Eliminates the dropped-in-LN₂ scenario and the cryovial-bomb hazard. Worth evaluating at the lab or institutional level.
  • Develop or revise the SOP for LN₂ storage work to specify:
    • Required PPE: cryogenic gloves, full face shield (not safety glasses alone), long-sleeve lab coat, closed-toe shoes, long pants. No skin exposed at wrist, neck, or lower leg.
    • Retrieval tool requirement: all retrieval from the dewar — routine or emergency — uses a designated tool. Hands never enter the dewar.
    • Dropped-item procedure: if an item falls into the LN₂, stop, retrieve the correct tool (tongs, forceps, or scoop), and use it to recover the item. If no tool is available, leave the item until one can be obtained. Never retrieve dropped items by hand.
    • Thawing procedure for submerged cryovials: behind a splash shield, with a face shield, allowing complete warming before opening.
    • Oxygen/ventilation requirement: LN₂ work in well-ventilated areas only.

Resources

 

QUICK ACTION TIPS 

Contact with cryogenic materials can rapidly freeze and destroy skin tissues. If exposed:

  1. Remove all clothing that may restrict circulation to the frozen area
  2. Flush affected area with tepid, not hot, water. The water temperature should be barely above body temperature; do not use dry heat
  3. Do not rub frozen body parts, before or after warming
  4. Cover thawed body part with dry sterile gauze and large, bulky protective clothing
  5. Seek medical attention
  6. Report the incident to your supervisor

Liquid Nitrogen

  • Liquid nitrogen cold vapors can cause cryogenic burns and tissue damage to the eye
  • Liquid-to-gas expansion ratio of nitrogen is ~700:1 at 20 °C (68 °F), which can generate great force
  • Might act as an asphyxiant in confined spaces