What are the misconceptions when adding liquid nitrogen?

What are the misconceptions when adding liquid nitrogen? You may have overlooked these details
Liquid nitrogen, as an ultra-low temperature medium at -196 ℃, is widely used in scientific research, medical and other fields. However, many users often have misconceptions during the refueling process, and these overlooked details may pose security risks or affect storage effectiveness. Here are a few key considerations:

Misconception 1: Quick refueling is more efficient
Fact: Intense boiling of liquid nitrogen can lead to "explosion boiling" phenomenon, and splashing droplets may cause frostbite
Correct approach: The "slow fast slow" three-stage filling method should be adopted, with an initial flow rate controlled at 1L/min

Misconception 2: The fuller the liquid level, the better
Fact: Overfilling can cause the exhaust port to freeze and block, posing a risk of pressure accumulation
Professional advice: Reserve 10% -15% gas phase space, and it is recommended that the liquid level of medical grade liquid nitrogen tanks should not exceed 80% of the volume

Misconception 3: Neglecting environmental ventilation
Actual test data: 1 liter of liquid nitrogen vaporizes and expands to 700 times its volume, which may cause oxygen deficiency in a closed space (oxygen concentration<19.5% is considered dangerous)
Solution: Ensure that the air exchange rate in the operating area is ≥ 12 times/hour and equipped with an oxygen alarm

The most easily overlooked details:

Pre cooling stage: The new tank needs to be cooled in a stepped manner for the first use, with 1/3 of the capacity added each time and an interval of 30 minutes

Pipeline treatment: Before filling, blow the pipeline with dry nitrogen to avoid water freezing and blockage

Personal protection: Face mask type protective equipment must be worn, ordinary gloves cannot protect against -196 ℃ low temperature

Lesson from a certain biological sample library: Directly adding liquid nitrogen tanks without pre cooling resulted in shrinkage and cracking of the inner container, leading to the loss of valuable samples. Experimental results have shown that standardized pre cooling can extend the lifespan of the tank by 3-5 years. Remember: the safety margin of liquid nitrogen operation is hidden in the details that are easily overlooked.