Handling liquid nitrogen safely

Today in the lab I was using liquid nitrogen to snap-freeze brain tissue at -196°C, in order to preserve it long-term. In order to use liquid nitrogen, I needed to wear appropriate PPE (personal protective equipment), as shown in the image below.

What I looked like with all the PPE for using liquid nitrogen.
What I looked like with all the PPE for using liquid nitrogen.

The PPE required to use liquid nitrogen includes cold-insulating gloves, a face shield made of material which specifically protects against liquid droplets and gas, a lab coat, and non-porous closed-toe shoes. Contact of the skin with liquid nitrogen can cause severe cryogenic burns (similar to frostbite). Liquid nitrogen should never be used in small and poorly ventilated rooms because it could displace enough oxygen to cause suffocation.

Tubes of samples that were stored in liquid nitrogen improperly can EXPLODE! Whilst this has never happened to me personally, I was once standing next to another scientist who had just removed a small tube from the liquid nitrogen tank and it immediately exploded in his hand causing him temporary hearing loss. This was likely due to liquid nitrogen being trapped into the tube and being tightly sealed. Therefore, never completely seal a container that holds liquid nitrogen! On the other hand, do not store liquid nitrogen in an uncovered container either. This is because the boiling point of oxygen is above that of nitrogen, and therefore oxygen can condense from the air into the liquid nitrogen (i.e., the oxygen gas from the air will turn into liquid oxygen). This liquid oxygen can build up to levels which may cause violent, highly explosive reactions with organic materials, even materials which are normally non-flammable.