5.9 Liquid Nitrogen and Pressurized Oxygen

Liquid nitrogen safety guidelines

It is crucial that everyone understands the potential hazards associated with using liquid nitrogen and follows proper safety procedures at all times. Laboratory personnel face the primary risk of frostbite or cold burns to the skin or eyes due to contact with this cryogenic material.

When handling, using, or storing liquid nitrogen, follow these safety precautions:

• Always wear the correct Personal Protective Equipment (PPE), including a laboratory apron, face shield, thermally insulated gloves, pants, and high-topped leather shoes.
• Spill hazards: Liquid nitrogen expands 696 times its original volume when changing from a cryogenic liquid to a room-temperature gas. Even small spills can displace enough oxygen to cause asphyxiation.
• Never use an elevator with a container or dewar filled with liquid nitrogen. If the elevator gets stuck, there is a risk of asphyxiation. A person can become unconscious without any warning symptoms.
• Always label liquid nitrogen containers clearly.
•  When transporting liquid nitrogen in elevators, use a sign that reads:
  “Transport of Liquid Nitrogen! Do Not Enter the Elevator!”

Liquid nitrogen can freeze and embrittle various materials, including lab plumbing, ice buckets, and flooring.

• Use containers specifically designed for liquid nitrogen transport.
• Never pour liquid nitrogen down the sink. Instead, allow excess liquid nitrogen to evaporate in a well-ventilated area.

Cryo Safefill - Liquid nitrogen filling station

In the room and the cabinet for dispensing liquid nitrogen, an oxygen detector monitors oxygen levels inside and outside the cabinet. If the oxygen level drops below 15%, the liquid nitrogen filling stops, and the system alarms.

• The oxygen sensor alerts when the level falls below 19.6%.
• Do not open the cabinet door if the oxygen level is below 19.6%.
• Always ensure that two qualified individuals are present during liquid nitrogen dispensing and transportation.

Pictogram	What shall be marked
	Dewars, laboratories and storage rooms containing liquid nitrogen shall be marked with this sing.

Pressurized oxygen safety guidelines

Oxygen, a highly reactive substance, must be kept separate from combustible materials.
When dealing with pressurized oxygen, such as oxygen gas cylinders, it’s essential to understand the potential hazards:

• Violent reactions: Pressurized oxygen can react violently in the presence of oil or other lubricants. When exposed to a spark or open flame, pure oxygen significantly accelerates the combustion of porous materials like clothing, textiles, and rubber.
• Leaking valves or hoses: A leaking valve or hose in a poorly ventilated room or confined space can quickly increase the oxygen concentration to dangerous levels.

To prevent oxygen enrichment and ensure safety:

• Keep oxygen equipment in good condition to prevent leaks and ensure proper functioning.
• Exercise care when using oxygen to avoid accidental ignition.
• Ensure good ventilation in areas where oxygen is present.

Pictogram		What shall be marked
		Compressed oxygen shall be marked with these pictograms.
		Laboratories and storage rooms containing compressed oxygen shall be marked with these labels.