Liquid nitrogen

Liquid nitrogen is a colorless, odorless, and tasteless liquid. It is neither toxic nor flammable. Its boiling point is -196°C at atmospheric pressure.

The extreme cold of liquid nitrogen can cause frostbite upon contact. Unprotected, moist skin can instantly adhere to metal objects cooled by liquid nitrogen, potentially leading to serious injuries upon removal. Equipment can explode due to the pressure increase when nitrogen transitions from liquid to gas. This may occur when storage tubes with samples are warmed to room temperature if liquid nitrogen has leaked into them during storage. Contact with eyes can lead to blindness.

Liquid nitrogen expands rapidly when it evaporates into a gas. Due to its low temperature, the gas is denser than oxygen and sinks towards the ground, displacing oxygen and possibly causing oxygen deprivation. Symptoms such as dizziness, unconsciousness, and even death can occur without warning—unconsciousness may ensue when oxygen levels drop below 17-18%, compared to the normal 21%.

There is a risk of slipping after spilling liquid nitrogen, as the soles of shoes may freeze and become slippery. Boots with thick soles reduce the risk of slipping.

Safety equipment

Eye protection and specialized gloves must be worn at all times when transporting, loading, or handling liquid nitrogen. Based on risk assessments, it may also be necessary to wear full-foot coverage shoes or boots and other protective clothing, such as protective trousers placed over the boots.

In areas where liquid nitrogen is used extensively, an emergency shower and eyewash station may be required, as well as localized extraction ventilation.

First aid

Exposure to high levels of nitrogen gas can result in suffocation, which may occur suddenly. Symptoms can include unconsciousness. If someone is experiencing difficulty breathing, move them to fresh air immediately. The affected person should be kept warm and immobile. Seek medical advice promptly. If the person stops breathing, initiate cardiopulmonary resuscitation (CPR). In the event of eye contact, rinse immediately with water for at least 15 minutes and seek medical attention.

For frostbite, thaw the affected area with lukewarm water until sensation and normal color return. Do not rub the frostbitten area, as this can worsen the damage. Always consult medical professionals for severe frostbite. Do not interrupt thawing en route to the hospital.

Vessels containing liquid nitrogen should be transported using a cart or a dedicated trolley when indoors. Secure the vessels to prevent tipping. Develop local procedures for the collection and drop-off of vessels—including securing methods such as lashing straps—in consultation with transport personnel.

For amounts greater than 10 liters, use a cart or specialized trolley for transport, ensuring the vessel is stable and will not tip over. If using an elevator for transportation, the vessel must ride alone; indicate that the elevator is in use for nitrogen transport to prevent accidental entry by persons.

Transportation by Vehicle

Vessels containing liquid nitrogen must NOT be transported in the passenger compartment of a vehicle. They should be isolated from the cabin, ideally on a ventilated flatbed or similar structure. Transporting vessels in a car boot connected to the passenger compartment is not permitted. Adherence to ADR regulations is required.

For transport volumes exceeding 1,000 kg, full ADR-S regulations apply. For less than 1,000 kg, ensure that the vessel is correctly marked, labelled, securely sealed with a safety valve, and accompanied by a transport document and fire extinguisher. The transport declaration should include details of the contents, the sender and recipient information, and the gross weight of the filled vessel. During transit, the vessel must be securely fastened to prevent tipping and placed in a well-ventilated area.

Only use materials (thermos flasks, vessels, pipes, etc.) specifically designed for liquid nitrogen. Clear written procedures must be available, outlining which equipment is approved for use with liquid nitrogen and instructions for their use (e.g., guidelines for filling smaller vessels). Monitoring devices for storage tanks can be integrated with an existing alarm system. If such devices are absent, a weekly check of the liquid nitrogen levels in storage tanks is essential to mitigate the risk of unnoticed tank failures. For certain storage tank types with adjustable vacuum functions, external adjustments are possible. Ensure that all facilities are well-ventilated and equipped with oxygen alarms, where necessary. It is advisable to protect floors with steel sheets (or an equivalent material) to prevent cracking due to spillage, which could lead to microbial contamination over time.

Sanitisation

In the event of a minor spill, vacate the area and assess whether further action is needed, considering space, operations, and ventilation. For significant spills, seal off the area. Sanitise by ventilating the area and prevent liquid nitrogen from entering drains.

In spaces where large quantities of liquid nitrogen are handled or stored relative to the room's volume, it may be necessary to implement an alarm system that verifies the presence of both supply and exhaust air. Simply confirming that the ventilation unit is operational is insufficient, as dampers may obstruct airflow within the ducts. It is crucial to ensure that fresh air is entering the space and that the extraction mechanisms are functioning effectively. An ideal indication method would be a two-lamp system located outside the space: green to signify that entry is safe, and red to indicate a fault, meaning entry is prohibited. If no light is illuminated, it could suggest a malfunctioning lamp or that the system is deactivated.

Gas warning system

• A gas warning system is always recommended when managing larger amounts of liquid nitrogen in confined spaces. While a portable gas detector can serve as a temporary measure, a permanently installed gas detector, correctly positioned within the space, is preferable for continuous and reliable operation. The detector should feature two alarm thresholds: a WARNING at 19.5% oxygen concentration and an EVACUATION alert at 18.5& oxygen concentration. The alarms should be both visual and auditory within the space and, if possible, outside the space as well.
• It is critical that the alarm triggers a local response to facilitate prompt assistance, and there should be established local procedures for responding to an alarm.
• Regular maintenance of the alarm systems is imperative, and there should be a designated individual accountable for ensuring that maintenance is conducted routinely.

Signage for Areas Where Liquid Nitrogen is Handled

The regulations of the Swedish Work Environment Authority on Skyltar och signaler stipulate the requirements for signage, markings, and signals.

The following are examples of signs that may be necessary:

• A warning sign should be displayed outside premises where liquid nitrogen is stored or handled in substantial quantities. Appropriate signage includes a warning symbol indicating a health-hazardous substance accompanied by the text "Liquid Nitrogen".
• A warning sign indicating the risk of low temperatures should be placed near equipment that contains condensed gases.
• A waring sign for the risk of asphyxiation is necessary in areas where there is a potential risk for oxygen depletion and suffocation.

Marking of containers

All containers holding nitrogen must be clearly labelled to identify their contents. Labels should specify "Liquid Nitrogen" along with the associated hazards.