Liquid Nitrogen
Introduction
Liquid nitrogen is the liquid form of nitrogen gas, known for its inert, colorless, odorless, non-corrosive, and non-flammable characteristics. It has an extremely low temperature. Nitrogen gas constitutes a significant portion of the Earth's atmosphere (approximately 78.03% by volume and 75.5% by weight). At standard atmospheric pressure, nitrogen has a boiling point of -196.56°C, and 1 cubic meter of liquid nitrogen can expand to 696 cubic meters of gaseous nitrogen at 21°C. Liquid nitrogen is typically produced in industries through the process of air fractionation and has a wide range of applications, but it requires careful handling due to the risk of frostbite upon contact.
Physical and Chemical Properties
Appearance and Characteristics: Colorless and odorless liquid.
Melting Point: -210°C
Boiling Point: -196°C
Heat of Vaporization: 5.56 kJ/mol
Critical Temperature: -147°C
Critical Pressure: 3.40 MPa
Solubility: Slightly soluble in water and ethanol.
Storage and Safety Precautions
Operating Procedures: Liquid nitrogen should be handled in a closed environment with adequate natural ventilation. Personnel working with liquid nitrogen must undergo specialized training and strictly adhere to safety protocols. It is advisable for personnel to wear cold-resistant clothing and gloves to prevent skin contact. Measures should be taken to prevent gas leakage into the workplace. During transportation, containers should be handled with care to avoid damage. Emergency leak response equipment should be readily available.
Storage Guidelines: Liquid nitrogen should be stored in a cool, well-ventilated storeroom, with storage temperatures not exceeding 30°C. The storage area must be equipped with emergency leak response equipment to ensure safety.
Engineering Controls: Employ closed operations while providing sufficient natural ventilation.
Respiratory Protection: Special respiratory protection is generally not required. However, when the oxygen concentration in the working environment falls below 18%, personnel must wear appropriate respiratory protection equipment, such as self-contained breathing apparatus, oxygen breathing apparatus, or full-face masks with long hoses.
Eye Protection: Personnel should wear safety goggles or face shields to prevent eye contact with liquid nitrogen.
Body Protection: Personnel should wear cold-resistant clothing to ensure body insulation.
Hand Protection: Gloves designed to resist extreme cold should be worn to prevent hand contact with liquid nitrogen.
Hazards
Routes of Entry: Inhalation
Health Hazards: Skin contact with liquid nitrogen can result in frostbite. In cases where excess liquid nitrogen evaporates at standard pressure, it can lead to a decrease in oxygen partial pressure in the air, potentially causing extreme cases of hypoxic asphyxiation. It is important to note that liquid nitrogen itself is not combustible or explosive.
Poisoning Treatment Emergency Measures
Skin Contact: Seek immediate medical treatment for frostbite.
Inhalation: In case of inhaling nitrogen gas or gas concentrations below normal, promptly move the affected individual to fresh air, ensuring unobstructed airways. If breathing difficulties occur, administer oxygen. If breathing ceases, perform artificial respiration and seek medical attention.
Firefighting Measures
Hazard Characteristics: When liquid nitrogen containers are exposed to heat, there is a risk of increased internal pressure, which may lead to rupture or explosion.
Hazardous Combustion Products: Liquid nitrogen itself does not burn, so there are no combustion products.
Firefighting Methods: Since liquid nitrogen does not burn, firefighting measures are not necessary. If there are concerns about container integrity due to heat exposure, misting with water can be used to cool the container. However, direct spraying of water onto liquid nitrogen should be avoided to prevent potential hazards.
Emergency Handling
Emergency Response:
In the event of a liquid nitrogen leak, evacuate contaminated areas promptly, move upwind, and establish isolation zones with restricted access. Emergency responders should wear self-contained positive-pressure respirators, cold-resistant clothing, and gloves to avoid direct contact with the leaked substance. Efforts should be made to cut off the source of the leak, and ventilation fans should be used to disperse leaked gases to open areas. Leaking containers should be handled carefully, repaired, inspected, and tested before reuse.
Handling of Liquid Nitrogen Spills:
When inhaling nitrogen gas at low concentrations, initial symptoms may include chest tightness, shortness of breath, and fatigue. Subsequently, restlessness, extreme excitement, agitation, running, shouting, vacant expressions, unsteady gait, and even coma or death may occur in severe cases. The following measures should be taken:
1. Promptly evacuate individuals from the contaminated area to an upwind location and establish isolation zones with restricted access.
2. Notify the fire department and relevant authorities.
3. Emergency responders should wear self-contained positive-pressure respirators, cold-resistant clothing, and gloves.
4. Prevent the leakage from flowing into basements or other enclosed workspaces. If this cannot be avoided, inform relevant authorities immediately.
5. Avoid direct contact with the leaked substance. Efforts should be made to cut off the source of the leak.
6. Misting with water can be used to accelerate the evaporation of the liquid, but water should not be sprayed directly onto the liquid.
7. Prevent the accumulation of gas in low-lying areas, and use exhaust fans to direct leaked gases to open areas. Prohibit personnel from staying in low-lying or downwind areas.
Applications Industrial Uses
Liquid nitrogen finds various applications in industrial processes, including:
1. Rapid freezing and transportation of food products or the production of ice. Utilization in low-temperature physics research.
2. Demonstrations of low-temperature states in scientific education, such as immersing objects at room temperature in liquid nitrogen, causing them to become as brittle as glass.
3. Providing the required temperature for high-temperature superconductors like yttrium barium copper oxide. Acting as a refrigerant for the rapid freezing of biological tissues to prevent damage.
4. Utilization in the manufacture of nitrogen fertilizers.
5. Application in chemical analysis, such as the BET surface area testing method.
Biological and Medical Uses
Liquid nitrogen also has various applications in biology and medicine, including:
1. Extermination of pests, such as red imported fire ants.
2. Assisting in hemostasis and the removal of superficial, excisable lesions from the skin through rapid freezing in surgical procedures.
3. Storage of living tissues, biological samples, sperm, and eggs through cryopreservation to maintain long-term viability and use.
4. Emphasizing again, liquid nitrogen is widely employed as a refrigerant for the rapid freezing of biological tissues to prevent damage.
Regulatory Information
The safe use of liquid nitrogen is subject to regulations and standards in various countries, encompassing storage, transportation, and handling. When using liquid nitrogen, strict compliance with local and international safety regulations is imperative to ensure the safety of personnel and the environment.
