Liquid Nitrogen Safety

1. Liquid Nitrogen Safety Environmental Health and Safety Environmental Health & Safety

2. What is Liquid Nitrogen? • Liquefied form of nitrogen (N2) gas. • When in the gaseous phase, it is a mostly inert gas, that is colorless, odorless, and tasteless. • In the liquid phase, it’s very cold (BP=-195.8°C), which makes it ideal to transport cold materials. • This however, can cause severe frostbite Environmental Health & Safety

3. Why Take Precautions? • The gas isn’t technically toxic, but it can easily start to replace oxygen in the air so your body can’t breathe in enough oxygen. This can cause affixation very quickly. • Oxygen becomes a liquid at a higher temperature than nitrogen, so liquid oxygen can become encased in liquid nitrogen. These oxygen enriched environments can cause materials to burn rapidly. Environmental Health & Safety

4. Why Continued • It’s very cold! • Since it’s so cold, any exposure to your skin can cause severe frostbite. • It will be very painful. Environmental Health & Safety

5. Lab Safety Do #1 • Wear Safety Gear! • Lab coats can save your body parts from freezing during an accidental spill! • Safety goggles are required but a full face shield is recommended. • Gloves are also required – preferably cryogenic but leather will work for smaller scale applications. • Long pants and close toed shoes are also required. Environmental Health & Safety

6. Don’t Forget To • Always follow general lab safety procedures. • (especially the do not drink the chemicals one). • Take your time and be careful! Environmental Health & Safety

7. Lab Safety Don’ts • Don’t completely seal off the container. • At room temperature, nitrogen is going to create a gas. • This requires exhaust, or the container could potentially explode. Environmental Health & Safety

8. More Lab Safety Don’ts • Funnel the liquid nitrogen • This could potentially cause spills and splashes that could come into contact with skin. • Dip a hollow tube into the container • Could potentially splatter. Environmental Health & Safety

9. Nitrogen Containers • Three types of containers • Dewar, Cryogenic Liquid Cylinder, and Cryogenic Storage Tank • Storage varies from a few liters to thousands. • Vaporization is always continuous. • This is because heat leaks are always present. • Know your specific container and proper handling procedures. Environmental Health & Safety

10. Container’s -Dewar • Non pressurized container. • Typical capacity is a liter. • Product may be removed to smaller containers by pouring, but larger sizes require a transfer tube. • A loose fitting dust cap over the outlet prevents moisture from plugging the vent, allowing gas to escape. Environmental Health & Safety

11. Container’s – Cryogenic Liquid • Insulated, vacuum jacketed pressure vessels. • Operate up to 350 psi and have capacities between 80-450 L. • Product may be withdrawn as a gas by passing through an internal vaporizer. • Or as a liquid under its own vapor pressure. • Come equipped with safety relief valves and rupture discs. • This protects from pressure build up. Environmental Health & Safety

12. Container’s – Cryogenic Storage • Typically includes a tank, a vaporizer, and a pressure control manifold. • May be spherical or cylindrical in shape. • Sizes range from 500-420,000 gallons • Powder and vacuum insulated. Environmental Health & Safety

13. Transfer Lines • Transfer lines are used to remove liquid from Dewar or cryogenic liquid storage containers. • Cryogenic lines are always connected to the cylinder’s liquid withdrawal valve. Environmental Health & Safety

14. Transfer Lines – Part II • A typical Dewar transfer line is connected to a bayonet. • This provides a means to remove product by pressure build up. • Use only transfer lines designed for cryogenic equipment. *Bayonet for vacuum transfer line Environmental Health & Safety

15. Transport • Find a cart • Don’t try to carry or roll the container. • Keep upright • Don’t try to pull the container, always push. • Avoid mechanical or thermal shock. • Sudden environmental change could potentially change the pressure. Environmental Health & Safety

16. Handling • Use cryogenic gloves when operating any valve or any place of a possible air leak. • Leather gloves can also be used, but for larger scale operations use cryogenic. • Be aware of the weight and design of your specific container. • This can help prevent laboratory accidents. • The figure on the right is a diagram of a liquid nitrogen storage tank. Environmental Health & Safety

17. Gas Withdrawal • Connect a control regulator to the gas withdrawal valve and the outlet of the valve to the system receiving gas. • Open withdrawal and pressure building valves until the container reaches desire pressure. • You may begin withdrawing gas. Environmental Health & Safety

18. Liquid Withdrawal • Always wear a face mask for liquid withdrawal. • Connect a transfer line from the liquid valve to the system being filled. • Open valve to desired rate of flow, close when finished. • To prevent back contamination, all valves should be closed when the container has been emptied. Environmental Health & Safety

19. Storage Part I • Keep in a well ventilated room • The room shouldn’t be a confined area to help exhaust any nitrogen gas off-gassing from the container. • A non ventilated room could very quickly become oxygen deficient. • It is also recommended that the building that the nitrogen is stored in has an exhaust ventilation system to outside the building. All lab buildings have this system. • Do not leave Dewar containers uncovered, but make sure to have an exhaust system • If the container is completely covered, the pressure could increase to dangerous levels, so exhaust is required. If left completely uncovered, the liquid nitrogen will evaporate much faster. Environmental Health & Safety

20. Storage Part II • Store in a controlled environment • Away from weather change. This will help the nitrogen from undergoing drastic changes in temperature or pressure. Environmental Health & Safety

21. In Case of Emergency • If your skin comes into contact with liquid nitrogen • Thaw slowly with warm water • Always seek medical attention though 911 • In case of a lack of oxygen, move immediately to a well ventilated area, or outside and acquire a respirator. • Reentry may only occur by trained personnel with air supplying respirators. • If an emergency happens, contact 911 then your lab coordinator and EHS ((740-593-1666). • Also, contact your lab coordinator if anything seems out of the ordinary. • If there is a fire call 911. • This is due to the possible asphyxiation hazard. Environmental Health & Safety

22. Other Resources • http://www.airproducts.com/responsibility/ehs/productsafety/productsafetyinformation/safetygrams.htm • http://engineering.dartmouth.edu/microengineering/ln2.html • http://www.physics.unc.edu/about/safety/content/N2operationSW_2.pdf Environmental Health & Safety