Gas cylinders, liquid nitrogen, dry ice

Gas cylinders with pressurised gas are frequently used in all types of laboratory work and carry many risk factors. Damage to a gas cylinder can cause it to explode because the gas is under high pressure. A broken valve can result in such a violent rush of gas that the cylinder becomes a projectile. The escaping gas from a damaged cylinder or a badly conducted experiment can cause an explosion and fire, poisoning, corrosion or choking, depending on the type of gas. A list over the most commonly used pressurised gases is found below: 

The pressure at 20°C in the cylinders we use:

Working with and storing liquid nitrogen and dry ice involves the risk of frostbite (N₂, -196 ° C ; CO₂, -78 ° C) and for asphyxiation (choking) (1 L liquid nitrogen at 20 °C, 1 atm will have a volume of ca. ¾ m³). Carbon dioxide also has a physiological effect and can cause immediate death in concentrations of 10 - 20%. Liquid nitrogen is widely used in cold traps and can cause atmospheric oxygen condensation both within the trap and in the liquid nitrogen tank. This oxygen can cause violent explosions in the presence of oxidizable substance, e.g. organic compounds. 

• Gas cylinders must be transported on a trolley and must be locked with a chain.
• Gas cylinders must not be moved when the reduction valve is in place. The protective cover must be in place when moved.
• Both empty and full gas cylinders must be secured against falling whenever they are used or stored.
• Gas cylinders must not be subjected to knocks or strong, especially exposed heating (sun, radiators, etc.)
• Gas cylinders must not be opened with heavier tools than those recommended.
• Gas cylinders must be protected against backward suction from wash bottles and reaction containers by inserting a safety trap.
• A triangular warning sign with the text “Gas cylinders to be moved in the event of fire”, must be found wherever gas cylinders are used or stored.
• Safety goggles or a face mask must be worn when drawing off or pouring liquid nitrogen.
• Liquid nitrogen and dry ice must not be transported in a manned elevator. Danger of choking! Neither should these substances be transported in a closed car.
• First Aid for frostbite and choking: See section on First Aid.