Avoiding the Dangers of Liquid Oxygen

Rubin Lab Safety Meeng

11/22/2010 What is liquid oxygen?

• Liquid oxygen is a cryogenic liquid – cryogenic liquids have boiling points less than -346 K

Oxygen BP: 90 K

• If we cool air below 90 K, we start to condense liquid oxygen

What does liquid oxygen look like?

•Liquid Oxygen is pale blue

•Liquid oxygen is paramagnec Why is liquid oxygen dangerous?

•Although nonflammable, oxygen is a strong oxidizer. •Liquid oxygen contains 4,000 mes more oxygen by volume than normal air How can we accidentally generate liquid oxygen in the lab?

•By opening a cold Oxygen BP: trap immersed in 90 K liquid nitrogen to the atmophere

•This is bad because Nitrogen BP: there are usually 77 K organic solvents trapped in the cold trap as well as grease à Kaboom! Shung down your vacuum line safely

PPE Needed: Lab Coat, Gloves, Safety Goggles/Glasses

1. Remove the Liquid N2 dewar.

2. Shut off vacuum pump and vent the manifold.

3. Once the dewars are taken down, allow the system to thaw to room temperature before safely disposing of any solvents. Never vent the system to air or turn off vacuum when any poron of the system is sll at liquid nitrogen temperature. This could condense oxygen which could result in a serious explosion (see below). Always make sure the liquid nitrogen is removed prior to turning off or venng vacuum. What do you do if you think you have generated liquid oxygen?

1.) If the liquid nitrogen dewar is removed and the liquid in the traps has a blue color or if any liquid is observed, then assume you have liquid oxygen in the trap. 2.) Immediately replace the liquid nitrogen to keep the traps cold. (Note: the longer the liquid nitrogen is there, the more oxygen is condensed. Only do this step very temporally, 1-2 minutes, to get ready to vent the traps as described below; otherwise do not do this.)

What do you do if you think you have generated liquid oxygen?

2.) Alert others to the danger, and evacuate the area of bystanders (except for a buddy at a safe distance).

3.) Place a blast shield around the traps and remove any nearby organic materials.

4.) Remove the liquid nitrogen dewar, quickly vent the system, and if possible lower the hood sash completely.

5.) Immediately leave the vicinity of the lab and warn others not to enter. What do you do if you think you have generated liquid oxygen?

6.) Aer the system has warmed to room temperature consider the traps sll dangerous . Liquid oxygen will not be present, but organic peroxides may have formed. Pour liquid into a clean beaker and flush assembled trap 5 mes with water. Do this behind the blast shield and with the sash lowered.

7.) Check the solvent for peroxides using a potassium iodide test strip. If a purple color forms on the text paper, peroxides are present. In that case, reduce soluon by adding sodium thiosulfate or sodium sulfite before disposing of waster.