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We currently have 1 large liquid nitrogen freezer, 3 medium 160 L dewars, and 4 smaller 40 L dewars.
Each dewar that is currently in use has a sheet attached to it which describes the contents as explained in Manual - Labeling.
There is a rotating schedule of one person to check the level and a different person to make sure the first person doesn't forget. Check the level by 11 am or earlier. Do this even if it's inconvenient and requires stopping other work. You may ask someone else to do the check if you are out sick for the day, for example.
On weekends, check the level remotely via security cameras and Patient Care Vault Software, and then text the backup person to let him know it was checked. On weekdays, log the level check into the Container Software rather than texting. At 11 am, if you are the backup person, you must follow up by talking with the the primary or by texting him. You must not just check the level yourself unless you cannot get in touch with the primary.
If any individual notices that another individual failed to check the level on a previous day for some reason, this gets written up on a "Dewar Level Adverse Event" form. This form must then be immediately submitted to management for followup. Every adverse event will result in a group meeting.
To check the level, open the lid slowly and slide the dipstick down until a sizzle is heard. Look at the measurement. Log the number in the Container Software. Lock the lid, and then on the way out of the room, pause at the door and look back one more time to ensure the lid is closed.
Filling is done approximately every 7 days. See the Safety Instructions and be sure you have been certified for this task. Gloves and glasses are a requirement. Check the hose connections. Open the valve for liquid dispensing. Allow the first blast of warm air to blow into the room, then aim into the dewar as liquid starts to come out. Position yourself to watch the lines inside the dewar and stop filling at the high fill level. Verify the exact final level with a dipstick and record this new level.
Liquid nitrogen is delivered to our facility in 230 L portable tanks. They only deliver to our neighborhood on Wed/Thurs, so some estimation must be made on when we might need the next delivery. We only want to have one tank at a time, but we also don't want to run out. In an emergency, we can go get 1/3 of an LR40 at the dock. Staff must be specifically trained and authorized for filling or LN pickup.
The 230 L tanks are very heavy. They can use the new sidewalk to bring the tank around to the proper door. The small aluminum ramp can help with the large threshold. The empty tank is always removed. When a tank is delivered, attach the hose to the liquid port. The end with the plastic cap must be attached to the tank so that the cap will not be exposed to low temperatures which would cause it to crack. Later, when a tank is empty, remove the hose and set it carefully aside so that you won't need to do it while the delivery person is waiting. Make sure the handle for the cart is leaning against something rather than poised to fall.
Patient Care Vault Software runs constantly to monitor the dewar for low level.