Liquid Nitrogen Pay-per-use
Location: 6159, 7159 and 8159 MRB3
A minimum of one liter will be billed for each logged use.
*Note #1: The gauges on the large tanks from AL Gas stick and can be misleading. I do everything I can to try and get an accurate read from these.
**Note #2: We go through 1 – 2 tanks per week. A tank can be drained in two days if enough labs are filling their cryostorage units.
Liquid nitrogen is available by the liter in the 6th, 7th and 8th floor autoclave rooms. There are 50 liter dewars which are for dispensing small volumes (< 10 liters).
For labs who have cryostorage tanks which need filling (> 10 liters), there is a large 230 L tank for that purpose. Please contact the Equipment Manager before you use this tank to fill your cryostorage device for the 1st time.
The VBI Equipment Resource has proposed to stabilize the cost/liter for liquid nitrogen PPU. Stabilizing the price (and hopefully lowering it eventually) will require everyone to be accurately recording the volume dispensed each and every time a tank is used.
Here are some facts and “best practices” for liquid nitrogen dispensing:
- KNOW THE TOTAL VOLUME CAPICITY OF THE DEWAR OR CRYOTANK YOU ARE FILLING! If you don’t know how big your dewar or tank is, then you can’t accurately make an estimate of how much you are dispensing.
- JUST BECAUSE IT LOOKS LIKE YOU HAVE A LITER IN YOUR DEWAR DOESN’T MEAN THAT IT ONLY TOOK ONE LITER FOR IT TO GET THERE! Dispensing from any tank causes significant evaporation. There is evaporation to cool the hose and fittings and there is evaporation when liquid hits your warm bucket that you are dispensing into.
- Dispensing from the large 230 liter tanks causes the most evaporation loss which is why I designated it for large volume fills. I have been told by AL Gas that it takes at least 5 liters of liquid nitrogen to cool down the fittings and hose before any liquid comes out. Additional evaporation occurs when the liquid hits a warm surface that one is dispensing into. Therefore, dispensing one liter of liquid by the 4’ hose means that at least 7 – 8 liters was used. Additionally, these large tanks will lose 5 – 7 liters/day just sitting in the room without anyone touching them.
- The smaller tanks in the corner will expel liquid out the stem with very little loss to cool fittings (< 0.5 liter). The only significant loss with them is what evaporates when it hits a warm surface. So, one liter dispensed might be 2 – 3 liters actual. The difference between 2 – 3 liters and 7 – 8 liters may not seem like much. But, there are hundreds of times that individuals dispensed small volumes from the large tanks. It adds up.
- Dry ice buckets are not designed to withstand liquid nitrogen temperatures over time. They will eventually crack. And, they are not cheap to replace.
- You really can’t dispense into a regular cylinder for measuring. Some of our labs in CDB have two liter or four liter cryo-dewars that they fill and take back to their labs for use. Using this type of container is the only reliable way to measure smaller volumes although it isn’t required. If you do have one of these and decide to use it, please use the smaller tanks in the corner for two – four liters.
- The only way to estimate the dispensed volume into a cryostorage tank is to know the TOTAL VOLUME CAPACITY of the tank. You can then count how many “stacked boxes” you have and divide it by the total volume capacity. Each stack equals approximately that much volume dispensed. Alternatively, you can wait until the tank is half-empty and fill. Obviously, you will record 1/2 of the total volume capacity.
- Some people have the tank specs from the company and they see that it has a “static loss” of 0.5L/day. They might wait a week and think that 3 liters fills it back to where it was a week earlier. The 0.5L/day is accurate under the most optimal conditions and when no one is accessing the tank. The temperature of the room where the tank is located plays a role. The warmer the room… the faster the evaporation. Also, each time someone opens the lid and gets a vial out, there is evaporation.
- TaylorWharton has a manual for their large cryotanks. Samples are can be stored in the liquid (where everything is at -196 C) or the vapor. They state that the temperature increases somewhat above the liquid but it is not significant in many biological storage applications. Their graph shows that the vapor temperature can stay near liquid temperature 8” above the liquid line. Of course, this graph is specific to their tank but it is relevant to the issue. Unless you have been directed by your PI to always keep it full, you might consider fewer fills with more volume which is less work for you. http://www.taylorwharton.com/assets/base/doc/products/refrigerators/TW-303_10K_and_24K_%28AutoTend_Controller%29.pdf
- The most convenient way to remember to do your cryostorage tank fill… have a monthly reminder in Outlook which pops up for fills. If you look and the level is higher than it would normally be for a fill, just press the “Snooze” for several days and the calendar reminds you again.
- If you know that specific individuals are not signing up for usage, please address them directly (if you are comfortable doing so) or let me know who they are and I will address them. Any PI who’s personnel consistently sign up is subsidizing the cost for liquid nitrogen for those who do not. That means that their cost is higher to compensate for people not logging usage. Essentially, if you know of labs not logging, then you are paying for their liquid nitrogen. People may not think that squirting a liter of liquid nitrogen into a bucket occasionally makes a difference… but remember… you’re never squirting just one liter. It all adds up.