0292 Management of the liquid nitrogen system

Summary

A description of the installation and maintenance of the liquid nitrogen tanks at Ki Biobank.

Purpose

To describe the installation and maintenance of the liquid nitrogen tanks at Ki Biobank.

Scope

The instruction includes all liquid nitrogen tanks at KI Biobank in room K141, Astrid Fagreus laboratorium (AFL).

Responsibility

  • The staff of the laboratory at KI Biobank are responsible for following this instruction.
  • The technicians of the laboratory are responsible for updating this instruction.  

Reference documents

Instructions for use 2300 LN2SU.TM - Rev.0403

Manual liquid nitrogen tanks, English version updated 2005. (Manual Kvävekärl, engelsk utgåva uppdaterad 2005).

Manual liquid nitrogen tanks – Costum Biogenic Systems- 2300LN2 Kryokärl Instalationsanvisning och teknisk beskrivning, svensk utgåva 2004.

Installing liquid nitrogen tanks

The setup of new tanks is performed by the supplier.

The supply of nitrogen is automatic from the outer storage tank via the inner storage tank to the liquid nitrogen tank. The storage tank on the outside of the building is directly connected to and is automatically refilled from AGA.

When starting the tank put in the key and turn the main switch (power) ON, see picture 1.

 

See instructions for use, p. 26,  Program Mode: Main Menu for a more detailed instruction.

  • Enter the key on the right side to switch program (picture 1 above).
  • Turn the key to programming.
  • Search for Liquid level in the Main Menu.
  • Choose centimeter.
  • The normal setting for Hi Set is 55 cm and Lo Set 30 cm.
  • To change these levels, use the arrows

Setting the limits for the temperature alarm

​Connecting the tanks to the alarm system is performed by service technicians at AFL and by medical technicians at KI Biobank.

To set the alarm limits, see instructions for use, p. 24, Program Mode: Main Menu 2 for a more detailed description.

  • Choose Program Mode: Main Menu 2
  • Press °C
  • Set -160°C as Lid Temp Alarm.
  • Press mute and thereafter reset.
  • Normal settings for Lid Temp should are in the interval -176°C - -183°C.

Maintenance

Documentation

All maintenance should be documented in the log-sheet for the nitrogen tank, and all services and errors should be documented in the form event-log (Händelselogg).

Temperature check and manual refilling of liquid nitrogen 

Temperature check and manual refilling of liquid nitrogen is done Mondays and Fridays during normal weeks. If any of these days is a holiday, the check should be done the closest working day. During longer holidays, the control is done according to a decision agreed upon by the staff and manager. Check that normal display is indicated in the window (see picture 2), read the temperature, the level of liquid nitrogen, refill with liquid nitrogen, and sign the log-sheet for each tank. Also check that there is nitrogen in the outer nitrogen tank for automatic refilling; if the level is lower than 200 a day before holiday, contact AGA.

Verifying the temperature measurements of the container

The temperature of liquid nitrogen is 196°C. To verify the temperature measurements of the container a check should be performed once a year. The check can also be done if one suspects that the temperature shown is incorrect. The medical technicians of KI Biobank are responsible for the verification of the temperature measurements.

 

Picture 2. The normal display of the nitrogen tank.

Adjusting the levels of liquid nitrogen in the tanks

Normally, the refilling of nitrogen is automatic. Before the refilling can start a connecting tubing between the phase separator and the tank needs to be emptied of air. This can be done by closing the air valve on the tank until the temperature in the tubing is in the interval -130°C - -140°C. Thereafter, the tank is filled up to the set value for high level

Checking the alarm

The function of the alarm should be checked every three months. The medical engineer of the laboratory is responsible for this check and for documenting it in the event-log. 

Testing the nitrogen tanks:

  1. Shut the electrical power off.
  2. Carefully pull out the temperature sensor from its container.
  • To test the air valve that should open when alarm for low oxygen level goes off: spray nitrogen in front of the sensors.

Nitrogen leakage

In rare cases it might happen that the valve to the tank will not open after the right temperature of the tubing has been reached, and then the nitrogen to be refilled will leak into the room. If this happens, make sure no alarm about low oxygen levels has gone off, then shut of the tap on the tubing above the nitrogen tank. If the alarm about low oxygen level has gone off, one is not allowed to enter the room without stopping the refilling by pressing the emergency button on the inside of the door. Before entering the room, the alarm should have stopped and the room should be ventilated.

When the oxygen level in the room is decreased an alarm goes off, an air valve in the ceiling is opened to reduce the level of nitrogen, and the supply of nitrogen to the phase separator is stopped.

Transportation tanks for liquid nitrogen

These tanks are used when the outer tank is empty, or when the automatic refilling isn´t working. The transportation tank is always empty and should only be used in case of an emergency.

1. Fill up the tank.
There are two ways to fill up the tank.

1.1 Call AGA Lillebil and order a refill. Telephone nr: 019 276 105

1.2 Contact SMI and fill it up there. Telephone nr: XXX XXX XX
 

2 How to fill it up.

  1. Connect the tube on the tap labelled LIQUID.
  2. Connect the other end of the tube to the source.
  3. Open the VENT tap on the tank (ca 4-5 turns).
  4. Open the LIQUID tap on the tank (ca 4-5 turns).
  5. Open the tap to the source.

Important information:

  1. The VENT valve is making a lot of noise, which is normal.
  2. Frost is formed around the tubes and taps, and around the yellow indicator of level.
  3. The yellow indicator of level shows how much liquid nitrogen is in the tank.
  4. It takes around 30 minutes to fill the tank (full=240 litres).
  5. If liquid nitrogen starts to pour out of the VENT tap, the tank is too full. Then it is IMPORTANT to close the tap to the source first.
  6. The manometer shows the pressure in the tank.
  7. There are two safety valves on the tank, one for 4 bars and one for 1,5 bars, which will get activated if the pressure in the tank gets too high.
  8. There is also a green tap, which is not used.

3 How to turn off the refilling. (Important to perform these steps in the right order!)

  1. ALWAYS start by closing the tap to the source.
  2. Then disconnect the tube between the source and the tank.
    1. Use gloves.
    2. Open little by little and let the pressure out.
    3. Be careful as there is liquid nitrogen in the tube.
  3. Close the LIQUID tap.
  4. Finally, close the VENT tap.
     

4 How to fill the nitrogen tanks from the transportation tank.

There are two ways to fill the nitrogen tanks; 4.1 and 4.2.

  1. If power is connected to the nitrogen tanks and the display is working, use this:
    1. Use the tube already connecting the nitrogen tank and the pipe.
    2. Close the tap on the pipe where the tube connecting it to the nitrogen tank is located. 
    3. Remove the tube from the pipe.
    4. Connect the tube to the tap named LIQUID.
    5. Open the LIQUID tap 3-5 turns.
    6. Press Start Fill on the display of the nitrogen tank.
    7. The refilling starts automatically and will turn itself off when the nitrogen tank is full.

IMPORTANT: Do not leave the room during the refilling, as when the refilling is finished the valve to the nitrogen tank will close, and some liquid nitrogen will get trapped in the tube between the nitrogen tank and the transportation tank. As liquid nitrogen expands up to 800 times to the gas phase, a high pressure will build up in the tube. The transportation tank has some safety valves for this, but the tube does not, and therefore it is important to remove the tube as soon as possible after the refilling finishes. Remember to use gloves.

  1. When the refilling has finished, close the tap on the transportation tank named LIQUID.
  2. Disconnect the tube from the transportation tank carefully, open little by little to let the pressure out. Remember that there might be liquid nitrogen in the tube.
  3. When the tube has defrosted, connect it back to the pipe
  4. Open the tap on the pipe to the nitrogen tank.
  5. Manual refilling (if no power to the nitrogen tank):
    1. Remove the screw-nut on the MANUELL FILL on the nitrogen tank
    2. Connect the tube between MANUELL FILL on the nitrogen tank and LIQUID on the transportation tank.
    3. Open the LIQUID tap 3-5 turns.
    4. The nitrogen tank will now start refilling.

IMPORTANT: Since there is no valve closing automatically when the nitrogen tank is full, there is a risk of overfilling. Therefore it is important to stop the refilling in time to avoid contamination. The nitrogen tank needs refilling for about 20 minutes after 24 hours..

  1. When you believe you have filled the tank enough, close the LIQUID tap.
  2. Disconnect the tube from the nitrogen tank carefully, as there might be liquid nitrogen in it.
  3. Put the screw-nut back on the nitrogen tank.

 

Service

Service on the nitrogen tank is done by Ninolab.
Calibrating the oxygen sensor is done by SICK AB.
Refilling nitrogen is done by AGA.

 

 

 

Citation

SOP collection, KI Biobank. 0292 Management of the liquid nitrogen system. The Molecular Methods Database. 2016/01/20

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