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SME's

Hazards and Mitigations

  • Asphyxiation
    • Oxygen deficiency monitors (ODM) are required to be around dewar
    • DO NOT ride with this on the elevators and use caution tapes inside the elevator
    • Don't do work in small confined areas, areas must be approved to have a dewar in it
  • Burns and fost bite
    • Wear proper cryogenic PPE
    • Keep heating gun around at all times.
    • Do not touch frosted items without gloves!
    • When inserting items into the dewar go slow! It needs to cool down or else it will boil.
    • Heat valves with heat gun as needed to operate them.
  • Crushing
    • Wear steel toe shoes when moving the dewar.
    • Do not tip dewar
  • Pressure
    • Vent the system in safe manner before doing work on the dewar  

PPE 

  • closed toe shoes
  • long pants
  • cryo gloves
  • face shield
  • a cryo apron

Equipment

  • He dewar bubbler
    • It is a long ~8ft section of 3/8" SS pipe with a dropper squeezer on the end. On the bubblier are two zip ties or clamps to help tell volume
  • All PPE called out above
  • Heater Gun
  • Ladder
  • Measuring tape

Procedure

  1. You and one other person review the Helium Dewar Valves Picture below.
  2. Bring a new dewar down to the hutch that needs the replacement. Do not ride on the elevator with it!
  3. On the old dewar, spin the needle valve counterclockwise to close the valve
  4. Turn off the roughing pump that is hooked up to the cryohead.
  5. Close the cylinder that is hooked up to the dewar.
  6. Close all valves on the dewar. You will not be able to close the vertical one because the stinger is in it.
  7. Vent the poly line to air and undo the swage fitting on the the dewar side of the poly line.
  8. Open the low pressure vent valve to vent out the ooliage of the dewar, reading is on the gauge.
    1. Keep an eye out for the PRV to freeze over. Use the heat gun to warm up the valve or the pressure relief device to stop them from freezing over.
  9. Start to unscrew the seal that holds the singer into the dewar. You may have to wiggle it a bit.
  10. Once the pressure is gone, deploy a ladder nearby the dewar.










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