1. Completed by: Patrick Scriven Staff/Student number:
The Writing Safe Work Procedures Guideline (OHS027) should be consulted to assist in the completion of this form Faculty/Division: School/Unit:
Science Physics / Quantum Electrodynamics Group Document number Initial Issue date Current version Current Version Next review date Issue date 25/7/11 25/7/11 1.0 25/7/11 SWP2
Title: RF-dipstick Operation
Description of activity:-
This work procedure describes the safe method for dipping the RF-dipstick into a liquid helium dewar.
Associated risk Hazards Controls
assessment Cryogenic liquids Personal protective clothing- cryogenic gloves, face shield and labcoat; safety
number and shower; low oxygen alarm; training.
RA2, WG8 Explosion Safety valve, pressure indicator.
Personal protective clothing- cryogenic gloves, face shield and labcoat; safety shower; lifting hoist; heat gun.
1. Ground all pins on breakout box
2. Connect sample puck to end of dipstick with M2 screws.
3. Connect LEMO and RF connectors to sample puck.
4. Using Teflon tape, secure electrical connectors to copper cold plate.
5. Carefully load sample into vacuum can -- make sure not to bash the fragile bond wires against the can!
6. Evacuate can and perform leak test, with special attention to the red silicone seal between steel and brass
segments of vacuum can.
7. Close valve and remove vacuum pump.
8. Introduce exchange gas to the can. To do so first fill a gas bladder with helium before attaching to the
valve. Remember to flush through the connection. Finally let two necks worth of exchange gas into the
9. Make sure the device is grounded at the breakout box before the can is cooled.
1. Check the dewar is connected to the helium recovery system through a one-way valve attached to the gas
meter. Ensure the valves from the dewar and to the recovery system are open.
2. Record gas meter reading and check that dewar pressure gauge reads zero. Excess pressure in the dewar
would be released when the dewar seal is opened, potentially resulting in cryogenic burns from the _______________________________________________________________________________________________________________ Page 1 of 4 OHS026 safe work procedure Current Version: 3.0, 04/03/2011
escaping cold gas. This should not be a problem provided the dewar is correctly connected to the recovery
3. Attach can to hoist and prepare to insert into the dewar. Make sure the can is secure in the hoist and hangs
vertically. Put on personal protective gear.
4. Open the dewar and begin lowering the can. Make sure the can is properly aligned with the neck of the
dewar. Work steadily once the dewar is opened until the sliding seal can be clamped to the dewar, this will
minimize helium loss from the dewar.
5. Clamp the dewar to the can at the sliding seal.
6. Continue lowering, but slowly now. Lowering the can quickly will boil off more helium than necessary:
aim for around two clicks/sec on the gas meter (2 L/s). Be aware that the sliding seal may stick or slip. If
lowering the hoist ensure the can is actually following, in case the seal is sticking. If the hoist is removed
be aware that the can may slip further into the dewar and needs to be watched
7. Stop lowering before the welded join at the cross: a clamp makes a good spacer if you need.
1. Make sure the device is grounded at the breakout box before raising.
2. Empty a gas bladder and attach to the valve. Open the valve to the gas bladder. There is a risk of explosion
in the event of a leak. The pressure of gaseous helium that leaks into the can at 4.2 K will increase by a
factor of around 70 at room temperature. The pressure associated with a leak of liquid helium into the can
is even greater: the volume of liquid helium in the can will expand by a factor of 780 to gaseous helium at
room temperature. A blow-off valve attached to the can should release the excess pressure, however it is
possible for the blow-off valve to fail. The gas bladder will indicate excess pressure in the can as it warms
in the event of a leak. The gas bladder is an immediate visual indicator of excess pressure in the can and is
an important additional safety measure. If the gas bladder indicates a leak the can should be lowered back
into the helium to cool the gas and reduce the pressure. The can will then need to be pumped out as it is
raised. Note that the blow-off valve should be arranged so as not to point directly down: in the event that
a blow-off occurs the escaping gas may cause cryogenic burns and should be directed away from people
hoisting the can.
3. Attach the hoist to the can and begin hoisting. Again make sure the hoist is secure and properly aligned
with the dewar opening. Be aware that the can and seals are now cold. Contact with the can or seals will
cause cryogenic burns. Use appropriate cryogenic gloves when touching the cold parts. Work steadily as
the can may freeze to the sliding seal. If the seal does freeze either wait till it thaws or use a heat gun. Keep
an eye on the gas bladder: if it begins to expand start lowering the can again to cool the gas and lower the
pressure. If this happens the can will need to be pumped out as it is lifted. For a major leak lower the can
to reduce the pressure and remove the gas bladder and hoist the can open to atmosphere. 4. Keep an eye out for the blue line around the can that indicates the end of the stainless section. Stop when
you reach it.
5. Undo the clamp between the dewar and sliding seal and hoist the can all the way out. Again, if steadying
the can by hand use protective gloves. Work quickly again to minimize the loss of helium. 6. Lower the can in the hoist just above the ground until it warms. Indicate that the can is cold. Alternatively
use a heat gun to warm the can quickly.
7. Reseal the dewar and record the gas meter reading. Leave dewar connected to the recovery system with
the valve open.
8. Once warmed (after around one hour) remove the can from the hoist and release the vacuum.
In the event of a leak lower the can back into the dewar to cool the gas and reduce the pressure inside the can.
Attach vacuum pump to the can and proceed to pump out the can as it is raised.
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Cryogenic burns – (minor) Remove any clothing restricting circulation run the affected area under cold water in the sink. For larger area burns a shower there is a shower in the toilets at the end of the corridor in the Newton building. Depending on the severity of the burn, contact first-aid officers on 55649 (Joji) and 54579 (Sue Fraser), or the UNSW health centre on 55425. Remain with the patient.
Cryogenic burns – (major) For spills affecting large or sensitive areas (eg eyes) contact an ambulance immediately on 5666 and proceed with the treatment above until emergency services arrive. Remain with the patient until medical officers arrive.
Spills or low oxygen alarm – Spills of liquid helium will evaporate quickly, displacing atmospheric oxygen with inert helium. Oxygen depletion may result in asphyxiation. WG8 is equipped with an oxygen level alarm which sounds if the oxygen level of the lab falls to dangerous levels. If the alarm sounds evacuate the room and contact. If a large volume of liquid helium is spilt evacuate the room and be prepared to treat associated cryogenic burns. Mark the door no entry and contact a senior group member:
Alex Hamilton: ext. 55736, mob. 0434 565 595
Zach Keane: ext. 55203, mob. 0422 857756
Oleh Klochanan: ext. 55203, mob. 0423 485 924
Adam Burke: ext. 55990, mob. 0435 548 381
Jack Cochrane: ext. 55329, mob. 0417 022 782
Other – In the event of another emergency in the lab (eg fire, major injury, etc) contact the relevant emergency services on 56666. For minor injuries contact either first-aid officers on 55649 (Joji) and 54579 (Sue Fraser), or the UNSW health centre on 55425.
Procedure developed in house with the help of persons experienced in cryogenic equipment.
Instruction by senior group member familiar with the apparatus.
Senior group member.
Responsibility for SWP review: Date of review:
SWP name and version:
In signing this section the assessor/ authorisor agrees that the following persons are competent in following this SWP
Name Signature Date Name of Assessor/Authoriser Assessor/Authoriser
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