NMR Facility
School of Chemistry, F11
The University of Sydney
NSW 2006 Australia
Phone: + 61-2-9351-2851
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Standard Operating Procedures Document
Operating Liquid Nitrogen Dewars for small volume liquid extraction Document Name
NMR‐SOP‐GP‐16 Procedure Class
 Class 0 Published
2014‐09‐01 Document Author
IAN LUCK Procedure Location
Procedure Type
 Class 1  Class 2  Class 3  Class 4 NMR FACILITY Website Procedures Document Folder Room 106  Specific Procedure or Instrument Use  Generic Procedure covering a class of processes or substances HIRAC Document
NMR‐HIRAC‐GP‐16 Required Training
 Cryogens Operator (Small Volume Transfer) 1 GENERAL This procedure is designated as a Class 3 procedure based on the School of Chemistry Handbook of Safety Regulations (work involving large volumes of cryogenic liquids (>5 L)). A case‐specific HIRAC may be considered to classify this operation as another Procedure Class. This procedure may only be carried out by operators who have, or are under the direct supervision of an operator who has, the Cryogens Operator (Small Volume Transfer) competency. Prior to undertaking this procedure: •
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All operators must be familiar with The University of Sydney's "TRANSPORTING LIQUEFIED GASES (CRYOGENIC LIQUIDS OR FLUIDS)" guidelines; available on the University website (http://sydney.edu.au/whs/guidelines/chemical/liquefied_gases.shtml ) All operators must be familiar with a recent SDS for liquid nitrogen All operators must be familiar with all equipment components described in this document. All operators must be familiar with the operation of the Teledyne 3350 oxygen sensor, and be competent in the interpretation of oxygen level readings within Room 116 All operators must be familiar with the correct emergency response actions described in this document, and in particular, the correct response actions in the event of oxygen sensor alarms All operators must be familiar with the correct operation of all required PPE described in this document All operators must have completed a local site induction All operators must be familiar with the associated HIRAC document NMR‐HIRAC‐GP‐16, or equivalent Adequate HIRAC measures must be undertaken for the safe transport of decanted liquid nitrogen to destination. 2 EQUIPMENT OVERVIEW 2.1 Taylor Wharton XL240 with pressure building circuit The Taylor Wharton XL240 is a vacuum insulated, stainless steel container designed to store, transport, and dispense cryogenic liquid nitrogen. A summary of relevant technical specifications are shown below. Capacity, Gross Capacity, Useable liquid Empty weight Maximum weight at full capacity, 22psig Relief Valve setting Inner container bursting disc Pressure building circuit setting Normal evaporation rate (% capacity per day) 250L 240L 156kg 191+156 = 347kg 22 psig (1.5 bar) 176 psig (12.1 bar) 15 psig(1.0 bar) 1.4% Pressure conversions : 1 atm = 101.3 kPa = 14.70 psi = 1.01 bar = 760 Torr  0 psig 5
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1 Liquid indicator float valve 2 Liquid outlet valve 3 Gas vent outlet valve 4 Pressure building circuit outlet 5 Pressure building circuit regulator 6 Pressure indicator / Relief valve / Inner container burst valve The pressure building circuit is used to increase pressure in the vessel if it falls below optimal delivery pressure of 15 psig. To operate the pressure building circuit, open outlet [4], and monitor the pressure gauge [6]. Close the pressure building circuit outlet [4] once internal vessel pressure reaches 15 psig. This circuit is designed to restrict pressure to below 15 psig. 2.2 Teledyne 3350 Oxygen Sensor The Teledyne 3350 is an oxygen alarm monitor that provides real‐time measurement of oxygen content of the atmosphere in close proximity to the sensor. The sensor is installed inside Room 116 along the southern wall. An overview of the monitor is shown below. 7 Digital LED meter indicating percent oxygen content, with a response time of less than 20 seconds at 25oC. 8 Alarm status indicator LED 7 It has three factory‐set alarm trigger points; 
CAUTION (oxygen content at 20.0%). When the CAUTION Alarm is activated, the LED on the front panel [8] will begin to blink. In addition, the digital readout [7] will flash alternately with the oxygen reading and the letters “CAUt” for CAUTION. The audible alarm is activated. 8 
DANGER (oxygen content at 19.5%). When DANGER Alarm is activated, the LED on the front panel [8] stays on continuously. In addition, the digital readout [7] will flash alternately with the oxygen reading and the letters “dAng” for DANGER. The audible alarm is activated. CELL FAIL. The SENSOR FAIL alarm is factory set to a reading less 
than 0.05% oxygen. When this alarm is triggered the digital readout [7] will blink, and the audible alarm activated. 3 SAFETY This SOP provides a summary safety briefing. Refer to the document NMR‐HIRAC‐GP‐16 (Operating Liquid Nitrogen Dewars for small volume liquid extraction) for a comprehensive listing of hazard identification, risk assessment and control measures for this procedure. Emergency Shutdown Procedure Personal safety is paramount in all operations. The following emergency procedures should only be carried out if safe to do so. In all cases, emergency response actions should adhere to the following priorities:  Evacuation of personnel from the exposed area  Prevention of re‐entry of personnel to the exposed area until all clear notification has been given by authorised member of staff (Laboratory Manager, Level 1 Emergency Warden, NMR Facility Manager) In the event of having to evacuate the area:  Stop the transfer of liquid nitrogen by turning off the liquid outlet valve [2] on the nitrogen dewar.  Secure the collection vessel so that it may be left safely unattended.  Close both doors to Room 116. In the event of a restricted flow transfer, suspected ice blockage or suspected pressure build‐up in the nitrogen dewar:  Stop the transfer of liquid nitrogen by turning off the liquid outlet valve [2] on the nitrogen dewar.  Notify NMR Facility Manager to enact troubleshooting. In the event of a breakage or spill:  Isolate the affected area.  If safe to do so, stop any transfer of liquid nitrogen by turning off the liquid outlet valve [2] on the nitrogen dewar.  Contain and clean the area if safe to do so. Liquid nitrogen spills contained within Room 116 should be left to evaporate  If required, enact emergency response. For minor incidents, notify NMR Facility Manager as soon as possible. In the event of the oxygen sensor CAUTION alarm sounding:  Stop the transfer of liquid nitrogen by turning off the liquid outlet valve [2] on the nitrogen dewar.  Leave the room immediately.  Ventilate the room by opening all doors.  Monitor oxygen levels from outside the room. If oxygen levels do not return to normal in response to changes in flow and ventilation , • Notify NMR Facility Manager, School Laboratory Manager or Floor Emergency Warden. • Do not re‐enter rooms until all clear notification is given by authorised staff member In the event of the oxygen sensor DANGER alarm sounding, or a suspected low oxygen atmosphere:  Leave the room immediately.  Ventilate the room by opening all doors.  Notify NMR Facility Manager, School Laboratory Manager or Floor Emergency Warden.  Do not re‐enter rooms until all clear notification is given by authorised staff member 3.1 User‐supplied Equipment Required 
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3.2 PPE:  Eye / Face: Splash‐proof safety goggles with side shield protection must be worn as minimum. Full face shield protection is an option  Hands: Leather or cryogen‐rated insulated gloves must be worn.  Body: Exposed skin should be covered. Long sleeve shirt or top and long pants without cuffs should be worn. Lab coat outerwear is an option for upper body protection, but provides inadequate lower body protection.  Feet: Fully enclosed shoes or boots made from low porosity, low absorbent, splash resistant material must be worn. Suitably rated cryogen collection vessel Suitable transport and/or lifting aids for full collection vessels that weigh over 16kg Stainless steel transfer line, normally attached to dewar in Room 116 Cryogen Hazards  Asphyxiation Operation within a confined space may present an asphyxiation risk due to the evaporation of excessive liquid nitrogen. Ensure oxygen sensor is correctly operating, and that all doors are open to allow for adequate ventilation  Cold Burns and Contact Direct contact with cold surfaces or liquid nitrogen may cause cold burns. Correct PPE (glasses and gloves) must be worn when handling cooled transfer lines and dewars.  Explosion and Fire Risk Excessive build‐up of pressure in nitrogen dewar or blockages in the transfer line and magnet may lead to explosion risk. Pressure safety valves on nitrogen dewar must not be closed. All collection vessels and transfer lines must be open systems or have pressure relief valves installed. Pooling of liquid nitrogen can lead to condensation of liquid oxygen which is highly explosive. Ensure that all transfer lines and collection vessel surfaces are free of oil and grease. The arrangement of the transfer line must ensure that condensing oxygen is unable to pool 3.3 Manual Handling  Physical injury – sprains and strains The nitrogen dewar weighs more than 100kg when full. Collection vessels may weigh more than 20kg when full. Correct procedures for manoeuvring heavy loads should be observed. 3.4 Housekeeping Hazards  Physical injury – slips, trips and falls This procedure involves working around areas prone to condensation forming on the ground, as well as near other equipment. All equipment is to be returned to its original location after each use, and the area left clean and tidy after each operation.  Exposure to other hazards All equipment is to be returned to its original location after each use. The heat gun may be hot from previous users. 4 PROCEDURE 4.1 Carry out pre‐procedure checks and preparation  Check the room for adequate access and safe positioning of operator and collection vessel  Open both doors of Room 116  Check the oxygen sensor is reading a normal value for the atmosphere within the room.  Normal oxygen content within air is 20.9%.  Readings above 20.0% are acceptable to commence operation, provided readings are stable  Assemble required equipment within room; collection vessel and PPE.  Ensure PPE is correctly in place.  Inspect all equipment for signs of wear and leakage, and manage accordingly.  Ensure the transfer line is connected securely.  Ensure the transfer line and collection vessel are free from water, grease and oil residues on all visible internal and external surfaces.  Check joins for excessive ice build‐up on storage dewar. Accumulation of hard ice may indicate a long term leakage.  Check liquid indicator float valve [1] to ensure that dewar has available liquid for dispensing  Check pressure indicator [6] to ensure there is suitable pressure within the dewar  If the internal pressure is below 15 psig, open the pressure building circuit valve [4] to allow pressure to build. Close valve [4] once sufficient pressure has built. This will cut out below 22 psig.  The maximum operating pressure of the dewar is 22 psig  Place the collection vessel securely on the ground directly below the transfer line. If required, an elevated pedestal may be used to ensure that the transfer line feeds directly into the collection vessel opening.  Collection vessels must not be placed at a height that allows splashing of liquid nitrogen onto the floor or other surfaces.  Extend the telescopic transfer line so that the opening feeds directly into the collection vessel opening 4.2 Commence liquid nitrogen transfer.  Extra care is required at the commencement of flow due to excessive boil‐off during the initial cooling of transfer line and collection vessel.  Slowly open the liquid outlet valve [2] on the nitrogen dewar until nitrogen gas begins to flow freely through the transfer tube. A flow of misty vapour should be evident coming out of the transfer line  Open the extraction tap on the liquid nitrogen dewar up to half a revolution to allow transfer of liquid nitrogen to commence.  Once liquid transfer has commenced, stand outside Room 116 and supervise the entire transfer procedure to ensure that:  The oxygen levels in Room 116 do not fall below 20%.  Pooling of condensed oxygen is not allowed to occur  Liquid nitrogen is not allowed to splash unnecessarily onto the floor  The transfer process is immediately terminated when the fill is complete.  Monitor the oxygen level in Room 116, and regulate the flow of liquid nitrogen to ensure that an oxygen level of greater than 20.0% is maintained. 
4.3 Termination of transfer procedure 
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4.4 The transfer procedure is complete either when sufficient liquid nitrogen has collected in the collection vessel, or the collection vessel is full.  Decanted volume can be determined by visual inspection, immersion of wooden dip‐stick or weight of collection vessel. Terminate the filling procedure by closing the liquid outlet valve [2] on the nitrogen dewar. Carefully remove any ice residue on the transfer line by warming with the fan heater mounted in Room 116. Collapse the telescopic arm of the transfer line to allow removal of the collection vessel Secure the collection vessel ready for transport Completion of procedure and return to normal operations 
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Remove the collection vessel from Room 116, in accordance with previously prepared protocol for cryogen transport procedures Ensure workplace is left clean and tidy prior to leaving Close both doors to Room 116 Review actions and provide appropriate feedback as required. 5 DOCUMENT HISTORY AND ADMINISTRATION Date 2013‐11‐18 Document created 2014‐09‐01 Document reviewed. Internet links updated. Changes to pressure building circuit operation. Added prefix clause in emergency procedures, and protocol for handling CAUTION alarm. Approved By Action Digitally signed by Ian Luck
Date: 2014.09.01 17:19:59 +10'00'