Design and implementation of a large-scale liquid nitrogen archive
1Lab Mode Ltd.
2Jencons-PLS.
* Corresponding author. 54 Tanners Drive, Blakelands, Milton Keynes, MK14 5BN, UK. E-mail: mark.fagan{at}labmode.co.uk
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Abstract |
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UK Biobank required a cryogenic facility to store, in vapour phase, a minimum of 5 000 000 1.2 ml capacity micro-tubes held in racks of 96 tubes below –180°C for a 20 year period. The archive would be housed in a 900 m2 industrial unit remote from the main laboratory area that would be generally unmanned and would require a complete cryogenic infrastructure. A commercial supplier was commissioned to provide a complete system including design, project management, supply and installation of all the cryogenic storage requirement including bulk tank, super insulated vacuum lines, Taylor Wharton LABS80K high capacity long-term vapour phase storage vessels with inventory control systems and all the local and remote software. The large-scale storage vessels were selected to give a high storage density, temperature stability and storage in vapour phase.
Keywords Cryogenics, vapour phase, Taylor Wharton
Accepted 10 December 2007
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Introduction |
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Three main factors were considered for this large-scale liquid nitrogen archive.
(1) The samples must be maintained below –180°C for the duration of the project. The storage vessel should therefore have excellent performance both in terms of temperature and evaporation rate. The storage vessel should be chosen on the basis of accommodating the highest number of samples that makes best use of the floor space whilst taking into account the total number of samples required by the project.
(2) The users must have a safe environment in which to work. The ergonomics of handling samples in the archive facility must also be addressed and users must be trained in the safe use of the equipment.
(3) The facility must be designed to meet the immediate requirements and any future plans. Its design must take into account the running and safety requirements of the storage vessels and the users. Wherever possible the design should incorporate redundancy features and the extent to which these features are implemented is based upon the risk of loss of samples.
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Methods |
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The consultation phase explored the three main factors described earlier and using our experience different options were discussed.
Samples
The storage vessel of choice was the LABS80K with the M505CE auto-fill controller. The LABS80K is a vapour phase storage vessel (a reservoir of liquid nitrogen is maintained below the samples) with an offset neck thereby ensuring temperatures of –190°C at the top of the vessel (Figure 1). Figure 2 shows a graphical representation of the temperature readout from thermocouples placed on top of the storage towers (warmest sample storage position) for a period of 48 h. Temperature readouts from two key conditions should be noted; removal of a storage tower and replacement with one at ambient temperature and leaving the lid of the vessel open for 3 h.
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The intelligent M505CE controller is one of the most sophisticated on the market allowing the vessel to be auto-filled when necessary, communicating with other vessels and the hot gas by-pass for simultaneous filling along with a whole host of alarm monitoring sensors. When a RS485 card is installed with the controller the entire cryogenic controls for the facility are accessible remotely. All controller events are logged and available for interrogation from a remote computer. These events include fill cycles, alarm conditions, user entry and temperature logging. First level fault diagnosis can be carried out and fill cycles may be instigated without the need to visit the facility.
Each LABS80K can hold 1034 of the 96 format storage boxes in specially designed towers and from this total the number of LABS80Ks required for the facility was decided.
The towers have individual barcode labels for identification and each aperture within the tower is also bar-coded. The design of the tower ensures boxes can be easily inserted or removed thereby reducing the time the tower, and its contents, are exposed to ambient temperatures.
Users
The LABS80K offer an ergonomic advantage for the users. The towers that hold the samples are located on an easy turn bearing free turntable. The overall operating height is 108 cm and the unit has a flat table-top work surface. The low level step is suitable for two people and also folds away when not in use.
The users are protected with oxygen monitoring systems that both alarm and shut down the vacuum pipeline should a low oxygen level be detected. There are also emergency shut down switches located at various points within the facility that can be activated manually. In addition the users were provided with a 2 day training course which covered cryogenic safety training, bulk tank process and instrumentation training, LABS80K and M505 controller training, alarm procedures and fault identification and software and networking training.
Facility
The infrastructure, which includes the bulk tank, vacuum pipe work, electrical and network distribution and security fencing was supplied and installed by Jencons-PLS. Owning a bulk tank rather than leasing offers greater choice in finding a supplier of liquid nitrogen. The tank was chosen after calculating the usage of nitrogen by the LABS80Ks and the amount used cooling the vacuum pipe work during filling along with factoring in delivery times. Air exchange calculations were carried out on the facility to determine the need for additional forced air changes and the location of oxygen sensors and emergency shut down switches were also identified.
The layout of the vacuum pipe line is important to minimize the distance from the furthest LABS80K to the bulk tank. A framework was required to carry the pipe line as the facility is open plan. This framework also carried the electrical and networking requirements of the LABS80K. The pipe line is designed to allow for increasing the numbers of LABS80K each year while maintaining the efficient use of liquid nitrogen during the fill cycles of the LABS80K already connected.
One of the future proof systems is a manual fill setup for each LABS80K that can be operated in the event of long-term power shortages. This setup would allow users to manually fill each LABS80K in the event of power loss in a timely and efficient way.
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Results |
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Once all of the various elements had been sourced installation took 4 weeks and site acceptance trails were signed off using Installation Qualification (IQ) and Operational Qualification (OQ) for all systems. A preventative maintenance contract has been established to carry out yearly checks on the main components of the infrastructure along with the provision for emergency call outs should the need arise.
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Discussion |
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Large-scale Liquid Nitrogen Archives need careful planning to ensure that the samples are maintained in a suitable environment for long-term storage and personnel using the facility are working in safe conditions. The graphical representation of the temperature readouts in Figure 2 highlights the temperature stability of the vessel under working conditions. It also shows the small temperature gradient in the vessel. Samples at the bottom of the vessel would experience temperatures of –196°C while samples at the top of the vessel experience temperatures of –190°C. These figures show samples stored in the LABS80K would be less likely to experience major temperature fluctuations during the normal use of the vessel.
It is also important that the system checks itself for faults regularly and automatically notifies the correct people in the event of a fault. The design described above addresses all these issues and provides a robust and fit for purpose back-up storage facility for UK Biobank.
Conflict of interest: None declared.
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