In short, cryogenic storage is all storage that takes place below -130°C degrees. It has been proven that at a temperature of -130°C degrees or colder, all living organisms come to a standstill. Below this temperature, the aging process stops and the cells can be stored indefinitely. The most well-known forms of cryogenic storage are: liquid nitrogen and mechanical freezers. But what are the advantages and disadvantages of these forms and what options are possible? Together with the director of Poly Temp Scientific, Robert van der Kuijlen, Poly Temp discusses these options, so that the customer can make the best choice.
Greater safety margin with liquid nitrogen
Liquid nitrogen (hereinafter LN2) has been used for cryogenic storage for years. In the liquid phase, this form offers a uniform temperature of -196°C. This means that the temperature remains stable over a longer period of time. Robert adds: ''This temperature of -196°C gives users confidence in storing their valuable research. If something goes wrong or the LN2 supplier is temporarily unable to deliver, it will take a while before the temperature reaches -130°C. Without opening the lid, the samples will still remain safe for several days.''
Store in the liquid or vapor phase?
Samples are often chosen to be stored in the liquid phase due to the certainty of -196°C, which offers a greater safety margin. Robert: ''Keep in mind that more LN2 is consumed in the liquid phase, because more evaporation takes place when removing a rack. In recent years, we have seen that more and more customers choose to store their samples in the vapor phase.''
In an article from 1995 was already written about the possibility of cross-contamination in the liquid phase. ''For that reason, more and more people choose to store in the vapor phase instead of fully immersing the samples in LN2. In the first case, any possibility of cross-contamination is eliminated, but the safety margin is reduced in case the LN2 supplier is temporarily unable to deliver,'' Robert states.
Difference between automatic and manual filling of LN2
In cryogenic storage in LN2 we make a distinction between automatic and manual filling. In automatically filled tanks the LN2 vessel is automatically filled by a system. In the case of manually filled vessels it is up to the user to fill the vessel himself.
Manually filled storage vessels have a smaller neck opening. The small neck opening reduces the rate of evaporation of the LN2, as the static evaporation rate is reduced. Automatically filled tanks are more convenient and offer much larger storage capacity. However, due to the larger neck openings and pre-cooling of lines during automatic refilling, they consume more liquid nitrogen.
Please see the brochure for exact storage quantities per application.
Ensure safety
It is common knowledge that liquid nitrogen is dangerous to work with. In addition, LN2 has the property that it evaporates, even if the container is sealed airtight. LN2 also extracts oxygen from the air. ''You don't smell it, you don't taste it, you don't see it, but if you are working and the oxygen level is too low, then it becomes dangerous. So it is important to be alert to this,'' says Robert. ''The room in which the LN2 is located must also be equipped with O2 meters. As an additional safety measure, it is recommended that there is always someone outside the room who keeps an eye on the user, in case the alarms in that room do not go off.''
Due to the constant evaporation of LN2, it also remains a continuous process to refill the LN2 vessels. As a result, LN2 must be purchased and budgeted on a consistent basis. Robert: ''Liquid nitrogen certainly provides a larger safety margin in temperature. However, the cost aspect, safety aspect and the fact that liquid nitrogen is not so user-friendly must be taken into account.''
Mechanical cryogenic freezers as an alternative
Ensuring the safety of laboratory workers is important and some organisations want to do away with liquid nitrogen for that reason. As an alternative, Poly Temp offers a mechanical cryogenic freezer of -150°C. Firstly, the freezer ensures a nice uniform temperature of -150°C. This means a safety margin of 20°C in the event of a power failure, for example. Robert adds: ''With liquid nitrogen, the user can store in the vapour phase, but this is at the expense of storage capacity. With mechanical cooling, this does not apply. The user can then fully utilise the 200 litres that are available for the samples. In addition, it is easier to put material in and take it out of this -150°C freezer than with an LN2 vessel. The freezer is only one metre high and therefore user-friendly.''
Furthermore, a cryogenic freezer is safer, because no liquid nitrogen is used. Robert: ''After installing the cryogenic freezer(s) in the room, it is important to ensure that the ambient temperature is correct. Although this -150°C freezer is energy-efficient, heat emission must be taken into account. This makes it important that the room is well-conditioned. This will affect power consumption. Finally, the freezer produces a noise level of around 55 dB.''
Precautions for Cryogenic Freezers
For example, if the freezer fails due to a power failure, the freezer will slowly start to warm up. Robert: ''If the freezer fails, for whatever reason, I always advise to be prepared for this. First of all, I advise to connect the freezer to an emergency generator of the building. Secondly, to connect an LN2 backup system to the freezer. In the event of a failure, LN2, in vapor form, can be injected into the freezer, so that the material remains below the critical temperature of -130°C. For this, an LN2 filling tank must be ready with LN2.''
Calculation of the Total Cost of Ownership
Robert concludes: ''We offer both options at Poly Temp so whether you need an LN2 storage tank or a mechanical freezer, it is entirely up to the customer. Both systems offer cryogenic temperatures for storing valuable samples.
We do recommend that you calculate the TCO over the longer term and include this in the final decision.
In the calculation, the comparison is made between these forms of cryogenic storage. Liquid nitrogen requires a specially equipped space and delivery of nitrogen. In comparison with our cryogenic freezer with electricity costs and climate control systems. Of course, it is possible to submit the issue to us and we are happy to do the calculation together with our customer.''
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