Is it Time to Upgrade from Aluminum Storage Container Freezers to a Larger Automated Freezer?

Image Credit: Air Products PLC

Generally, research projects or sample storage facilities will begin with using just one or two containers – typically known as ‘dewars’ – to store a few samples. As the facility or project expands, additional containers are added until you have an improvised cryo-room which may look something like the above image.

More often than not, researchers or laboratory staff never throw away their samples. This may result in the exponential growth of a collection of containers, increasingly consuming more and more space as time goes on.

Dewar or not?

‘Dewar’ tends to be the accepted term for this type of aluminum container though this is a bit of a misnomer.

Invented in 1892 by Scottish inventor James Dewar, the dewar, or ‘vacuum flask’, was a basic double-walled glass flask with the air removed from the cavity between the two walls. Thus, the interior of the flask and whatever was stored inside avoided potential heating as there were no air molecules for the heat to pass through.

People may use the term ‘dewar’ concerning containers for sample storage or those which are used to store samples in nitrogen vapor for transportation. Both products are far removed from James Dewar’s initial creation, though they still make use of the vacuum design. However, in the technical sense ‘dewar’ refers only to containers with a capacity of up to 50 L.

Aluminum sample containers, also known as ’cryogenic freezers’ differ as they are developed specifically with sample storage in mind. Samples are confined in racks and suspended in liquid nitrogen inside the dewar. The sub-zero temperature is way below the glass transition point of water (-135 °C), this is where almost all biological functions cease.

The problem with aluminum containers

For some, the economic benefits of aluminum containers often override the storage issues caused by these otherwise space-hogs. Yet, the problem with cryogenic dewars or containers far exceeds the space they take up in a facility because they can sometimes pose a safety risk to researchers.

Due to the tendency of cryogens to suddenly expand when heated, an uncontrolled release of cryogens - such as during refilling - can displace oxygen in the air. This can result in oxygen deficiency and possibly lead to asphyxiation. Furthermore, when it comes to sample safety, most aluminum containers don’t offer the same safety features as more progressive storage solutions.

Additionally, when in use for extended periods of time, cryogenic dewars can prove to be unreliable. While some storage containers might have built-in temperature monitors, many don’t and this means an external monitor to check temperature is required. Yet, if a temperature monitor isn’t used, it could lead to a rapid temperature increase, which may not be detected until it is too late.

For the most efficient early warning system, all monitors should be interlinked to the Building Management System (BMS) whether that be to a wired or wireless system: subsequently, the number of complex issues will increase with the number of dewars.

Furthermore, the footprint of storing in several aluminum freezers should also be considered since even some of the biggest automated stainless steel freezers take-up little more floor space than four aluminum freezers. By comparison, they can also provide nearly four times the storage capacity.

When storing essential, invaluable samples, making use of an aluminum container for long-term storage is far from the appropriate solution.

The next step

So, it is worth asking, has the need for sample storage exceeded the capacity for storage containers? Or perhaps the value of your samples means you can no longer rely on a basic solution?

Therefore, investing in a full-size, automated cryogenic freezer is the next logical step for most research and sample storage facilities. Though these sacrifice the portability benefits of aluminum containers, the sample security advantages are unrivaled.

Available as standard with liquid or vapor phase storage, LN₂ storage freezers such as the HEco are installed inside the facility and plumbed into an exterior LN₂ supply tank. The LN₂ is then carried efficiently via a Super Insulated Vacuum Line (SIVL) into the building’s interior. Moreover, the risks associated with manual handling of liquid nitrogen for staff is further reduced as external bulk storage tanks are simply filled by a professional supplier.

However, the principal advantage of liquid nitrogen freezers is long-term storage capability. Theoretically, with a constant supply of LN₂, a freezer such as the HEco could protect and keep samples frozen indefinitely.

LN₂ freezers also include built-in temperature monitors and alarms to curb failure and loss of samples. Additionally, in the event of a supply failure, samples will remain viable for several weeks due to the slow burn-off rate of liquid nitrogen, assuming the freezer remains closed during this period.

Some researchers may favor the upright mechanical ‘ultra-low’ freezer route. However, these units are not suitable for long-term cryogenic storage of samples as they typically operate at -80 °C. While it is true that there is an availability of mechanical freezers that can operate down to -150 °C, for cryogenic storage (below 135 °C) that is trustworthy, the best option is a liquid nitrogen freezer.

For many facilities just starting out, dewars or cryogenic containers are indeed an economic solution, but there will inevitably come a time when upgrading becomes essential. Therefore, it may be better for facilities to upgrade sooner rather than later, even if there is plenty of room. Fully automated stainless-steel liquid nitrogen freezers are a secure, long-term solution for cryogenic storage, offering a multitude of benefits.

About Air Products PLC

Air Products touch the lives of consumers around the globe in positive ways every day. With approximately 16,000 employees and operations in 50 countries, we serve customers across a wide range of industries from food and beverage to medical, energy, and transportation. We supply a unique portfolio of atmospheric and process gases, equipment, and services.

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