Are you relocating an entire freezer full of research specimens? The ideal scenario is to leave the specimens in the cold storage unit and to transport the entire unit—which means keeping it in operation while it is in transit. However, refrigerators and freezers were never designed to operate while in motion, and keeping them running while bumping along a highway can damage the compressors, void the warranty, cause unit failure, and—why risk it?—allow your samples to thaw.
However, there is a way to transport freezers with the specimens inside, maintain correct temperature, and still protect the compressors: turn the units off and use controlled injection of liquid nitrogen (LN2) to maintain correct temperature.
We’ll talk more about the LN2 injection shortly. First, consider why the engineers who design freezers do not recommend operating these units while being moved:
- Freezer compressors use pistons to circulate the oil and while the unit is in operation, the oil continually flows through the compressor and other components. If the freezer is jolted while in operation, the oil can splash onto the sides of the housing, allowing it to pump past these components and cause a restriction.
- The compressors are spring-mounted, and can strike against the motor. If the unit is in operation, the heat can melt the wax coating that protects the windings from shorting. A severe bump can break the compressor free of the mounts.
- If the unit fails in transit, what do you do for back-up, if the back-up is at the same risk?
- The reliability of the truck generator that supplies the units also needs to be considered: If the one generator in the truck fails, what is your alternative?
- Even if there is no mechanical failure, the temperature stability inside the unit is only as good as the unit, which was not designed to operate in motion or in the cargo area of a truck on a hot summer day.
Secondly, if you’re moving a collection of samples that are stored at different temperatures, you will need separate transport arrangements for the materials stored at/around -20°C and at ultra-low temperatures. And generator trucks cannot be used to transport materials stored under cryogenic conditions.
Using LN2 to keep the contents of a freezer at the correct temperature not only eliminates the risk of motion-induced damage to the mechanical components, it also offers better temperature control, and it allows materials maintained at different temperatures to be transported in the same load—including cryogenically preserved samples. It works like this:
- The contents of the freezers are braced so they cannot shift within the unit. The units are turned off and wheeled onto the LN2-equipped truck. A technician installs the LN2 piping/injection as well as the temperature monitoring probes into each unit. In addition, the compressors in the freezers can be bolted down to prevent movement during transport.
- The on-board piping system controls the LN2 injection, and can maintain the temperature of the various freezers or dewars within a narrow and optimal range. The allowable temperature range is customized for each unit being transported, so -20°C freezers, ultra-low units, and LN2 tanks can be moved at the same time.
- The LN2 system has no moving parts and is highly reliable compared with generators and mechanical refrigeration systems. Unlike generator trucks, which typically have a single on-board generator, on-board LN2 systems have built-in redundancy (multiple solenoids, controllers, and LN2 tanks) on each truck.
- Unlike generator-based operations, the LN2 piping system can run on battery back-up should there be a system failure and the truck be disabled. A battery charger is all that is needed to keep the system running in the extremely unlikely event that the truck is down for an extended period of time.
There are other advantages to using LN2 systems for transport:
- You don’t have to move the freezers! On-board LN2 injection systems will maintain the temperature of the cargo in many types of transport containers.
- Depending on a number of factors, moving your samples in LN2 temperature-controlled transport chambers may allow for exemption DOT-E 11799 in the transport of infectious materials.
The most critical variable in relocating research materials is maintaining the correct temperature, to preserve their molecular integrity. Maintaining correct temperatures and protecting your freezers at the same time is good biobanking practice as well as good science.
There are certainly number of merits of using the LN2 truck system, but i'd be interested to learning your experiences or thoughts on this subject. Feel free to share them in the comment section below!
I would also be happy to provide assistance with your next biobank or freezer relocation/transport project. Simply click here to request for more information about our Cold Chain Logistics services.
Meanwhile, you may want to check out our recent eLearning modules with part 3 on "How do I maintain sample integrity during transport?"