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Measuring Temperature Performance for Reliable Vaccine Storage

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Biological materials and reagents can be extremely sensitive to temperature changes, requiring efficient and reliable storage solutions to maintain viability and maximize product shelf life. Vaccine storage, in particular, demands rigid temperature control and uniformity. Variations in temperature can considerably impact the integrity of the vaccines, resulting in loss of time and resources. It is therefore critical to measure the temperature performance of fridges and freezers to protect samples, using methods such as peak variation.  


Technology Networks recently spoke to Drew Buskirk, senior product manager, Thermo Fisher Scientific, to learn more about peak variation and why it is so important to measure. Buskirk also discusses NSF 456 – a new vaccine standard published by NSF International – and how its implementation could help to reduce vaccine wastage.


Anna MacDonald (AM): Can you explain what peak variation is?

Drew Buskirk (DB): Peak variation is the difference between the coldest and warmest measured temperatures during performance testing for a refrigerator or freezer. There are no averages or additional calculations, just the delta. There can be variations in how many probes used, and what type of probes, whether weighted or open air, but the metric is a representation of worst-case temperatures throughout the cabinet.

AM: Why is awareness of peak variation so important?

DB: Peak variation is important for two reasons. First, it gives users a good indication of how well a unit circulates air throughout the cabinet which is a great indication of overall unit performance. Second, it gives the user clear views of potential cold or warm spots within the cabinet that could be problematic for more temperature sensitive cargo. The more probe locations in the test, the better coverage and visibility the user has to potential problem areas.

AM: How is peak variation in life science refrigerators traditionally measured? What are the limitations of this approach? 

DB: Traditionally peak variation is measured in a cabinet with nine probe locations, four in the corners on the top shelf, four in the corners on the bottom shelf, and one in the center of the cabinet. While the corners would intuitively seem like the areas most likely to experience temperature extremes, that’s not always the case. Air flow throughout the cabinet is based on more than just the corners inside the cabinet and can be changed depending on fan and baffle locations.  This can create cold spots in unexpected areas along the side or back walls that wouldn’t be covered with traditional peak variation testing. The more locations and the more coverage of the cabinet the better representation of air flow.

AM: How does Thermo Fisher Scientific measure temperature performance of its products?

DB: Thermo Fisher Scientific measures 24 locations within the cabinet and calculates peak variation, stability and uniformity. Stability is the maximum temperature difference over the entire test for any specific location. The average stability during the cycle is the value published. Uniformity is the maximum temperature difference for all thermocouples at any specific moment in time. Thermo Fisher Scientific publishes the average uniformity during the cycle portion of the test. 

In addition to temperature measurements across the cabinet another critical metric is the 1-minute door open recovery (DOR). This is the time it takes a unit to recover to set point after a 1-minute door opening and is an excellent measure of the unit’s heat load capacity and ability to circulate air.  Refrigerators rarely remain closed all day and are frequently opened. Laboratory grade refrigerators have to be able to meet the demanding use of customers while still maintaining suitable temperatures for sensitive cargo.

AM: Can you tell us more about the NSF 456 standard and its significance?

DB: Vaccine wastage is a significant problem globally and the World Health Organization estimates that approximately 50% of all vaccines are wasted every year. This is a tremendous cost in not only dollars, but in being able to deliver critical healthcare solutions globally. 

Historically, guidance for vaccine storage has been vague and resulted in customers using a range of solutions for vaccine storage. The new NSF 456 vaccine standard provides clear guidance to both users and manufacturers as to the design, thermal performance and documentation requirements needed to ensure that vaccines are stored in optimal and secure conditions. This new standard is a great example of the industry working together to help solve a critical infrastructure problem and we as Thermo Fisher Scientific are incredibly proud to have been a partner in helping develop this standard.

AM: How do the TSX Series of high-performance refrigerators and freezers ensure sample integrity?

DB: Thermo Fisher Scientific TSX laboratory refrigerators and freezers all use V-Drive technology which includes a variable speed compressor which can adjust its speed depending on the cooling needs and automated tuning control to optimize the compressors running speed to current conditions. If there are frequent door openings or samples are added to the refrigerator or freezer it can ramp up cooling capacity to ensure the unit returns to set point as quickly as possible.  This is what allows TSX refrigerators and freezers to maintain tight peak variation numbers as well as provide faster door open recovery.

Drew Buskirk was speaking to Anna MacDonald, Science Writer for Technology Networks.