1. Larry Schlussler
  2. Supply chain and logistics
  3. Thursday, 01 March 2018

A new PQS freeze protected vaccine carrier has been approved. The incorporation of this new carrier would solve a serious problem but at a considerable cost. PATH estimates that 2 million carriers would have to be replaced.

Several years ago we had been working on a freeze protection method which incorporated water as a phase change barrier between the stored vaccines and the ice packs. This appears to be the same freeze protection mechanism incorporated in the PQS approved carrier. The water barrier in our freeze protection method was created by a water pack which would have the same height and width as a .6 liter pack however it would be much thinner, only about 5 mm thick. When the ice packs are loaded the barrier packs would be clipped against the frozen ice packs. In the carrier the barrier would sit between the stored vaccines and the cold ice packs. The barrier packs would be stored at room temperature.

As a consequence of not having to replace the carrier this technique would be much less  costly to implement. Using water pack barriers also offers the flexibility of working with different sized carriers. In addition it would reduce the amount of plastic waste produced with replacement.

Sun Frost did not go further with the commercialization of this technique because we did not have the funds for implementation at that time. We would be glad to consult with any company interested in implementing this technique.

Larry Schlussler Phd

Sun Frost

Accepted Answer Pending Moderation


Thanks for your interest in our freeze protection barrier.

We designed our phase change barrier so that it could be used with a variety of carriers. When a sub cooled ice pack is placed in a carrier incorporating a phase change barrier the temperature of the ice pack increases to 0 C as a consequence of heat leaking into the carrier and the heat released by the barrier as it changes phase. To test the barrier we created worst case conditions. This was done by simulating a carrier with minimal heat gain. The phase change barrier would than have to absorb almost all the “coolth” stored in the sub cooled ice pack. For this test a -25 C ice pack was placed in direct contact with the phase change barrier.  Heat gain into this sandwich was minimized by placing 5 cm of foam insulation  directly around the barrier and ice pack. The test was carried out in a 15 C room. The temperature of the barrier surface away from the ice pack was monitored, it stayed above 0 C. For protection under harsher conditions, colder ice packs or a colder environment the quantity of water in the barrier could increased.

We are currently not in a position to manufacture the barrier. However we would be willing to work with a manufacturer to make this technology available.



* I can’t see any advantage to setting the freezer temperature as low as -25 C . The freezer will be periodically warmed when thawed ice packs are placed in the freezer. The freezer could not than be used where a consistent low temperature is required. At -25 C freeze protection and conditioning will also be more difficult. From some back of the envelope calculations it appears that the possibility of freezing a vaccine increases exponentially as the temperature of the ice pack is lowered. Another disadvantage of an unnecessarily low freezer temperature is that the capacity of the compressor decreases at lower freezer temperatures and the energy consumed increases. A cooling system keeping a freezer at -25 C will run about twice as long as a cooling system in a -15 C freezer. The energy consumption will also increase about 1.8 times. To experience the consequences of running a freezer at -25 C try running your home freezer at -25 C. If this temperature can be achieved the compressor will probably run continuously increasing wear problems. In addition frost build up will be much more rapid which could cause additional problems.

  1. more than a month ago
  2. Supply chain and logistics
  3. # 1
Accepted Answer Pending Moderation

This is interesting news and if confirmed important savings of money and effort could be made ! I understood that the current re-design of vaccine carriers and boxes to protect against freezing vaccine was necessary to meet the current PQS performance specification and to maintain carrying capacity.

Have you achieved the current specifications, in particular the +15C ambient test and can you offer sufficient vaccine capacity? If you can achieve acceptable results at +10C ambient, you would have a highly competitive solution.

  1. more than a month ago
  2. Supply chain and logistics
  3. # 2
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