Wednesday, 06 February 2013
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What range of humidity is permitted in a refrigerator to ensure vaccine safety?
11 years ago
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#2586
In general, WHO is not aware of any specifications for humidity range for refrigerators. Humidity inside the refrigerator is not a vaccine safety issue per se; however, it may pose a challenge for the stability of the vaccine particularly for freeze-dried vaccines (it depends also on the quality of the container closure system). If you can tell us more on your particular reason for this query, maybe we can assist you better. Nora DELLEPIANE, Scientist QSS WHO
11 years ago
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#2587
Dear Nora: Thanks for your answer. The question is directed to know whether there is any information about the amount of condensate that may form inside the refrigerator for the safe conservation of vaccines, since this system can keep the temperature between 2 and 8 degrees Celsius even though staff open the door between 100 and 200 times to get the vaccines and administer them, without losing the temperature stability in continuous working time of 8 hours, inclusive with the compressor operation of only 40 per cent maximum power consumption. Condensation only forms in small quantities in the door frame and sometimes on the interior walls.
11 years ago
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#2588
Storage requirements for an increasing number of medicines manufactured in the US and Europe are +15C/+25C @ relative humidity of 60%. Nevertheless the problems of humidity higher than 60% are very real: I am aware of the following: [indent]- Loss of vial labels when adhesive is water soluble[/indent] [indent]- Loss of print when surface of label starts to disintegrate[/indent] [indent]- Mould forming around the vial surfaces[/indent] [indent]- Accumulation of water in the base of the refrigerator.[/indent] If opened vials are kept according to the multi-dose vial policy, additional issues are: [indent]- Contamination of the exposed vial septum if vial floats in water (perhaps also if[/indent] [indent] condensate forms on the septum)[/indent] [indent]- Disintegration of secondary packs and difficulty in managing vaccine vials[/indent] [indent]- Matching wrong diluent to vaccine because batch numbers unreadable.[/indent] High RH is therefore a problem not yet regulated in vaccine storage; this needs attention.
11 years ago
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#2589
Most of the problems mentioned by John Lloyd occur as a consequence of moisture rather than water vapor. Liquid water making contact with a label will be much more problematic than high humidity. I have a domestic refrigerator with high humidity. I have some labeled jars which have been in there for over a year and the labels are still in good shape. If water is collecting in the bottom of a refrigerator it is probably because the refrigerator has poor drainage. Decreasing the humidity in a refrigerator can have additional ramifications such as larger temperature swings and increased energy consumption. These would be a consequence of a colder evaporator. Before changing test standards I suggest investigating weather the problems out by John Lloyd could be eliminated by removing liquid water rather than water vapor. If a vaccines are not stored in a sealed container humidity may be more of an issue. Larry Schlussler, Sun Frost
11 years ago
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#2590
In the course of the Optimize solar direct-drive refrigerator demonstration in Vietnam, we saw a great deal of condensation in the SureChill refrigerators, given the high humidity here, especially in the north. In other refrigerators, this moisture forms frost which requires regular defrosting, but in the SureChill, with no freezing surfaces inside the refrigerator, the humidity generates a lot of water. The manufacturer responded with a number of design changes to help manage this moisture. In addition, we found that keeping vaccine boxes in sealed plastic containers inside the refrigerator helped protect them from the blast of moisture everytime the door was opened. (Based on a suggestion from John Lloyd!) Joanie Robertson PATH Vietnam
11 years ago
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#2591
In a working refrigerator, the amount of relative humidity is kept constant at around 60%. This is due to the fact, that humidity entering the refrigerator will always condense on the evaporator (the coldest spot). This is, in a first moment, independent from the relative humidity of the air. The condensed humidity on the evaporator is going to freeze, and ice is being built up inside the refrigerator. This is a problem, whenever you have to deal with high compressor running times due to high ambient temperature, lots of door openings, undersized systems. If the system has enough power reserves, the compressor break times are sufficient to melt the ice. Then make sure the equipment has a drain plug in front in order to remove any drain water on a daily basis. Whenever the refrigerator is not working properly and can not keep the temperature on a constant level, the RH will go up and might have an negative influence on the stored goods. Gilles Ries, Dometic
11 years ago
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#2592
A refrigerator cooling system can be designed so that no ice forms on the evaporator. If the evaporator goes below 0 deg C ice will begin to form on it. A box which is well insulated and has a sufficient evaporator surface area can maintain temperatures between 2 deg C and 8 deg C with the evaporator above 0 deg C. It is important to control this moisture so that it flows away from the stored vaccines. If the humidity is high there will be more condensation and good moisture control becomes more important. I think moisture not water vapor is the primary cause of problems in the vaccine storage compartment. This could be verified by some controlled testing. I think it’s important to verify the cause of the problems before changing of the test standards. Lowering the evaporator to lower humidity would increase energy consumption and may also increase temperature swings. Our Sun Frost RFVB-134a has also been tested in Vietnam by Project Optimize. This refrigerator has an evaporator in the refrigerator compartment and it functions without ice being formed in this compartment. I have not heard of any problems related to moisture with our RFVB-134a, perhaps Joanie has some first hand experience with our refrigerator in Vietnam?
the best way to insure vaccine safety is the use of top door refrigerator which specific for vaccines like MK refrigerators. i am using these refrigerators with no problems of accumulation of water in bottom of it or over humidity.
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