Cold chain: difference between revisions
Diff·revision 48 → 49·04:26, 26 Mar 2025
Difference between revision 48 and revision 49 of Cold chain. 7 lines changed; the page grew by 1,422 bytes.
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| 123 | The trade-off is that a material with a higher melting point stores its latent heat at a smaller temperature difference from ambient and therefore protects for a shorter time against a warm environment, while providing protection against freezing that water ice cannot. Where a shipment must survive both a hot and a cold ambient profile, dual-material configurations are used.{{r|matthias2007}} | 123 | The trade-off is that a material with a higher melting point stores its latent heat at a smaller temperature difference from ambient and therefore protects for a shorter time against a warm environment, while providing protection against freezing that water ice cannot. Where a shipment must survive both a hot and a cold ambient profile, dual-material configurations are used.{{r|matthias2007}} |
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| + | 125 | == Failure modes == | |
| + | 126 | Failures cluster at a small number of predictable points, and the empirical literature is consistent about which. | |
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| + | 128 | '''Freezing.''' A 2007 systematic review of vaccine cold chains examined studies from high- and low-income settings and found evidence of freezing exposure in the majority of those examining shipments, and in a large proportion of those examining storage. Its conclusion — that inadvertent freezing was the more prevalent problem, and more damaging for the products concerned, than heat exposure — was surprising to practitioners at the time and has been sustained by a later review of the same question.{{r|matthias2007,hanson2017}} The mechanisms are direct contact between payload and frozen coolant, refrigerators controlling to a set point without regard to compartment gradients, and domestic refrigerators used for storage, in which the coldest region may be several degrees below zero. | |
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| + | 130 | '''Custody transfers.''' Airport handling, customs holds and courier depots are the points at which a shipment is most likely to sit outside a controlled environment, and are also the points at which no party is monitoring. A hold of unpredictable duration at an unpredictable ambient temperature is the characteristic risk of cross-border movement, and it is the reason [[Customs seizure|customs interventions]] have thermal consequences independent of their legal ones.{{r|eugdp2013}} | |
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| 125 | == References == | 132 | == References == |
| 126 | {{reflist}} | 133 | {{reflist}} |