Unless the context specifically precludes this option, it most likely refers to the 'cold chain' designed to ensure the safety of perishable goods (food, etc.).

Cold chain - Wikipedia, the free encyclopedia
en.wikipedia.org/wiki/Cold_chain
1 Origin; 2 Uses; 3 Validation; 4 Cold Chain Professional Training; 5 See also ... Cold chains are common in the food and pharmaceutical industries and also in ...
‎Origin - ‎Uses - ‎Validation - ‎Cold Chain Professional Training
Cold Chain Food Quality and Logistics Summit
www.coldchainfoodlogistics.com/
IQPC is proud to present the 2014 Cold Chain Food Quality and Logistics Summit. The 2014 event will address the top trends and challenges impacting the ...
Cold Chain - Food Logistics
www.foodlogistics.com/cold-chain
Food Logistics -- articles, analysis, and best practices for the global food supply chain, with a focus on the Cold Supply Chain and Cold Storage Management.

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Note added at 31 mins (2015-02-24 20:52:57 GMT)
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@Chris - re your note below:
As noted in the wikipedia ref., cold chains are used not only for food but also (relevant to your context) in the pharmaceutical industry - and that extends to the proper storage of drugs in health centres (especially in the tropics).

The change to gas quite likely refers to the use of gas-powered refrigeration systems instead of electric-powered systems. If you've never heard of (or are sceptical about) gas-powered refrigerators, read here:

Gas and Propane Refrigerators - HowStuffWorks
home.howstuffworks.com/refrigerator5.htm
If you own an RV, chances are you have a gas- or propane-powered refrigerator. These refrigerators are interesting because they have no moving parts and use ...