By Norman Quesnel
Senior Member of Marketing Staff
Advanced Thermal Solutions, Inc. (ATS)
A cold chain is a series of packaging, shipping, and distribution steps, all conducted at controlled temperatures. A successful cold chain keeps products within their required temperature ranges even when shipping between continents or hemispheres. Cold maintenance preserves the optimal shelf lives of produce, seafood, frozen food, pharmaceuticals, and other products that must be kept constantly chilled or frozen to maintain their quality.
About 70% of all food consumed in the United States is handled by cold chains. Without proper cooling or freezing, most of this food would show signs of perishing before reaching its end user and could potentially be inedible and unsafe.
For pharmaceuticals, consider a vaccine supply shipped to a third world country without a cold chain infrastructure. Excess exposure to heat could make the vaccine inactive and, even worse, this may not be discovered until after the shots have been distributed.
It is critical for shipping parties (food companies, drug companies, et al.) to have sufficient scientific knowledge of their products and the environments they will travel through before reaching the end users. With that knowledge in hand, the cold chain can accommodate almost every product that must ship under cold temperatures.
Cold transportation and storage standards have been developed by the U.S. as well as countries in Europe and Asia. Guidelines are also provided by the World Health Organization (WHO). The most common temperature standards in the food cold chain are “banana” (13°C), chill (2°C), frozen (-18°C) and deep frozen (-29°C); each is related to specific product groups. These standards are mainly used in the produce (agricultural) industry.
For vaccines and other pharmaceuticals, the cold chain must be compatible with labeled instructions such as “Store in a refrigerator, 2°C to 8°C (36°F to 46°F),” or “Store in a freezer, -25°C to -10°C (-13°F to 14°F).”
Food and pharma providers apply science to make products that will better withstand warmer temperatures. But most of these products must still be kept cold or frozen once they are packaged and shipped out. Poor temperature conditions or delays of an in-shipment food product or a drug can damage that product enough so it loses any market value or utility. 
The pharmaceutical industry factors in potential temperature fluctuations during transit and storage. For many of pharma products, there is an MKT (mean kinetic temperature). This is a “thermally equivalent” temperature that degrades the same amount of a drug as degraded by the different temperatures during a particular period of time. 
MKT is a complex calculation with many data points. Per Wikipedia, the mean kinetic temperature can be expressed as shown in Figure 4:
Here is a simple analogous example of working out an MKT:
A dozen eggs sat:
- In a 20°C room for two hours.
- In a 2°C refrigerator for four hours.
- And on a 25°C loading dock for one hour.
Using MKT, a company can calculate that the temperature profile of the eggs was “thermally equivalent” to storing them at 10.096°C for seven hours. 
Cold Chain Packaging
Ensuring that a shipment will remain within a temperature range for an extended period of time comes down largely to the type of container and the refrigeration method. Duration of transit, the size of the shipment, and the outside temperatures experienced are all important in deciding the type of packaging. Examples of packaging used in shipping range from small insulated boxes that require dry ice or gel packs, rolling containers, or a 53-foot truck with its own refrigeration unit.
The major cold chain technologies used for providing a temperature controlled environment during transport involve a range of materials and vehicles. Below is a quick summary 
Dry ice – Solid carbon dioxide is about -80°C and is capable of keeping a shipment frozen for an extended period of time. It is widely used for the shipping of pharmaceuticals, dangerous goods, and foodstuffs and in refrigerated unit load devices for air cargo. Dry ice does not melt, instead it sublimates when it comes in contact with air. 
Gel packs – Large shares of pharmaceutical and medicinal shipments are classified as chilled products. This means they must be stored in a temperature range of 2-8°C. The common method to provide this temperature is to use gel packs, or packages that contain phase-changing substances that covert from solid to liquid and vice versa to control an environment. Depending on the shipping requirements, these packs can either start off in a frozen or refrigerated state. Along the transit process they melt to liquids, while at the same time capturing escaping energy and maintaining an internal temperature. 
Eutectic plates – These are also known as cold plates. The principle is similar to gel packs, but the plates are filled with a liquid and can be reused many times. Eutectic plates have a wide range of applications, such as maintaining cold temperature for rolling refrigerated units. They can also be used in delivery vehicles to keep temperature constant for short periods of time. 
Liquid nitrogen – An especially cold substance at about -196°C, it is used to keep packages frozen over a long period of time. Liquid nitrogen is commonly used to transport biological cargo such as tissues and organs. It is considered a hazardous substance for the purpose of transportation. 
Quilts – These are Insulated pieces that are placed over or around freight to act as a buffer against temperature variations and to maintain a relatively constant temperature. Using quilts, frozen freight will remain frozen for a longer time period, often long enough to make the usage of more expensive refrigeration devices unjustifiable. Quilts can also be used to keep temperature sensitive freight at room temperature while outside conditions can substantially vary (e.g. during the summer or the winter). 
Reefers – Their name derived from ‘refrigeration’, reefers are temperature controlled, insulated vans, small trucks, semi-trailers or standard ISO containers. They are specially designed to allow temperature-controlled air circulation maintained by an attached and independent refrigeration plant. A reefer is therefore able to keep the cargo temperature cool and even warm. The term reefer increasingly applies to refrigerated 40-foot ISO containers with the dominant size being 40 high-cube footers (45R1 being the size and type code). A reefer carries around 20-25 tons of refrigerated cargo and is fully compatible with the global intermodal transport system, which implies a high level of accessibility to markets around the world. 
The first reefer ship for the banana trade was introduced in 1902 by the United Food Company. This enabled the banana to move from an exotic fruit that had a small market, because it arrived in markets too ripe, to one of the world’s most consumed fruit. Its impact on the reefer industry was monumental.
It takes time and coordination to efficiently move a shipment and every delay can have negative consequences, notably if this cargo is perishable. The greater the physical separation, the more likely freight can be damaged in one of the transport operations involved. Some goods can be damaged by shocks while others can be damaged by undue temperature variations.
For a range of goods labeled as perishables, particularly produce, quality also degrades with time. Ensuring that cargo does not become damaged or compromised in shipment, businesses in the pharmaceutical, medical and food industries are increasingly relying on the cold chain.
A recent industry forecast sees the global cold chain market growing by 7% every year, reaching $340 billion by 2025.