Refrigerants

Based on the temperature requirements of your product and a number of other important factors which will be discussed in this paper, a variety of different refrigerants may be used in the insulated shipper. These products, often called temperature stabilizers or phase change materials (PCM), can be formulated and conditioned at specific temperatures and can be used in concert with your product and the rest of your packaging to create an environment within the shipping container to thermally protect your product. These refrigerants include but are not limited to dry ice, wet ice, gel packs and foam bricks, all of which will be addressed in this paper. The purpose of this paper is to give a general description of these refrigerants and provide a set of advantages and disadvantages that can be associated with them. This paper is not intended to provide exhaustive detail on the subject matter or to advise on any preferred refrigerant or method of application. Rather this paper’s purpose is to provide general information that may be beneficial in gaining a general understanding of refrigerants used for cold chain distribution.

Dry Ice

Dry ice, either in pellet or block form, is solid carbon dioxide (CO2) that sublimates directly to gaseous form through sublimation. Carbon dioxide is used because it maintains a temperature of -78°C as it sublimates. Most chemicals, such as water, change phase from a solid (i.e. ice) to a liquid state, and then evaporate to a gaseous state. Each of these phase changes requires energy to complete. Dry ice combines both of these phase changes into a single step, giving it the advantages of a high absorption of energy (heat) and eliminating the need to contain a messy liquid. Because carbon dioxide’s unique characteristics it is a no-mess refrigerant with an exceptional high latent heat of fusion that can be beneficial in certain applications. Dry ice is the most efficient refrigerant for absorbing heat because of its double-phase change characteristic.

Advantages

• Temperature – At -78°C (-109°F), dry ice is well below the freezing point for most products. Dry ice is predictable in its temperature and duration, however there are applications where product cannot experience temperatures below a certain level, such as -40°C. More on this below.
• Weight – Although an equal volume of dry ice will weigh about double that of wet ice, the performance at low temperatures is far better and the overall savings can be significant.
• Performance:  As mentioned, dry ice has a very high latent heat and will remain at its phase temperature longer than most other refrigerants, particularly those that are formulated to phase at lower temperatures.
• Performance Indication – Once arrived at its destination, the remaining weight of the dry ice can help indicate its performance. The evidence of remaining dry ice is a clear indication that the product was or was not held at the correct temperature. This can eliminate the need for expensive and time-consuming data monitors.
• Low Cost – The cost of dry ice can be negotiated based on volume required, but a conservative estimate would be $0.20 per pound. Additionally, dry ice incurs no disposal fees.
• Availability – There are many local distributors of dry ice that will deliver dry ice on a daily or weekly basis
• No Preconditioning – It is unnecessary for dry ice to be preconditioned before use. Ideally, dry ice would be delivered daily and used the same business day. Dry ice can be delivered in a durable container and positioned on the distribution line for easy packing.  
• Reduced Disposal – Recipients of dry ice shipments are not left with solid refrigerant that must be disposed of. This reduces landfill waste and is a good ecological practice.

Disadvantages

• Temperature – Even if the product is approved to reach -78°C during shipping, some of the primary packaging may not be. A common problem that many companies experience is the inability of their product vials to drop below a certain temperature (around -40°C) due to use of rubber stoppers. At this temperature, rubber reaches its glass transition state and sterility may be compromised. In these instances, dry ice may still be utilized, but the extreme temperature must be buffered from the product using creative and some times expensive packaging techniques.
• Gas Expansion – Dry ice cannot be used in an air-tight container due to the expansion of particles as the solid sublimates to gas. The gas from the dry ice must be allowed to escape the container without building up a dangerous amount of pressure. EPS and PUR containers allow for this to occur. If sterility requires a closed container for shipments, dry ice should not be used. One pound of dry ice can expand to over 8 cubic feet of carbon dioxide gas.
• Freshness – Dry ice is best used within a few days of manufacturing. As dry ice in exposed to ambient temperatures, its extreme cold temperature can freeze water in the air and create a layer of wet ice. This wet ice layer can insulate the dry ice and prevent it from effectively maintaining the
  -78°C temperature and can affect the performance of the dry ice.   
• Packing Efficiency – Unlike gel packs or gel bricks which come in pre-weighed packages, dry ice must be weighed by some means before the package is sent. This can be accomplished through automatic machinery, pre-validated scoops, or on a calibrated scale. Whatever the method, it must be consistent and defined in your operating procedures.
• Head Space – As dry ice sublimates, it creates space inside the container for product to shift around. In the later hours of the shipment, this additional space may allow for product to become damaged from increased shifting. This can be prevented through the packaging configuration using custom dry ice trays or die-cut corrugate inserts to protect the product from movement.
• Occupational Hazards – There are many regulations that restrict dry ice shipments. Dry ice is considered a hazardous substance for three reasons. First, it can be an explosion hazard if a sealed container holds dry ice that sublimates and expands. Second, it is a suffocation hazard based on the quantity of carbon dioxide gas produced. This gas can displace oxygen from a closed environment. Third, dry ice is extremely cold and is a physical hazard if handled without proper protection. Holding dry ice with bare hands can cause a cold “burn” and can damage skin, similar to frost-bite.
• Regulations –
  • Many carriers have their own regulations for dry ice shipments. For example, FedEx requires containers with over 5 lbs of dry ice to be properly labeled. UPS and DHL have similar requirements.
  • For international shipments, be sure to check the regulations in the destination country to assure that all of the proper paperwork is completed and the regulations allow for the shipment to reach its destination.
  • IATA (International Air Transport Association) regulations limit the amount of dry ice weight to be under 200 kg (400 lbs) per container for air transport. It also requires labeling that clearly marks the presence of a hazardous substance. These labels should include the substance name (“dry ice” or “carbon dioxide solid”), the net weight of the dry ice in kilograms, the shipper and the recipient, as well as the code that applies for the standard (UN 1845)

Wet Ice

Wet Ice, or better recognized as ice cubes, is simply frozen water.  Water is one of the most unique compounds on earth particularly it’s thermal properties. It has more capacity to absorb heat than most any other substance. This means that when wet ice is melting or changing phases from a solid to a liquid it will maintain its phase temperature, in case 0ºC, for a long time. Wet ice is generally frequently placed in plastic bags but is sometimes placed directly into a shipping container.

Advantages

• Temperature – At 0°C, wet ice is safe to use for most refrigerated shipments. Wet ice can be predictable in its temperature and duration.
• Performance – Because of water’s high heat capacity it will hold temperature longer than other materials formulate to maintain refrigerated temperatures.
• Performance Indication – Wet ice can help indicate its performance once it has arrived at the destination by its remaining weight. The evidence of remaining wet ice is a clear indication that the product was, in most cases, held at the correct temperature.
• Low Cost – The cost of wet ice is usually not an issue when developing packaging. It is inexpensive to make and often companies design packaging to be used at local hospitals or doctor’s offices where wet ice is considered to be readily available.
• Availability – There are many local distributors of wet ice that will deliver wet ice on a daily or weekly basis. In addition, wet ice makers are simple to set up and can run using electricity and tap water without much hassle. Wet ice is also readily available in hospitals and doctor offices, making it ideal for shipping configurations which originate from these locations.
• Reduced Disposal – Recipients of wet ice shipments are left with only liquid water that must be disposed of. This reduces landfill waste and is a good ecological practice. The plastic bags used to retain the ice can often be recycled or reused.

Disadvantages

• Temperature – Although wet ice has a phase change temperature of 0°C, it is generally stored in a freezer, possibly as low as –20°C, and can freeze product and generate product temperatures below 0°C if taken directly from the freezer and placed into the container. As a possible solution, it can be left at room temperature for a specified period of time to assure it has reached 0°C before packing. Additionally, wet ice offers little protection from colder temperatures and must be buffered in order to keep temperatures above 0°C particularly when shipping in winter conditions.
• Preconditioning – Wet ice can be stored for an unlimited amount of time in a freezer, unlike dry ice, and can be conditioned at any temperature below 0°C as long as you freezer is capable.
• Leakage – The good news is that it is only water; however, it is still not a good idea to have any liquid uncontrolled in the container. Corrugate and chipboard components can become weakened when wet and may not perform correctly. If the liquid escapes the container, it could be denied transport by the carrier, especially if it has any indication of shipping medical supplies or drug substances. It may only be water but they won’t know that.

Gel Ice

Gel ice, or gel packs, is a commonly used refrigerant. There are a variety of gel pack manufacturers in the United States and more worldwide. Many of these manufacturers are listed in ColdChainInfo.com Refrigerants Directory. The most common types of gel packs are made primarily from water and behave similarly to wet ice. However, gel packs come in a variety of forms.  Variations include but are not limited to phase change temperature, latent heat capacity, physical structure, film strength and texture, size, weight and shape. 

Advantages

• Simplicity – Gel ice can be much simpler than dry or wet ice because it is not necessary to weigh the refrigerant for each shipment. Gel is received in individual plastic pouches (generally polyethylene PE) with a specified weight, such as 24 oz or 48 oz, so that a specified number of gels are placed in a shipment instead of a specified weight. It is simple and efficient for packing large numbers of containers, and reduces the possibility of weighing errors.
• Low Cost – Gel packs are generally a low cost refrigerant. Other than wet ice and dry ice, there are few refrigerants that cost less per ounce than most commonly sold water based gel packs. The exception to this may be special phase change gel packs or those that utilize higher grade films that that are stronger or reduce condensation.
• Availability – Gel packs are sold by numerous manufacturers and can be received anywhere in the world. Gel ice is can be produced very quickly using form-and-fill machines. This allows for quick adjustments to an increase in demand.
• Versatility – A well-designed container can utilize combinations of gel packs to hold your product at specific temperature ranges during transit. The availability of a variety of types of gel packs can be advantages in designing effective packing configurations. 
• Safe – The majority of gel pack manufacturers use material in the manufacture of gel packs that are non-toxic and safe to handle or even ingest. Confirm with your preferred manufacturer and obtain an MSDS sheet, if available.

Disadvantages

• Reusability – Gel packs are often cheap to purchase, but expensive to ship. Once received by the end-user, it is often fiscally unwise to ship them back for re-use, even if they arrive in good condition. Occasionally, in closed-loop systems, gel packs may be re-used if inspected first.  
• Staging – Gel packs that are delivered unfrozen on pallets can take anywhere from a few days to several weeks to freeze depending on several factors such as density of the load and freezer capabilities. This has to be taken into account when ordering gel packs. Alternative delivery such as pre-frozen or special pallet configurations can add cost. 
• Leakage – Similar to wet ice, any gel leakage in the container could damage product and essential packing components. Gel packs are particularly subject to leakage in heavier packing configurations leading to the need for tougher films, formulations or the use of alternative designs that may add cost to the pack-out.

Foam Bricks

Foam bricks, also called gel bricks, are a less common refrigerant in the industry compared to gel packs. This is mostly due to the higher relative costs. There are a variety of gel brick manufacturers in the United States and Internationally, see the Supplier Directory on ColdChain.info for a complete listing. Foam bricks are, like gel packs, mostly comprised of water. The name “brick” comes from the shape of the refrigerant which is formed from a foam (or sponge) piece that is impregnated with liquid and enclosed in a plastic (normally polyethylene PE) film.

Advantages

• Simplicity – Gel bricks can be much simpler than dry or wet ice or gel packs to place into a packing configuration. This is because of the consistent shape and rigidity at any temperature. 
• Fit – Because of the aforementioned rigidity and consistency of shape packing configurations can be simplified creating more efficient use of refrigerants, thus possibly reducing material and shipping costs. 
• Leakage – Unlike gel packs, gel bricks do well retaining liquid because most of the liquid within the gel brick is trapped within the foam block. Although some may leak out, most will be retained within the bag.
• Versatility – A well-designed container can utilize combinations of gel bricks to hold your product at specific temperature ranges during transit. Generally there is less versatility of phase temperatures, shapes and sizes than gel packs but there are still a variety of options. 
• Safe – The majority of gel pack manufacturers use material in the manufacture of gel bricks that are non-toxic and safe to handle or even ingest. Confirm with your preferred manufacturer and obtain an MSDS sheet, if available.

Disadvantages

• Cost – The cost per ounce is generally higher than wet ice, dry ice and most gel packs. 
• Availability – Gel bricks have a slower production speed than that of gel packs and there are less manufactures that produce them. Gel bricks are less available making it necessary to plan more effectively and/or inventory more to account for demand fluctuations.
• Contingency Sources – With fewer manufacturers of gel bricks, having multiple suppliers for a specific size and weight gel brick may be difficult. 

There are many refrigerant options when creating a packing configuration for cold chain distribution.  When making those decisions it is important to be as informed as possible about the advantages and disadvantages of each option.  This paper has provided some information that may be valuable to you.  However, it is important to note there are other types of refrigerants and even more information about the refrigerants described in this paper. In this dynamic industry, we will continue to keep you updated with more papers in the future that will expand on this subject.

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