An article for ColdChainInfo.com by package design expert Scott Dyvig
Introduction
Shipping temperature-sensitive products using dry ice can seem deceptively simple. It is not enough to place your product into a cardboard box and cover it with dry ice. In this example you can see a few of the design considerations for dry ice shippers.
Dry Ice Shipper Design Example
A local bakery has decided to sell pies through their web site and wants a packaging system to keep the product frozen until it reaches the customer. They have provided these specifications for the shipper:
- 8” or 10” pies
- Pies are 3” tall and have diameters of 8” or 10”. Weights are 3 or 4 lbs, respectively
- 1 pie per container
- Pie temperature must stay below -20C
- Shipped using UPS or Fed Ex 2-day air
Recommended Configuration
Here is one potential configuration for this example. Let’s review some of the components and features to find out the rationale behind choosing them.
Dry Ice Carton
Why a carton for the dry ice?
This recommended packaging system includes a carton to contain the dry ice pellets during packaging, while in distribution, and for unpacking by the customer. The dry ice carton will reduce packing time for the assembly line (this could be designed to require no taping) as well as prevent direct contact between the dry ice and the product. Perhaps most importantly, customers can easily unpack the container without risk of directly touching the dry ice. Contact between dry ice and exposed skin can cause injury.
When customers first open the insulated container they will see the top of the dry ice carton rather than just loose dry ice. This will give the shipper the opportunity for showing instructions, order information or the shipper’s contents before the customer proceeds with unpacking.
At the end of the shipment, the dry ice will have dissipated into carbon dioxide gas and the solid mass will be reduced. By incorporating the folding carton, the space for the dry ice will remain occupied, which will prevent movement of the product that could cause damage. If the bakery simply placed the pie in the bottom of an EPS container and filled the remaining space with dry ice pellets, by the end of the shipment there will be nothing but a pie loose in a large container, certainly damaging to the pie if the container is handled roughly.
If temperatures are too high during thermal testing, holes can be added to the bottom of the carton to increase cold air distribution to the product. However this will reduce the duration of the dry ice sublimation.
Why pellet dry ice?
Pellets are the most common form of dry ice for shipping and are the default choice unless there is a reason not to use them. Dry ice bricks will last longer due to having less surface area, however they are difficult to order in custom sizes and if they arrive with the wrong weight per block, it takes significant effort to correct for this. Pellets can be purchased cheaply, filled into any size container, and can be adjusted to consistent total amounts. They are easier to handle than the rice dry ice and last longer.
How much dry ice?
The amount of dry ice necessary is based on the duration of the shipment and the ambient profile used in testing. While there are guidelines available on reference web sites, these are only estimates. The quality of the EPS container (wall thickness, density, fit) will affect the amount of dry ice used. The expected temperatures that the container will encounter during the trip (which create the ambient profile used in thermal testing) will also have a large affect. These estimates can be used as a starting point and adjusted based on the criteria of this project. One tip is to overestimate for the first thermal test, then weigh the remaining dry ice to get an idea of how much can be potentially removed.
Corrugate Insert
Why an insert?
Without an insert, the product could be crushed under the weight of the dry ice box. This insert also defines the allowable product space for this shipper and is important when designing a thermal shipper. By keeping each component (refrigerant and product) in the proper location during transit, the thermodynamics and heat flow are more predictable.
What material for the insert?
To keep the cost low, the standard C-flute corrugate can be utilized for the insert. It is critical to orient the corrugate fluting vertical within the container to improve the stacking strength of the insert.
EPS Container
Why EPS?
Expanded polystyrene (EPS) still dominates the industry for insulated containers. It is the most widely-available type of insulated container and will be recognizable by customers. There are many standard, stock containers available from manufacturers and resellers. EPS is also inexpensive compared to other insulating materials on the market.
For this application, a 2” molded EPS container with outer corrugate carton is recommended. This is a common style and is easily sourced within the U.S. The use of 6-panel EPS containers should be avoided unless necessary. For more information, see the ColdChainInfo.com article “Shipping Containers”.
Why 2” thick?
In this example, the contents are fairly heavy and the shipper will want the strength of a 2” thick EPS container to prevent damage. A thicker insulation for the container will also reduce the amount of dry ice required.
Why locking lid?
One of the largest “thermal shorts” (areas of high heat transfer) is between the insulated container tub and lid. A locking lid will help reduce this heat transfer, thus creating a more efficient design and more predictable performance. A non-locking lid may perform well during testing in a thermal chamber, but in real shipping situations it may develop gaps that will allow warm air to enter the container and sublimate the dry ice faster.
Performance Testing
In order for this configuration to become a “solution”, it is important to prove that it works. Here are a few of the factors that should be considered for testing.
Product Loads
In thermal testing, it is important to test the lowest and highest product mass to ensure that the packaging configuration is successful for all applications. In this example, a minimum product load of 1 x 8” pie and a maximum product load of 1 x 10” pie should be tested.
Ambient Profile
In general, cold chain packaging systems should be tested against the warmest and coldest temperatures that it will be likely to experience in order to confirm it will protect the product under all weather conditions. However, for products that do not have a lower temperature limit (i.e. must stay frozen), it is not necessary to test in winter conditions. See the ColdChainInfo.com web site white paper on ambient profiles for more information on how to choose an ambient profile for thermal testing.
Thermocouple Probes
During testing, thermocouple probes are used to measure temperatures. The placement of these probes is critical to ensure that all of the product is protected from extreme temperatures. In this case, the center and edges of the pie should have thermocouple probes to record temperatures.
Preconditioning
The product (pies) and the packaging should be preconditioned at the temperature they will be stored at before packing. The dry ice should be delivered fresh the morning of the testing.
Distribution Testing
For small parcel shipments, the industry recommends that the ISTA 3A testing be used. The packed container should include the maximum amount of dry ice and the product should be the maximum size (10” pie) that will be shipped.
Author
Scott Dyvig has designed more cold chain shipping systems than he can remember. During his tenure as a Lab Manager for ISC Labs, he worked with many of the world’s largest pharmaceutical and biotech companies to develop custom packaging that was innovative, efficient and reliable. He now works as a freelance cold chain packaging designer and can be reached at scott.dyvig@gmail.com.