Thermal blankets for cold chain shipping: an effective control, but watch out for surface-color effects

The use of a thermal blanket—a fitted sheet that can be wrapped around a pallet of goods—is increasingly common in pharma distribution, especially for international air cargo, and most especially for CRT (controlled room temperature) products that don’t require refrigeration. Increasingly, national regulators are looking for documentation not just that refrigerated products were kept in their designated temperature range, but also that CRT products have, indeed, been protected from extremes of hot or cold.

Test data on thermal blankets were the subject of a trio of presentations at the recent PDA Cold Chain Conference (Bethesda, MD; Nov. 15-16). Karl Kussow, quality and validation manager at FedEx Custom Critical (Uniontown, OH) presented data on both use of tailored blankets (from AmSafe Inc., an aerospace equipment provider in Phoenix), demonstrating that the blankets kept tarmac-positioned pallets in Boston in January (outside temperature 0°C) between 11 and 17°C, an in Mumbai and Dubai in summer (outside temperatures 30 and 38°C) between 21 and 25°C. (Cargo is frequently staged on a runway tarmac for several hours preparatory to loading an airfreighter.)

Through FedEx Healthcare Solutions, the business unit by which Custom Critical markets its pharma services, FedEx can offer door-to-door temperature-controlled shipping (including ground assets) that is “very reliable and cost-effective,” says Kussow. The company is also promoting its growing fleet of Boeing 777F cargo planes, which feature cockpit-controlled heating and cooling in cargo bays.

Solar radiation: the bad actor

Complementary presentations by Jean-Pierre Emond, director of cold chain research at the Georgia Tech Research Institute (Atlanta) and Mike English, associate director, packaging technology at Merck, highlighted the need for tighter specifications in thermal blanketing practices. Emond’s tests showed that the blanketing materials vary widely in their performance; the best he tested were blankets employing Tyvek membranes (a DuPont brand). Solar radiation is a key environmental factor; with the wrong cover (one that doesn’t reflect radiation well) temperatures above ambient conditions can be experienced (in effect, the pallet cover is collecting and concentrating heat, rather than protecting against it).

At Merck, testing showed that the worst possible setup is brown-cardboard cartons (which absorb both heat and humidity) combined with polyethylene wrapping (a common shipping protection) while leaving some headspace below the cover: the result is heating from solar radiation and a greenhouse effect under the polyethylene. Merck’s testing suggests that simply using white rather than brown cartons can provide protection roughly equivalent to a metalized bubble sheeting (which implies that the sheeting can be dispensed with, at least in some shipping scenarios). “Air freight will be exposed to extreme conditions,” English stresses, recommending shippers to study both their products’ temperature sensitivity, and conditions along a trade lane, including stopover points, to ensure safety.