United States Department of Transportation
i
The Sublimation Rate of Dry Ice Packaged in Commonly Used Quantities by the Air Cargo Industry
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2006-08-01
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[PDF-291.00 KB]
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Abstract:Dry ice is used as a refrigerant for the shipment of perishable goods in the aviation industry. The sublimation of dry ice can, however, lead to incapacitating levels of carbon dioxide in the aircraft cabin environment, as exemplified by the National Transportation Safety Board's (NTSB's) probable cause determination in a 1998 Brownsville, Texas, incapacitation incident. This incident prompted the NTSB to request that the Federal Aviation Administration (FAA) revisit the dry ice sublimation rate published in FAA Advisory Circular AC 103-4. The sublimation rate used in AC 103-4 to calculate permissible dry ice loads was based on a study conducted by Pan American Airlines where a single, large piece of dry ice (100 lb block) was used. Today, the majority of dry ice shipments contain smaller amounts of dry ice obtained in pellet form (< 5 lb). This study focuses on the sublimation rate of dry ice packed in such commonly encountered amounts. In this study, approximately 5 lb of dry ice, in pellet form, was added to each of 20 pre-weighed TheromoSafe® shipping containers. The boxes were then weighed to obtain “preflight” weights and placed in an altitude chamber located at the FAA's Civil Aerospace Medical Institute. The chamber was depressurized to an altitude of 8000 ft at a rate of 1000 ft/min. The total “flight” time was 6 h. The containers were then removed and immediately weighed to obtain “post-flight” measurements. Using the differences in weight as well as the total flight time, an average sublimation rate of 2.0 +/- 0.3%/h was determined. Results indicate that the sublimation rate is greater when dry ice is packaged in pellet form in small quantities. These results contrast the Pan American Airlines study that employed one solid 100-lb block of dry ice. The current study improves air cargo safety by providing a sublimation rate for dry ice shipped in small, more representative quantities. The updated sublimation rate can be used to calculate safe dry ice loads for containers commonly used today.
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