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4Project Background Solid carbon dioxide, or dry ice, is widely used to keep perishable goods cold while in transit. Dry ice does not melt, but sublimes (meaning that it passes directly from the solid to the gaseous state) at a temperature of -78°C (-108°F). This combination of a cold temperature and lack of a liquid product from phase change makes it par- ticularly suitable for temporary refrigeration of goods in transit. Because dry ice produces gaseous carbon dioxide and because exposure to excessive amounts of gaseous carbon dioxide can present a health hazard, it has long been recog- nized that there is a need to specify limits on the amount of dry ice that is present in the passenger and cargo compart- ments of commercial aircraft. Many aircraft operators have established such limits. Several recommendations and advisory circulars have been formulated to establish safe limits for the amount of dry ice that may be used on board aircraft. However, the tests and analyses used to develop these recommendations are in need of updating; some date back to 1963. Although airframe manufacturers may provide some information or guidance on dry ice carriage limits, the ulti- mate responsibility rests with the air carrier. However, there is no requirement that air carriers document the engineer- ing basis for the dry ice limits they use, and in some cases, different air carriers use quite different limits for the same airframe. Thus, there is a concern that these recommendations and limits are based on information that is incomplete or dated, and there is a recognition that the entire topic of dry ice limits for aircraft needs to be reviewed and updated. In order to address this need, the Hazardous Materials Cooperative Research Program authorized HMCRP Project 09, âTechnical Assessment of Dry Ice Limits on Aircraft.â Project Objectives and Scope Objectives The objectives of the project were to develop an under- standing of the parameters affecting the buildup of carbon dioxide on both passenger and cargo aircraft and to develop a tool or tools for operators of passenger and cargo aircraft to use in determining the maximum quantity of dry ice (solid carbon dioxide) that can be safely carried on board passenger aircraft or cargo aircraft. Scope A series of tasks were planned and executed that taken together would enable the overall project objective to be met. The objective of Task 1 was to collect information devel- oped by others either through experience in handling dry ice packages or through documented analyses of carbon dioxide buildup in passenger and cargo-only aircraft. The objective of Task 2 was to identify the parameters affecting buildup of carbon dioxide in passenger and cargo- only aircraft. The parameters were identified by considering the physical and engineering understanding of heat transfer and dry ice behavior, as well as building on the information collected from Task 1. The objective of Task 3 was to develop a topology of dimen- sionless parameters* using the equations governing the trans- fer of heat to the dry ice and subsequent sublimation of carbon dioxide from the packaging and transport through the airplane ventilation system. C h a p t e r 1 Introduction *Dimensionless parameters are combinations of several individual parameters and provide a minimum set of parameters that have to be specified to model the carbon dioxide concentration in the airplane compartments.
5 The objective of Task 4 was to develop a test protocol that would provide data to identify which of the topology of vari- ables must be specified, monitored, and controlled if airplane operators are to predict the buildup of carbon dioxide in pas- senger and cargo-only aircraft. The objective of Task 5 was to collect high-quality, in-flight data on the parameters identified in Task 3. In particular, data were collected by making measurements of CO2 concentrations on flight segments with a known amount of dry ice on board. The objective of Task 6 was to analyze the data collected in Task 5. In particular, the relative importance of various parameters was estimated. The objective of Task 7 was to develop a decision tool that provides simple rules for controlling the important parameters identified in Task 6. The decision tool developed in Task 7 will enable the operator of a passenger or cargo-only airplane to decide when adding additional cargo on a specific type of airplane would result in too much dry ice being on board. The purpose of Task 8 was to meet with stakeholders to present the proposed decision rules and their bases. The pre- sentations made to the stakeholders were intended to dem- onstrate that the proposed decision rules are based on sound science and can be implemented by the airlines. The objective of Task 9 was to revise the decision rules based on the stakeholder input obtained in Task 8. The objective of Task 10 was to summarize the findings from each of the tasks, thereby accomplishing the overall objective of the project.
