New European Union Aviation Safety Agency (EASA) guidance issued Thursday on the use of dry ice for preserving Covid vaccines illustrates the dangers of CO2 evaporation—or sublimation—during the handling and transport of the packages aboard aircraft. The recommendations come a week after the FAA issued a Safety Alert for Operators (SAFO) outlining the safety measures ground and flight crew should take when preparing to transport Covid-19 vaccines at temperatures of minus 70 deg C.
As in the FAA alert, the EASA Concept Paper addresses special considerations centering on the sublimation rate of dry ice, or the rate at which the material transitions directly from a solid to a gas, at temperatures higher than minus 78 deg C under normal atmospheric pressure. Risks associated with dry ice sublimation include the possibility of gaseous CO2 replacing oxygen in aircraft compartments and interfering with the ability of occupants to breathe. High levels of CO2 gas can lead to unrecognized loss of cognition and present asphyxiation hazards to ground crew who handle the loading and unloading of cargo containers, for example. The hazards increase with the amount of dry ice carried, its sublimation rate, and any aircraft ventilation deficiencies.
However, the EASA guidance goes far further in its recommendations, explaining, for example, the optimum locations for the dry ice on board and its effects on other cargo such as live animals, which operators may not co-locate in cargo compartments. Specific recommendations include lowering the temperature in the cargo compartment as much as possible to minimize sublimation and to load dry ice as late as possible and unload it as early as possible to minimize exposure to ground crew.
Other information includes the effects of potential departure delays, extended taxi times, and additional time needed on the ground, as well as potential diversion times and the need to use alternate routes when necessary.
The EASA guidance specifically addresses actions needed for ensuring proper ventilation and air conditioning operation. OEM guidance should account for a single next critical failure to enable the continuation of the flight, while the total failure of the ventilation system should require immediate diversion to the nearest alternate airport.
Separately, the EASA document notes that running the air-conditioning systems at maximum volume could lead to additional risk when opening the doors due to potential residual overpressure. The operator should consider the hazard when drafting the operational procedures for the transportation of vaccines, it said. The operator also should consider the case of the build-up of CO2 concentration in the cabin as a possible emergency situation and should develop a procedure to require the donning of oxygen masks for the remaining duration of the flight.
Flight crewmembers need proper training prior to the flight on the hazards of transporting dry ice and operators need to check with their operations manuals to determine whether or not to allow passengers on board, said EASA. If occupants not considered flight crew need to be on board, they must have access to supplemental oxygen equipment ready for use, undergo proper training on the use of the equipment, and training on the various hazards and procedures associated with the transport of dry ice. EASA also recommends the availability of CO2 detectors in the cabin.
The EASA guidance notes that the major aircraft manufacturers have each specified the maximum dry ice allowance for each model of aircraft.