Dry ice is a hot commodity. It is a primary way COVID-19 vaccines will be preserved during transport from the manufacturer to administration sites and for storage in some locations.
But too much of a good thing can be hazardous in a confined space.
On Wednesday, the Federal Aviation Administration cautioned commercial aircraft operators to pay close attention to the risk of carrying too much dry ice in the cargo hold.
“Operators may plan to carry dry ice quantities larger than quantities they may carry during typical operations. This volume of dry ice may present risks that existing mitigations do not adequately address,” the agency said in a safety alert.
The reason for the FAA’s concern is that dry ice is the solid form of carbon dioxide. Increasing the volume of dry ice may present risks that existing mitigations do not adequately address.
Many COVID vaccine shipments kept at ultra-cold temperatures will require more dry ice to maintain safety and efficacy. That is especially true for the product developed by Pfizer (NYSE: PFE) and German partner BioNTech, which must be kept at minus 94 degrees Fahrenheit (minus 70 Celsius). A Food and Drug Administration advisory panel on Thursday recommended the agency grant the Pfizer/BioNTech vaccine emergency use authorization.
A vaccine from Moderna Inc. (NASDQ: MRNA) has temperature requirements of minus 4 F.
By comparison, the typical seasonal flu vaccine is preserved at 35 to 46 degrees F (2 to 8 degrees C) — the temperature range for refrigerators.
Vaccines moving by air are typically packed in large insulated containers with compartments for dry ice, although some types of equipment use battery-powered refrigeration systems instead.
Dry ice breaks down and transitions to a gas at temperatures higher than minus 108 F (minus 78 C) under normal atmospheric conditions. At reduced pressures, like those in an airplane cabin, the sublimation rate of dry ice will increase. The risk is that gaseous CO2 will replace oxygen in the aircraft compartments and interfere with the crew’s ability to breathe. High levels of carbon dioxide can impair cognitive function and lead to asphyxiation, a concern for ground handling crews as well.
The risk of hazardous conditions depends on the amount of dry ice carried, the sublimation rate and the amount of available ventilation.
The FAA recently granted United Airlines (NASDQ: UAL) permission to carry five times the normal amount of dry ice when operating in freighter-only mode, The Wall Street Journal reported. And South Korean regulators eased limits on dry ice, enabling aircraft operators to triple the number of coronavirus vaccine containers they can transport, according to Reuters.
There is one aircraft in the world that can carry unlimited amounts of dry ice. As FreightWaves reported, the Russian-built An-124 super-freighter has a cavernous cargo hold that enables some CO2 to dissipate and a special ventilation system that is separate from the one used in the crew quarters. All-cargo carrier Volga-Dnepr would like to use the planes to support the global vaccination campaign, but one plane was damaged in an accident and the rest of the fleet is grounded while authorities investigate the accident’s cause.
The FAA’s recommendations for mitigating the risk from dry ice include:
- Check with aircraft manufacturers on the maximum recommended dry ice quantities that the aircraft ventilation can accommodate, based on the sublimation rate.
- Accurately determine how quickly the dry ice will break down. That is essential to determine the correct quantity of dry ice that may be safely transported aboard an aircraft.
- As the dry ice sublimates, weight is lost, affecting the aircraft’s center of gravity.
- Make sure all air conditioning packs and auxiliary power units are fully operational to enable effective ventilation for ground operations and inflight contingencies.
- Install CO2 sensors or have crew wear them to detect hazardous concentrations of the gas.