Transportation of vaccines using large quantities of solid carbon dioxide (dry ice) - Civil Aviation Safety Alert (CASA) No. 2020-15


Commercial air services operators

File Classification No.: Z 5000-35
RDIMS No.: 17113410
Document No.: CASA 2020-15
Issue No.: 01
Effective Date: 2020-12-30


This Civil Aviation Safety Alert (CASA) provides information and recommendations to commercial operators concerning safety precautions when transporting vaccines by air, which may require larger-than-normal quantities of solid carbon dioxide (dry ice) for preservation.


International vaccine suppliers are starting to deliver initial shipments of the COVID-19 vaccine to Canada. It is anticipated that the international effort to rapidly distribute vaccines worldwide will lead to an unprecedented demand for this type of cargo. As part of the supply chain for these shipments, Canadian commercial operators may be requested to transport these vaccines at a temperature of -70°C for proper preservation. Transportation methods using dry ice have been developed to meet these temperature requirements. While dry ice is regularly and safely used to transport perishable goods, operators may plan to carry larger-than-normal quantities of dry ice during this vaccination effort. This larger-than-normal volume of dry ice may present risks that existing air operators procedures may not adequately address.

Dry ice continually sublimates (transitions directly from a solid to a gas) at temperatures higher than -78°C under standard atmospheric pressure. At reduced pressures, the sublimation rate of dry ice will increase, all other factors being equal. A potential risk associated with the sublimation of dry ice is the increase in concentration of gaseous carbon dioxide (CO2) which will replace oxygen in aircraft compartments and progressively affect the health of occupants.

Symptoms of mild CO2 exposure may include headaches and drowsiness. At higher concentrations of CO2 gas, rapid breathing, confusion, increased cardiac output, elevated blood pressure, and increased arrhythmias may occur. The seriousness of symptoms is dependent on the concentration of CO2 and the length of time a person is exposed.

Breathing high concentrations of CO2 gas can lead to unrecognized degradation of cognitive functioning and present an asphyxiation hazard. High concentrations of CO2 gas may be anticipated in areas adjacent to cargo with sublimating dry ice, such that it may affect flight crew during flights and ground crew who handle the loading and unloading of cargo. The risk of hazardous concentrations of CO2 gas increases proportionately with the amount of the dry ice carried, the sublimation rate of that dry ice (variable dependent upon ambient temperature and pressure), the exposure time and degradation in the ventilation system of the aircraft.

Additional information regarding dry ice is available in Appendix A of this CASA.

Recommended action:

When preparing to transport cargo containing large amounts of solid carbon dioxide (dry ice), operators should consider the information in this CASA. Additionally, operators with an approved Safety Management System (SMS) must conduct safety risk assessments in accordance with their SMS. Operators without an approved SMS should conduct a risk assessment and apply appropriate risk mitigations. The risk assessment should consider what safety procedures may be necessary in view of the quantities of dry ice carried, flight time, and aircraft manufacturer recommendations.

Transport Canada recommends that air operators consider the following:

  1. Aircraft manufacturers provide information on maximum recommended dry ice quantities that the aircraft ventilation system(s) can accommodate, dependant on that cargo’s dry ice sublimation rate.
  2. An accurate determination of the dry ice sublimation rate is necessary to determine the quantity of dry ice that may be safely transported aboard an aircraft.
  3. As the dry ice sublimates, a loss of weight occurs, affecting the aircraft center of gravity.
  4. Dispatch with fully operational environmental control systems, including all air conditioning packs and auxiliary power units, to enable effective ventilation for ground operations and in-flight contingencies. The same applies to the ventilation systems and related components of unpressurized aircraft.

    Note 1: Running the air-conditioning systems at maximum volume may lead to an additional risk when opening the doors due to potential residual overpressure. The operator should consider this hazard when drafting the operational procedures for the transportation of vaccines.

    Note 2: The operator should consider the case of 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.

    Note 3: The operator should consider the use of ground cart conditioned air in lieu of use of the onboard air conditioning systems while the aeroplane is stationary on the ground.
  5. CO2 detectors installed or carried in the aircraft or worn by the flight crew and other crew members will assist the operator and crew in recognizing hazardous concentrations of CO2 and implementing effective risk controls.
  6. Flight crew member training on specific conditions and procedures can improve decision-making in the event of a CO2 detector alert or other system abnormalities.
  7. Maximum ventilation, including during the ground de-icing and anti-icing process, will mitigate CO2 accumulation in the aircraft.

Reference documents:

  1. Federal Aviation Administration Advisory Circular (FAA AC) No 91-76A Change 1 — Hazard Associated with Sublimation of Solid Carbon Dioxide (Dry Ice) Aboard Aircraft
  2. DOT/FAA/AM-06/19 — Sublimation Rate of Dry Ice Packaged in Commonly Used Quantities by the Air Cargo Industry — August 2006, Office of Aerospace Medicine, Washington, DC 20591
  3. International Air Transport Association (IATA) — Guidance for Vaccine and Pharmaceutical Logistics and Distribution — Edition 2, December 16, 2020
  4. International Civil Aviation Organization (ICAO) — Safe transport of COVID-19 vaccines on commercial aircraft — December 21, 2020

Appendix A Dry Ice and CO2 Gas Information

Dry Ice and Its Hazards:

Dry ice is solid (frozen) carbon dioxide (CO2) pressed into dry blocks or pellets used as a refrigerant to package items that must remain cold or frozen during transport, such as biological samples, vaccines, or foodstuffs.

When dry ice melts, it does not pool on the ground or form a puddle; it sublimates — changes directly from solid to a gas.

Dry ice can be hazardous in poorly ventilated, enclosed spaces due to CO2 inhalation/ overexposure; skin contact with dry ice can result in frostbite.

CO2 Gas and Its Hazards:

CO2 gas is:

  • A naturally occurring component (0.04%) of the atmosphere;
  • A physiological respiratory gas;
  • Colorless, odorless, and nonflammable; and
  • 1.5 times heavier than air and tends to accumulate near the ground.

Increased levels of CO2 cause drowsiness; higher concentrations increase the rate and depth of breathing and heart rate.

CO2 gas in higher concentrations is both an asphyxiant and a toxicant. It causes suffocation by displacing and diluting the amount of oxygen (O2) in the air, leading to hypoxia (lack of oxygen) and is toxic to brain functioning.

Difference Between CO2 Gas Overexposure and Hypoxia:

Symptoms of CO2 overexposure are different from hypoxia symptoms. Flight crew should not rely on typical hypoxia symptoms (e.g. breathlessness, excessive yawning, euphoria, tiredness, and fatigue) to detect CO2 overexposure. Standard hypoxia awareness training IS NOT training for overexposure to CO2 gas.

Symptoms of CO2 Overexposure and Health Effects:

  • 0.04% CO2 (400 ppm): typical outside air CO2 levels; no physiological symptoms.
  • 0.5% CO2 (5,000 ppm): Transport Canada regulatory limit for transport category aircraft (AWM 525.831); subtle to no physiological symptoms.
  • 1% CO2 (10,000 ppm): drowsiness.
  • 2% CO2 (20,000 ppm): headache and difficulty breathing during exertion.
  • 3% CO2 (30,000 ppm): mild sleepiness, reduced hearing, sweating, increased heart rate, difficulty breathing at rest.
  • 5% CO2 (50,000 ppm): lethargy, dizziness, confusion, rapid breathing/shortness of breath (noticeable inability to breathe fast and deep enough).
  • 8% CO2 (80,000 ppm): dimmed vision, muscle tremor/twitching, and unconsciousness.
  • >10% CO2 (100,000 ppm): immediate unconsciousness, seizures, and imminent death.

Effects of Sublimation of Dry Ice on Air Transport:

  • The sublimation rates recommended in FAA AC 91-76A, Hazard Associated with Sublimation of Solid Carbon Dioxide (Dry Ice) Aboard Aircraft, are established under a specific set of conditions. If the operational conditions are not the same, the actual sublimation rate will be different.
  • Decreased pressure, e.g., 8000-foot cabin altitude, will increase the sublimation rate.
  • Reducing cabin pressure will draw CO2 gas from a package(s), increasing the CO2 concentration in the compartment. For this reason, existing smoke/fire/fume procedures should not be used unless they are modified to address this phenomenon.
  • At the end of a flight, compartments containing dry ice will tend to have a high CO2 concentration that can take several minutes to dissipate. When the cargo door is opened, the area immediately outside the door also experiences a high CO2 concentration for several minutes.

Contact office:

For more information concerning this issue, contact a Transport Canada Centre; or contact Nilvio Vezzaro, Manager of Aircraft Design Standards (AARTC/D) in Ottawa, by e-mail at

Original signed by

Félix Meunier
Standards Branch

The Transport Canada Civil Aviation Safety Alert (CASA) is used to convey important safety information and contains recommended action items. The CASA strives to assist the aviation industry's efforts to provide a service with the highest possible degree of safety. The information contained herein is often critical and must be conveyed to the appropriate office in a timely manner. The CASA may be changed or amended should new information become available.