U.S. Department 

of Transportation 

Federal Aviation 

Administration

Advisory 

Circular

Subject: Hazard Associated with Sublimation 

of Solid Carbon Dioxide (Dry Ice) Aboard 

Aircraft 

Date: 9/30/2004

Initiated by: AAM-630 

AC No: 91-76 

Change: 

1. What is the purpose of this Advisory Circular (AC)? 

This circular discusses the potential hazard associated with the sublimation of dry ice 

aboard aircraft. Precautionary measures and simple rules of thumb are indicated in 

order to preclude environmentally hazardous conditions affecting crews and passengers

aboard aircraft. 

2. Does this AC supersede any existing ACs? 

This AC replaces AC 103-4, hazard associated with sublimation of solid carbon dioxide 

(dry ice) aboard aircraft, dated 5/01/74. 

3. What do some of these words mean?

a. Dry Ice: Solidified carbon dioxide (CO2 ) with a melting point of -78.5°

C (-109.3°F). 

b. Carbon dioxide: A colorless odorless gas that is a natural product of animal 

respiration and other energy releasing processes. 

c. Sublimation: The process of converting a solid substance (dry ice, solid CO2) into 

a gas (CO2 gas). 

4. Why is an AC about the transportation of dry ice aboard aircraft important? 

Dry ice sublimates to gaseous CO2 at aircraft environment temperatures. Excessive 

CO2 in the aircraft can cause aircrew incapacitation. Dry ice is generally carried aboard 

aircraft to keep food (galley or cargo), medicine, or biological materials in a frozen or 

chilled condition. The quantity of dry ice used on the aircraft may vary depending on the 

amount of material that must be maintained in a frozen/chilled condition, the shipment 

time, the insulative nature of the packaging, the desired temperature of the shipment, 

and other characteristics. Dry ice is a hazardous material under Title 49 of the Code of 

Federal Regulations (CFR). Additionally, gaseous CO2 that can result from sublimation 

of dry ice and other sources is regulated under 14 CFR. Dry ice sublimation producing 

excess CO2 gas may be dangerous in confined spaces where there is an absence of 

ventilation or ventilation rates are low. The conversion rate of dry ice to gaseous CO2 
AC 91-76 

will vary depending on package insulation, dry ice particle size, surrounding 

temperature, and cabin pressure. 

Tests conducted by Pan American Airlines in 1963 indicated that a sublimation rate of 

one pound per hundred pounds of dry ice per hour (1%/hour) can be expected for 

packages containing large amounts of dry ice, i.e., packages containing 100 lbs. of dry 

ice. More recent tests conducted by the Federal Aviation Administration demonstrated 

that the sublimation rate for small insulated shipping packages containing 4.6 to 5.3 lbs. 

of dry ice averaged 2%/hour. 

There have been very few reported incidents of carbon dioxide hazards aboard aircraft 

resulting from sublimation of dry ice. In the incidents that have been reported, the 

aircrew recognized symptoms that they considered to be related to potential air 

contamination and took appropriate procedures to avoid any serious problems. 

Modern aircraft reprocess or recirculate a portion of their cabin air. Even though the 

recirculated air passes through filters, these filters do not remove very small molecules 

such as CO2. Even with recycled air, a properly functioning modern aircraft 

environmental control system provides fresh air for a substantial number of complete 

cabin air exchanges per hour, making buildup of carbon dioxide in the cabin an unlikely 

event. If aircraft ventilation is not effective, a buildup of CO2 could occur. 

5. What are the physiological effects of carbon dioxide? 

CO2 is categorized by the National Institute for Occupational Safety and Health (NIOSH) 

as a simple asphyxiant with symptoms resulting only when such high concentrations are 

reached that the gas affects the brain and other physiologic functions. The signs and 

symptoms of CO2 poisoning are similar to those that precede lack of oxygen, namely 

headache, dizziness, muscular weakness, drowsiness, and ringing in the ears. CO2

poisoning does have a greater effect on breathing than simple lack of oxygen, causing a 

significant increase in the rate and depth of breathing as an early symptom. Removal 

from exposure results in rapid recovery. 

Exposures to CO2 in aircraft should not exceed a sea level equivalent to 0.5% CO2

(5,000 parts of CO2 per million parts of air or 5,000 ppm). 5,000 ppm is also used by 

the Department of Labor, Occupational Safety and Health Administration (OSHA) as an

8-hour Time Weighted Average Permissible Exposure Limit (PEL) in general industries. 

Production of symptoms is related to the effect of increased CO2 on certain bodily 

processes. No symptoms occur from inhalation of CO2 if the atmosphere contains only 

slightly more than normal amounts of CO2. When the concentration of CO2 approaches 

2%, the depth of respiration is increased so that the amount of air into the lungs with 

each breath increases up to 30%. If the concentration of CO2 is as high as 4%, there is 

not only an increase in the depth of respiration but also an increase in the rate of 

respiration. At this point, breathing is deeper and somewhat faster and considerable 

discomfort is produced. A CO2 concentration of 4.5-5% causes breathing to become 

extremely labored and almost unbearable in some individuals. The highest 

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AC 91-76 

concentration of CO2 that can be tolerated is 7% to 9%. More than 10% can cause loss 

of muscle control and unconsciousness. 

6. What are the hazards associated with dry ice? 

The hazard associated with the carriage of dry ice aboard all aircraft is considered 

minimal under normal cabin ventilation conditions. However, in the absence of proper 

ventilation, the sublimation of dry ice could result in unacceptable levels of CO2 in the 

cabin environment that could produce the symptoms described in paragraph 5. 

7. What are the precautions and recommendations for the transportation of dry

ice aboard aircraft? 

Maintaining adequate input and circulation of fresh air is the single most important 

precaution that must be taken when dry ice is transported. Additionally, the aircrew 

should be aware of the hazards involved in the transport of dry ice and be prepared to 

take appropriate emergency procedures. Emergency procedures should include 

instructions that if symptoms occur or if a buildup of CO2 is suspected, the use of 

emergency oxygen should be considered. When dry ice is stored aboard aircraft, if the 

normal ventilation system is not functioning, auxiliary cabin ventilation is needed before 

takeoff. This will avoid the buildup of CO2 concentration prior to boarding. In the 

absence of ventilation, it would take a small amount of dry ice to produce an 

unacceptable level of CO2 in an aircraft. 

Estimations of the amount of dry ice that can be transported relative to the volume of 

fresh air circulation in the aircraft can be calculated as follows. 

The dry ice sublimation rate will depend on the amount of dry ice stored in a package, 

the packaging of dry ice, and numerous other variables. The experimentally determined 

sublimation rate for large (100 lbs.) amounts of dry ice per single package is 1%/hour. 

The experimentally determined rate for small (5 lbs.) amounts of dry ice per single 

package is 2%/hr. One lb. of dry ice sublimates to 8.5 cubic feet of CO2 gas. Thus, a 

sublimation rate can be defined as X ft3

 CO2 gas per hour. A dry ice sublimation rate of 

1% per hour provides 8.5 ft3

 CO2 gas per 100 lbs. dry ice per hour. A 2% per hour 

sublimation rate provides 17 ft3

 CO2 gas per 100 lbs (20 x 5 lb packages) of dry ice per 

hour. 

NOTE: If the packages in a given load contain less than 100 lbs. of dry ice, it is 

recommended that shippers use the 2%/hour sublimation rate or conduct evaluations to 

determine the sublimation rates for variable-weight dry ice packages. 

The following formula provides a rule-of-thumb for dry ice loading relative to the volume 

of air circulation. Examples include calculations using a 1%/hour sublimation rate and a 

2%/hour rate. 

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AC 91-76 

X = Dry ice loading in lb 

 (CO2 concentration) (Aircraft Volume, ft3

) (Complete air exchanges per hour*) 

X = ------------------------------------------------------------------------------------------------------------- 

 (sublimation rate) 

Example 1a: 

Aircraft volume: 5000 ft3

Complete air exchanges per hour: 10 

Allowable CO2 concentration (TLV, 0.5%): 0.005 

Sublimation rate of 1%/hour (8.5 ft3

 CO2/100 lb dry ice/hour): 0.085 

 (0.005) (5000) (10) 

X = --------------------------------- = 2941 lbs. of dry ice 

 (0.085) 

Example 1b: 

Conditions same as example 1 except that the complete air exchange has doubled. 

Complete air exchanges per hour: 20 

 (0.005) (5000) (20) 

X = --------------------------------- = 5882 lbs. of dry ice 

 (0.085) 

Example 2: Applies when the shipment consists of small (5 lb) packages of dry ice. 

Aircraft volume: 5000 ft3

Complete air exchanges per hour: 20 

Allowable CO2 concentration (TLV, 0.5%): 0.005 

Sublimation rate of 2%/hour ((2 x 8.5 ft3

 CO2)/100 lbs. dry ice/hour): 0.17 

 (0.005) (5000) (20) 

X = --------------------------------- = 2941 lbs. of dry ice 

 (0.17) 

* Since newer models of airplanes recycle as much as 50% of the cabin 

ventilated air, instead of providing 100% fresh air as older models did, the 

number of complete cabin air exchanges of fresh air is required to determine 

the amounts of dry ice that can be transported. 

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AC 91-76 

REFERENCES

Pan American Maintenance Engineering Report #ME 124, Feb. 6, 1963, Air Conditions, 

Dry Ice Quantity Limitations, DC-7CF Flight Test. 

Dangerous Properties of Industrial Materials, 1957, N. Irving Sax. 

Textbook of Toxicology, 1959, DuBois and Ceiling. 

Industrial Hygiene and Toxicology, Vol. II, 1963, Frank A Patty. 

Goodman and Gilman’s Pharmacological Basis of Therapeutics, 10th Ed, 2002, Joel 

Hardman and Lee Limbird 

Gibbons HL. Carbon Dioxide Hazards in General Aviation. Aviat. Space Environ. Med., 

48, 261 (1977) 

Martin-Saint-Laurent A, Lavernhe J, Casano G, Simkoff A. Clinical Aspects of Inflight 

Incapacitations in Commercial Aviation. Aviat. Space Environ. Med., 61, 256 (1990) 

Carbon Dioxide Fact Book. Htpp://www.airspill.com/co2report.html (accessed Oct 2002) 

Jon L. Jordan, M.D. 

Federal Air Surgeon 

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