Sublimation Rate of 

Dry Ice Packaged 

in Commonly Used 

Quantities by the Air 

Cargo Industry

Douglas C. Caldwell

Russell J. Lewis

Robert M. Shaffstall

Robert D. Johnson

Civil Aerospace Medical Institute

Federal Aviation Administration

Oklahoma City, OK 73125

August 2006

Final Report

DOT/FAA/AM-06/19

Office of Aerospace Medicine

Washington, DC 20591
NOTICE

This document is disseminated under the sponsorship 

of the U.S. Department of Transportation in the interest 

of information exchange. The United States Government 

assumes no liability for the contents thereof.

___________

This publication and all Office of Aerospace Medicine technical reports are 

available in full-text from the Civil Aerospace Medical Institute’s publications 

Web site: 

www.faa.gov/library/reports/medical/oamtechreports/index.cfm
i

Technical Report Documentation Page 

1. Report No. 2. Government Accession No. 3. Recipient's Catalog No. 

DOT/FAA/AM-06/19 4. Title and Subtitle 5. Report Date 

August 2006 

6. Performing Organization Code 

The Sublimation Rate of Dry Ice Packaged in Commonly Used Quantities 

by the Air Cargo Industry 

 7. Author(s) 8. Performing Organization Report No. 

Caldwell DC, Lewis RJ, Shaffstall RM, Johnson RD 

9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) 

11. Contract or Grant No. 

FAA Civil Aerospace Medical Institute 

P.O. Box 25082 

Oklahoma City, OK 73125 

12. Sponsoring Agency Name and Address 13. Type of Report and Period Covered 

Office of Aerospace Medicine 

Federal Aviation Administration 

800 Independence Ave., S.W. 

Washington, DC 20591 14. Sponsoring Agency Code 

15. Supplemental Notes 

This work was accomplished under the approved task AM-B-05-TOX-204. 16. Abstract 

Dry ice is used as a refrigerant for the shipment of perishable goods in the aviation industry. The sublimation 

of dry ice can, however, lead to incapacitating levels of carbon dioxide in the aircraft cabin environment, as 

exemplified by the National Transportation Safety Board’s (NTSB’s) probable cause determination in a 1998 

Brownsville, Texas, incapacitation incident. This incident prompted the NTSB to request that the Federal 

Aviation Administration (FAA) revisit the dry ice sublimation rate published in FAA Advisory Circular AC 

103-4. The sublimation rate used in AC 103-4 to calculate permissible dry ice loads was based on a study 

conducted by Pan American Airlines where a single, large piece of dry ice (100 lb block) was used. Today, the 

majority of dry ice shipments contain smaller amounts of dry ice obtained in pellet form (•5 lb). This study 

focuses on the sublimation rate of dry ice packed in such commonly encountered amounts. In this study,

approximately 5 lb of dry ice, in pellet form, was added to each of 20 pre-weighed TheromoSafe®

shipping

containers. The boxes were then weighed to obtain “preflight” weights and placed in an altitude chamber 

located at the FAA’s Civil Aerospace Medical Institute. The chamber was depressurized to an altitude of 8000 

ft at a rate of 1000 ft/min. The total “flight” time was 6 h. The containers were then removed and 

immediately weighed to obtain “post-flight” measurements. Using the differences in weight as well as the total 

flight time, an average sublimation rate of 2.0 +/- 0.3%/h was determined. Results indicate that the 

sublimation rate is greater when dry ice is packaged in pellet form in small quantities. These results contrast 

the Pan American Airlines study that employed one solid 100-lb block of dry ice. The current study improves 

air cargo safety by providing a sublimation rate for dry ice shipped in small, more representative quantities. 

The updated sublimation rate can be used to calculate safe dry ice loads for containers commonly used today. 

17. Key Words 18. Distribution Statement 

Carbon Dioxide, Sublimation, Dry Ice, Aircraft Accident 

Investigation

Document is available to the public through the 

Defense Technical Information Center, Ft. Belvior, 

VA 22060; and the National Technical Information 

Service, Springfield, VA 22161

19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price 

Unclassified Unclassified 8 

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized 

1

The Sublimation Rate of Dry Ice Packaged in Commonly Used

Quantities by the Air Cargo Industry

Introduction

The air cargo industry has seen a dramatic increase in 

the number of packages containing solid carbon dioxide 

or “dry ice” over the past 30 years. The FedEx® Dangerous 

Goods Administration Office reported that 50% of its 

workload, approximately 15,000 packages per day, contain 

dry ice.1 The large volume appears to be predominantly 

due to the increased diversity of items shipped with dry 

ice. The Air Canada Web site lists fresh fish and meat as 

well as organs for transplant, human blood, drugs, and 

serums as some of the items they ship that contain dry 

ice for temperature control.2 In recent years, the largest 

single area of increase is in the bio-medical industry, which 

requires overnight delivery of frozen specimens, reagents, 

and supplies all over the world.1 The market for fresh 

foods has also expanded from predominantly seafood to 

include companies selling freshly prepared frozen foods 

over the Internet for at-home, overnight delivery.3 The 

quantity of dry ice used aboard an aircraft varies depending on the amount of material that must be maintained 

in a frozen/chilled condition, the shipment time, the 

insulative nature of the packaging, and the desired temperature of the shipment. FedEx® reported that the vast 

majority of their dry ice shipments contain less than 5 

lb of dry ice.1 The small size (<5 lb) of these packages 

allows them to avoid the special handling requirements 

instituted by Title 49 of the Code of Federal Regulations 

(CFR) and subsequent surcharges imposed by air cargo 

shippers such as FedEx®.

1, 4, 5

Dry ice is designated as a miscellaneous hazardous 

material because it sublimates to gaseous carbon dioxide 

(CO2) at aircraft environment temperatures, and high 

concentrations of CO2 in the aircraft can cause aircrew 

incapacitation.5, 6, 8 Dry ice is listed as a miscellaneous 

hazardous material under 49 CFR, and gaseous CO2

resulting from the sublimation of dry ice and other 

possible sources is regulated under 14 CFR. Dry ice 

sublimation may be dangerous in confined spaces where 

there is an absence of ventilation or low ventilation rates. 

The conversion of dry ice to gaseous CO2 varies depending on package insulation, dry ice particle size, ambient 

temperature, and cabin pressure. 

Carbon dioxide is categorized by the National Institute 

for Occupational Safety and Health as a simple asphyxiate 

with symptoms resulting only when such high concentrations are reached that the gas affects the brain and other 

physiologic functions.9 The signs and symptoms of CO2

poisoning are similar to those of oxygen deprivation, 

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

 poisoning has a greater 

effect on breathing than a simple lack of oxygen. An early 

symptom of CO2 poisoning is a significant increase in the 

rate and depth of breathing. Removal from exposure results 

in rapid recovery. Exposures to CO2 in aircraft should not 

exceed a sea level equivalent of 0.5% CO2 (5000 parts of 

CO2 per million parts of air - 5000 ppm). Five-thousand 

ppm is also used by the United States Department of 

Labor, Occupational Safety and Health Administration 

as an 8-h time-weighted average Permissible Exposure 

Limit in general industry.10 Increased CO2 concentrations 

negatively affect the human respiratory system. Few, if 

any, noticeable effects are produced when CO2 levels are 

only slightly above normal. However, significant effects 

begin to occur with increasing concentrations of CO2, 

as can be seen in Table 1. 

High concentrations of CO2 have the potential to 

cause in-flight incapacitation, which is defined as “any 

state that affects a pilots’ health during the performance 

of their duties, preventing them from performing normal 

operations and coping with emergency situations.”11 Two 

recent incidents show the gravity of such incapacitation 

and why data on the sublimation of dry ice in small 

packages has become increasingly important. One of 

these incidents occurred on April 29, 1998. “At approximately 2100 CDT, a Douglas DC-8-51 cargo airplane 

was taxiing for takeoff at Brownsville/South Padre Island 

International Airport when all four crewmembers became 

short of breath. They acted appropriately by donning 

oxygen masks and the pilot taxied back to the ramp. The 

crewmembers were later treated and released from a local 

hospital. The NTSB determined that this near accident 

was caused by a buildup of gaseous CO2 in the cockpit, 

with the CO2 originating from the cargo hold, where numerous containers with dry ice were present.”12 Although 

no one was injured, the presence of CO2 in the cabin at 

higher than normal concentrations caused a significant 
2

distraction for the flight crew, forcing them to respond 

to their increased rate of respiration. Stimulation of the 

respiratory center and subsequent rapid breathing caused 

by an increased concentration of CO2 posed the threat of 

incapacitation to this crew. This threat was averted by the 

proper use of supplemental oxygen. It must be pointed 

out, however, that the normal aircraft ventilation systems 

were not functioning, and prior to departure, auxiliary 

cabin ventilation was not used.

A second incident involving CO2 occurred in an 

Air France transport aircraft. In this incident, the crew 

was preparing for takeoff. “The flight was loaded with 

perishable goods preserved using dry ice. The plane was 

loaded and sealed for 40 min before engine start-up. The 

ventilation system in this type of aircraft does not operate 

without the engines running, and auxiliary ventilation 

was not being used at the time. Headaches and rapid 

breathing occurred among all crewmembers due to the 

increased concentration of CO2. The prompt use of oxygen 

masks by the crew relieved all respiratory symptoms, and 

starting the engines resulted in proper ventilation, which 

dissipated the high CO2 concentrations.”11

In 1963, Pan American Airlines designed an experiment utilizing 100 lb blocks of dry ice to determine the 

sublimation rate of CO2 and subsequently evaluate the 

performance of the air conditioning units they used in 

their cargo aircraft.13 Based on this study, a recommended 

CO2 sublimation rate of 1%/h was established in FAA 

Advisory Circular AC103-4. In 1977, H. L. Gibbons 

et al.14 measured the sublimation rate of 1 lb and 5 lb 

blocks of dry ice that were wrapped in paper and placed 

in the cockpit of a Cessna 150 that remained on the 

ground for the duration of the experiment at an ambient temperature of 72°F. This study found that under 

these specific conditions the sublimation rate for dry ice 

was 14%/h. In actual practice, the shipment of dry ice 

must comply with the provisions of 49 CFR 173.217, 

which specifies that the shipment must be appropriately 

packaged. Paper wrappings would not generally be used 

to ship a perishable item frozen in dry ice. Therefore, 

experimentation was needed to determine CO2 sublimation rates utilizing commonly used shipping containers, 

conditions, and practices. 

Experimental Evaluation

This experiment was designed to determine the 

sublimation rate of dry ice during operational conditions most commonly encountered by flight crews in 

present-day transport aircraft. Twenty TheromoSafe®

model 318 shipping boxes (8x6x4.25 in inside dimensions, 11x9x7.25 in outside dimensions, with 1.5 in-thick 

Styrofoam walls) were obtained from Polyfoam Packers 

Inc. (Waukegan, IL). The boxes were numbered and 

then weighed using an Ohause (Pine Brook, NJ) Precision Plus electronic balance. Dry ice was acquired at a 

local Air Liquide (Oklahoma City, OK) outlet in the 

form of pellets. The pellets were uniform in size with 

dimensions of approximately 1 x 2 cm. Approximately 

5 lb of dry ice was added to each container. Any remaining headspace was filled with common carpet padding, 

as recommended by a dry ice shipping Web site.15 The 

size and shape of the dry ice mirrored a style commonly 

utilized by the air cargo industry. Following the addition 

of dry ice to each individual shipping container and the 

filling of extraneous headspace, the boxes were immediately taped shut. Each container was then weighed to 

determine an initial “pre-flight” weight. The boxes were 

stacked in 4 columns, each column containing 5 boxes, 

on a cart approximately 3 ft above the floor and placed 

in an Environmental Techtronics (Southampton, PA) 

altitude chamber at the FAA’s Civil Aerospace Medical 

Institute. The initial temperature inside the chamber 

was 72°F. The chamber was depressurized to an altitude 

of approximately 8000 ft at a rate of 1000 ft/min. This 

Table 1. Physiological effects of CO2 at Various Concentrations.7

CO2 concentration (%) Physiological effect 

0.3 Normal Respiration 

0.5 Slight increase in respiration 

2 Respiration increased 50% 

3 Respiration increased 100% 

5 Respiration increased 300% 

12-15 Unconsciousness 
3

depressurization process took 7.2 min, at which time the 

final altitude had been reached. An altitude of 8000 ft was 

maintained for 5.75 h, at which time the decent began 

and the chamber was pressurized back to ground level at 

a rate of 1000 ft/min, resulting in a total “flight” time of 

6 h. The final temperature of the chamber was 84°F. The 

containers were then removed and immediately weighed 

to obtain a “post-flight” weight. The total time between 

the two weight measurements was 6.25 h.

Results and Discussion

The average sublimation rate of dry ice packaged in 

5 lb quantities was determined to be 2.0±0.3 %/h with 

a range of 1.59 to 2.88%/h. Individual data for each 

shipping container are shown in Table 2. The sublimation rate of solid CO2

 determined in this experiment is 

substantially lower than the 14%/h produced by Gibbons 

et al.14 in 1977, but is double the 1%/h rate determined in 

196313 and used until recently to establish dry ice shipping 

regulations. It is clear that the sublimation rate of dry ice 

depends on the particle size, the shipping container, and 

how the shipping containers are packaged; thus, recommendations regarding dry ice load and aircraft ventilation 

requirements should be based on commonly used shipping 

containers and dry ice characteristics. While the two early 

sublimation studies do not reflect “real world” shipping 

practices, the current study incorporates commonly used 

shipping industry boxes, dry ice amounts, and dry ice 

pellets. Thus, our results should closely reflect what is 

experienced during air cargo transportation of dry-ice 

refrigerated goods.

The complete sublimation of 1 lb of dry ice results 

in 8.8 ft3 of CO2 gas.6 Therefore, a sublimation rate can 

be defined as X ft3 CO2 gas per h. A dry ice sublimation 

rate of 1%/h produces 8.8 ft3 CO2 gas per 100 lb (20 x 

5 lb packages) of dry ice per h. A 2%/h sublimation rate 

produces 17.6 ft3 CO2 gas per 100 lb (20 x 5 lb packages) 

of dry ice per h. The following formula provides a ruleof-thumb for dry ice loading relative to the volume of 

aircraft air circulation. Examples, including calculations 

using a 1%/h sublimation rate and a 2%/h sublimation 

rate, are shown below.

X = Dry ice weight in lb

(CO2 concentration) (Aircraft Volume, ft3) (Complete air exchanges per h*)

*Since newer aircraft models recycle as much as 50% of cabin air, 

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

of complete cabin air exchanges is required to determine the amounts 

of dry ice that can be safely transported.

X =

(Sublimation rate)

(0.005) (5000) (10)

(0.088)

(0.005) (5000) (20)

(0.088)

Example 1a: A shipment that consists of one large 

block (100 lb) of dry ice.

Aircraft volume: 5000 ft3

Complete air exchanges per h: 10

Allowable CO2 concentration (TLV, 0.5%): 0.005

Sublimation rate of 1%/h (8.8 ft3 CO2/100 lb dry ice/h): 0.088

X = = 2841 lb of dry ice

Example 1b: Conditions are the same as example 1a 

except that the number of complete air exchanges has 

doubled.

Complete air exchanges per h: 20

X = = 5682 lb of dry ice

 

Example 2: A shipment that consists of 20 small (5 

lb) packages of dry ice.

Aircraft volume: 5000 ft3

Complete air exchanges per h: 20

Allowable CO2 concentration (TLV, 0.5%): 0.005

Sublimation rate of 2%/h ((2 x 8.8 ft3 CO2)/100 lb dry ice/h): 

0.17

X = = 2841 lb of dry ice (0.176)

These examples demonstrate the need for a more 

representative CO2 sublimation rate for today’s air cargo 

industry. Following the guidelines that were established in 

1963, the aircraft used in example 1b could have carried 

5882 lb of dry ice in the cargo hold without fear of cabin 

air contamination from elevated CO2 levels. However, 

when dry ice is utilized as pellets in small quantities 

instead of large blocks the sublimation rate increases by 

a factor of two. This means that under the same conditions as example 1b, this aircraft should only safely carry 

2941 lb of dry ice, half the amount. It becomes obvious 

that two variables must be known before the amount of 

dry ice that may safely be carried on an aircraft can be 

calculated. These variables are the aircraft volume, and 

the number of complete air exchanges per h. If one of 

these variables is unknown, a reliable calculation cannot 

be made. However, if these variables are known, dry ice 

loads can safely be calculated using the “realistic” sublimation rate of 2%/h.

(0.005) (5000) (20)
4

Table 2. CO2 sublimation rate for 20 insulated shipping containers filled with 

approximately 5 lb of dry ice pellets.

Sublimation Rate of Small Dry Ice Pellets in 5-lb Quantities 

Box # 

Box 

weight 

empty 

Initial wt. 

box and 

ice

Final wt. 

box and 

ice

Wt. initial 

ice

Wt. final 

ice

Total ice 

loss

Sublimation 

rate (%/h) 

1 1.448 6.360 5.823 4.912 4.375 0.537 1.75 

2 1.383 6.322 5.738 4.939 4.355 0.584 1.89 

3 1.367 6.313 5.782 4.946 4.415 0.531 1.72 

4 1.391 6.154 5.561 4.763 4.170 0.593 1.99 

5 1.431 6.682 6.148 5.251 4.717 0.534 1.63 

6 1.383 6.263 5.669 4.880 4.286 0.594 1.95 

7 1.397 6.614 5.840 5.217 4.443 0.774 2.37 

8 1.418 6.085 5.488 4.667 4.070 0.597 2.05 

9 1.396 6.122 5.575 4.726 4.179 0.547 1.85 

10 1.404 6.293 5.755 4.889 4.351 0.538 1.76 

11 1.500 6.029 5.412 4.529 3.912 0.617 2.18 

12 1.380 6.042 5.399 4.662 4.019 0.643 2.21 

13 1.399 6.632 5.689 5.233 4.290 0.943 2.88 

14 1.407 6.651 6.130 5.244 4.723 0.521 1.59 

15 1.405 6.402 5.813 4.997 4.408 0.589 1.89 

16 1.406 6.298 5.641 4.892 4.235 0.657 2.15 

17 1.387 6.204 5.654 4.817 4.267 0.550 1.83 

18 1.431 6.503 5.792 5.072 4.361 0.711 2.24 

19 1.401 6.503 5.963 5.102 4.562 0.540 1.69 

20 1.393 6.693 5.905 5.300 4.512 0.788 2.38 

All weights in lb. Average 2.00 

Time between weighings was 6.25 h. s.d. 0.32 

Chamber temp at T=0 was 72°F, at T=6h was 84°F C.V. 15.82 
5

Conclusions

There have been very few reported incidents involving 

carbon dioxide incapacitation aboard aircraft resulting 

from the sublimation of dry ice. In the incidents that 

have been reported, the aircrew recognized symptoms 

of air contamination and took appropriate precautions 

to avoid any serious consequences. The incidents that 

have occurred demonstrate that maintaining adequate 

input and proper circulation of fresh air into the cabin 

environment is the single most important precaution 

that can be taken when dry ice is transported.16 In the 

absence of adequate ventilation, a small amount of dry 

ice can produce unacceptable levels of CO2 in an aircraft. 

The current research found that the amount of dry ice 

used in a shipment of perishables is generally less than 5 

lb per container and that this amount of dry ice, packaged in an appropriate manner, sublimes at a rate of 

2%/h. Based on these findings, revisions in ventilation 

requirements were incorporated into the FAA Advisory 

Circular 91-76.

In addition to ventilation considerations, aircrew 

should be aware of the hazards involved with the transportation of dry ice and should be prepared to take appropriate emergency precautions if CO2

 levels increase 

in the cabin. The first emergency precaution would be 

the use of supplemental oxygen supplies. This should be 

followed by attempts to ventilate the cabin to outside 

air. If dry ice is stored aboard aircraft, and the normal 

ventilation system is not functioning, auxiliary cabin 

ventilation is necessary before takeoff.

References

1. FedEx®. Dangerous Goods Administration Office. 1-800-463-3339. personal conversation. 

(08/2003). 

2. Air Canada. www.aircanada.com/cargo/products/

perishables.html (04/2006).

3. Omaha Steaks. www.omahasteaks.com 

(04/2006).

4. Fed Ex®. www.fedex.com/us/services/options/express/dangerousgoods/fees.html#1 (04/2006).

5. U.S. Government Printing Office. www.gpoaccess.

gov. 49CFR173.140 (04/2006).

6. Airgas. Carbon Dioxide – CO2 MSDS (doc # 

001013).

7. Smith Garry K. Carbon Dioxide, Caves and YOU. 

(1997) http://thelances.org/hr3/CO2paper.html 

(04/2006).

8. W.E. Kuriger Associates. Carbon Dioxide Fact 

Book. www.airspill.com (04/2006).

9. Centers of Disease Control, National Institute 

for Occupational Safety and Health. www.cdc.

gov/niosh/homepage.htm (04/2006).

10. Occupational Safety and Health Administration. 

www.osha.gov/dts/hib/hib_data/hib19881130.

html (04/2006).

11. Martin-Saint-Laurent A, Lavernhe J, Casano G, 

Simkoff A. Clinical Aspects of In-flight Incapacitations in Commercial Aviation. Aviat Space Environ 

Med, 61, 256 (1990).

12. National Transportation Safety Board. www.

ntsb.gov/aviation/FTW/1narr_98A196.htm 

(04/2006)

13. Pan American Airlines. Pan American Maintenance 

Engineering Report #ME 124, Feb. 6, 1963, Air 

Conditions, Dry Ice Quantity Limitations, DC7CF Flight Test.

14. Gibbons HL. Carbon Dioxide Hazards in General Aviation. Aviat Space Environ Med, 48, 261 

(1977)

15. Advantage Dry Ice. www.advantagedryice.com 

(04/2006).

16. The Boeing Company. Boeing Service letter, ATA: 

2100-010, 19 November 1998.