Dry Ice Tests to Support Safe Shipment ofSARS-CoV-2 Vaccines:
Preliminary Results
January 2021

Disclaimer••••This document describes tests performed by the Fire Safety Branch of the WilliamJ. Hughes Technical Center at the Atlantic City International Airport in New Jersey(“Technical Center”) in November and December of 2020 in support of the FAA’seffort to aid in the safe shipment of SARS-CoV-2 vaccines.
The FAA notes the contents of this document do not have the force and effect oflaw and are not meant to bind the public in any way. This document is intended
only to provide clarity to the public regarding existing requirements under the law
or agency policies.
The tests were performed with high urgency due to the COVID-19 public healthemergency, which did not allow for the time necessary to define a formal research
program.
The results and observations presented here should therefore be consideredpreliminary because:––

Strict control of initial conditions was not possible due to the state and availability of thelaboratory equipment at the time of testing and the difficulty in obtaining large quantities of dry ice
as it was in high demand and supplies were limited.
A rigorous experimental design protocol was not followed due to the urgent need for test results.

Preliminary Results – see Disclaimer

2Disclaimer (cont.)•••

As additional tests are performed, the FAA will publish updated results andobservations, as appropriate.
The results and observations presented here should be considered together withother available information, including the specific details of particular operations.
They do not relieve regulated parties of their independent obligations to analyze
and appropriately manage safety risks to their operations.
The sample vaccine thermal container that the FAA used to conduct these tests isjust one example of COVID-19 vaccine packaging; different packaging may affectdry ice sublimation differently.

Preliminary Results – see Disclaimer

3Objectives
1.

Sublimation of Dry Ice Tests––

2.

Tests were performed to evaluate the impactof certain parameters on the rate of carbon
dioxide gas evolution from dry ice inpackages for air shipment.
Several parameters were varied, including:•••Specific Packaging (sample vaccine thermalcontainer vs. generic box).
Dry Ice Pellet Size (the diameter of thepellet).
Altitude (the ambient air pressure).

Preliminary Results – see Disclaimer

Cargo Compartment CO2 Evacuation
Tests––Tests were performed to evaluate the timerequired to achieve a safe concentration ofcarbon dioxide gas near the exterior of alower deck cargo compartment door.
Several parameters were varied, including:•••Cargo compartment loading (space occupiedby cargo).
Initial volumetric concentration of CO2.
Use of exhaust fan to expedite evacuation.

4

Objective 1 – Sublimation Tests••Tests were performed to evaluate theimpact of certain parameters on therate of carbon dioxide gas evolution
from dry ice in packages for airshipment.
Several parameters were varied,
including:–––•

ProcedureSpecific Packaging (sample vaccine
thermal container vs. generic box).
Dry Ice Pellet Size (the diameter of thepellet).
Altitude (the ambient air pressure).

–––––

Preliminary Results – see Disclaimer

An empty test container was placed on ascale, and the scale was zeroed.
Dry ice of specific pellet size was added
to the test container.
The weight of the dry ice was recorded
over extended periods (up to 18 hours).
For simulated altitude tests, the test
container and scale were placed within acylindrical pressure vessel, which wasevacuated to achieve a pressure of 10.9
psia, roughly equivalent to 8,000’altitude.
The mass loss rate and sublimation rate
were calculated over the duration ofeach test.

5Sublimation Test Parameters•

2 test containers were tested––•

2 ambient pressure scenarios were tested––•

SARS-CoV-2 vaccine thermal container.
Generic dry ice container typical of frozen meat shipments.
Sea level (14.7 psia).
Simulated 8,000’ cabin altitude (10.9 psia) in reduced pressure in vacuum chamber.

3 dry ice pellet sizes were tested––––¼” (6.35 mm) nominal diameter.
½” (12.70 mm) nominal diameter.
⅝” (15.88 mm) nominal diameter (vaccine thermal container only due to limited availability of dryice).
Note: The ½” pellets ordered for the generic box tests were not uniformly ½”. A randommeasurement with calipers revealed some pellets measuring a pellet size of nearly ¾”. The
uniformity of the pellet size for all tests performed or the accuracy of the actual diameter to thenominal diameter was not confirmed.

Preliminary Results – see Disclaimer

6

Vaccine Thermal Container

Sample Vaccine Thermal
Container.

Vaccine Thermal
Container – InternalView.

Dry ice pellets filledaround the internal
payload area.

Preliminary Results – see Disclaimer

Dry ice pellets held inbag above the internal
payload area.

Dry ice bag closed,
Thermal Container
sealed by closing thelid.

7Generic Box

Preliminary Results – see Disclaimer

8Vaccine Thermal Container in Reduced
Pressure ChamberPreliminary Results – see Disclaimer

9Calculated Values• Mass Loss Rate

• Sublimation Rate𝑚2 − 𝑚1
pounds=𝑡2 − 𝑡1hour

𝑚2 − 𝑚1∗ 100 % weight loss
𝑚1
=𝑡2 − 𝑡1hour

𝑚1 = initial weight of dry ice, lb
𝑚2 = final weight of dry ice, lb
𝑡1 = time at which 𝑚1 was observed
𝑡2 = time at which m2 was observed

Preliminary Results – see Disclaimer

10Results – Dry Ice Weight vs. Time

Preliminary Results – see Disclaimer11

Results – Vaccine Thermal Container

Preliminary Results – see Disclaimer

12Results – Generic Box

Preliminary Results – see Disclaimer

13

Measurement→Ambient Pressure

PelletPelletDiameter Diameter

Package

VaccineThermalContainer
14.7 psia
Sea Level
GenericBox

10.9 psia
8,000' Altitude(Simulated in Pressure
Vessel)VaccineThermalContainer

GenericBox

Dry Ice
InitialWeightDry Ice
InitialWeightDry Ice
Final
WeightDry Ice
Final
WeightElapsedTime

Average
Mass Loss
Rate

Average
Mass Loss
Rate

Average
Sublimation
Ratein.

mmlb.

kglb.

kg

hr

lb/hr

g/hr

% mass loss
/ hr

1/4

6.35

46.13920.92843.64919.79913.89

0.179281.300

0.40

1/2

12.70

39.80918.05737.09516.82616.67

0.162873.852

0.42

5/8

15.88

44.49020.18044.05019.9814.17

0.105647.899

0.24

1/4

6.35

49.44222.42642.02219.06112.00

0.6183280.471

1.35

1/2

12.70

49.77822.57941.59818.86914.00

0.5845265.108

1.28

5/8

15.88

n/an/an/an/an/an/an/an/a

1/4

6.35

43.45219.70941.79

18.9578.27

0.189685.983

0.45

1/2

12.70

35.26415.99533.40015.15010.48

0.177980.713

0.52

5/8

15.88

40.33018.29338.502

17.46410.73

0.170377.266

0.43

1/4

6.35

49.25622.34245.292

20.5446.36

0.6265284.167

1.32

1/2

12.70

39.63217.97732.88414.91613.00

0.5192235.515

1.43

5/8

15.88

n/a

n/a

n/a

n/a

n/a

n/a

n/an/aPreliminary Results – see Disclaimer

14

Observations•

The generic box loses carbon dioxidemass at a higher rate than the vaccinethermal container.

•Mass loss rate (lb / hr) was observed tobe highly linear in all tests over the timeintervals tested.

•Smaller diameter dry ice pellets
sublimate faster than larger diameterpellets.

•Sublimation rate (% mass loss per hour)is mathematically dependent upon theinitial weight of dry ice over the timeinterval considered.

•

Reduced ambient pressure canincrease the mass loss rate, but it was
not observed to be consistent across all
tests performed in this study.
––

Physical effects of starting each test withthe same weight of dry ice were notdetermined in this study but could havean impact on sublimation rate.

This could be due to combined effects ofvarying initial conditions and uncontrolledparameters in this initial investigation.

Preliminary Results – see Disclaimer

15

Observations•

The vaccine thermal container, under theconditions tested, was observed to have thefollowing values for:–

Mass loss rate•••–

Vaccine Thermal
Container

Sublimation rate••••

Min 0.1056 lb/hr
Max 0.1896 lb/hr
Avg 0.1642 lb/hr
Min 0.24 %/hrMax 0.52 %/hr
Avg 0.41 %/hr

–Mass loss rate
•
•
•

–

Min 0.5192 lb/hr
Max 0.6265 lb/hr
Avg 0.5871 lb/hr

lb/hr% mass loss / hrlb/hr% mass loss / hr

0.10560.24

0.5192

1.28

Max 0.1896

0.52

0.6265

1.43Avg

0.41

0.5871

1.34

MinThe generic box, under the conditions tested,
was observed to have the following values
for:

Generic Box

0.1642Sublimation Rate•••

Min 1.28 %/hr
Max 1.43 %/hr
Avg 1.34 %/hr

Preliminary Results – see Disclaimer16

Recommendations•

A fixed sublimation rate for a dry ice
container should not be considered aconstant property of the container, as
the sublimation rate provided bycontainer manufacturers may havebeen determined under known and
fixed environmental conditions.
Users should–––

Be aware of the conditions the container
manufacturer used in determining thesublimation rate, and compare to therange of conditions that the shipment
may experience in transit.
Consider applying a conservative safety
factor to the manufacturer-provided
sublimation rate when determining
maximum allowable dry ice amounts.

•The mass loss rate may be the more
useful parameter than thesublimation rate since:––•Mass loss rate is independent of initial
weight of dry ice.
Mass loss rate is highly linear.

Ultimately it is the total amount ofcarbon dioxide released into theairplane that is of interest. This isdetermined with knowledge of themass loss rate of a specificcontainer, the number of containers,
and the duration of time in transit.

Preliminary Results – see Disclaimer

17Sublimation Tests – Potential Impacts toResults••All tests were performed with no contents in the containers aside from thedry ice load.
The ½” pellets ordered for the generic box tests were not uniformly ½”. Arandom measurement with calipers revealed some pellets measuring apellet size of nearly ¾”.
– Measurements were not performed for the other tests, so the deviation of the actual
diameter from the nominal diameter is unknown.

••

The ¼” generic box test was the only test performed in which additional
dry ice was added at the conclusion of the 8,000’ altitude test prior tostarting the sea level test.
The ⅝” vaccine thermal container sea level test was accidentally
terminated early due to a forced operating system update on the dataacquisition PC.

Preliminary Results – see Disclaimer

18

Objective 2 – Cargo Compartment CO2
Evacuation Tests••

Tests were performed toevaluate the time required toachieve a safe concentration ofcarbon dioxide gas near theexterior of a lower deck cargocompartment door
Several parameters werevaried, including:•Test Setup– Cargo compartment loading (spaceoccupied by cargo).
– Initial volumetric concentration of
CO2.
– Use of exhaust fan to expedite CO2evacuation.

Preliminary Results – see Disclaimer– Tests were performed in andaround the aft cargo compartmentof the FAA Technical Center’s DC10 fire test fuselage.
– Carbon dioxide gas was plumbed
into the compartment from anexternal liquid carbon dioxide tank.
– Gas analyzers were used tomeasure the volumetricconcentration of carbon dioxide gas
at several locations inside thecompartment and outside the cargocompartment door.

19

CO2 Evacuation Test Parameters•2 Loading Configurations were tested– 93% (6 LD3 Containers filled with cardboard boxes, and 140 cardboard boxes
to fill the rest of the compartment).
– 37% (3 LD3 Containers filled with cardboard boxes).

•

3 Initial CO2 concentrations were tested– 5% CO2.
– 20% CO2.
– 50% CO2.

•

2 Fan Configurations were tested– Fan Off.
– Fan On.
Preliminary Results – see Disclaimer

20Typical Cargo Loading of a Lower
Deck Cargo Compartment

LD3 Container

Preliminary Results – see Disclaimer

Lower Cargo Compartments

21

STA 1-4 = CO2 Sampling Station 1-4
AFT = toward the tail end of the fuselage
FWD = towards the forward end of the fuselageTest Compartment and CO2 Gas Sampling Locations
Preliminary Results – see Disclaimer

22Test Compartment Loaded with LD3 Containers and Fan Located AFT of the Cargo Door
93% Cargo Loading
Preliminary Results – see Disclaimer

23

CO2 Evacuation Test Procedures• Compartment is filled with the target CO2 concentration
with the door closed.
• Fan is turned on for designated tests.
• Door is opened.
• Test is conducted until the concentration in thecompartment reaches 0.5%.
– 0.5% is the FAA regulatory limit for transport category aircraft (14CFR § 25.831) and Occupational Safety and HealthAdministration (OSHA) occupational exposure limit (29 CFR §1910.1000 Table Z-1).
Preliminary Results – see Disclaimer

24

Results – CO2 Evacuation Testing

Preliminary Results – see Disclaimer

25

Observations• The compartment takes longer to evacuate CO2 as the initialconcentration increases.
• Utilizing a fan to circulate air away from the door reduces the CO2
evacuation time.
• Increase in the amount of cargo in the compartment reduces theCO2 evacuation time.
– Increase in loading percentage leads to reduction in free volume.
– Because of the smaller free volume, less CO2 is needed to reach target
concentration.

Preliminary Results – see Disclaimer

26

Observations• Amount of CO2 needed to reach 5% initialconcentration in each loading configuration:– 7ft3 – 93% Loading.
– 67ft3 – 37% Loading.

• Greater amounts of CO2 require more time to evacuate
the compartment.

Preliminary Results – see Disclaimer

27

Recommendations•

At the end of a flight, compartments containing dry ice will tend to have a high CO2
concentration that will take time to dissipate. When the cargo door is opened, theareas immediately outside the door also experience a high CO2 concentration
temporarily. How long it will take for these high CO2 concentrations to dissipate
depends upon a variety of factors and should be assessed based upon the specificdetails of particular operations.
––––

Prior to removing cargo, wait for the compartment and containers to air out upon opening.
Use a fan to circulate fresh air around the ground crew personnel and to reduce the concentration of CO2.
Use CO2 monitors to be aware of hazardous quantities/concentrations of CO2.
Beware of the potential for hazardous concentrations of CO2 to be present under the aircraft, since CO2 isheavier than air and tends to accumulate near the ground.

Preliminary Results – see Disclaimer

28