Modeling the Fate of Expiratory Aerosols and the Associated Infection Risk in an Aircraft Cabin Environment

Figures & data

FIG. 1 Dimensions of the aircraft cabin geometry.

TABLE 1 Measured size distribution of injected droplets in the validation experiments and the factorization of each tracer droplet in the simulations

			Corresponding residue size [μm]
Droplet size (Initial) [μ m]	Measured number fraction at the droplet generator	Number of actual droplet represented by each tracer droplet∗	100 L/s, 200 L/s	ECS failure
2	0.01	0.11	0.6	1.2
6	0.27	2.02	1.6	3.7
12	0.39	2.87	4.7	7.3
20	0.20	1.51	7.8	12.2
28	0.03	0.25	11.0	17.1
45	0.04	0.30	17.6	27.5
87.5	0.02	0.16	34.3	53.4
137.5	0.01	0.09	53.8	83.9
225	0.01	0.08	87.8	137.3
∗10,000 tracer droplets were injected for each size in the simulations.

TABLE 2 Boundary conditions and inputs for numerical simulations

Boundary Conditions
Supply air temperature: 19.5°C (100 L/s), 21.5°C (200 L/s), 22.0°C (ECS failure)
Supply air absolute humidity: 0.9 g/kg (100 L/s, 200 L/s), 16.8 g/kg (ECS failure)
Cabin wall temperature: 18°C (100 L/s, 200 L/s), 22°C (ECS failure)
Heating cylinder surface temperature: 32°C
Droplet injection location: Seat C4
Aerosol volatile fraction: 94% by volume (100 L/s, 200 L/s), 77% by volume (ECS failure)
Air velocity at droplet injection outlet: 10.6 m/s
Discrete phase boundary
Air supply slots:	Reflect	Air exhaust pipes:	Escape
Injection outlet:	Reflect	All other solid surfaces:	Trap

FIG. 2 (a) Predicted lateral airflow velocity profile on the XZ plane cutting through the center of the cabin. (b) Predicted longitudinal airflow velocity profile on the YZ plane cutting through the center of the cabin.

FIG. 3 (A) PIV measurement results at location A indicated in Figure 2a. (B) PIV measurement results at location B indicated in Figure 2a. (C) PIV measurement results at location C indicated in Figure 2a. (D) PIV measurement results at location D indicated in Figure 2b.

TABLE 3 Comparisons between numerically predicted and measured airflow velocity magnitudes at selected locations

	Airflow velocity [m/s]
Locations	Numerical prediction	PIV measurement
Outlet of supply air slot	2.6	2.9
Location B	0.2–0.6	0.2–0.5
Location C	0.2–0.3	0.1–0.3
Location D	0.1–0.3	0.1–0.3

FIG. 5 (a) Mean lateral positions for aerosols of 2 to 45 μ m in size for the 200 L/s case. (b) Mean lateral positions for aerosols of 2 to 45 μ m in size for the 100 L/s case. (c) Mean lateral positions for aerosols of 2 to 45 μ m in size for the ECS failure case.

FIG. 5 (a) Mean longitudinal positions for aerosols of 2 to 45 μ m in size for the 200 L/s case. (b) Mean longitudinal positions for aerosols of 2 to 45 μ m in size for the 100 L/s case. (c) Mean longitudinal positions for aerosols of 2 to 45 μ m in size for the ECS failure case.

FIG. 6 (a) Deposition fractions for different sizes of aerosols. (b) Deposition velocities for different sizes of aerosols.

FIG. 7 (a) Size composition of the aerosols deposited on Seat B4 and A6 under the 200 L/s condition. (b) Size composition of the aerosols deposited on the heating cylinder in Seat B4 and A6 under the 200 L/s condition.

FIG. 8 (a) Distribution of deposited mass fraction in percentage for the 200 L/s case (simulation and experiment). (b) Distribution of deposited mass fraction in percentage for the 100 L/s and ECS failure cases (simulation).

TABLE 4 Literature data used for infection risk analysis

Parameter	Value	Remarks	Reference
c	5 × 10^5 TCID50	Median concentration from 7 patients	Murphy et al. 1973
Human infectious dose	ID50 = 1.8 TCID50 r = 0.385	Infectious dose for aerosols ≤ 3 μ m (mean value of the range: 0.6–3.0) β = 0.6	Alfard et al. 1966
	ID50 = 223.5 TCID50 r = 0.0031	Nasal infectious dose, for larger aerosols and mucous membrane (mean value of the range: 127–320)	Douglas 1975
f(t)	75% after aerosolization, 1%/min additional decay within 15 min	Extrapolated from Figure 2B in Schaffer et al. 1976. Under 21°C, 5% RH	Schaffer et al. 1976
f s	18 cough/h	Median cough frequency of 60 patients	Loudon and Brown 1967
f h	3/h	Assumption
f m	0.7/h	Frequency of eye-rubbing and nose-picking of 124 adults	Hendley et al. 1973
c h	0.00251	Transfer efficiency of influenza virus to finger pad from porous material	Bean et al. 1982
	0.0794	Transfer efficiency of influenza virus to finger pad from non-porous material
b	∼6.4/h	Influenza virus survived on skin for more than 0.03 day	Walther and Ewald 2004

TABLE 5 Estimated exposure to airborne expiratory aerosols for the case of 200 L/s when 1 droplet injection was made

	Estimated exposures to airborne expiratory aerosols
Method	A4	A3	Aisle	A2	A1
Experimental	1.4	1.2		5.8	2.8
Numerical	1.23	2.70		1.86	1.80
	B4	B3		B2	B1
Experimental	18.6	7.5		0.9	3.9
Numerical	19.9	4.39		1.56	3.13
	C4	C3		C2	C1
Experimental	Injection point	1.5		2.6	3.8
Numerical		1.02		5.10	3.35
Unit: 10^− 6 ml

TABLE 6 Estimated infection risks by inhalation of pathogenic aerosols

	Estimated infection risk via inhalation at seat
Case	A4	A3	Aisle	A2	A1
100 L/s	0.016	0.013		0.010	0.002
200 L/s	0.005	0.012		0.017	0.016
ECS Fail	0.032	0.045		0.018	0.014
	B4	B3		B2	B1
100 L/s	0.659	0.132		0.050	0.013
200 L/s	0.580	0.070		0.018	0.030
ECS Fail	0.643	0.127		0.033	0.040
	C4	C3		C2	C1
100 L/s	Index patient	0.094		0.037	0.034
200 L/s		0.024		0.041	0.029
ECS Fail		0.095		0.052	0.023

TABLE 7 Estimated infection risk via airborne (aerosol size < 5 μ m) and droplet (aerosol size > 5 μ m) transmission modes for the 200 L/s case

	Estimated infection risk at seat
Transmission mode	A4	A3		A2	A1
Airborne	0.004	0.005		0.006	0.005
Droplet	0.001	0.007		0.011	0.011
	B4	B3		B2	B1
Airborne	0.049	0.012	Aisle	0.009	0.009
Droplet	0.559	0.060		0.009	0.021
	C4	C3		C2	C1
Airborne	Index patient	0.017		0.013	0.010
Droplet		0.008		0.029	0.019

TABLE 8 Estimated infection risk by hand contact with surfaces contaminated by deposited pathogenic aerosols

	Estimated infection risk via hand contact at seat
Case	A4	A3	Aisle	A2	A1
100 L/s	1.50 × 10^− 7	7.87 × 10^− 8		2.74 × 10^− 8	3.08 × 10^− 8
200 L/s	1.62 × 10^− 7	9.06 × 10^− 8		2.70 × 10^− 7	2.96 × 10^− 7
ECS Fail	1.50 × 10^− 7	1.39 × 10^− 7		3.36 × 10^− 8	2.80 × 10^− 8
	B4	B3		B2	B1
100 L/s	4.38 × 10^− 6	3.63 × 10^− 6		1.18 × 10^− 7	1.19 × 10^− 7
200 L/s	4.51 × 10^− 6	3.75 × 10^− 6		1.15 × 10^− 7	1.10 × 10^− 7
ECS Fail	4.97 × 10^− 6	3.56 × 10^− 6		1.18 × 10^− 7	1.13 × 10^− 7
	C4	C3		C2	C1
100 L/s	Index patient	5.34 × 10^− 6		1.27 × 10^− 7	1.14 × 10^− 7
200 L/s		5.57 × 10^− 6		1.21 × 10^− 7	1.13 × 10^− 7
ECS Fail		5.33 × 10^− 6		1.20 × 10^− 7	1.10 × 10^− 7

TABLE 9 Estimated infection risks by hand contact with an extra laptop keyboard surface in each seat for the 200 L/s case

	Estimated infection risk via indirect contact at seat
Case	A4	A3	Aisle	A2	A1
Keyboard	2.18 × 10^− 7	2.18 × 10^− 7		3.62 × 10^− 7	3.62 × 10^− 7
30/hr keyboard + original	9.49 × 10^− 6	9.41 × 10^− 6		1.55 × 10^− 5	1.55 × 10^− 5
	B4	B3		B2	B1
Keyboard	3.22 × 10^− 6	3.22 × 10^− 6		3.97 × 10^− 6	3.97 × 10^− 6
30/hr keyboard + original	1.42 × 10^− 4	1.41 × 10^− 4		1.71 × 10^− 4	1.71 × 10^− 4
	C4	C3		C2	C1
Keyboard	Index patient	1.17 × 10^− 5		5.39 × 10^− 6	5.39 × 10^− 6
30/hr keyboard + original		5.05 × 10^− 4		2.30 × 10^− 4	2.30 × 10^− 4

Schaffer , F. L. , Soergel , M. E. and Straube , D. C. 1976 . Survival of Airborne Influenza Virus: Effects of Propagating Host, Relative Humidity, and Composition of Spray Fluids . Arch. Virol. , 51 ( 4 ) : 263 – 273 .

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