Source of Fresh Air

Environment

Airplanes

Trains

Hospital Delivery & Operating Rooms

Office Buildings

School Classroom*

Typical School Classroom

Typical Home

(Boeing, 2013)

(Boeing, 2013)

(Boeing, 2013)

(Boeing, 2013)

(ASHRAE, 2021)

(CMTA, 2020)

(Aviation Public Health Initiative, 2020)

Typical Occupancy Level

High

High

Medium

Medium

Medium/High

Medium/High

Low/Medium

Typical Air Changes per Hour (ACH)

Ventilation

(Displaced Air Indoors, with Air from Outdoors)

10 - 15

8

5

1 - 2.5

6 - 10

4 - 6

0.25

HEPA Air Filtration

10 - 15

6

20

3 - 7.5

0

0

0

Combined

(Ventilation + HEPA Air Filtration)

20 - 30

14

25

4 - 10

6 - 10

4 - 6

0.25