Table 2.

Time (in min) to remove airborne particles based on the air changes per hour (ACH) of a room*

Air changes per hour	Time (mins) required for removal (99% efficiency)	Time (min) required for removal (99.9% efficiency)
2	138	207
4	69	104
6	46	69
8	35	52
10	28	41
12	23	35
15	18	28
20	14	21
50	6	8

Derived from the CDC: Guidelines for Environmental Infection Control in Health-Care Facilities (2003). Available from URL: https://www.cdc.gov/infectioncontrol/guidelines/environmental/appendix/air.html34

*Assuming airborne particles are NOT continuing to be generated (i.e., after tracheal intubation)