Update: October 2023
24.1 Calculation of air change per hour (ACH)
To calculate the ACH in a room:
- Measure the dimensions of the room and calculate its volume (in cubic meters).
- Measure the dimensions of the openings (e.g. window, vents) and calculate their surface (in square meters).
- Determine the airflow direction across the openings.
- Measure the air speed (in meters per second) using an anemometer.
0.65 x air speed (m/s) x opening area (m²) x 3600
ACH = ––––––––––––––––––––––––––––––––––––––––––––––––
Volume of the room (m³)
24.2 Required ACH
|
Areas |
Required ACH |
Remarks |
|---|---|---|
|
Wards or rooms, diagnosis rooms, corridors, etc. |
Minimum 12 |
Use GUV if required ACH is not reached. |
|
Sputum and other respiratory specimen collection areas |
Minimum 20 |
|
24.3 Time required for air cleaning after patient discharge
Rooms should be extensively ventilated between each patient.
The following table shows the ventilation time required to reduce airborne pathogens by 99.9% based on the ACH achieved (adapted from CDC
[1]
Citation
1.
Centers for Diseases Control. Guidelines for Preventing the Transmission of Mycobacterium tuberculosis in Health-Care Settings. MMWR. December 30, 2005 / 54(RR17);1-141.
https://www.cdc.gov/mmwr/preview/mmwrhtml/rr5417a1.htm?s_cid=rr5417a1_e#tab2
).
|
ACH |
Time (in minutes) |
|---|---|
|
6 |
70 |
|
12 |
35 |
|
15 |
30 |
|
20 |
25 |
- 1.Centers for Diseases Control. Guidelines for Preventing the Transmission of Mycobacterium tuberculosis in Health-Care Settings. MMWR. December 30, 2005 / 54(RR17);1-141.
https://www.cdc.gov/mmwr/preview/mmwrhtml/rr5417a1.htm?s_cid=rr5417a1_e#tab2