Appendix 24. Recommendations for air change per hour

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    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

    • Where possible, perform sputum collection outdoors. 
    • Use GUV if required ACH is not reached. 

     

    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

     

    References