1. Unit Ventilation concepts; natural ventilation TB Infection Control Training for Managers at National and Subnational Level
Photo credit: WHO/TDR/Crump

2. Objectives By the end of this unit, participants will be able to:
Describe the concept of ventilation
State the recommended air changes per hour (ACH) for airborne precaution rooms
Calculate ACH
Utilize directional air flow to reduce the risk of TB transmission
Describe how to maximize natural ventilation
[Review slide]

3. Outline A. Ventilation concepts Air changes per hour
Directional airflow
Types of ventilation systems
B. Natural ventilation
Wind
Stack
C. Exercise
[Review slide]

4. A. What is ventilation? Movement of air
“Pushing” and/ or “pulling” of particles and vapours
Preferably in a controlled manner
It is much better to be able to control ventilation, so that the air movement flows in the way it is planned.
This is always the case with mechanical ventilation but not with natural ventilation since it is difficult to control the direction of the wind.

5. WHO recommends that health facilities implement ventilation systems
the better ventilated the area, the lower risk of transmission of TB and other airborne infections
[Review slide]
Citation
WHO. WHO policy on TB infection control in health-care facilities, congregate settings, and households WHO/HTM/TB/

6. Air changes per hour (ACH)
Calculating ACH is the most simple way to assess ventilation
ACH = Volume of air moved in one hour
One ACH means that the volume of air in the room is replaced in one hour
[Review slide]
Citation
WHO. Infection prevention and control of epidemic- and pandemic-prone acute respiratory diseases in health care; WHO interim guidelines WHO/CDC/EPR/2007.6

7. Air changes per hour (ACH)
WHO recommends at least 12 ACH to prevent airborne infection
The higher the ACH, the better the dilution and the lower the risk of airborne infection
But too much airflow can be uncomfortable (too much draft)
[Review slide]
Citation
WHO. Infection prevention and control of epidemic- and pandemic-prone acute respiratory diseases in health care; WHO interim guidelines WHO/CDC/EPR/2007.6
WHO. WHO policy on TB infection control in health-care facilities, congregate settings, and households WHO/HTM/TB/

8. ACH and time required for removal of 99% of droplet nuclei2
138 minutes 4 69 6 46 12 23 15 18 20 14 50
400
<1
This table shows how many minutes it takes to reduce the concentration of droplet nuclei by 99% depending on the number of ACH.
The first row shows that at low ventilation rates (only 2 ACH), it takes 138 minutes to remove 99% of the droplet nuclei.
The higher the ventilation rate (moving down the table), the faster 99% of droplet nuclei are removed.
WHO recommends at least 12 ACH to prevent TB transmission. Notice that even at this ventilation rate, it takes 23 minutes after droplet nuclei are released, to clear 99% of them from the room.
Citation
Centers for Disease Control and Prevention (USA). Guidelines for preventing the transmission of Mycobacterium tuberculosis in health care settings, MMWR 2005:54(No. RR-17). (See also errata published on 25 September 2006)

9. ACH, time required for removal of 99% and 99.9% of droplet nuclei2
138 minutes
207 minutes 4 69
104 6 46 12 23 35 15 18 28 20 14 21 50 8
400
<1 1
Now we’ve added another column to shows how many minutes and ACH it takes to reduce the concentration of droplet nuclei even further to removal of 99.9%, which is even better protection.
This table assumes a one time (not continuous) release of droplet nuclei. If the patient continues to generate droplet nuclei in the room these tables cannot be used.
The table is used to decide when it is safe to enter a room after an infectious TB patient has left
For example, you have separated a coughing patient in an examination room in a clinic, provided services, and now the patient has left. This chart can help you decide how long you have to wait before you bring another patient into the examination room.
After you are done using a room for an infectious patient, a sign should be posted on the door to say the time it is safe to re-enter. If a health care worker has to enter sooner, a respirator should be used.
(Note: This table assumes perfect air mixing within the room and constant ACH.)
Citation
Centers for Disease Control and Prevention (USA). Guidelines for preventing the transmission of Mycobacterium tuberculosis in health care settings, MMWR 2005:54(No. RR-17). (See also errata published on 25 September 2006)

10. Dilution ventilation Here is a graph of ACH and dilution.
The y axis is the concentration of bacilli (colony forming units per cubic metre), and the x axis is time in hours.
At one hour, the higher the ACH the lower the concentration of bacilli
Here is another way to look at this graph. When the number of ACH increases, less time is needed to ensure the same dilution.
Courtesy of Rod Escombe

11. What do you need to measure ACH?
A tape measure
Vaneometer
Smoke tube
Calculator
Note pad
[Review slide]
In a few slides, we’ll talk about what are vaneometers and smoke tubes, and how to use them.

12. Measure dimensions of the opening to calculate area
We’ll work through two examples of ACH calculations. Here is example 1.
The first step is to measure the open area of the window.
Photo courtesy of Paul Jensen
Area of window opening = length x width
Example 1:
Area = 0.5 m x 0.5 m = 0.25 m2

13. Use the vaneometer to measure velocity, direction
The second step is to measure average air velocity with a vaneometer.
Air speed is measured in metres/sec.
A vaneometer costs about 20 US dollars.
The vaneometer also measures the direction of the flow (positive, negative).
For additional information:
Speed = metres per second = m/s

14. Never put fingers on the open space of the vaneometer
In this picture, the direction of the flow is from outside into the room (as shown by the red arrow).
The black flap in the vaneometer has swung toward the inside of the room (seen below the person’s forefinger).
The arrowhead also indicates the open area of the vaneometer, which you do not want to cover with your fingers!
Should the direction of the wind be from inside towards outside, the vaneometer needs to be turned around and a negative sign added to the figure.
For better estimation, calculate an average of multiple air flow measurements. Add them together, then divide by the number of measurements.
Photo courtesy of Paul Jensen

15. Is air flowing the right direction?
The picture shows how to use a smoke tube to monitor air flow through a door.
The sputum collection booth is inside the door. We are standing in the hallway.
[Ask participants]: Is air flowing the way we want it to?
Yes. This means that droplet nuclei stay in the sputum collection booth, rather than escape into the hall.
Photo courtesy of Paul Jensen
Is air flowing the right direction?

16. Calculate air flow rate
Example 1:
Air velocity through window measured by vaneometer = 1 m/s
Flow rate = Open window area x air velocity
= 0.25 m2 x 1 m/second
= 0.25 m3/s x 3,600 seconds per hour
= 900 m3 / hour
The slide shows how to calculate the air flow rate.
In our example, the vaneometer measures the air velocity to be 1 metre per second (m/s) through the window.
The air flow rate is the area of the window (0.25 m2 in our example ) multiplied by air velocity (1 m/sec in our example).
This gives us 0.25 cubic metres per second (m3/s).
To change to cubic metres per hour, we need to multiply by 3,600 sec/h.

17. Calculate room volume Room volume = width x depth x height Example 1:
Next we’ll use the tape measure to measure the dimensions of the room.
To determine the volume, multiply width x depth x height.
Photo courtesy of Paul Jensen
Room volume = width x depth x height
Example 1:
3 m wide x 5 m deep x 3 m high = 45 m3

18. Example 1: ACH calculation
Window area = length x width = 0.25 m2
Air velocity through window= 1 m/s
Air flow rate
= window area x air velocity = 900 m3/h
Room volume
= width x depth x height = 45 m3
ACH
= Air flow rate divided by room volume
= 900 m3/hour = 20 ACH
45 m3
Let’s work through our example of ACH calculation.
We’ve measured the open window area by multiplying height times width.
We used the vaneometer to measure the air velocity through window.
We calculated the flow rate (this is the numerator of ACH).
We measured the room volume (this is the denominator of ACH).
Now we find the ACH is 20.

19. Example 2: ACH calculation
Window
Window closed
Each open window = 1m x 1m = 1m2
Bed
Window closed
Window
Here’s example #2. Now let’s follow the same steps to calculate ACH for a room with 4 windows
The 2 closed windows are contributing nothing to ventilation on the day we are visiting, so we disregard them
First, calculate the open window area. The 2 open windows are in red. The open area for each window is 1 m by 1 m, so the area of each window opening is 1m2
Bed
Door

20. 1 m2 Area of open windows = 2 m2 1 m2 Window closed Window
Bed
Window closed
1 m2
Window
To calculate the total open window area, add the areas of each window.
Bed
Door

21. Average air velocity = 0.10 m/s 0.20 +0.10 m/s 2 =0.15 m/sec 0.20 m/s
Window closed
Window
Average air velocity =
m/s 2
=0.15 m/sec
0.10 m/s
Bed
0.20 m/s
Window
Now measure the average air velocity through the 2 windows
In the left window, the vaneometer measures 0.2 m/second; in the right it measures 0.1 m/s.
Sum the two and divide by the number of measurements to get the average, in this case 0.15 m/s
As the wind changes direction and speed every second, ACH will vary because of changes in average air velocity measurements.
One can also average the measures in each window over time.
Bed
Door

22. Average air velocity 0.15 m/sec
Average Flow Rate =
Average air velocity m/sec
X Area of windows 2 m2
X 3,600 sec/h
= 1,080 m3 / h
Window closed
Window
Bed
Average air velocity 0.15 m/sec
Window
Next we’ll calculate the average flow rate (which is the numerator for ACH).
The average flow is the the average velocity times the area of the windows.
We also multiply by 3,600 seconds per hour to convert to cubic meters per hour.
Bed
Door

23. ACH = flow rate room volume = 1,080 m3 / h Room volume: 63 m3
Window
ACH
= flow rate
room volume
= 1,080 m3 / h
63 m3
= 17 ACH
Bed
Room volume:
4.5 m x 4 m
x 3.5 m= 63 m3
Window
To calculate ACH, the numerator is the flow rate we just calculated.
The room volume is the denominator.
[Ask participants]:
Does this meet WHO standards for an airborne precaution room?
Yes, since the WHO standard is at least 12 air changes per hour.
Bed
Door

24. ACH examples Room volume Average air flowrate (Air volume x h) ACH
4m x 4m x 2.5 m
m3 x h
Flow/ volume
40 m3 40 1
200 5
300
7.5
600 15
This is a table showing different air flow rates per hour through the same 40m3 room
You can see as the air flow through the room increases, higher air changes per hour are achieved.

25. Window openings
We talked about the open area of a window. These photos show that different types of windows allow different airflows.
In the picture on the left, they are <10% opened.
In the picture on the right, windows are 100% open.
In calculating ACH with the window type in the bottom photo, you would need to consider that only about 10% of the window area can actually exchange air.
Photos courtesy of Paul Jensen from: Control de infecciones de tuberculosis en establecimientos de salud- Módulo de capacitación. Ministerio de Salud, Peru

26. Ventilation is more effective if:
Air flows from “clean” to “contaminated” (directional airflow)
There is good air-mixing (no stagnation or short circuiting)
Now that we’ve discussed ACH, we’ll continue with additional ventilation basics.
[Review slide]
Now let’s look at examples of the first concept.
We’ll cover the short circuiting in the next unit.

27. Directional airflow
Locate the health care worker (or other patients) near the clean air source
Locate the person who may be infectious near a place where the air is exhausted away
[Review slide]

28. Correct working location
The slide shows correct organization of consultation room.
Staff should always be closest to the clean air source, and the patient near the outflow.
Here the natural ventilation blows from the health care worker (HCW) to the patient.
Citation
WHO. TB infection-control in the era of expanding HIV care and treatment. Addendum to WHO Guidelines for the prevention of TB in health are facilities in resource-limited settings
Health care worker (HCW) is near the clean air source

29. Incorrect working location
But when the wind changes direction, the health care worker is no longer near the clean air source.
If the patient is infectious, potentially contaminated air flows toward the worker’s breathing zone.
The easiest solution is for the health care worker and the patient to switch places. If this is not possible, the next slide shows a possible compromise.
Citation
WHO. TB infection-control in the era of expanding HIV care and treatment. Addendum to WHO Guidelines for the prevention of TB in health are facilities in resource-limited settings
Resolve by switching places so the health care worker is near the clean air source

30. Good compromise
If the health care worker and patient cannot switch places, this slide shows a compromise.
Citation
WHO. TB infection-control in the era of expanding HIV care and treatment. Addendum to WHO Guidelines for the prevention of TB in health are facilities in resource-limited settings

31. Types of ventilation Natural
If feasible, maximize the use of natural ventilation before considering other ventilation systems.
Mechanical
Mixed mode
There are 3 types of ventilation: natural, mechanical and mixed mode
In existing health care facilities with natural ventilation, the use of natural ventilation should be maximized before considering other ventilation systems.
(We won’t discuss Mechanical and mixed mode ventilation until the next unit.)
Citation
WHO. WHO policy on TB infection control in health-care facilities, congregate settings, and households WHO/HTM/TB/
WHO. Epidemic-prone and pandemic-prone acute respiratory diseases; Infection prevention and control in health-care facilities. Summary guidance WHO/CDS/EPR/2007.8

32. B. Natural ventilation
Created by the use of external airflows generated by natural forces such as:
Wind
Differences in temperature (stack)
Naturally ventilated rooms can achieve very high ventilation rates (ACH) under ideal conditions
The second part of this unit focuses on natural ventilation.
Here is a definition.
[Review slide]
Citation
WHO. Epidemic-prone and pandemic-prone acute respiratory diseases; Infection prevention and control in health-care facilities. Summary guidance WHO/CDS/EPR/2007.8

33. In the pre-antibiotic era, ventilation was ensured by large open windows, kept open also during winter.
Notice that the patients are well covered, to survive the low temperatures.
Photo courtesy:

34. Sanatoria were designed to maximize natural ventilation.
This is a sanatorium in Sondalo, Italy, built in the 1940s.
TB patients spent a large part of the day on a porch open to the outside (left side of photo).
When patients moved indoors, the windows of their rooms could be opened completely (right side of photo).
Photo courtesy of GB Migliori

35. This photo illustrates the use of natural ventilation today.

36. Natural ventilation Beds A B Direction of air flow C D E F Beds
Open Window A B
Open Window
Direction of air flow
Door C D E F
Let’s look at this diagram of natural ventilation in a hospital ward.
Windows located on opposite sides of the room allow the wind to flow across the ward from the left of the picture to the right.
[Ask participants]:
If the wind usually blows this way, and you have no single patient rooms available, which bed would you use for your smear positive MDR-TB patient?
Using bed B would place this infectious patient nearest to the air outflow from the room.
Citation
Modified from:
WHO. Guidelines for the prevention of TB in health care facilities in resource-limited settings WHO/TB/
Beds

37. Photo courtesy of GB Migliori
This is a rural TB/Leprosy hospital in Angola.
The waiting area is situated outside (photo on the right) with direct access to the out-patient department (photo on the left).
Photo courtesy of GB Migliori

38. Maximize natural ventilation
Openings on opposite walls (cross ventilation)
Openings are unrestricted (stay open)
10% of floor space should be openable window area on each wall
Upper levels of the building (higher from the ground floor)
Building and openings are oriented to use the prevailing wind, without obstruction by other nearby buildings
Here are ways to maximize natural ventilation.
[Review slide]

39. Stack ventilation
Stack ventilation is another type of natural ventilation
It is driven by differences in temperature.
When the room air is warmed, it is lighter and rises.
This building is designed to let the warmed air escape near the top, which is then replaced by fresh air entering through the lower opening.
Courtesy of Hans Mulder
Citation
WHO. Infection prevention and control of epidemic- and pandemic-prone acute respiratory diseases in health care; WHO interim guidelines WHO/CDC/EPR/2007.6

40. Turbine driven ventilation (whirly bird)
A whirly bird (turbine) can draw even more air once it starts spinning.
These take advantage of the stack effect.
Photo courtesy of Hans Mulder

41. Natural ventilation Advantages Can often be implemented immediately
Often low cost
Can achieve high ACH
Disadvantages
Uncontrolled
Unpredictable
Safety, comfort
Insects, noise, dust
Not suitable in cold weather
Let’s summarize the pros and cons of natural ventilation.
Natural ventilation has some advantages:
By simply opening existing windows and doors, it can be implemented right away without a big expense.
Depending on the wind and the size of the windows, natural ventilation can achieve high ventilation rates.
Natural ventilation also has some disadvantages:
It can be uncontrollable and unpredictable. People can close the windows and doors, or the wind direction can change outside.
Keeping windows open may be too cold, or may not be safe, or private.
Wind can bring in unwanted elements, such as insects, noise, dust. In malaria areas, windows can be screened, or patients provided with netting.
While natural ventilation may not be suitable in cold climates, it could still be used for at least a few months of the year in most areas.
Photo courtesy of Rod Escombe
Citation
WHO. WHO policy on TB infection control in health-care facilities, congregate settings, and households WHO/HTM/TB/

42. Summary
WHO recommends at least 12 room air changes per hour to prevent airborne infection
Locate the health care worker (or other patients) near the clean air source
Locate the patient who may be infectious near a place where the air is exhausted away
In existing health care facilities with natural ventilation, the use of natural ventilation should be maximized before considering other ventilation systems.
[Review slide]

43. Exercise
How would you improve the ventilation of the following health facility, using natural ventilation concepts?

44. Poorly ventilated waiting area in an out-patient clinic
Plane view
Front view
Chairs, waiting area
Office
X X X X
Side A
Office
Windows
Examination rooms
Doors in
Office
The figure shows a building with a long side B, where the rooms (and the windows) are placed, and a shorter side A .
The main doors allowing patient and staff to enter the building are indicated (blue) as well as windows (red).
From there a long corridor starts, in which the waiting area is located (in green).
Modified from:
WHO. Guidelines for the prevention of TB in health care facilities in resource-limited settings WHO/TB/99.269
Pharmacy
Doors in/ out
Side B

45. Waiting area maximizing natural ventilation
Plane view
Front view
Office
Office
Waiting area
Waiting area
Examination rooms
Office
Side B
Side A
The waiting area of the building shown in the picture is largely open.
Patients are accessing examinations rooms directly from the semi-open space, since three windows have been converted into doors.
Modified from:
WHO. Guidelines for the prevention of TB in health care facilities in resource-limited settings WHO/TB/99.269
Pharmacy
3 Windows tranformed into doors
Doors in/ out
Side B

46. Maputo, Mozambique
Photo courtesy of GB Migliori