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Unit 6.1. Ventilation concepts; natural ventilation TB Infection Control Training for Managers at National and Subnational Level.

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Presentation on theme: "Unit 6.1. Ventilation concepts; natural ventilation TB Infection Control Training for Managers at National and Subnational Level."— Presentation transcript:

1 Unit 6.1. Ventilation concepts; natural ventilation TB Infection Control Training for Managers at National and Subnational Level

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 2

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

4 A. What is ventilation? Movement of air Pushing and/ or pulling of particles and vapours Preferably in a controlled manner 4

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 5

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 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) 7

8 ACH99% 2138 minutes 469 646 1223 1518 2014 506 400<1 ACH and time required for removal of 99% of droplet nuclei 8

9 ACH99%99.9% 2138 minutes207 minutes 469104 64669 122335 151828 201421 5068 400<11 ACH, time required for removal of 99% and 99.9% of droplet nuclei 9

10 Dilution ventilation

11 What do you need to measure ACH? 1.A tape measure 2.Vaneometer 3.Smoke tube 4.Calculator 5.Note pad 11

12 Measure dimensions of the opening to calculate area Area of window opening = length x width Example 1: Area = 0.5 m x 0.5 m = 0.25 m 2 12

13 Use the vaneometer to measure velocity, direction Speed = metres per second = m/s 13

14 Never put fingers on the open space of the vaneomete r 14

15 Is air flowing the right direction? 15

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 m 2 x 1 m/second = 0.25 m 3 /s x 3,600 seconds per hour = 900 m 3 / hour 16

17 Room volume = width x depth x height Example 1: 3 m wide x 5 m deep x 3 m high = 45 m 3 Calculate room volume 17

18 Example 1: ACH calculation Window area = length x width = 0.25 m 2 Air velocity through window= 1 m/s Air flow rate = window area x air velocity = 900 m 3 /h Room volume = width x depth x height = 45 m 3 ACH = Air flow rate divided by room volume = 900 m 3 /hour = 20 ACH 45 m 3 18

19 Bed Window Window closed Each open window = 1m x 1m = 1m 2 Door Example 2: ACH calculation 19

20 Area of open windows = 2 m 2 Bed Window Window closed 1 m 2 Door 20

21 0.20 m/s 0.10 m/s Average air velocity = 0.20 +0.10 m/s 2 =0.15 m/sec Bed Window Window closed Door 21

22 Average air velocity 0.15 m/sec Average Flow Rate = Average air velocity 0.15 m/sec X Area of windows 2 m 2 X 3,600 sec/h = 1,080 m3 / h Bed Window Window closed Door 22

23 Room volume: 4.5 m x 4 m x 3.5 m= 63 m 3 ACH = flow rate room volume = 1,080 m 3 / h 63 m 3 = 17 ACH Bed Window Door 23

24 ACH examples Room volumeAverage air flowrate (Air volume x h) ACH 4m x 4m x 2.5 m m 3 x hFlow/ volume 40 m 3 401 40 m 3 2005 40 m 3 3007.5 40 m 3 60015

25 25 Window openings

26 Ventilation is more effective if: 1.Air flows from clean to contaminated (directional airflow) 2.There is good air-mixing (no stagnation or short circuiting) 26

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 27

28 Correct working location Health care worker (HCW) is near the clean air source 28

29 Incorrect working location Resolve by switching places so the health care worker is near the clean air source 29

30 Good compromise 30

31 Types of ventilation 1.Natural If feasible, maximize the use of natural ventilation before considering other ventilation systems. 2.Mechanical 3.Mixed mode 31

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 32

33 33

34 34

35 35

36 Natural ventilation Open Window Door C D E F B Direction of air flow Beds A 36

37 37

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 38

39 Stack ventilation

40 Turbine driven ventilation (whirly bird)

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 41

42 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.

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

44 Poorly ventilated waiting area in an out-patient clinic Side A Side B Office Pharmacy Examination rooms X X Doors in/ out Doors in Plane viewFront view Chairs, waiting area Windows 44

45 Waiting area maximizing natural ventilation Side A Side B Office Pharmacy Examination rooms Doors in/ out Plane viewFront view Waiting area 3 Windows tranformed into doors Side B Waiting area 45

46 46


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