Unit 6 1 Ventilation concepts natural ventilation TB

Unit 6. 1. Ventilation concepts; natural ventilation TB Infection Control Training for Managers at National and Subnational Level

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

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

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

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

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

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

ACH and time required for removal of 99% of droplet nuclei ACH 2 4 6 12 15 20 50 400 99% 138 minutes 69 46 23 18 14 6 <1 8

ACH, time required for removal of 99% and 99. 9% of droplet nuclei ACH 2 4 6 12 15 20 50 400 99% 138 minutes 69 46 23 18 14 6 <1 99. 9% 207 minutes 104 69 35 28 21 8 1 9

Dilution ventilation

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

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

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

Never put fingers on the open space of the vaneometer 14

Is air flowing the right direction? 15

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

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

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

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

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

Window Bed Window closed 0. 10 m/s Average air velocity = Window 0. 20 +0. 10 m/s 0. 20 m/s 2 =0. 15 m/sec Bed Door 21

Window closed Average air velocity 0. 15 m/sec Bed Window Average air velocity 0. 15 m/sec Bed Average Flow Rate = X Area of windows 2 m 2 X 3, 600 sec/h Door = 1, 080 m 3 / h 22

Window ACH Bed Window Room volume: 4. 5 m x 4 m x 3. 5 m= 63 m 3 Bed Door = flow rate room volume = 1, 080 m 3 / h 63 m 3 = 17 ACH 23

ACH examples Room volume ACH 4 m x 2. 5 m Average air flowrate (Air volume x h) m 3 x h 40 m 3 40 1 40 m 3 200 5 40 m 3 300 7. 5 40 m 3 600 15 Flow/ volume

Window openings 25

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

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

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

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

Good compromise 30

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

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

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

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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

Stack ventilation

Turbine driven ventilation (whirly bird)

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

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. 42

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

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

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

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