Unit 6.2. Mechanical and mixed mode ventilation TB Infection Control Training for Managers at National and Subnational Level

2 Objectives After this unit, participants will be able to: Understand the principles of mechanical and mixed mode ventilation Describe the importance of maintenance for all ventilation systems Note: A public health manager should understand the principles and applicability and when to consult a ventilation engineer

3 Outline A. Principles of mechanical ventilation –Single pass vs. recirculated –Air mixing –Negative pressure –Exhaust ventilation B. Mixed mode ventilation –Fans C. Maintenance and monitoring for all ventilation systems

4 A. Mechanical ventilation Is created by using a fan to force air exchange and to drive air flow Works by generating negative pressure in the room to drive airflow inward To be effective, it is essential that: All doors and windows kept closed A minimum of 12 ACH is maintained The ventilation system is well- designed, maintained and operated

5 Principles of ventilation Which is an easier way to extinguish the flame? Inhale (pull, exhaust) Exhale (push, supply)

6 Two ways to dilute and remove contaminated air First choice: Single pass Re-circulation + HEPA filtration Rooms in a health facility

7 Designs to provide air mixing Airflow patterns are affected by: Air temperature Location of furniture Space configuration Movement of health care workers (hcw) hcw supply exhaust hcw exhaust

8 Short circuiting Clean air is removed before it is mixed with room air Contaminated air in the room is not effectively diluted or removed supply exhaust

9 Negative pressure keeps droplet nuclei in the room Air flows from a higher pressure area to a lower one A room under negative pressure has a lower pressure than adjacent areas, so air is drawn into the room; negative pressure directs the airflow Negative pressure is achieved by exhausting more air from a room than is supplied

225 m 3 /h200 m 3 /h 25 m 3 /h 200 m 3 /h225 m 3 /h135 m 3 /h Patient room (Negative) Nurse room (Positive) What is negative pressure ?

11 Negative pressure room A ir flows into room, from higher to lower pressure 10% flow differential is minimum required Keep doors and windows closed Monitor to ensure negative pressure is maintained

12 Negative pressure evaluation Smoke tube Pressure sensor Flutter strips Velocity meter

13 Vaneometer

14 TB transmission in a TB dispensary, Russia

15 Checking airflow in the TB dispensary

16 Exhaust ventilation

17 Where does the air go?

18 Where does the air go?

19 Exhaust Supply

20 Exhaust Supply

21 B. Mixed mode ventilation Combines the use of mechanical and natural ventilation Is done through the installation of an exhaust fan to increase the rate of air changes in the room Can be useful in places where –natural ventilation is not suitable (e.g. very cold weather) –fully mechanically ventilated rooms are not available

22 Fans

23 Window exhaust fan

24 Corridor Patient room Window fan Airflow with window exhaust fan

25 Window exhaust fan

26 Where goes that air? Short-circuiting

27 C. Regular cleaning and maintenance

28 Routine monitoring, recording The operation of ventilation systems should be regularly monitored Is the air moving? Is it moving in the right direction? Record performance and dates of all routine monitoring activities

29 Smoke test to visualize air movement

Maintenance and inspection of natural ventilation systems Are the windows open? Designate a person to routinely inspect Record results 30

31 Summary Mechanical ventilation systems must be well-designed, maintained and operated A room under negative pressure has a lower pressure than adjacent areas, so air is drawn into the room. This prevents infectious particles from escaping Mixed mode ventilation systems combine the use of mechanical and natural ventilation