unit 6.4. filtration tb infection control training for managers at national and subnational level
TRANSCRIPT
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Unit 6.4. Filtration
TB Infection Control Training for Managers
at National and Subnational Level
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Objectives
After this unit, the participant will be able to:
• List situations where air must be filtered
• Define the characteristics of a HEPA filter
• Describe why maintenance is important for filters
• Describes advantages and disadvantages of HEPA filtration devices
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Outline
• When air needs to be filtered
• HEPA filter characteristics
• Placement of HEPA filters
• Maintenance of filters
• Room air cleaners– HEPA filtration devices
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Filters
Filters
Filters
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What needs to be filtered?
• Any contaminated air that might be recirculated into the room or other rooms
• Any contaminated air that might be exhausted near:– Air intakes– People– Open windows
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Ventilation fibrous filters
Glass fibres Polymeric fibres
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Efficiency: ability to remove (collect) particles
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Examples of filter designs
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None About half Essentially all(depends on rating)
Ability to remove particles the size of TB droplet nuclei (1-5 micrometres)
Lint Pleated HEPA
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What is a HEPA filter?
• High Efficiency Particulate Air (HEPA) filter
• Removes more than 99.97% of particles 0.3 micrometers or larger at a specified flow rate of air.
100.000particles
30 particles
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International norms
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Placement of HEPA filters
• In sputum collection booths or biologic safety cabinets for filtration before exhausting air to the outside
• In the ducts of central ventilation systems for filtration before air is recirculated into a room
• Inside units that recirculate room air (free standing HEPA filtration devices) – Moveable– Mounted on ceiling or wall
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Maintenance of filters (1)
Change out is dependent on:
• Amount of loading
• Environmental conditions
• Flow rate
• Type of filter
• Location in ventilation system
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Maintenance of filters (2)
Change out is dependent on:
• Velocity
• Electrostatic charge
• Maintenance
• Safety
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Room air cleanersOzone generator
Negative Ion Generator
Electrostatic precipitator
HEPA filtered UVGI box
Electrically enhanced filter
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HEPA filtration devices
Consist of
• A HEPA filter to remove small particles
• A pre-filter to remove coarser particles (and thereby prolong the life of the HEPA filter)
• A fan to circulate air past the HEPA filter and into the room
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Advantages of HEPA filtration devices
• Useful in settings with inadequate ventilation
• Can be implemented right away, and room by room
• Relatively inexpensive
• Are moveable, or mounted on the wall
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Disdvantages of HEPA filter devices
• Unpredictable if controls are accessible to staff and patients to turn off
• Generate drafts and noise• Do not bring in outside air
or filter odours• Many factors limit
effectiveness (see next slide)
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Ways to increase effectiveness of HEPA filtration devices
Optimize the amount of room air that passes through the HEPA filter by:
• Maximizing air mixing in the room (avoid short circuiting, check placement of device with respect to air inlet and exhaust)
• Avoiding obstacles that could disrupt airflow (furniture, equipment, walls)
Ensure the device has sufficient airflow (see next slide) 17
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Selection of HEPA filter devices• Determine the ACH you need (WHO
recommends 12 ACH)
• Calculate airflow needed as follows:
Airflow in cubic meters per hour = Room volume X ACH divided by 60 minutes per hour
• Chose a unit whose published airflow (when running at the low speed setting) is at least the airflow you calculated
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Operation of HEPA filtration devices
• Consider as a source of clean air (and secondly as a removal device for contaminated air)
• Operate continuously while room is occupied
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Portable HEPA filtered device
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Room air cleaners
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Portable HEPA filtered room
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Summary (1)
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• Any contaminated air that might be recirculated into a room or exhausted near people must be filtered.
• A HEPA filter removes essentially all particles the size of TB droplet nuclei from the air passing through it.
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Summary (2)
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• Maintenance of filters is critical because as dust accumulates, the fan can move less and less air through the filter. This means reduced dilution and removal of infectious particles.
• Adequately maintained HEPA filtration devices can help clean room air if there is sufficient room air mixing and the device’s airflow is adequate to the size of the room