Unit 6.4. Filtration

TB Infection Control Training for Managers

at National and Subnational Level

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

3

Filters

Filters

Filters

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

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

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

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.

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