How do filters work in a Cleanroom?

1) What filter classes are there in cleanroom technology?

2) How does a ULPA filter work?

3) When does a filter need to be replaced?

1) What filter classes are there in cleanroom technology?

For the planning and design of an air conditioning system in the Cleanroom a well thought-out filter system is crucial. As a rule, a multi-stage filtration system is used – with the aim of cleaning the air step by step from coarse to suspended particles.

Why? Quite simply, the higher the filtration efficiency of a filter, the more sensitive and expensive it is. Targeted grading of the filter classes can protect the particularly fine final filters and extend their service life.

Typical structure of a 3-stage filtration system

In a standard configuration, the air is filtered in three stages – from coarse to fine:

1. 1st filter stage: Coarse filter (G filter)
   • Use in the fresh air duct
   • Filters larger particles such as pollen, dust and fibers
   • Objective: Protection of the system and downstream filters
2. 2nd filter stage: fine dust filter (F or ePM filter)
   • Located in the air conditioning/ventilation unit
   • Filters smaller particles such as fine dust and smoke particles
   • Serves to further reduce the load on the final filter
3. 3rd filter stage: HEPA filter (H or U filter)
   • Terminal filters on the clean room side, e.g. in the FFUs (Fan Filter Units)
   • Filters ultra-fine particles (e.g. bacteria, aerosols)
   • This is where the cleanroom class is decided

Why is multi-stage filtering so important?

• Protection of the high-quality final filters: Coarse and fine dust filters trap the coarse particles so that the expensive HEPA filter is not clogged prematurely.
• Cost-effectiveness: The staggered filtration reduces operating costs as the final filters need to be changed less frequently.
• Ensuring cleanroom quality: The required ISO or GMP class can only be reliably maintained with an optimally coordinated filter chain.

Important note: Certification from filter class H13

Particularly strict requirements apply from filter class H13:

• It must be individually tested and proven that the filter fulfills the required separation efficiency.
• The test is carried out in accordance with EN 1822.
• Each filter receives its own certificate, including proof of freedom from leaks.

Overview of filter classes in cleanroom technology

2) How does a ULPA filter work?

ULPA filters (Ultra Low Penetration Air) belong to the family of HEPA filters, which were developed for the highest purity requirements. Developed for maximum safety, it reliably filters even the tiniest particles from the air.

What is a ULPA15 filter?

ULPA stands for Ultra Low Penetration Air. Compared to the familiar HEPA filters, ULPA15 filters have an even finer structure and achieve an extremely high separation efficiency:

• Separation efficiency: 99.9995 %
• Particle size: 0.1-0.2 micrometers
• Approval: For all ISO cleanroom classes (1-9) and GMP areas

This means that a maximum of five out of every million particles make it through the filter – and that’s with particles smaller than a bacterium.

Where are ULPA15 filters used?

Thanks to their extreme performance, ULPA15 filters are particularly suitable for cleanrooms with the highest requirements, e.g:

• Semiconductor and microchip production
• Optics and laser technology
• Pharmaceutical and biotechnological plants
• Medical manufacturing (e.g. implants)

How does filtration work?

ULPA15 filters consist of fine glass fiber layers that are folded and layered several times. They combine several physical filter mechanisms:

1. sieve effect

Larger particles (> 10 µm) cannot pass through the fine pores of the filter and are mechanically retained. The particles are held back by the distance between the fibers in relation to the particle diameter, i.e. they simply do not fit through the narrow pores of the filter medium.

2. inertia effect

The mass of the particle (>1 µm) is so large that it is too inert to follow the flow line around the fiber and therefore hits the fiber of the filter medium and gets stuck there. This effect increases with increasing air velocity, larger particles and smaller fiber diameter.

3. blocking effect

A small particle is brought so close to the fiber in its streamline that it collides with it and gets stuck. The particles separated are mainly 0.1 to 3 µm in size. The more fine filter fibers with the same diameter as the particle to be separated, the better the effect. The effect of fiber attraction is enhanced if the filter fibers are also electrostatically charged.

4. diffusion effect

Ultrafine particles (<1 µm) move in an uncontrolled manner through Brownian molecular motion – i.e. microscopic tremors. As a result, they tend to collide with fibers and stick to them. The trembling motion is caused by constant collisions with surrounding gas particles.

Combination of effects = ULPA performance
All four mechanisms work together. The “most critical” point is the MPPS (most penetrating particle size) – the particle size that is the most difficult to filter. The separation efficiency at this size determines the filter class.

By combining these mechanisms, ULPA15 filters can efficiently remove even the smallest airborne pollutants such as viruses, bacteria, aerosols and nanoparticles.

3) When does a filter need to be replaced?

Filters are at the heart of every cleanroom ventilation system. They protect processes, products and people from particles, germs and other contaminants. But at some point, the filter has to be replaced. But when exactly?

Why filters don’t last forever

Over time, more and more particles are deposited in the filter material. This increases the differential pressure – i.e. the pressure difference before and after the filter. Interestingly, this also increases the separation efficiency somewhat – but this comes at a price: higher energy consumption and possible impairment of the air volume.

Three clear indications for a filter change:

• Mechanical damage
  Cracks, holes or pressure points impair the function and pose a risk.
• Reaching the service life
  Each filter has a defined service life – depending on the type and place of use.
• Final pressure loss reached
  The filter manufacturer’s recommended maximum pressure loss has been reached – a clear signal for replacement.

Recommended service life at a glance

HEPA filters – special case with risk assessment

The replacement time for HEPA filters (e.g. HEPA 14 or ULPA 15) depends heavily on the area of application. This is where a risk analysis often comes into play:

• Is there a possibility that deposited microorganisms (e.g. bacteria, viruses) could multiply in the filter?
• Could this lead to a germ breakthrough to the cleanroom side?

If so, the filter should be replaced prematurely, i.e. after the specified service life – usually after 3 to 5 years.

If the microbiological risk is low, the filter can continue to be used until the final pressure drop is reached.

Regular testing in accordance with ISO 14644-3

As part of routine cleanroom qualification, the air velocity and the volume of air conveyed are measured, among other things. These values are also used to assess whether the filters are still performing to their full capacity – and help to identify the need for replacement at an early stage.

Conclusion:
A filter change is not a gut decision, but depends on clear technical and hygienic criteria. If you check regularly, observe the service life and pay attention to warning signals such as pressure loss, you are on the safe side – for a permanently safe and efficient Cleanroom.