Operation of vacuum cleaners make dust particles, allergens, young and adult fleas, mites etc to become airborne. If the exhausting air is not properly filtered, all those 'nice' things could end up in human lungs – this can cause severe health problems for operator and for all those nearby.
There are several methods used for filtering exhaust air – most vacuum cleaners use several filtering methods for achieving the best filtration possible:
- Bag – dirt bag is typically used to collect vacuumed dirt and dust from floors. As air flow passes through the bag, it gets filtered. Bags are usually made from paper or fabric and can be disposable or reusable vacuum bags. Often behind a bag, but before fan and electric motor, there is at least one additional filter that should be also regularly cleaned or replaced.
- Bagless – bagless models use container and reusable filter instead of a bag. There can be several filters, each one with finer pores for better filtration.
- Cyclonic separation – this bagless vacuum cleaners use rapid rotation of air flow in circular container to separate dust particles from main air flow (centrifugal force). To improve filtration even further, additional mechanical filters can be used.
- Water filtration – some vacuum cleaners use water as filter. During operation, air flow with dirt is forced through the water before it is exhausted out of the vacuum. These vacuum cleaners must be emptied after each cleaning, but they can clean dry and wet surfaces and even larger liquid spills.
- Ultra fine air filter or HEPA (High Efficiency Particulate Air) filter – this is high quality second or even third filter in vacuum cleaner that remove any remaining dust particles that could otherwise be returned into the cleaned room. According to the United States Department of Energy definition of HEPA filters, they can remove at least 99.97% of particles 0.3 micrometer in size. Some HEPA filters are cleanable, but should be replaced after some time. In order to achieve even better filtration, these filters are sometimes combined with bag filtration or cyclonic separation, followed by HEPA filter and then followed by activated carbon filtration system (or activated carbon is part of dirt bag or HEPA filter) - these systems can be pricy, but their exhaust is practically pure air.
Note - size of dirt particles commonly found in human environment are:
- bacteria 0.3-10.0 micrometers,
- pollen 10.0-100.0 micrometers,
- pet and human hair 30.0-200.0 micrometers,
- dust mites 90.0-600.0 micrometers,
- sand 50.0-1000.0 micrometers, etc.
In the European Union, filtration is defined by standard EN 1822:2009. This standard defines several classes of EPA/HEPA/ULPA air filters by their ability to retain the most penetrating particle size (MPPS) particles. MPPS for most filters is in the 0.1 and 0.3 micrometers range.
Note: EPA Filters - Efficiency Particulate Air Filters, HEPA Filters - High Efficiency Particulate Air Filters, ULPA Filters - Ultra Low Penetration Air Filters.
The following table shows the various classifications of EPA/HEPA/ULPA filters according to the EN 1822 standard - in plain English, this table describes 'worst case scenario' filtration level regarding most penetrating particles, which are usually in 0.1 and 0.3 micrometers range - far below size of dirt like sand, mites, pollen and similar. But, small bacteria fits this size, as well as most of the viruses.
|Filter Group||Filter Class||Integral Value||Local Value|
|Filtration Efficiency||Penetration||Filtration Efficiency||Penetration|
|EPA Filters||E10||85 %||15 %||-||-|
|E11||95 %||5 %||-||-|
|E12||99.5 %||0.5 %||-||-|
|HEPA Filters||H13||99.95 %||0.05 %||99.75 %||0.25 %|
|H14||99.995 %||0.005 %||99.975 %||0.025 %|
|ULPA Filters||U15||99.9995 %||0.0005 %||99.9975 %||0.0025 %|
|U16||99.99995 %||0.00005 %||99.99975 %||0.00025 %|
|U17||99.999995 %||0.000005 %||99.9999 %||0.0001 %|
Integral value shows efficiency of the air filter as a system and that is what average user should be focused on. EN 1822 standard doesn't define Local Values for E10-E12 filters.
US HEPA standard vs. EU HEPA standard - according to the table, US HEPA standard is little bit better than H13 standard and US standard defines exact size of the particle, while EU standard uses MPPS, so it is fair to say that US HEPA is more or less equivalent to EU H13 HEPA.
Note that filters cause air pressure drop and for HEPA filters it is around 300 pascals (300 Newtons per square meter, 0.044 psi, 0.003 atm) for nominal air flow rate.
To filter and purify exhausted air even more, some vacuum cleaners also can use:
- UV light for germicidal irradiation. Ultraviolet lamp irradiates air flow before air is exhausted from vacuum cleaner. Additionally, one more filter can be positioned after UV lamp. Also, to prevent mites and allergens from 'hiding' behind larger particles, air must be also filtered before it passes the UV lamp. Warning – if your vacuum cleaner has UV lamp, DO NOT take it apart and try to test run it – UV light is very dangerous and can cause skin burns or even cancer! UV light is not common feature on home vacuums, but it practically disinfects air flow. Although such light sources are rather cheap, they are not often used, because oxygen molecules 02 reacts with UV light and produce ozone 03, which is very harmful. To minimize ozone production, instead of full spectrum UV lamps, UV lamps that emit light above 260 nm are used.
- Scent can be added to vacuum cleaner – as air passes through, scent can be added to increase feeling of 'freshness' in the cleaned room. Scent is added usually in the form of pebbles to the specially designed storage container of vacuum cleaner. Some powdered scents can be simply vacuumed into the vacuum bag, but if one has activated charcoal filters, hardly anything will pass it.
- Charcoal or activated carbon filtration system can absorb various chemicals on a molecular basis, but can be problematic with larger particles. Charcoal filtering is often combined with HEPA filters, or at least, good vacuum bag or cyclonic particle separation system.
- Ionizer purifiers use charged electrical surfaces or sharp needles to generate electrically charged gas or air ions. Ions attach to airborne particles which are then collected electrostatically on collector plate. Also, these devices produce some trace amounts of ozone, which can be hazardous in larger amounts. Ionizer purifiers are not very often part of home vacuum cleaners – mostly can be found as standalone devices in homes and industrial areas where they are called electrostatic precipitators.
Which methods of exhaust air filtration are going to be used, depends on construction of vacuum cleaner and model type.
For example, drum vacuum cleaner can use water filtration in combination with HEPA filter - most of the particles are trapped in the water and only small amount of dirt gets to the HEPA filter itself. This way, HEPA filter will function properly for longer period of time, before it needs to be cleaned or replaced. Water in such vacuums is changed after each cleaning.