Filtration Explained
Filtration
One of the very best ways of creating an indoor airborne health hazard is to suck all the bacteria, fungal spores, dust mite faecal particles, and any other particulate allergens out of the floor covering and then blow them liberally into the surrounding air where they travel easily from room to room contaminating the whole building.
This happens daily in practically every building in the land in the name of cleanliness.
The practice is so common that it is seldom challenged even in hospitals, nursing homes, and other health care establishments that should know better!These particles are microscopic, cannot be seen by the naked eye individually, and can usually only be perceived as a mist or fogging of the air when present in huge numbers.
The air may look perfectly clear but can be loaded with tens of millions of biologically active particles per cubic metre ready to transmit disease and allergens wherever they land.
We have put together the information below to help you understand vacuum cleaner filtration, the different levels available and dispel some myths.
Hospital Grade Filtration? - No such thing!
Filtration of 99.99% - Beware of Percentages
Even a HEPA filter may not mean HEPA filtration
What about cyclone machines and Water FIlters
How is the filtration in vacuum cleaners tested?
The Victor Long-life HEPA filter
Hospital Grade filtration? - No such thing!
There is no Official Hospital Grade Filtration. Don't by vacuum cleaner manufacturers that claim Hospital grade filtration or 3-stage or multi-stage filtration, this is just a way making inferior levels of filtration sound better. These levels of filtration do not match HEPA filtration or ULPA filtration. Furthermore, products approved by certain organisations are usually approved for a fee. Pay your fee get your approval. Association approvals do not necessarily mean a product performs better than others.
Filtration of 99.99% - Beware of percentages
While a filtration percentage of 99.99% may sound impressive it is at what particle size that matters. Clearly if it lets through one tennis ball sized particle in ten thousand this is not very good as everything smaller is probably being missed. But if the particle size is that of bacteria (between 1 and 10 microns in size) then this is much better, no tennis balls are getting through! HEPA filtration is tested at 0.3 microns far smaller than bacteria.
Even a HEPA filter may not mean HEPA filtration
Just because the machine has a HEPA filter doesn't necessarily mean that it is providing HEPA filtration. Many cheaper vacuum cleaners are not built particularly well and have holes and leaks between the point where the sucked up dirt enters the machine and passes through the filter. At these leak points air and dust particles can exit the machine back into the room. This is not ideal as the aim of vacuuming is to keep the dirt in the machine!
Also, filtration media tested at much lower airflow rates (e.g., for use in respiratory face masks) than in an actual vacuum cleaner may lead to an artificially high percentage efficiency 'claim', sometimes by a factor of 50 or more.
What about Cyclone machines and Water filters?
Air cyclones can separate debris and particles down to about 100 Microns under ideal conditions. Filtration is usually worse than this, however, as performance deteriorates with varying flow rates.
Water based machines can filter down to about 10 Microns. This means that millions of microscopic particles and organisms escape back into the room, the reason is that water is really quite porous and anyway produces microscopic droplets of its own!
To provide reliable filtration a physical barrier type of filter is necessary even on machines where other filter methods are employed. A traditional vacuum cleaner fitted with a standard textile dust bag can filter down to about a 30 micron particle size.
A normal two ply paper dust bag will usually filter down to a particle size of 15 microns (twice as small). To eliminate biological contamination the level of filtration must be many times better than this since bacteria are between 1 and 10 Microns in size.
Specifying ‘HEPA’ rated vacuum cleaners will ensure that the exhaust air is ‘biologically’ clean and filtered down to 0.3 Microns (100 times as small).
‘HEPA’ - an acronym for High Efficiency Particulate Air filter. The HEPA filter was specified by NASA as early as the 1960’s for satellite and space probe assembly clean-room areas where the air is required to be ‘biologically’ clean (all living organisms having been mechanically removed by the filter). The Apollo moon-landers for example, were assembled in this standard of clean room environment.
To meet the ‘HEPA’ standard of filtration the unit must remove particles larger than 0.3 Microns in diameter with more than 99.97% efficiency (i.e., fewer than 300 particles per million of 0.3 Micron size should penetrate). Even the smallest bacteria are somewhat larger than this!
A particle of 0.3 microns is smaller than the wavelength of visible light, and too small to be seen with even the most powerful optical microscope.
With good filter design this standard can be exceeded, for example the Victor V-9 HEPA tub vacuum, in tests, achieves an efficiency of 99.9965% - passing only 35 particles per million which is 8 times better than the standard allows.
How is filtration in vacuum cleaners tested?
IEC60312 is the only international standard available for the measurement of air filtration efficiency of vacuum cleaners for household and similar use.
The test is performed with the complete vacuum cleaner mounted inside a sealed test rig specified by the standard. The cleaner inlet is dosed with measured amounts of standard dust, and particles in the discharge air are counted into six separate size bands down to 0.3 microns. The test approximates to actual use conditions and the results are standardised as a single percentage efficiency figure enabling the direct comparison of one vacuum cleaner with another.
Particle sizes are measured in Microns. A Micron is one-thousandth part of a millimetre (one-millionth part of a metre).
The following table shows the size in Microns of various types of particle.
|
Particle |
Size in Microns |
|
One inch |
25,400 |
|
One millimetre |
1,000 |
|
Dust Mites |
150 - 300 |
|
Thickness of a Human Hair |
70 - 100 |
|
Traditional Vacuum Cleaner Filtration |
30 - 50 |
|
Pollen Grains |
30 - 50 |
|
Dust Mite Faecal Particles |
15 - 30 |
|
Fungal Spores (Alternaria) |
10 - 15 |
|
Limit of Naked Eye Visibility |
10 |
|
Dander from Domestic Pets |
2 - 15 |
|
Diesel Engine Exhaust Particles |
2 - 10 |
|
Bacteria (Microbes) |
1 - 10 |
|
Fungal Spores (Aspergillus fumigatus) |
1 - 3 |
|
Tobacco Smoke |
under 1 |
|
Wave of Red Light |
0.7 |
|
Limit of Optical Microscope Visability |
0.5 |
|
Wavelength of Violet Light |
0.4 |
|
HEPA Vacuum Cleaner |
0.3 |
|
ULPA Filtration Test Particles |
0.1 |
|
Viruses |
Under 0.1 |
Here are some other terms that are fairly commonly quoted where vacuum cleaner filters are discussed:-
‘ULPA’ filter - an acronym for Ultra Low Penetration Air filter.
A standard of air filter specified for use in industrial ‘super-clean’ room areas where microchips are produced. The filter must remove particles larger than 0.1 Microns in diameter with more than 99.999% efficiency (i.e. fewer than 10 particles per million of greater than 0.1 Micron size should penetrate).
This produces a ‘super-clean’ environment many times cleaner than naturally occurring anywhere on earth (even fewer particles per cubic metre than at the poles or in the stratosphere above the middle of the Pacific Ocean). Despite this ultra high filtration, the air is not ‘biologically’ cleaner than HEPA filtered air, and will still pass viruses which are less than 0.1 Microns in size.
‘S’ class and ‘H’ class filter types are sometimes referred to in advertising literature. They are both filter media classifications using a German DIN standard for the certification of air filter materials to be used in air conditioner units and room ventilators.
The test measures the penetration of an oil mist through the material at low airflow rates. The term ‘H’ class filter under no circumstances should be confused with an ‘H’ class vacuum cleaner which is a machine specially designed and certified for use with hazardous dust (e.g., asbestos) according to BS5415.
The Victor Long-life HEPA Filter
The Victor HEPA filter is a two stage filter. The first stage consists of a robust non-woven material which filters down to 25 Microns and has the ‘tap to clean’ feature of nylon fibres.
The second layer is a special air filter pad consisting of a unique blend of synthetic fibres composing a highly stable coarse fibre electrostatic filter media.
The differing fibre types generate static electric fields within the thick filter mat and capture particles very much smaller than the passages through which the air is travelling. With much more room within the filter to retain particles without ‘blinding’ filter life is greatly enhanced.
The capacity of a Victor HEPA filter to retain trapped microscopic particles is over 100 times more than a comparable ‘porous paper’ air filter.
Click here to see the Victor V-9 tub vacuum featuring Victor HEPA filtration.