The science behind a HEPA Filter

Before explaining the science behind the HEPA (High Efficiency Particulate Air) filter, let's look at what one is. These filters are designed to trap both small and large particulate contaminants at a very high level. To qualify as a HEPA filter, a filter must trap a minimum of 99.97% of pollutants that are 0.3 microns in size according to standards set by the Institute of Environmental Sciences and Technologies (IEST). This is not to say that a HEPA filter can only trap particles this size; in fact, the filter is even more efficient in capturing contaminant particles that are smaller and larger in size. For more information on what a HEPA filter is please read our article: What is a HEPA filter and what are their benefits? How does a HEPA filter work? Different size particles in the air actually behave differently. It turns out that particles 0.3 microns in size are the hardest to trap. HEPA filters are cleverly designed to make use of different techniques so that the pesky 0.3 micron particles, as well as the larger and smaller ones, are all filtered out of the air. Sieving – Most particles are removed from the air by a HEPA filter by sieving. This occurs when particles are so large that they do not fit between through the spaces between fibres in the filter. These large particles are trapped at the fibres and do not move any further. Inertial Impaction - This mechanism operates on the particles which fit through the fibre gaps but are still fairly large and heavy. The air in a HEPA filter is pushed through a fine matt of intricately woven fibres. As the air flow bends around the fibres the heavier, larger particles don’t manage to bend round with the air and instead they collide with the fibres. Diffusion – The smallest polluting particles in air are too tiny to be carried in the air flow. So they randomly travel through, or diffuse through, the filter until they hit a fibre and become trapped in filter. Interception – Mid size particles, around 0.3 microns in size are carried quite well in the air flow through the filter. They are not trapped by the above mechanisms, but because of the quality and thickness of HEPA filters, the air flow will cause the particle to eventually collide with a fibre so that it can be removed from the air. How does a HEPA filter help in the home? An air purifier with a HEPA filter will remove at least 99.97% of pollutants in the air, improving the air quality dramatically. Air quality is so important to our health so making sure you breathe clean air when you are indoors is crucial since most of us spend 90% of our time there. In our homes we’re actually surrounded by chemicals such as harmful VOCs and formaldehyde which are given off from paint, furniture, carpets, fabrics and plastics. 72% of the chemicals we expose ourselves to, actually come from our homes – not our work places and not out in the city centres. Additionally mould, dust, pollen and skin particles from our pets all float around indoors causing allergy symptoms. Using an air purifier to clean the air of these nasties will mean that allergy and asthma symptoms improve, it will mean lower risk of respiratory diseases later on and you’ll probably find yourself sleeping a whole load better too. In fact we spend on average 2,372.5 hours a year sleeping so even just making sure you have an air purifier in your bedroom could really benefit your health.