HEPA filters known as High-Efficiency Particulate Arrestance filters were originally developed to filter fine radioactive particles. A HEPA filter will filter with a minimum efficiency 99.97% of particles 0.3 microns and 95% of particles 0.1 microns. With 1 micron measuring just 1/10,000 of a centrimetre and the smallest particle visible to the naked eye being 40 microns. 0.3 microns is many times smaller than dust mites, mould spores, pet allergens and pollens. HEPA filters are widely used in medical applications including: cleanrooms, pharmaceutical manufacturing and any environment where clean or sterile conditions are required.
Medical grade HEPA filters are made from highly efficient filter paper. The paper is folded in a concertina configuration to maximise the surface area of the filter and allow air to flow through with minimal resistance. There is a certain ratio of filter paper to airflow volume which must be followed in the construction of the filter to achieve the 99.97% efficiency rating. If there is not enough filter paper, efficiency will not be to HEPA standards.
How are HEPA filters made?
The filter paper is bonded airtight inside a filter casing made from steel. HEPA filters are delicate, they cannot be vacuumed or cleaned but due to the considerable surface area of the filter paper they will generally last 3 years or more when used with proper pre-filtration. HEPA filters must also have an airtight seal or gasket on the external face to prevent air from bypassing around the filter.
Air bypass is a common problem with air purifiers, where due to lack of a proper seal or filters are made from less than ideal sealing materials such as cardboard, paper or plastic, air bypasses around the filter resulting in efficiency being a fraction of the stated 99.97%. All InovaAirŪ HEPA air purifiers are factory certified to filter 99.97% @ 0.3 microns efficiency.
NB: Most residential HEPA air purifiers sold in Australia do not conform to medical grade HEPA standards. There is no regulatory authority which monitors claims by manufacturers that HEPA filters sold in either vacuum cleaners or air purifiers are actually 99.97% efficient.