This article is the first in our new series about air purification technologies. It concerns the air purifiers with HEPA filters efficiency.
An air purifier with filters is a device intended to reduce or eliminate industrial and domestic pollution. It consists of several superimposed filters and covers a surface of area of about 5 to 150 m².
The « HEPA » appellation is often presented to consumers as a guarantee of excellence. This special designation is given only to product that have successfully undergone the DOP (Dispersed Oil Particulate) test. This test, developed in the 50’s, is used to test the filters ability to remove 99.97% of all particles of 0.3 microns mean diameter. In the air purifiers markets, there are a lot of products that do not necessarily meet the HEPA standard. Products that claim to be "HEPA-type", "HEPA-like", "HEPA-style" or "99% HEPA" may not have been tested in laboratories. Producers would play consumers for fools.
The Test Dop does not allow to determine the filters ability to trap particles smaller than 0.3 micron, which represent 90% of suspended particles. Concerning products that meet the HEPA standard, they are often inefficient on particles smaller than 0,3 µm, i.e on 90% of particulates. Then, filtration efficiency and purification are not synonym. The air speed through a filter must be fast if the purifier is to work well. So, the device becomes noisy.
A lot of factors limit the efficiency of HEPA filters :
According to a recent Canadian study, air purifiers with HEPA filter remove 68% of ultrafine particles and 63% of fine particles.
HEPA filters require a maintenance routine in order to work efficiently.