Slowly But Surely
A high efficiency particulate air or HEPA filter is a type of air filter that satisfies certain standards of efficiency such as those set by the United States Department of Energy. HEPA filters are composed of a mat of randomly arranged fibres typically composed of fiberglass and possess diameters between 0.5 and 2.0 micrometer. HEPA filters are designed to target much smaller pollutants and particles which it traps (they stick to a fibre) through a combination of the following three mechanisms:
A HEPA air purifier may take longer to purify the air in a room in comparison to other regular purifiers. But it creates less noise and deals with particles that regular air purifiers are unable to do. Sometimes, doing it slowly but surely is much better than faster but lacking.
- Interception – particles following a line of flow in the air stream come within one radius of a fibre and adhere to it.
- Impaction – larger particles are unable to avoid fibres by following the curving contours of the air stream and are forced to embed in one of them directly.
- Diffusion – similar to Brownian motion, an enhancing mechanism is a result of the collision with gas molecules by the smallest particles, especially those below 0.1 µm in diameter, which are thereby impeded and delayed in their path through the filter.