You have surely heard of the precision micro etching, especially in the latter period, for example when you have bought a vacuum cleaner or have looked for information on an air purifier. But what does this term mean and how does this ancient technology work?
What is a HEPA filter?
HEPA filter operation
Types of HEPA filter
Why is it useful to use a HEPA filter?
HEPA and virus filter
Conclusion
Ether and the effectiveness of the hepa filter
The term HEPA, from the English High Efficiency Particulate Air, indicates a particular high efficiency filtration system for fluids, liquids or gases. The precision micro etching is composed of microfiber filter sheets, thousands of glass fibers that intertwine with each other in multiple layers, separated by aluminum septa. These layers of filter sheets have the task of blocking the polluting particles.
HEPA filters were already common during the Second World War by scientists with the aim of capturing the radioactive particles release during the creation of atomic bombs. They were then certified in 1983, and have since been common as standard in household appliances for cleaning and air purification as well as in a wide variety of healthcare facilities and life science applications.
In fact, many professional engineering organizations recommend precision micro etching in hospitals, infection control clinics and other healthcare facilities to eliminate microbes and other dangerous particles.
The HEPA standard, born in America, requires that filters effectively retain a minimum percentage of 85% of particles up to the size of 0.3 microns, depending on the level classes, as we will see in the next paragraph.
precision micro etching can block these particles in various ways, using airflow, depending on their size:
Larger particles are physically blocked by the filter fibers
Medium- sized particles only partially follow the current flow and with the impact they are still trapped between the filter meshes.
Smaller particles collide with each other and behave more erratically, but are slowed down by diffusion and knocked down by inertia. In a true HEPA filter these methods join forces to remove contaminants.
These filters are part of the category of the so-called "absolute filters" and are characterized by a high filtration efficiency, in accordance with the UNI EN 1822 standards. They have classification according to the filtration efficiency of the particles of 0.3 µm , and for this reason they is easy to group into 5 classes (from H10 to H14) with increasing performance characteristics:
As we have seen, the HEPA filter is the best tool to retain polluting particles dispersed in the air. When it comes to air quality in enclosed spaces, homes, offices and other buildings, it is important to remember that indoor air can be 5 to 50 times more polluted than the outside.
This happens because normal indoor human activities and the substances present in all the furnishing elements.
We have talked several times about the size of the particles retained by the HEPA filter, down to the size of 0.3 microns. But what does this figure concretely mean? To understand the dimensions we are talking about; just think that a grain of sand has a diameter of 90 microns.
They are therefore invisible particles to the human eye and the smaller they are, the more dangerous they are for our health.
As they are able to pass the respiratory system and enter deep into the lungs, up to go into circulation. We talk about particulate matter to indicate the set of solid or gaseous substances suspended in air which vary in size, composition and origin. They can vary in size from a few nanometers to 100 µm.
We want to devote a paragraph to this very topical topic: can a HEPA filter retain viruses?
Let's start by analyzing the virus propagation mechanism in the air: it links to the propagation of droplets (droplets) on which it nestles. There are two mechanisms of transmission of a virus by air:
These appear on surfaces no further than 1-2 m from the infected person. The droplets come from coughing and sneezing.
These can remain suspended in the air for hours and is easy to transport over long distances. These are also generated by coughing, sneezing and the action of speaking.
The viruses are normally appearing in size between 0.02 and 0.30 microns. It is easy to filter through hepa filter cloth. For example, the new Coronavirus has dimensions between 0.10 and 0.15 microns as evidenced by a study by the San Rafaela University. As we have seen, propagation occurs because these nanoparticles are airborne by adhering to the larger particles.
Their sedimentation speed, i.e. their average travel time, increases proportionally to the diameter of the particle to which they join, consequently increasing the risk of coming into contact with people present in the same enclosed space. Hence the importance of reduce the airborne particulate to obtain a substantial reduction of microbiological contamination.
Given the above, let's summarize the essential points: The viruses have rounded morphology and dimensions ranging from 0.02 and 0.30 microns in diameter.
