The Concept of HEPA
How To Design An Effective Anti-epidemic Mask
What’s the concept of HEPA?
And why ACTife’s mask is the only mask design on the market that uses both HEPA principles and physical antibacterial materials to achieve the effective epidemic prevention?
What is HEPA?
HEPA stands for High-Efficiency Particulate Air Filter, which can be made of filter paper, non-woven fabric, or glass fiber. According to the definition of the U.S. Department of Energy, a filter that can block more than 99.7% of suspended particles with a size of 0.3 microns is a HEPA filter. It is interwoven by very fine fibers, which can capture particles very effectively.
The way how HEPA filters air is not like sieving particles, in fact, HEPA filters rely on the adsorption of fiber to hold the fine dust below PM2.5. The point is, how to use a larger grid to block particles smaller than the grid? The answer is down below.
We can consider the following two benefits:
When the particles are collided by molecules in the air, and the virus aerosol particles that produce Brownian motion move toward the mask, they will move in the space in a non rectilinear random motion. This motion is divided into a combination of linear motion (when not impacted) and non-differentiable transient reversible motion (when impacted), causing these virus aerosol particles to be effectively blocked by the fiber of the mask, even if the density of the mask fabric or fiber does not reach the mesh size that is smaller than the virus aerosol, it will still stick to the mask fiber due to these random movements.
When we further analyze the Brownian motion of these virus aerosol particles in the air, we can get the following four conclusions:
The simple conclusion is, the smaller the mass and the volume of the virus aerosol, and the hotter the weather, the thinner the air, the more intense the Brownian motion of the virus aerosol. So we find that the virus is more likely to be grabbed by the mask fabric.
In the design of mask, in order to block these particles that’s doing Brownian motion, we can usually see the following strategies:
Strategy 1: Use electrostatic adsorption. When the virus aerosol particles approach the mask in a Brownian motion, they will be very easily attracted by the electrostatic adsorption layer and stick to the mask.
Strategy 2: Use various design methods of HEPA filter. For example, let the surface of the filter show a 3D texture, which increases the proportion of virus aerosol particles adsorbed by the mask material.
The above two strategies seem to have a high barrier effect, but we have to pay attention to several important risks:
An extremely important key concept here is to allow virus aerosol particles to stay on the mask longer due to Brownian motion in the air. If the mask has no antibacterial function, all we can do is passively wait for the virus to slowly lose its activity over time. The time that the virus can survive in the aerosol is often longer than the time the particles stay on the mask that has HEPA or electrostatic design. The conclusion is that the epidemic prevention effects of these methods are actually very limited.
Using the ACTife’s ACT sputtered antibacterial material in the mask design can achieve breathability and extend the time that the particles stay on the mask. When the virus can stays on the mask for more than tens of seconds, the antibacterial ACTife material on the mask will achieve effective sterilization (please refer to the test report), allowing the mask to not only breathable, but also achieve a very safe epidemic prevention effect. This is one of the important concepts of ACTife antibacterial protective masks and 3D beatify masks. This is a technology that makes the mask have both breathable and anti-epidemic ability.
The term “aerosol” refers to solid or liquid particles suspended in the gaseous medium, including all common substances in life such as dust, fog, smoke, PM2.5, fungal spores, droplets, and inhaled drugs for clinical treatment of respiratory diseases, etc., all belong to aerosols, and the particle size are different from the types and sources. Everyone will produce many visible or invisible particles in the process of breathing (quiet breathing and deep breathing), speaking, sneezing, and coughing, with a diameter ranging from 0.01 to 500 microns (μm，10-6 m). When the particle diameter is greater than 10 microns, it can sink to the ground due to gravity, which is called “dust fall”, and when the particle diameter is less than 10 microns, it can be suspended in the air, which is called “suspended particles”. Simply use the thickness of the hair to illustrate the concept of particle diameter. For example, the diameter of a 10-micron particle is about 1/7 of the diameter of a human hair, and a 2.5-micron particle is about 1/28 of the diameter of a human hair.