Regarding “Understanding the ‘Scope’ of the Problem: Why Laparoscopy Is Considered Safe during the COVID-19 Pandemic”

SARS-CoV-2 range in size from 0.06 to 0.125 μm, falling squarely within the particle-size range that HEPA filters capture with extraordinary efficiency: 0.01 micron and above. It is incorrect to state that HEPA filters are not able to catch particles below 0.3 micron, like SARS-CoV-2 virus. This belief is based on a misunderstanding of how HEPA filters work. The particles size of 0.3 micron is used as a standard to measure the effectiveness of HEPA filters, but this does not mean they are not able to catch smaller particles. A paper from the NASA1 well explains that HEPA filters are highly effective in capturing a very high proportion, up to 100%, of nanoparticulate contaminants, ranging in size from 0.1 to 0.001 micron (diffusion regime) because they don’t fly straight, collide with other fast-moving molecules, move around in random pathways and hit the filter fibers remaining stuck in them. This is known as the Brownian movement. The intersecting regime has just a small drop in efficiency that affects the particles of around 0.3 μm, defined as most penetrating particle size (MPPS). This value for a typical HEPA filter varies from 0.2 to 0.3 micron, depending on flow rate, and lowering the flow speed, a simple HEPA will perform as an ULPA filter.