Via Glenn Reynolds, this bit of fascinating news.
The coronavirus’ particle has a diameter of about 0.125 micron, he said, pointing to recent studies. HEPA filters are designed to filter particles that are 0.01 micron and above, Cuomo said, a figure he based on a previous NASA study on HEPA filtration.
Oh dear. It’s really a shame when non-STEM people try to do STEM without one iota of training or education. The problem with this is that none of it is true, at least, not exactly.
To rehearse what we’ve discussed before, while he has his sources that the virus is 125 nm in diameter, there are other sources that put it at around 80 nm in diameter. Furthermore, when he says that HEPA filters remove particles down to 0.01 µm in size, he’s referencing a NASA study of HEPA filters that essentially aren’t in use anywhere but space vehicles. Without observing the testing and performing my own independent analysis of the data, I question the study, but let’s move ahead anyway.
Most of the HEPA filters available for industrial use are nuclear grade HEPA filters, which remove particles to 0.3 µm in size. This means that a SARS-CoV-2 virus is 80E-9 / 0.3E-6 = 0.27 the minimum size necessary for even the most expensive nuclear grade HEPA filters to remove it from an air stream.
Furthermore, these systems are extremely expensive to design, build, maintain, flow balance and test. The filter housing themselves must be sealed and tested, the HEPA filters must be disposed of as hazardous material, the HEPA filters must be procured (there is a marginal market for that since these systems are only used in biological labs and nuclear power plants). A TAB (testing and balancing) engineer must test them and flow balance them, and the fans are powerful compared to normal use industrial fans since the ΔP is much higher across these filter trains than an ordinary industrial grade filter system.
The testing involves injection of DOP (Dioctyl Phthalate) to test penetration of fine particles through potential tears in the filter media and especially bypass around the filters themselves due to lack of proper sealing against the frame of the filter housing. The testing engineers for this sort of thing reside in one place, i.e., commercial nuclear reactors and utilities which run them.
I could go on about this, but it’s embarrassing to folks who know nothing about STEM to weigh in like this on subjects way above their head. I’ve done air filtration engineering, TAB and testing of penetration before. I know these things by education, training and experience.
The governor is essentially telling businesses in his neck of the woods that they must go out of business. That is the only alternative. No store or mall will be able to afford something like this, or the highly paid personnel to install it, test it, monitor it and equip it. Finally, these systems, if installed, wouldn’t create a virus-free environment anyway. It doesn’t work that way. A virus is like any other contaminant, which means that buildup and depletion of contaminants (based on a production term and loss constant) would be modeled with an ODE (ordinary differential equation).
The point is that the concentration of a contaminant can be reduced based on the terms, but not made to go away. Belief in risk free living based on science is belief in a myth. But someone who was studied in STEM would already know this. Only non-STEM people believe that science can work magic for free.