American Know-How: Indian Tribe Shows Us How To Make A COVID Filter

Eureka CA

Description

Improved ventilation is one way to protect yourself from Covid (and whatever future respiratory-driven pandemics are coming down the pike). The Journal of American Medicine summarizes the current state of the science and the engineering in “Indoor Air Changes and Potential Implications for SARS-CoV-2 Transmission,” April 16, 2021. Controlling concentrations of indoor respiratory aerosols to reduce airborne transmission of infectious agents is critical and can be achieved through source control (masking, physical distancing) and engineering controls (ventilation and filtration). With respect to engineering controls, an important flaw exists in how most buildings operate in that the current standards for ventilation and filtration for indoor spaces, except for hospitals, are set for bare minimums and not designed for infection control….. To reduce far-field airborne transmission of SARS-CoV-2 in small-volume indoor spaces (eg, classrooms, retail shops, homes if guests are visiting), the suggestions include targeting 4 to 6 air changes per hour, through any combination of the following: outdoor air ventilation; recirculated air that passes through a filter with at least a minimum efficiency rating value 13 (MERV 13) rating… Those are the specs, then. ….or passage of air through portable air cleaners with HEPA (high-efficiency particulate air) filters. We won’t be looking at portable air cleaners in this post. Instead, we’ll look at DIY box fans to filter the air, and increase air changes per hour. And just to let JAMA hammer home airborne transmission yet once more: Despite the dose-response for SARS-CoV-2 being unknown, and continued scientific debate about the dominant mode of transmission, evidence supports these suggestions. First, SARS-CoV-2 is primarily transmitted from the exhaled respiratory aerosols of infected individuals. Larger droplets (>100 μm) can settle out of the air due to gravitational forces within 6 feet, but people emit 100 times more smaller aerosols (<5 μm) during talking, breathing, and coughing. Smaller aerosols can stay aloft for 30 minutes to hours and travel well beyond 6 feet. Second, high-profile and well-described SARS-CoV-2 outbreaks across multiple space types (eg, restaurants, gyms, choir practice, schools, buses) share the common features of time indoors and low levels of ventilation, even when people remained physically distanced. Third, these suggestions are grounded in the basics of exposure science and inhalation dose risk reduction. Higher ventilation and filtration rates more rapidly remove particles from indoor air, thereby reducing the intensity of exposure and duration that respiratory aerosols stay aloft inside a room. Fourth, this approach is consistent with what is used in hospitals to minimize risk of transmission To the box fans! On the personal level, making an anti-covid box fan could be a fun project if you’re good at DIY (which I am not, so please bear that in mind). Institutionally, CDC’s blather about layered strategies has managed to leave hygiene theatre firmly ensconced in the minds of officialdom (see e.g. at “deep cleaning”), which means that schools, especially, may not spend money on ventilation, not even HEPA air cleaners. Hence the need for a cheap, DIY ventilation solution. (How to bring in outside air by getting doors and windows open, especially windows that have been sealed or even painted shut, is another question entirely. For them, I can’t think of any solution that doesn’t start with removing a pane, and moving on from there.) The box fans serve two purposes: One is to circulate air and dilute the virus, as well as bringing in air from the outside, if there is a draft. The second is to filter the air to remove particles from it, including aerosols. Since air circulation is more or less a given with a fan, most of the focus here will be on the filters. Box fan designs come in two flavors; type (A) uses an actual “box fan” with a filter attached (the square kind you place on the floor or in a window); type (B) is a cube made from filters, a box on which a box fan is placed. (A) Here’s a video that shows how to assemble a box fan with a MERV 13 filter: 'Box Fan Filter A DIY Users Guide Colville Tribes Air Quality Program', https://www.youtube.com/watch?v=ukyF2xm8cws (There is also a double-filter design shown at the end.) Here is a handy diagram (see above). Note that the fan pulls air through the filter. You will need to position the MERV filter’s airflow arrow accordingly. From my reading, there seem to be two issues with the box fan: Fastening, and leakage. For fastening the filter to the fan, the video uses what looks like blue painter’s masking tape. The classical solution would be, of course, duct tape. Duct tape leaves a sticky residue, icky when changing the filters. Painter’s masking tape does not, but secures the filter less effectively. An alternative is to use a rubber bands (shown above). Others suggest a cube instead of a triangle. This increases the total surface area of the filter and allows for more throughput as well as decreasing the frequency of filter replacement (see above). Why a cube? Blue House Energy explains: The challenge with filters is they create a barrier between the fan and the room, slowing down the amount of air that gets delivered. Filters that are more tightly woven, catching more of the smaller PM2.5 also make it harder for air to pass through. This creates a decrease in air flow and a higher pressure drop. So there are concerns about overheating the fan motor when you add a high-MERV filter. The pressure drop makes the fan work harder to push air through the fan. The tent and box versions reduce pressure drop by increasing the amount of filter surface area, decreasing the effect of air resistance. Bonus points: more filter surface area means you don’t have to replace the filters as often. Do box fans work? According to Tex-Air filters (quoted in Wired above) they do: The current thinking is that particles containing viable Covid-19 viruses start at about one micron. Particles less than 5 microns settle out of the air very slowly. They can remain airborne for hours. These particles are called aerosols and are one of the major methods for transmission of Covid-19. Consequently, the one to five micron particle size range is a good target for filter removal. So how did we do in our tests with our “Box Fan with a MERV 13 filter” cleaning device? In the tool room, the device removed 59.7% of the one micron sized particles and 86.4% of the five micron sized particles. In the breakroom, the device removed 74.6% of the one micron sized particles and 80% of the 5 micron sized particles. In short, the results show meaningful reductions in the target particle size range. The “Box Fan with a MERV 13 Filter” should be a useful tool in the fight against Covid-19.. One thing we need to make clear – this device is not a HEPA air purifier. It does not have a Clean Air Delivery Rate (CADR) which is the standard for measuring the effectiveness of air cleaners. Purchasing and using a HEPA air purifier is the better option. However, their cost may be prohibitive. In this case the “Box Fan with a MERV 13” filter is a reasonable option. More info: https://www.nakedcapitalism.com/2021/06/fun-with-diy-box-fans-and-protection-from-covid-through-filtration-better-ventilation.html This is much cheaper than having everyone wear a mask, better for everyone's health, and a better solution to the problem of keeping the air clear of very small particles. Do the math! It cleans the entire volume of air in the room, over and over and over. However, keep some masks around, for whenever officials visit... lest you lose your children to The Honorable Christopher Wilson and his krewe of merry Child Welfare Services kidnappers, for not protecting your little snowflakes from the Big, Bad COVID Delta Force Monster.