Patient Safety COVID-19
Whole building air purification to protect from SARS-CoV-2
At Anacortes Dermatology we have a state-of-the-art air purification system to reduce exposure to SARS-CoV-2. This is accomplished in two steps. First, 100% of the air circulated through our HVAC system is filtered through an advanced medical-grade HEPA filter with over 170 square feet of surface area. This filter removes even ultra-fine particles, less than 1/20th the size of the SARS-CoV-2 virus. It effectively eliminates 95% of particles down to 0.003 microns, the smallest particles that exist. This system can clean the entire volume of air in the building approximately 125 times per day. The circulation of air has also been modified, such that HVAC air intakes are outside exam rooms. This leads to positive pressure with clean filtered air. We have the same system that was used to help fight the SARS virus outbreak in Asia, and it is the #1 system used in hospitals. Second, our exam rooms have a stand-alone air filtration system that combines granulated aluminum and carbon filters, along with a medical-grade HEPA filter. This device removes 99.5% of all ultra-fine particles down to 0.003 microns. The total air volume in our entire exam room is filtered approximately every 2.5 minutes. This means during the average appointment, the air in our exam room will have been purified over 12 times!! As you can see from the graph below, starting at time zero (0) with heavily contaminated air, our purifiers rapidly remove particles of all sizes within minutes. This was verified by two independent particulate meters in the exam room, measuring everything from ultrafine particles <0.3 microns, to more than 10 microns (y-axis is the number of particles/volume).
A word about COVID-19 and “normal” HEPA filters
SARS-CoV-2 is very small, around 80 to 120 nanometers (0.12-0.08 microns). It is believed that the main mode of infection from Coronavirus is via respiratory transmission, where the virus is emitted into the atmosphere on much larger droplets of moisture or saliva, around 12-21 microns. These droplets can dehydrate and shrink to some degree, and remain suspended in the air for eight to fourteen minutes on average, but can persist for hours depending on air movement patterns. The micro-droplets can also adhere to much larger particles such as dust or pollen (15-200 microns). These particle sizes are effectively captured by even by “normal” HEPA filters, which filter out particles greater than 0.3 microns (100 times larger than our ultra-fine HEPA filters remove).
Current data suggests that SARS-CoV-2 is transmitted when a patient coughs, sneezes, talks, or even just breathes normally. Because SARS-CoV-2 is a new virus, the literature is very confusing regarding air purification with HEPA filters. Recent data suggests it's unlikely respiratory droplets less than 1 micron are infectious because nearly all emitted droplets are larger than that size, and the probability that the original hydrated 3-micron drop (which would dehydrate to 1 micron) contains an infectious virus particle is less than 0.01%.3
Use of HEPA purifiers to filter infectious pathogens is well documented in Positive Pressure Powered Air Respirators, where the HEPA purifiers have been used to block a variety of viruses.4 Recently scientists have designed systems utilizing HEPA purifiers to protect physicians when intubating patients with COVID-19.5 During the initial SARS outbreak in 2003, HEPA air purifiers were widely used to control infection throughout hospitals in Taiwan.6 Further, HEPA filters can effectively block the particle transmission of Porcine Respiratory Virus (PP-RSV), which is approximately half the size of SARS-CoV-2.7 Use of HEPA filters are recently described as surgical 'best practices' during neurosurgical procedures where negative air pressure is combined with HEPA filters for clean areas.8 Finally, according to the Centers for Disease Control, HEPA filters capture 99.9% of particles (bacteria, fungi, and larger viruses or virus clumps) 0.1-0.3 micrometers in diameter. We feel the predominance of the evidence suggests that HEPA filters are an excellent addition to our clinic and will make it a much safer environment for our patients. This is especially true since our HEPA filters effectively eliminate particles even 1/20th the size of SARS-CoV-2.