The topic for today is Air Purification.
During this podcast, we will take a deeper dive into Air Purification Systems. It is our intent to make you more knowledgeable of the choices and technologies available so you can make the best decision for your practice.
By now you have been back in your practice working hard every day to adapt to the new “normal”. We are realizing that we are in this COVID-19 Pandemic for the long haul now and that our work practices today may persist for the foreseeable future…this may, in fact, be the “new normal”.
As concern for the transmission of HIV, AIDS, and Hep B ushered in the OSHA Blood Borne Pathogens Standard in the early 1990s, it is possible we may see an “Airborne Pathogens Standard” emerge from the present COVID-19 Pandemic. Especially since we understand better that infection with COVID-19 comes primarily from breathing air in indoor spaces where people with the coronavirus have been. The greater the exposure, the greater the risk of becoming infected.
After urging steps like handwashing, mask-wearing, and social distancing, researchers say proper ventilation indoors should join the list of necessary measures. Health scientists and mechanical engineers have started issuing recommendations to schools and businesses for how often indoor air needs to be exchanged, as well as guidelines for the fans, filters, and other equipment needed to meet the goals.
We are all concerned about the health of our patients and staff and desire to provide care in the safest worksplace and in the safest manner possible. Dentists maybe thinking about, or have already purchased devices such as air filters, UVC lights, and suction devices to help reduce dental aerosols as well as “clean”, filter, and purify operatory air where aerosols are generated. Products marketed today to sanitize and reduce dental aerosols may lack research to support efficacy claims.
Before you move forward and pull the trigger on “air purification” technology lets spend some time reviewing the terms, vocubulary along some of the pertainant science.
Today, we are at a unique and unexpected intersection of infectious disease transmission, aerosols, filtration, HVAC (heating, ventilation, and air conditioning) and mechanical engineering. Who would have every thought, as dentists, we would be so concerned with HVAC, room layout, air purification, and filtration along with room air exchanges per hour.
We need to remember that the OSHA Gold Standard for High Risk, aerosol generating procedures is an Airborne Infection Isolation Room (AIIR) with proper ventilation. AIIRs are single-patient rooms with negative pressure that provide a minimum of 6 to 12 air exchanges per hour. An AIIR ensures that the room air exhausts directly to unoccupied areas outside of the building, or passes through a HEPA filter if recirculated.
As we look to “hang our hat” on sound science and information we can begin with some facts as we understand them today.
First, transmission…
SARS-CoV-2, the virus that causes COVID-19, is thought to spread primarily between people who are in close contact with one another (within 6 feet) through respiratory droplets produced when an infected person coughs, sneezes, or talks. Airborne transmission from person-to-person over long distances is unlikely. However, COVID-19 is a new disease, and we are still learning about how the virus spreads and the severity of the illness it causes. The virus has been shown to persist in aerosols for hours, and on some surfaces for days under laboratory conditions. SARS-CoV-2 can also be spread by people who are not showing symptoms.
Second, how do droplets move…
Droplets of all sizes are emitted when a person coughs, talks, or sneezes. How they travel depends on many factors. Some research has found that droplets can be carried by a moist gas cloud, which an MIT researcher has said can travel up to about 26 feet after a sneeze. Some of the droplets will fall as the cloud moves. Others ultimately evaporate, producing aerosols that can linger in the air and travel with airflow patterns.
Scientists emphasize there is no distinct size cut-off between droplets and aerosols. Some disagree about size ranges for each. Researchers are working to better understand the infectiousness of various-sized droplets and aerosols, and how it may change over time.
Here are some facts we know at present…
- Small Aerosols: 3 microns or less, Can linger for hours
- Small Droplets and Large Aerosols: 100 microns or smaller, Can linger in the air for 30 minutes or more
- Large Droplet: 100 microns (diameter) or larger, these heavier droplets fall to the ground within seconds
How about Risks to Dental Health Care Providers…
The practice of dentistry involves the use of rotary dental and surgical instruments, such as handpieces or ultrasonic scalers and air-water syringes. These instruments create a visible spray that can contain particle droplets of water, saliva, blood, microorganisms, and other debris. Surgical masks protect mucous membranes of the mouth and nose from droplet spatter, but they do not provide complete protection against the inhalation of infectious agents. There are currently no data available to assess the risk of SARS-CoV-2 transmission during dental practice.
From these facts, dental professionals concluded that air flow control can help prevent transmission of SARS-CoV-2.
Current recommendatins from
The CDC suggests dentists consider using a portable air filter that meets the high-efficiency particulate air standard while performing aerosol-generating procedures and immediately afterward. The CDC states using a filter will reduce the particle count in the room, including droplets, as well as increase the room air exchanges provided by the existing building HVAC system alone.
There are additional factors dentists need to consider when using air filters, however. These include the direction of the air flow in their operatories and the capacity of the filters.
Ideally, air would flow from a vent behind the head of the patient, where aerosols are produced, down to a filter at the patient’s feet, with dentists and their staff on either side of the patient so they don’t come between the aerosol and the filter. That is easier said than done, however, because in some operatories, air may be flowing from a vent on the ceiling or from other sources, such as windows.
Also, some practices may have portable filters dentists can place in different parts of the operatory, while others may have filters that are part of their ventilation system. Comparing the two is hard to do because both come with their own specifications. While portable filters allow dentists to control their placement, their capacity may not be as large as the ones that are built into the ventilation system.
Just how effective are these filters at trapping the coronavirus??
Filters that meet the high-efficiency particulate air standard (HEPA filters) have a 95% chance of trapping particles that are 0.3 microns or greater. The virus is 0.06 to 0.14 microns in size, but as long as it is traveling on a large enough particle in the aerosol, it would be caught by the filter.
Another array of products dentists may be considering to help sanitize the air in their practices are ultraviolet lights with wavelengths between 200 and 280 nanometers, known as UVC lights. The CDC states dentists may consider using upper-room ultraviolet germicidal irradiation as an adjunct to higher ventilation and air cleaning rates.
While UVC lights are germicidal, many factors can impact their effectiveness, including the amount of organic matter in the air, the intensity and wavelength of the light, the type of aerosol suspension generated by the procedure that is performed, the ambient temperature in the room, the microorganism to be killed, the distance between the light and target and the cleanliness of the light tube.
Safety is another consideration. There are still questions regarding what is the safe UVC wavelength for human exposure.
When it comes to suction devices, the ADA states that dentists should use high-velocity evacuation whenever possible. When using suction devices, dentists should hold high-volume evacuators about 2-5 inches from the instrument being used in the procedure and place extra-oral vacuum aspirators 6-12 inches from the patient.
Overall, research on dental aerosols is lacking. No studies have identified viruses in dental aerosols because researchers weren’t looking for them.
Let’s shift to…
THE ADDITION OF AIR PURIFICATION SYSTEMS
Today, in addition to all of the above recommendations, dental providers that perform aerosol generating procedures should implement an air management plan utilizing a layered application of technology and behavior to minimize the risk of SARS-CoV-2 transmission.
This layered approach could include:
1. Enhancing your Current HVAC system by increasing outdoor air into the building, ventilating indoor air to outside spaces, keep humidity between 40-60 % (lower humidity may favor SARS-CoV-2 viability}, use the highest rated MERV filter compatible with the system, reprogram the system to avoid shut off during occupied hours and leave exhaust fans on in rest rooms.
2. Installing Ultraviolet Light (UV) technology inside the HVAC ducts. Consider Far UVC, which can inactivate the virus. without human health risks in occupied spaces. In occupied spaces consider suspending UVGI lamps from ceilings or upper portion of walls to direct the radiation upward and outward and away from room occupants. Ultraviolet germicidal irradiation (UVGI) has the potential to cause human health diseases, including skin cancer and eye disease. UVGI cannot be used in an occupied space, except when installed in an upper-room fashion.
3. Add Air Scrubbing to the HVAC system: Wet scrubbing uses a damp or wet medium to filter particles and contaminants out of the air. Dry scrubbing utilizes the properties of positive and/or negatively charted ions to destroy certain molecules, disrupt the vitality of airborne organisms and viruses, and cause airborne particles to aggregate, fall, and/or be caught in filters. Though the absolute benefit of air scrubbing for decreasing SARS-CoV-2 transmission in a dental office is unclear, it may still be beneficial to improve the general air quality and reduce the recirculation of contaminants. The ions created through air scrubbing are dispersed. throughout all the air in the workspace extending to areas where UVGI or even some fogged disinfectants may not reach.
4. Finally are HEPA filters: No direct research exists to verify if a HEPA air purifier reduces the transmission of COVID-19. SARS-CoV-2 is generally carried in respiratory droplets, which are much larger than other particles known to be captured by HEPA filters. HEPA filters can be used as an adjunct to the HVAC system to enhance room air exchanges. Portable units can be placed in an operatory where aerosol-generating procedures are performed.
We are at an interesting cross road here, now calling on such diverse professionals as infectious disease experts, mechanical engineers along with HVAC contractors. When doing my research for this podcast I found a wealth of essential information along with the answers to many of my questions, which I anticipate are also your questions, from the documents and specs outlined by ASHRAE, the American Society of Heating, Refigeration, and Air-Conditioning Engineers.
Let’s check it out:
Question: WHAT FILTERS ARE RECOMMENDED FOR HVAC SYSTEMS?
Answer: Our current recommendation is to use a filter with a Minimum Efficiency Reporting Value (MERV) of 13, but a MERV 14 (or better) filter Is preferred. Of course, the ultimate choice needs to take the capabilities of the HVAC systems into consideration. Generally, increasing filter efficiency leads to increased pressure drop which can lead to reduced air flow through the HVAC system, more energy use for the fan to compensate for the increased resistance or both. If a MERV 13 filter cannot be accommodated in the system, then use the highest MERV rating you can.
Question: WHAT IS THE SIZE OF THE SARS-COV-2 VIRUS, AND CAN IT BE CAPTURED BY VENTILATION FILTERS?
Answer: Research has shown that the particle size of the SARS-CoV-2 virus is around 0.1 µm (micrometer). However, the virus does not travel through the air by itself. Since it is human generated, the virus is trapped in respiratory droplets and droplet nuclei (dried respiratory droplets) that are predominantly 1 µm in size and larger.
ASHRAE currently recommends using a minimum MERV 13 filter, which is at least 85% efficient at capturing particles in 1 µm to 3 µm size range. A MERV 14 filter is at least 90% efficient at capturing those same particles. Thus, the recommended filters are significantly more efficient at capturing the particles of concern that a typical MERV 8 filter which is only around 20% efficient in the 1 µm to 3 µm size range. Filters with MERV ratings higher than 14 would capture an even higher percentage of the particles of concern. High-efficiency particulate air (HEPA) filters are even more efficient at filtering human-generated infectious aerosols. By definition, a HEPA filter must be at least 99.97% efficient at capturing particles 0.3 µm in size. This 0.3 µm particle approximates the most penetrating particle size (MPPS) through the filter. HEPA filters are even more efficient at capturing particles larger AND smaller than the MPPS. Thus, HEPA filters are more that 99.97% efficient at capturing airborne viral particles associated with SARS-CoV-2.
Question: IS ULTRAVIOLET ENERGY (UV-C, ULTRAVIOLET GERMICIDAL IRRADIATION, GERMICIDAL ULTRAVIOLET) EFFECTIVE AGAINST THE SARS-COV-2 VIRUS?
Answer: Ultraviolet energy (ultraviolet germicidal irradiation or germicidal ultraviolet) could be a powerful tool in the fight against COVID-19. ASHRAE’s position on UVC is expressed in the UVC air and surface disinfection is used in many different settings – residential, commercial, schools, as well as healthcare. Germicidal light (particularly 254 nm UVC produced by low-pressure mercury vapor lamps, which operate near the most effective wavelength of ~265 nm) has not, to our knowledge, been tested on SARS-CoV-2, but it has been tested on an airborne coronavirus (Walker 2007). The sensitivity of that coronavirus to 254 nm was high enough that it seems like a good candidate for UV disinfection.
Another way to install UV is in an “upper-air” configuration. Specially designed fixtures mounted on the wall create an irradiated zone above the occupant and disinfect the air in the space as air circulates naturally, mechanically, or by means of the HVAC system. This sort of system has been approved for use in the control of tuberculosis by CDC for nearly 20 years and there is a NIOSH guideline on how to design them.
Finally, mobile UV systems are frequently used for terminal cleaning and surface disinfection in healthcare and other spaces. Systems such as these are typically used in unoccupied spaces due to concerns of occupant exposure. All three system types may be relevant, depending on the building type and individual spaces within the building.
The design and sizing of effective ultraviolet disinfection systems can be a complex process because of the need to determine the dose delivered to a moving air stream or to an irradiated region of a room. In-duct systems are further complicated by the air handling unit and ductwork configuration and reflections from surfaces that can help achieve higher irradiance levels. Upper-air systems require adequate air mixing to work properly while paying close attention to reflective surfaces that could result in room occupants being overexposed to the UV energy. Reputable manufacturers and system designers can assist by doing the necessary calculations and designing systems specific to individual spaces.
So, we have covered a lot of ground here, but are still left with the question…
What am I to do?
What’s the take home actionable point?
We know the threat of COVID-19 is significant and it can be transferred via the airborne route through coughing, sneezing, and secretions as well as through aerosols generated during our treatments.
For patients diagnosed with or suspected of COVID-19 infection, the gold standard is a negative pressure isolation room.
However, in our present practice, negative pressure rooms are probably not available or practical. From the above discussion, science, and technology it appears a multi tiered approach may prove the most practical.
Consider the following strategies to enhance the air purfication in your office;
1. Enhance your current HVAC system by running it more frequently, start earlier to allow more time for airflow and filtering before your normal office hours begin.
2. Choose HVAC filters that can remove a large portion of airborne particles, such as a MERV 13. If such a filter is incompatible, choose the most efficient filter.
3. Increase the HVAC system’s supply of outdoor air, to as much as the system can handle, in order to reduce reliance on recirculated air.
4. Consider centrally placed HVAC air treatment. Options here could include UVC germicial irradiation or ionic air scrubbing. Consultation with your HVAC contractor can help recomment the best options for your facility and system.
5. Provide air filtration in operatories where aerosols are generated. Using portable air purifiers with high-efficiency particulate air, or HEPA, filters. Vendors today also integrate UVC chambers, ion generators with HEPA filtration for a powerful viracidal combination.
6. Recirculate room air to achieve the equivalent of 6 to 12 air exchanges per hour. This can be difficult to achieve with your existing HVAC system. The addition of a portable air purifier can greatly improve your room air exchanges. Remember that larger spaces may need multiple units to achieve the recommended air exchanges.
7. Finally, some offices may choose residential and construction-grade air purifiers in patient care areas. Caution must be advised since units can create turbulent outflow in treatment rooms risking spreading aerosols.
Each office facility may use a different combination and method to reach their goal.
One prescriptive method does not exist, so no single strategy can be recommended. We will end with a statement from the ADA…
“When we look at dental aerosols, at this point, there’s nothing that we can nail down and say that this virus or salivary organisms spread through dental aerosols, but again, absence of evidence is not evidence of absence, and therefore, use precautionary prevention protocols,”
REFERENCES:
https://www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.134)
https://www.cdc.gov/coronavirus/2019-ncov/community/office-buildings.html
https://www.cdc.gov/niosh/docs/2009-105/default.html
https://www.cdc.gov/coronavirus/2019-ncov/hcp/dental-settings.html)
https://www.epa.gov/indoor-air-quality-iaq/what-merv-rating-1
https://www.ashrae.org/
https://www.osha.gov/SLTC/covid-19/dentistry.html
https://www.osha.gov/SLTC/covid-19/healthcare-workers.html)
(https://www.cdc.gov/infectioncontrol/guidelines/environmental/background/air.html
https://www.wsj.com/articles/key-to-preventing-covid-19-indoors-ventilation-11598953607?st=f297vi6xszkva69&reflink=article\_email\_share
https://success.ada.org/en/practice-management/patients/infectious-diseases-2019-novel-coronavirus?utm\_source=adaorg&utm\_medium=adanews&utm\_content=covid-19-virus&utm\_campaign=covid-19) .
https://www.grainger.com/know-how/equipment-information/kh-what-is-merv-rating-air-filter-rating-chart
https://www.epa.gov/indoor-air-quality-iaq/what-merv-rating-1
WSJ research; Linsey Marr, Virginia Tech University; Lydia Bourouiba, Massachusetts Institute of Technology
Caitlin McCabe, Alberto Cevantes, Josh Ulick/THE WALL STREET JOURNAL
pd_infectiousaerosols_2020.pdf
Air_Management_For_The_OMS_during_the_COVID-19_Pandemic (1).pdf
Air_Management_Strategies.pdf
