This is a guest post by Dr Sarabeth Buckley, a postdoctoral research fellow at Cambridge University. She recently received a PhD from BU’s Earth and Environment Department, where her research focused on ventilation and rooftop gardens.
Towards the beginning of the whole pandemic in early February, there was a story that came out of Hong Kong that was particularly frightening. In a large apartment building, one person on one floor initially tested positive for Covid-19. The virus was still primarily circulating in China at the time. What was scary was that someone ten floors away also then tested positive and that although they did not know each other and had not had any contact, their apartments did share some pipes and there was a leak in the second apartment. This was a very early indication that Covid-19 might be airborne.
WHO denied this, saying that the evidence overall suggested Covid-19 was not airborne. It took five whole months for this article, citing this paper to come out. The article says coronavirus is, in fact, airborne. We all need to take this fact seriously. When anyone coughs they release water droplets of different sizes. Some of these are large and they will fall right to the ground. Others are very tiny, around five μm, which is too tiny to see. Droplets of this size can travel tens of meters away from the person who exhaled them, which is a much longer distance than the length of a normal room, and definitely longer than the length of many of our small BU classrooms. Scientists had hoped that Covid-19 viral particles would not be able to survive in these tiny droplets and might only survive in the bigger droplets that people expel directly, next to themselves. If this had turned out to be the case, it would be enough to just stay out of spitting range of people while sitting inside.
The article states that Covid-19 can survive in these tiny droplets for three hours, which is longer than any of the classes I ever took at BU. This means that if you are in a room where someone who is infected with Covid-19 has been, even if you are on the other side of a large room, you could still catch the virus by breathing in air that someone, perhaps in an earlier class, breathed out a good couple of hours ago. I think about all the classes I took at BU and the little rows of desks a foot or two away. Even if half or more of those desks are removed and the ten people left coming to in-person classes all sit awkwardly, far apart, one person being infected means some portion of the air in the class is going to contain viral particles.
Before the July 4 article, the WHO’s official statement was still that the virus was only airborne in hospitals after medical procedures. It took 239 scientists in 32 countries writing an open letter, explaining the way in which Covid-19 is airborne, for this discovery to be taken seriously.
Masks certainly help, but they can’t prevent you from breathing in particles. They’re not sealed. When you breathe in while wearing a mask, you can feel the slightly cooler air rushing in through the little areas on the sides of your nose where the mask isn’t quite flush with your skin, and this air hasn’t gone through the cloth. What masks do help with is preventing your own water droplets from being sent off to mingle in the air. Therefore, if everyone wears a mask the entire time they are around other people, then, hypothetically, all of the viral particles infected people breathe out should be caught on the inside of the mask fabric and stop their journey there.
There are a few other things that can be done. Classrooms can be cleaned very frequently with cleaning implements like ultraviolet lights, for example. But one of the most important things that can be done is ensuring that rooms have good ventilation. If potentially contaminated air is being continuously pulled out, recycled air is heavily filtered, and new fresh air without Covid-19 is pushed in at a fast enough rate, this should help get rid of the viral particles twirling about above our heads, threatening to infect us.
This is basically about trying to create a situation reminiscent of an outdoor environment, where the air is moving around so much that it fairly quickly whisks away any viral particles just hanging about (unless you are within direct firing range). This is where some of my work comes in. The recommended ventilation level for removing Covid-19 particles is thirty cubic feet per minute per person (Allen and Macomber, 2020), but how do you know what the current ventilation rate is?
A primary method for testing what ventilation rates actually are is measuring CO2 concentrations in rooms with multiple people in them. This is because, as everyone knows, people are constantly breathing out large amounts of CO2 that build up in confined spaces like classrooms; the more people, the more CO2 builds up. If CO2 concentrations get too high, this indicates that ventilation is not sufficient. Governing bodies set limits for CO2 concentrations in rooms. Generally these are:
5000 ppm – Upper limit of what should ever be found (ACGIH, 1999; OSHA, 1997)
1000 ppm – Suggested limit for classrooms, in particular (ASHRAE, 1989)
800 ppm – Suggested limit in Massachusetts (MADPH, 2020)
As part of my PhD research, I took CO2 measurements in BU classrooms to understand how well ventilation there is working. You can see for yourself how well some of the rooms in the College of Arts and Sciences building did on this test.
Each color is CO2 measurements taken in a different classroom over the course of a week. They obviously go far above the 800 and 1000 ppm limits.
From one perspective, CO2 can affect how well you perform mentally, meaning high concentrations can make you a bit slow and sleepy, and you have probably experienced this first hand. High concentrations are also known to be associated with other pollutants, such as particulate matter, sulfur dioxide, or, as is critical in this case, biological contaminants. This is usually referred to as Sick Building Syndrome, but in the present context, you might as well just call it Covid-19.
What I found was a sign that current ventilation, at least in CAS classrooms, is far from efficient enough to deal with even normal contaminants, let alone something as contagious and virulent as Covid-19. This is good and bad. It means BU is not ready for normal classes at this point, but it highlights a clear step BU must take in order to make the campus safe in the fall. At this point, BU has said they will be doing “a comprehensive review of all HVAC systems, upgrading filters as needed.” This must include increasing ventilation rates and actively monitoring CO2 concentrations in these rooms, in order to keep tabs on whether or not ventilation is actually functioning at a high enough level. There are even third parties who BU could hire to help them test building ventilation and set up a system that will keep everyone safe. They just need to make this a priority and let us know what their plan is.
– ACGIH (American Conference of Governmental Industrial Hygienists). (2011). TLVs and BEIs. Cincinnati, OH: American Conference of Governmental Industrial Hygienists.
– Allen J. and J. Macomber. Healthy Building: How Indoor Spaces Drive Performance and Productivity. Cambridge, Massachusetts: Harvard University Press, 2020.
– ASHRAE. 1989. Ventilation for Acceptable Indoor Air Quality. American Society of Heating, Refrigeration and Air Conditioning Engineers. ANSI/ASHRAE 62-1989.
– MA EOHHS (Massachusetts Executive Office of Health and Human Services). (May 8th 2020). Massachusetts Environmental Public Health Tracking: Ventilation. https://matracking.ehs.state.ma.us/Environmental-Data/indoor-air-quality/ventilation.html
– OSHA. 1997. Limits for Air Contaminants. Occupational Safety and Health Administration. Code of Federal Regulations. 29 C.F.R 1910.1000 Table Z-1-A.