In our last Industrial Hygiene blog, Airflow in the Laboratory, we discussed the importance of evaluating the airflow of a lab as a whole, and that there’s no one magic ACH (Air Change per Hour) number that automatically makes the lab safer.
With the recent discussion around the SARS-CoV-2 virus and the role that airborne transmission may play, this subject has now reached mainstream media. So should indoor spaces such as labs and offices increase their air changes? And can we treat the air to make it safer?
Everyone is looking for a way back to “normal” and assessment of the ventilation in a space is one key factor to consider.
Case Study: The First Evidence of Airborne Transmission
The first evidence of airborne transmission was from a restaurant in Guangzhou, China. One patron was positive for COVID-19, and became the index case-patient, infecting 9 other customers. These customers were not necessarily closer in proximity to the patient than the 6 feet guideline during their meals.
They were, however, in line with a wall-mounted air conditioning unit that was recirculating air from 2 adjacent tables.
The conclusion drawn by Lu, et al. during a review of this case study, was that the air conditioning unit was moving virus-laden air through the space occupied by these tables in a manner that allowed the airborne spread of disease. Interestingly, tables that were in the restaurant, but not in line with the airflow from the system, did not exhibit disease transmission.
This case study was the first indication that airborne transmission, and as a matter of course, ventilation, must be considered when evaluating the risk of COVID-19 transmission in indoor spaces.
CDC Recommendation for Ventilation System Review
Current guidance from the CDC recommends conducting a hazard assessment of the workspace, which includes a review of the ventilation system.
Some suggestions for mitigation of potential disease transmission include:
- increasing outside air supply
- filtering the air with HEPA or higher rated MERV filters (13 or greater)
- considering the directionality of the airflow
These factors must all be considered because each plays an important role in the effectiveness of the airflow.
Why Increasing Outside Air Supply is Not Enough
We know that in order for the disease to spread, a susceptible person must be exposed to a certain number of viral particles, which can be from an instantaneous exposure (as in the case of direct exposure to a sneeze, for example) or to a smaller number of particles but over a short period of time such as having a conversation with an infected person closer than 6ft while not wearing masks.
Increasing the amount of outside air, or better filtration of the return air helps to reduce the viral load that persons in the area could be exposed to. This reduction works hand-in-hand with the directionality of that airflow.
Air movement that sweeps contaminated air away from people will have a much greater effect than dilution alone. In fact, increasing airflow without consideration of direction can actually be detrimental if it moves contaminated air (even if it’s been diluted!) towards people.
This is why the use of fans and other air moving equipment in a space must be carefully considered.
With the Potential for Airborne Transmission, More Factors Must Be Considered
When considering improvements to indoor spaces, many factors must be considered, not the least of which is ventilation. With the increased coverage of the potential for airborne transmission of the SARS-CoV-2 virus, this piece of the infection control puzzle has gained more attention in recent weeks.
Although increases in the ventilation rates can have a very positive effect, it is equally important to consider the direction of that airflow and ensure that a more hazardous situation is not created as an unintended by-product.
For additional information on ventilation for COVID-19, or for assistance with your company’s ventilation assessment, please email firstname.lastname@example.org.