Sustainably Protect Humans Against Harmful Aerosols

Lessons learned from a global pandemic - and the remaining problem

Many countries worldwide recently succeeded in containing the spread of the COVID-19 disease by drastic confinements, regular testing, and an increasing vaccination rate. However, these measures are unsuitable for an extended period of time nor is it possible to vaccinate humans against every harmful aerosol. There is an urgent need for actionable and effective procedures to sustainably contain the risks of infection without harming the economy and society.

This pandemic taught us how easily and vehemently pathogens can be transmitted via airborne particles. This fact is accepted and documented by WHO, ASRAE and several national building and public health authorities. In closed spaces with insufficient ventilation, one single person can easily infect a large number of others. Nevertheless, investigations of infectious events repeatedly showed that humans became infected only in certain areas of the room, depending on the position of the spreading person and the ventilation situation. Interestingly, the infected person does not need to be in the room when the infection happens. The contaminated air they left behind can be enough to infect others entering the room at a later time. Improving the air quality with effective ventilation systems has the potential to mitigate the effect of diseases with airborne transmission. This includes seasonal illnesses, like influenza, common colds, and other virus infections as well. As a consequence, proper ventilation for optimized airflow matters.

Effects & consequences of the problem - a need for action

The latest guidelines and advice to reduce infection risks by regular fresh air supply are still based on limited knowledge about the individual situation. In fact, fundamental influencing factors and their dependencies for being able to effectively maintain air quality remain unaddressed:

• How uniform is the air exchange based on the selected ventilation method?
• How do the number of people in the same space, their activities, the ventilation configuration, temperature, etc. influence the air quality and air circulation?
• What measures could improve the uniformity of air exchange?
• What are the most effective protection measures to minimize infection risks while considering the associated investments?

In the case of natural ventilation by opening windows:

• How wide and how many windows should be opened to exchange the air equally?
• What is the best position for CO2 sensors to warn early enough that windows should be opened?
• What is the best position for a CO2 sensor to inform about the acceptable level of fresh air that windows can be closed?

In the case of air filter devices:

• How effective are air filter devices to improve the air quality in the selected situation?
• What is the best number, performance, and position of air filter devices to achieve the highest effectiveness?

The absence of satisfying answers to these questions causes companies to struggle in getting acceptable risk appraisals of their facilities. Transport associations and operators have difficulties in winning back people's trust in the safety of public transportation. Planners, operators, and facility managers have difficulties ensuring safety for the people using their facilities. There is a need for solution approaches that consider the nature of individual environments, ventilation systems, and occupancies. 

Based on the open-source CFD software OpenFOAM, ESI developed a solution that allows you to evaluate ventilation situations in a small amount of time. This solution is based on physically validated simulation models for turbulence, buoyancy, droplet size distribution, heat flux, radiation, as well as transient impulses. 

1. Assessment of natural ventilation possibilities

Many offices, schools and universities, administrative facilities, community centers, religious and cultural facilities do not have ventilation systems and need to rely on natural ventilation. For operators and users, it is unclear at what time and to what extent the used air can be replaced by fresh air.

In open-plan offices and, even more frequently, public transportation, many people meet in confined, enclosed spaces for an extended period of time. To evaluate the risk of workers or passengers being exposed to a critical number of pathogens, further aspects must be considered in addition to the ventilation system and the number of people. These are people’s activities like breathing, talking, and shouting, as well as protection measures such as wearing a mask.

The comparison of manifold settings of all influencing parameters allows identifying best and worst cases scenarios as well as acceptable occupancy levels considering predefined thresholds of aerosol concentration. Also, informed decisions can be made on which additional protection measures like installing air filters or glass shields between seating rows would be necessary and effective. In the image you can see the air exchange rate is about~ 9/hr with low occupancy (left) and medium occupancy (right).

Supplying large halls evenly with fresh air is a challenge. Ventilation systems should be designed to protect workers in factories or manufacturing plants from cumulated exhaust gases or airborne pollutants from the machines and increase occupancy comfort by avoiding high velocities.

In case of extreme respiratory events like coughing or sneezing, trajectories of exhaled particles illustrate direct contamination of the environment. Additionally, the effectiveness of work plans and work instructions aiming to protect workers from excessive exposure to potential toxicants can be easily investigated in the interactive Virtual Reality environment IC.IDO and the effect of alternative ventilation configurations and designs can be evaluated comparatively.

Displacement ventilation in medical treatment rooms and operating theatres are designed to deliver uniform, non-turbulent air to the controlled parts of the room.

Aerosols are invisible to humans. Consequently, humans cannot perceive danger zones in which virus-laden aerosols can accumulate.  

Do you need to know how to improve air quality in your area of responsibility?

• Watch our On-Demand Workshop: COVID-19 Minimize the risk of infection & increase confidence in safety.
• Register to our upcoming 10th OpenFOAM digital conference on November 8, 2022 and join OpenFOAM peers for this dynamic and engaging virtual event that covers all areas of CFD applications and process integration.

updated on: June 23, 2022