Ventilation to Prevent the Airborne Spread of InfectionsVentilation to Prevent the Airborne Spread of Infections
According to Dr Morawska, Shelly Miller and 33 authors, ventilation is the first step in preventing the airborne spread of infections, including coronavirus.
Currently, the main measures recommended by the World Health Organization (WHO) to prevent contracting infections, including COVID-19, are hand washing and social distance. Unfortunately, the above steps do not prevent infection by inhaling tiny droplets exhaled by an infected person, which can carry their viral material through the air at distances of tens of meters.
Two new scientific and engineering research papers have recently been released (May and June 2020) advocating the use of ventilation, in addition to other engineering controls and measures, to limit the risk of infection. Both papers conclude that mechanical ventilation is an “additional important measure globally to reduce the likelihood of transmission and thereby protect healthcare workers, patients and the general public”.
Despite this evidence, “no countries or authorities consider an airborne spread of COVID-19 in their regulations to prevent infections transmission indoors”, says Dr Morawska. “It is therefore extremely important,” she insists, “that national authorities acknowledge the reality that the virus spreads through the air, and recommend that adequate control measures be implemented to prevent further spread of the SARS-CoV-2 virus, in particular, removal of the virus-laden droplets from indoor air by ventilation”.
Ventilation to Prevent Airborne Spread
According to Dr Morawska, Shelly Miller and 33 other authors, ventilation is the first step in preventing the airborne spread of infections, including coronavirus.
Ventilation, in the context of a home or office, is the process of improving indoor air quality by exchanging stale or “dirty” air with fresh outdoor air. Mechanical heat recovery ventilation (HRV) adds a step to this process, where a heat exchanger is utilised to recover heat from the exhaust air and transfer it to the fresh supply air. This process captures up to 94% of heat energy and ensures a comfortable and stable indoor temperature. Any airborne pollutants are expelled along with the exhaust air, and the fresh air is filtered before entering the dwelling.
Currently, only hospital buildings typically have proper ventilation which promotes airflow and extracting of any airborne infections. However, ventilation in shops, offices, schools, kindergartens, restaurants, conference rooms and libraries may not be adequate. This potentially exposes a large portion of the general public and is currently being overlooked by authorities.
Avoiding Recirculated Air
Many dwellings may currently have in place an air conditioner, which may or may not include forms of air filtration to remove airborne particulate matter. Recirculated air may potentially increase the risk of infection, as air is distributed from one space to another space inside the dwelling.
“Particulate filters and disinfection equipment in recirculated air streams can reduce this risk, but they need to be purposely designed to control risk of airborne infection and need regular service to maintain their effectiveness”, one paper advises.
Ventilation systems do not necessarily take the place of heating/cooling air conditioners, however work independently of one another. Depending on the level of air tightness in the dwelling air conditioners may not even be required, such as in homes built following Passive House principles.
Open Window Fresh Air Supply
An open window may be useful for supplying fresh air to a localised indoor area. However, there are limitations and drawbacks to using an open window as your method of ventilation.
Opening windows cannot guarantee the extraction of infected air back outside, and fans may be required to accomplish this. Also, in colder climates or during winter, opening windows may no be a realistic option as too much heat might be lost. Ventilation with heat recovery (HRV) is superior as the cross-flow heat exchanger will recover heat and maintain the comfort of occupants.
Other Ways to Prevent Airborne Spread
There are various other methods which may prevent the spread of airborne infections, but ventilation remains the first step recommended by the authors. Other methods include air cleaning through air filtration and the use of ultraviolet light.
Portable air filter devices may work, but it must be adequate for the volume air in the dwelling. Ventilation with inline air filters remains superior to a mobile filtration device as a centralised system ventilates the entire volume of air instead of a localised portion of a room.
“All bacteria and viruses tested to date (many hundreds over the years, including other coronaviruses) respond to UV disinfection. Some organisms are more susceptible to UVC disinfection than others, but all tested so far do respond at the appropriate doses”.
The most basic form of preventing airborne spread, however, remains to minimise the number of occupants in an indoor environment.
Ventilation Units Centralised and Decentralised
References
How can airborne transmission of COVID-19 indoors be minimised? – https://scholar.colorado.edu/concern/articles/8w32r666s
Airborne transmission of SARS-CoV-2: The world should face the reality – https://www.sciencedirect.com/science/article/pii/S016041202031254X