The impact of the pandemic on rail travelPublic transportation has seen a sharp drop in passengers in the wake of the COVID-19 pandemic. One reason for this is the assumption or fear that viruses can easily spread in confined spaces such as trains or via on-board HVAC systems – infecting multiple passengers. Studies, however, have shown that the opposite is true – uniformly ventilated train interiors can actually hinder the spread of viruses.
How do modern HVAC systems hinder the dispersion of viral particles on board trains?
Modern HVAC solutions on board trains hinder the risk of infection on the train – and they do so without any additional modifications. They do this by:
- Introducing a high volume of fresh air into the carriage. Depending on the vehicle type and HVAC mode, approximately 10% - 30% of a carriage’s interior volume is replaced with fresh air per minute.
- Enabling a high air exchange rate of the air inside a carriage. Used air, and any viral particles it might carry, remains in the carriage for just two to three minutes before it is sucked out again.
- Eliminating dead space. Fresh air is evenly distributed into the interior while used air is very evenly extracted from the interior out again. There are no spaces in the carriage in which aerosols can collect.
Collectively, these measures work very effectively to hinder the risk of direct transmission from passenger to passenger within our trains. A residual risk of infection, however, is still possible.
Flushing out used air while cooling or heating
The spread of aerosols without ventilation
Depending on temperature conditions within the space, exhaled aerosols move through the room in a concentrated cloud. People in the direct vicinity and breathing direction of the infected person are exposed to a very high concentration of aerosol particles before the cloud is dispersed – putting the passengers at risk of infection.
Over a longer period of time, the aerosol cloud disperses throughout the space – where they can accumulate in dead spaces such as corners. Without extraction or dilution via HVAC systems, the infected particles can remain in the space for more than 30 minutes and up to hours.
The impact of ventilation on exhaled aerosols
The ventilation and resulting air movement created by the HVAC system is in equal effect all over the carriage.
The powerful ventilation dilutes the exhaled aerosol cloud quickly and strongly – thus reducing its concentration – before it is removed via the HVAC system. Research shows that only a very low fraction of exhaled aerosol is directly inhaled by other passengers.
The quick refresh of air within a carriage also means that both light and heavy droplets are mostly removed before they have the chance to collect or adhere to surfaces. Research shows COVID-19 infection via surface contact seems to be subordinate to other forms of infection – but both personal hygiene and regular cleaning are still important means by which one can hinder the spread of viruses.
The distribution and extraction of exhaled aerosolsWhat happens when a passenger sneezes or coughs? HVAC systems ensure that both heavy and light droplets are dealt with quickly and effectively. Here are some facts and figures below on what happens to exhaled viral particles on board a train.
Facts and figures at a glance
Maximum time even very light particles remain in the carriage before being extracted by the uniform ventilation.
The breathing volume per person of about 0.5m³ air per hour is diluted to a supply air volume of 3000-4000m³/h including a fresh air volume of 400-1800m³/h.
Research shows passengers are exposed to less than 0.01% of aerosols from an infected passenger via HVAC systems.