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Covid-19 and air conditioning

What role does air conditioning play in the Covid-19 epidemic? A few cases traced to a restaurant in China have prompted researchers to ask whether ventilation systems can spread the virus.1 “No,” says engineer Cyril Verdun, SNCF’s top air conditioning expert.

Updated on

What French health authorities say

France’s High Council for Public Health (HCSP)2 has issued two recommendations on Covid-19 and air conditioning: use outside air to exchange the inside air as frequently as possible, and favour systems with indirect air flow.

How we’re responding

The high-performance ventilation systems in our trains meet the first recommendation because they routinely exchange inside air with outside air. Here’s how it works: the system draws air from inside the train, filters it, then mixes it with filtered air from outside the train. This mixture is heated or cooled as needed, and circulated inside the train. The exact proportion of outside air varies depending on the train. Aboard high-speed TGV INOUI and OUIGO, the mix is around one-third outside air and two-thirds inside air, which is refiltered every three minutes. That means that the entire volume of air is exchanged every nine minutes.

Aboard TER regional trains, the mix averages 40% outside air and 60% inside air, so the entire volume of air is exchanged every five to eight minutes—again, depending on the trainset.

The second public health recommendation is to avoid air flow that’s too direct. Although data isn’t conclusive, two cases of contagion have made experts question whether direct air flow can spread Covid-19 by propelling droplets from an infected person toward others and transmitting the virus to them (if they aren’t wearing masks). But since there’s no direct air flow aboard our trains, we can rule out this scenario. To keep passengers comfortable, our trains routinely use light, indirect flows and channel air up from the floor, reducing the risk even further.

Going the extra mile to protect our passengers

Our current cleaning and maintenance practices—including filter replacement—are more than enough to ensure optimum air quality aboard our trains. We continue to insert new filters every 90 days on average, and we now thoroughly disinfect the air inlet and ducting completely whenever a new filter goes in.

Onboard air quality: How it works

Onboard air quality: How it works

Air quality aboard SNCF trains

high-speed and long-distance service in France and Europe

Our trains are designed with ultra-high-performance ventilation systems

The air supply is filtered and exchanged throughout your journey

The air filtration system aboard SNCF trains is designed to meet the same standards as a surgical mask

Aboard TGV INOUI and OUIGO:

  • The system filters the air and draws in a steady stream of outside air.
  • Every 3 minutes all of the air is filtered and it takes 9 minutes for all of the air to be exchanged.

Aboard INTERCITÉS and other trains:

  • The system draws in a steady stream of outside air.
  • Every 6 minutes all of the air is exchanged.
  • There is no accumulation or stagnation of inside air.

Air flows vertically, preventing droplet transmission between passengers.

What the specialists say/

If the air inlet is on the outside, as with a TGV, there is virtually no risk.

- Dr Daniel Camus, an infectious disease specialist at the Pasteur Institute in Lille, France

Ventilation + mandatory mask = virtually no risk of virus transmission

Learn more about how we’re keeping you safe at SNCF.com

1 A possible case of transmission that took place in January 2020 at a restaurant in Canton, China.

2 Among its other responsibilities, the High Council for Public Health (HCSP) advises the French State on its public health strategy.