Swiss news magazine Blick TV accused SBB of operating ‘Covid catapults’.
The news broadcaster sent a journalist to test various locations such as schools, nightclubs and trains – in this case the long-distance double-decker FV-DOSTO trains – for levels of carbon dioxide. The measurements by this journalist found CO2 values in excess of 3,000 parts per million in the DOSTO trains. The scientific consensus is that a CO2 concentration of more than 1,200ppm is considered “too high”.
The news report then added a segment on aerosols and the coronavirus, implying (along with the headline) that the high levels of carbon dioxide measured were correlated with high levels of the virus in these trains. However, nothing other than CO2 was measured.
“The DOSTO has a powerful recirculation unit, meaning that the air is recirculated through the air-conditioning unit, during which it is filtered. This results in a 10–11x air exchange. This means a large amount of virus-free air is pumped into the carriages and therefore (...) the viral load in them is fine.”
It would therefore seem that the ‘Covid catapult’ headline was quite misleading. However, there is still the question of the elevated carbon dioxide level measured by Blick TV.
Train operating company SBB said that the air-conditioning units in the Bombardier-built DOSTO trains continuously measure the carbon dioxide levels in every carriage. These data showed that there were no elevated carbon dioxide levels measured in the trains. SBB also conducted some measurements with a certified handheld device. The values measured were all between 600 and 1,300ppm and for a few minutes an outlier of 2,000ppm was measured. SBB stressed: The values measured were in no way a health risk and there was no connection between them and aerosols.
SBB further said it would verify the values measured through an accredited process. These measurements will be conducted by the SBB’s independent test facility Schweizerische Akkreditierungsstelle. SBB said it would implement additional measures if necessary.
There is an air-conditioning unit at either end of every carriage. Installed in them are two carbon dioxide sensors, meaning there are four sensors per carriage. The air-conditioning unit measures the carbon dioxide values of the outside and inside air and depending on the values automatically draws in the relevant amount of fresh air. This amount also varies depending on the outside temperature and on how many people there are in a carriage. That means that the air in each carriage is replaced in full by outside air between six and ten times per hour on average, leading to a constant exchange of air.
When commenting on the discrepancies between the values achieved SBB’s continuous measurements and additional checks with handheld devices and those achieved by the reporter spot-checking some carriages (first class, second class and restaurant car with roughly 50 % occupancy) with a handheld device, he said he “didn’t know under what conditions the SBB conducted its measurements”.
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