We ventilate our trains to prevent contagion
Along with cleaning and disinfection, at TMB we have paid the utmost attention to ensuring the efficient ventilation of all our means of transport.
The air of the metro network is constantly renewed through the stations and wells located in the tunnels between stations by means of powerful fans that drive or extract air 24 hours a day. Changing the air dilutes viruses floating in the environment in small clouds, called aerosols.
Outside this is achieved by the effect of natural air currents, while in enclosed spaces, a good electromechanical system is needed to force the movement of air masses.
Public transport is not a significant scenario of Covid-19 infection. The rate of air change and the widespread use of masks drastically reduce the chances of a sick person who does not observe the rules of hygiene passing the coronavirus on to a large number of users with no way to track them.
Inside the carriages, air conditioners move air more efficiently than in restaurants, schools and other indoor spaces, according to aerosol experts.
In the Covid-19 section you will find all the information about the new normality on public transport
Located on the ceiling, it constantly sucks in air from inside and air from outside. The mixture of recirculated air and outside air is filtered and cooled and sent through ducts to the passenger compartment. The air outlet is via extraction ducts near the gangways.
In addition, at each stop, the opening of the doors (20 on each side) causes air to rush out from the inside and enter from the outside.
At any given time, one-third of the air comes from outside and the other two-thirds from recirculated air.
The continuous flow of air through the ventilation ducts helps to limit the accumulation of viral particles that may have entered a carriage after it was disinfected.
Every carriage has two ventilation units, one at each end. Between the two they completely change the indoor air every few minutes and disperse particles and microorganisms.
Fans extract air through filters and cooling coils. Filters trap large and small aerosols before air enters the ducts.
In metro trains, the filters have a wavy design that increases their surface area and, therefore, the opportunities to trap the droplets in which viruses and bacteria travel.
The filters are made of fibres that force the incoming air to change direction and trap particles as air passes through them.
We are installing recirculation flow shut-off gates in the train’s air conditioning equipment to further renew the air inside each car.
These gates are adjustable from an initial level of 13.5 air changes/hour to a level of 24.4 changes/hour. We are also installing new filters capable of retaining 2.5 micron particles with an effectiveness of up to 70%. With the new parameters, air conditioners mix 60% outside air (initially it was 33%) and 40% recirculated air.
The air in each carriage is thus changed every 2.5 minutes instead of the initial 4.5 minutes