The beginning of the so-called new normal in Spain has coincided with the arrival of summer and the general rise in temperatures. One of the concerns of citizens facing these months, marked by the COVID-19 pandemic, is to know if air conditioning systems can favor the transmission of SARS-CoV-2.
Among the news that have raised the alarm on this issue is the case of an outbreak that occurred in January in a restaurant in Guangzhou (China). The results of a tracing study that was done to explain what had happened revealed that the direction of air flow caused by the ventilation of the air conditioning could have been key for the transmission, since only people seated at tables receiving were infected. this recirculated air stream, while neither the waiters nor any of the customers at the rest of the tables were infected.
Transmission of SARS-CoV-2 by air
What could have happened in the Guangzhou restaurant is explained by the importance that the spread of the virus could have in the air at medium distances, especially in indoor environments. “When a person is infected and coughs, sneezes or speaks loudly, they emit large droplets, above 5 microns, which have a fall path of between one and two meters, and that is why we recommend maintaining that minimum safety distance” , explains Jose María Lagarón, researcher of the Group of New Materials and Nanotechnology of the Institute of Agrochemistry and Food Technology (IATA-CSIC). “But there is another fraction of finer aerosols that could also carry enough viral load to be of concern. In closed environments, we think that these small droplets can spread to greater distances, up to eight meters, and also remain in the air for several hours. This explains some of the reported cases in which people have been infected despite being at a fairly prudent distance from the source. “
Not all air conditioners are the same
SARS-CoV-2 is a new virus about which little is still known, and much of the evidence is changing as scientific knowledge advances. When it comes to the influence of air conditioning, there are no absolute certainties, but experts agree on one thing: the key is to recirculate the air . It is something very intuitive: a ventilation system that takes air from outside every little time is safer, because in the case of aerosols that carry the virus, they will leave the room more easily and transmission through the air. Another aspect to take into account, in addition, in the case of recirculated air, is the ability of the filter to eliminate those aerosols that could carry the virus.
A few weeks ago the CSIC published a report, signed by a multidisciplinary team of experts, that analyzes air filters in different industrial sectors and the possibility of eliminating SARS-CoV-2 in each of them. ” One of the conclusions we have reached, for example, is that the aircraft system – at least the ones Airbus uses, which have been the ones we have analyzed – is quite safe, ” explains Lagarón, who has also participated in this report. “On average, the air inside the plane regenerates completely every 3 minutes. There is a part that enters from the outside and another that recirculates but passes through a filter that is also powerful enough to reduce the possibility that the aerosols carrying the virus, if any, do not return to the cabin ”.
And what about conventional air conditioners? “There it is more difficult to generalize, because it will depend a lot on the brand and the filter. It is one of the unknowns that we have now and that will have to be analyzed, but in general we have doubts about its ability to eliminate risks ”.
The air of restaurants
For all that we have discussed so far, one of the safest recommendations for the summer is, obviously, to spend as much time as possible in open spaces, where the possibility of permanence of the virus in aerosols and of spreading is much lower. In fact, according to a recent study that is still in the pre-publication phase, indoors the chances of infection could be twenty times higher outdoors, according to a recent study in Japan. In case of being in closed spaces, avoiding crowds, maintaining a safe distance, wearing a mask and ventilating every so often are some of the basic measures that guarantee more effective prevention.
“One of the biggest problems can be in places where there is no efficient air conditioning system and we also have to remove the mask, for example in a restaurant or in a hotel room. If, in addition, the music is very loud, you will have to shout more and there will be more possibility of emitting droplets with the virus if you are infected ”, reflects Guillermo Quindós Andrés, professor of Medical Microbiology at the University of the Basque Country. “In these places, in addition to the type of air conditioning, it is essential to have windows and to be able to ventilate every little bit. The air that comes in from outside helps the droplets to dehydrate and limits the permanence in the air of SARS-CoV-2 ”.
I have a restaurant: how can I improve my air conditioning system?
The American Society of Heating, Refrigerating and Air-Conditioning Engineers published in April a position paper on infectious aerosols, the conclusions of which are also included in the CSIC report. In general, for typical HVAC systems used for winter heating and summer cooling (HVAC), it does not appear that even the most sophisticated ones can completely prevent the spread of an infectious aerosol. . ” The impact of the HVAC system will depend on the location and strength of the source, the distribution of the aerosol released, the size of the droplets, the distribution of the air, the temperature, the relative humidity and the filtration “, indicates the document.
“One of the recommendations is that the air be renewed with a flow rate of 8 liters per second per person, ” explains Mª Cruz Minguillón, researcher at the Environmental Geochemistry and Atmospheric Research Group, within the Institute for Environmental Diagnosis and Water Studies ( IDAEA), CSIC, and that has also participated in the report. “You can do the calculations based on the volume of your premises and your capacity to renew the air and calculate the capacity accordingly. Another idea is to limit the time the clients stay in the premises, as this also reduces the chances of contagion ”.
Regarding the filters, the expert reminds us that “although the ideal is to have a HEPA filter ( High Efficiency Particle Arresting ), not all air conditioning systems accept it, because for example this type of filter needs more power . But what could be done is to contact the manufacturer and carry out a study to find out which is the most efficient filter that allows the system that is already installed on the premises ”.
The Spanish Technical Association for Air Conditioning and Refrigeration has also published a document of recommendations regarding the proper use of air conditioning during this unusual summer. Before reopening a premises, it is recommended, for example, a general review of the air conditioning and ventilation installation in which cleaning and disinfection of grilles, diffusers, filters and batteries are carried out, as well as changes in the operation are necessary to minimize the chances of contagion.
