I cannot make up my mind Turbspeed whether you are a journalist, a rabble rouser or just had a troubled childhood. On a similar topic (ba crews, is this really necessary?), you were quoting that all the hospitals were full in Hong Kong and not admitting any foreigners. That complete untruth was answered well and firmly by Christep but here you go again! It is possible to frighten people over anything as ignorance and gullibility is a world wide problem – please stop adding to it.
I quote our company guidelines below in an attempt to explain the system.
“The recirculation system supplements airflow and improves ventilation. These fans are automatically controlled based on flight phase and air conditioning pack supply, they optimize airflow during all phases of flight.
Each filter plenum has a HEPA (High Efficiency Particulate Air) filter element attached to it, should the fans be switched off the filters would effectively be removed for the system. The recirculation system is the only system that filters the air inside the cabin. The HEPA filters have a 99.97% efficiency rating, which effectively filter out bacteria.
The recirculation fans assist in providing cooling, particularly during ground operations, by supplementing cabin airflow. Airbus and Boeing both recommend that these fans remain switched on for maximum cabin ventilation. Recirculation fans must not be switched off, unless so required by a non-normal condition. The pack flow rate is regulated automatically, no manual intervention is normally required. However, crew may select pack to high flow should hot or humid conditions in the cabin warrant this selection.
In flight fresh air is introduced into the cabin and mixed with filtered air in a 50:50 proportion. The volume of fresh air introduced is such that the entire volume of air within the cabin is replaced every 3-5 minutes. An office building’s air-conditioning system by comparison will typically mix only 10% to 18% of fresh air with recycled air.
The dry air in aircraft cabins is inhospitable to germs, as most thrive in a moist environment. Whenever groups of people congregate in close proximity there will be a risk of disease transmission. However, the air quality in an aircraft provides no more risk than other forms of public transport. The airline industry's experience with other transmissible respiratory diseases supports the view that air travel poses minimal risk of infection.”
Let’s not get hysterical and talk ourselves back into the Stone Age. There are risks all around in life – assess them correctly and stop jumping at every loud noise.