Cabin air is circulated with air thats in the cabin and the air thats coming from the engine compressors. The air that comes from the engine is bleed air. The bleed air is then run through a cooler because the compressed air is really hot, it then comes in through the cabin through the Ac units above your seats. Although majority of the time it is very clean air and it gets filtered before coming into the cabin the air is still at risk for contamination. If the plane is over fueled or the seals are not tight enough, the air can get contaminated and some of the fumes can't be detected. What are the dangers of these fumes you ask.
The fumes can lead to nausea, vomiting and fever. It can also make you very drowsy. These are symptoms that many people confuse with catching a bug from one of the other passengers. What are airlines doing to fix this issue? Nothing. The filters and detectors they would need for the planes would cost airlines thousands of dollars so thats why they haven't done anything about the situation. The staff are more at risk because they are in the fumes for hours at a time. This can lead to memory loss and many other symptoms. Even if they had a detector to detect the fumes once in the cabin, it wouldn't get them far because some of the fumes can't be detected. Many flight attendants and pilots have gone through this while on a flight. The pilots are some of the first to smell it if there is a smell and it can put the whole plane at risk because of the drowsiness it causes.
There are more airlines doing research now on their flight crew but it might take time for the airlines to make some healthy changes. So make sure to read more about your airline the next time you travel.
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