Thirty years ago, commercial airplanes used 100 percent fresh air, which was recirculated every three minutes. This is currently reduced to a 1:1 ratio of fresh and recirculated air every seven minutes.
What is the reason airlines cite for making this change?
A)It is more fuel efficient and therefore cost efficient, although it may increase risk to passengers.
B)There was not enough oxygen present in the 100 percent fresh air at altitudes above 25,000 feet, making the air quality poor for passengers.
C)The carbon monoxide levels were higher with more frequent recirculation,

Question

Thirty years ago, commercial airplanes used 100 percent fresh air, which was recirculated every three minutes. This is currently reduced to a 1:1 ratio of fresh and recirculated air every seven minutes.
What is the reason airlines cite for making this change?
A)It is more fuel efficient and therefore cost efficient, although it may increase risk to passengers.
B)There was not enough oxygen present in the 100 percent fresh air at altitudes above 25,000 feet, making the air quality poor for passengers.
C)The carbon monoxide levels were higher with more frequent recirculation,

anonymous · Answer

so the recirculation frequency was decreased to every seven minutes.
D)
By not recirculating the air as frequently, airlines were actually able to reduce the risk of spreading airborne diseases among passengers.
E)
It is easier to maintain acceptable humidity levels in the mixed air than using 100 percent fresh air, making it more comfortable for passengers.