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[at-l] RE: Obscure Question

kahlena <kahley7@ptd.net> writes:

>A couple recent hikes in super high humidity
>have introduced me to new levels of oxygen starvation.  Again, a
>simple concept that I can grasp...if the air is overfull with water
>vapor (humidity), there is less room for oxygen.  Or is it that the
>oxygen is less accessible to the lungs?  And had anyone ever compared
>the effects of exercise in high humidity to exercise in high altitudes?
>Could pulmaonary prob;ems happen at lower altitudes if one is exposed to
>constant high humidities?

Along with elevation, heat decrease the density of the air, making less
oxygen available.  Humidity also "dilutes" the oxygen slightly, but more
importantly it decreases the air's capacity to cool the body by
perspiration and respiration.

"Standard" air (29.92 inches of mercury sea-level barometric pressure, 15
deg. Celsius, in the aviation context) heated to 30C has a "density
altitude" of about 8000 feet:  An airplane taking off from Denver, CO in
hot weather performs as if it were at 8000 feet, and needs considerably
more runway.

Density altitude affects aircraft more than it does cars or people; in
addition to degrading engine power and cooling, it reduces wing lift and
propellor thrust.  It even affects birds in hot weather; they can take off
but can't climb rapidly, and get smashed on the front of semis.  Density
altitude can be negative at low elevation in extreme cold.

I don't know the formula for density altitude including the humidity term.
The calculation is one of the functions of the "E6B," a specialized
circular sliderule used in aviation.

>And is more energy needed to 'push' through the heavy air?

It actually takes less energy to push through thin air but it seems like
more because we have less available.

 --  Frank     reid@indiana.edu    C-I-SEL
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