Evening star. [volume] (Washington, D.C.) 1854-1972, 1930-05-18
Heat, Air and Humidity Charted
To Fix Safety for Human Body

distress. 1t was those symptoms scien-
lists studied carefully-increased circu-
lation, the heart pumping more hot
blood into the radiator" (the capil-
larteS at the surface of the skim in an
effort to cool on; congestion of the
blood under the skin; flushing; profuse
perspiration; further heart strain, re-
duction of the blood supply going back
to the heart; palpitation of the heart:
extreme thirst; dizziness; loss of the
power to concentrate; extreme irrita-
bility at noises and lights. and finally
feeling of floating In the air" that
led up to heat stroke. Short of that
point the subjects were always hastily
brought out of the hot chamber. After
drinking considerable of water, they
complained of no i'll effects except ex-
IRENE lassitude.
Ninety Degrees Average Limit.
1t was found that temperature could
be raised, without perceptible effect, as
much as 10 degrees by reducing the
relative humidity, thus increasing the
cooling rate of evaporation. Reducing
relative humidity and increasing the
air motion made it possible to run the
temperature even higher without the
change being perceptible to the sub
JeSV' 1AC AeouiCo vi tAicSS teStS, IcOuCeQ
to simple diagram, are shown in the
accompanying chart.
The upper limit, beyond which the
body could not diSsipate its own heat
without effort and distress, was 90 de-
grees; average, in still air saturated
with water vapor. That was for per-
sons at rest and relaxed. When the
subject was doing physical work that
high limit dropped in relation to the
amount Of muscular work being done
When the amount of work was brought
to peak of hard labor 100000 foot
pounds an hour the limit of tempera-
ture under which the body compensated
itself without distress dropped to 80 de-
grees Farenheit in calm, saturated air
A man lifting a 16-pound sledge feet
and letting 1t fall once every four sec
onds is doing 10000 foot-pounds Of
work an hour. Under those conditions,
in air above 80 degrees, he creates heat
faster than he can give 1t off. Miners,
stokers. steel-mill workers, potters and
many others customarily work under
conditions hotter than that.
Averages so Per Cent.
Reducing humidity to 80 per cent in
air at 100 degrees Fahrenheit enabled
men to do four times as much physical
work as they could do with the air sat-
urated with moisture.
With humidity Of so per cent (Which
is an average figure outdoors on a Sum-
mer day. they could do only one-flfth
as much at 100 degrees as they could
at 30 degrees. The maximum amount of
work, 1t was found could be performed
between the effective temperatures "a
temperature arrived at by reckoning in
relative humidity with actual heat) of
40 degrees to rs degrees
This merely supported the experience
of man through many thousands of
years. No civilization of any impor-
lance has grown up outside the tenn
perate zones, where the range of effec-
tive temperatures through most Of the
year is between 40 degrees and rs de-
grees. This is based upon effective tenn
perature, not mere thermometer read
ings Colder conditions produce the
barbarism of the Eskimo or the Pata-
gonian, whose struggle to survive gives
him no time or energy for rrogress.
Hotter conditions produce the tropical
broad belt around the globe.
1t isn't only the heat, then, but the
humidity and the air motion that af-
feet the destiny of whole races
Weather to primitive man was the most
important factor in life. In the tropics
and the subpolar regions it still re-
mains master of the situation
Civilized man, however, from the time
Of the domestication of fire has been
progressing slowly in the art of making
his own weather indoors. 1t is now
possible to control heat, relative hu-
nudity and rate of air motion In any
space between four walls, a ceiling and
a floor. From factories and public
buildings the art Of manufacturing
weather and controlling it is spreading
into homes and apartments. The next
few years will see radical progress.