PRINCIPLES 
OF 
ENVIRONMENTAL STRESS 
ON 
SOLDIERS 
ON 
ENVIRONMENTAL PROTECTION SECTION 
Research and Development Branch 
Military Planning Division 
Office of the Quartermaster General 
25 August 1944 
Reissued February 1947 CONFERENCE ON THE 
PRINCIPLES OF ENVIRONMENTAL STRESS ON SOLDIERS 
For the Purpose of 
Developing a Climatic Index Suitable for Mapping Purposes 
for the Protection of Troops Operating in All Climates 
Climatology & Environmental Protection 
Research and Development Branch 
Military Planning Division 
Office of The Quartermaster General 
2£ August 19hh TABLE OF CONTENTS 
Page 
List of Graphical Illustrations 1 
Preface ii 
List of Attendance iii 
MINUTES OF MEETING 
Welcoming Address 
Colonel Georges Fo Doriot 1 
Lt0 Colo David Bruce Dill 2 
Introduction 
Major Paul A« Siple 3 
lo Convection 
£)r0 Jesse Ho Plummer 8 
Discussion 13 
IIo Conduction 
Mrso Margaret lonides Cochran 111 
Discussion 20 
III. Evaporation 
Dr0 Lyman tfourt 23 
Discussion 26 
IV« Radiation 
Mrso Elizabeth Schickele 28 
Discussion 36 
Vo Summary 
br7 Jesse Plummer 37 
Discussion i£. 
APPENDIX 
lo Discussion of Climatic Data Ulx 
IIo Clo Values and Tolerance Times I4.7 
Clo Value Equation 
Metabolic Heat Loss as a Function of Activity 
Tolerance Time Equation & Graphs 
III. Proportion of Heat Lest from Various Portions of £l 
the Body 
Cochran LIST OF GRAPHICAL ILLUSTRATIONS 
Graph 
Following 
Page 
Figo 1 Convective Heat Loss as a Function of Wind Velocity, 11 
Temperature, and Diameter of Cylinder 
Fig® 2 Convective Heat Loss and Thermal Resistance as a 12 
Function of Wind Velocity and Diameter of Cylinder 
Figo 3 Arctic Univom - a Clo 15 
Fig« 1* Combat Uniform - 3 Clo 15 
Figo 5 The Relationship of Effective Insulation to Surface 17 
Area 
Figo 6 Clo Values 19 
Figo 7* Evaporation for Fabrics of Various Air Permeabilities 23 
Figo 8 Evaporation as a Function of Cylinder Size 23 
Fig> 9* Evaporation - Effect of Wind on Fabric Permeability 21* 
Figo 10* Evaporation - Effect of Wind and Size of Cover 2k 
Figo 11* Evaporation - Unit Wind Speed & Air Permeability 25 
Fig* 12 Evaporation for Average Human Body 2?i 
Figo 13 Radiation due to Direct Sunshine Falling on the Human 35 
Body 
Figo 11* Radiant Heat Exchange Between Erect Human Body and 35 
Ground 
Map 1 Clothing Requirements for^January - Central Europe 38 
Figo 15 Comparison of Index with Pierce Laboratory 39 
Figo 16 Comparison of Index with ASHVE Experiments 1*0 
Figo 1? Comparison of Index with Robinson’s Data for Clothed Men 1*0) 
Figo 18 Comparison of Index with Robinson's Data for Nude Men 1*0 
i 
Charts in Appendix:- 
Tolerance Times for Sleeping 51 
Tolerance Times for Sitting Still 51 
Tolerance Times for Standing 51 
y „-i — .. . -.. .. — ..... — 
These charts are included by the courtesy of the Bureau of 
Standard's Textile Foundation0 PREFACE 
These are not strictly the minutes of a meeting - if by the 
term MminutcsM is meant a brief and formal summary of a conference 
in curt and outlined form0 Such a summary would seem useless with 
such a preponderance of material on a subject so vast„ Instead 
this is an attempt to reconstruct the papers as they were presented 
together with a small amount of the welcomed comments and 
criticisms which were offered by our guests0 We deeply regret 
that we were unable to include all the discussion0 The omission 
arises not from any editing of the dialogue$ but simply because 
the remarks were not recorded at the time, and we feared lest we 
might do an injustice to our kind critics, if we put inadequately 
remembered sentences into their mouths„ 'a hope that this- 
summary will bring more comments from tt m„. 
In addition to what was actually said at the meeting, an 
appendix has been added with ouch information as may be necessary 
to put the index in usable form0 The index as it now stands does 
not represent a final piece of work0 Instead it is a first and 
tentative approximatione It is hoped that everyone will use it 
as he sees fit, and report either correlations or discrepancies- 
to us, so that it may be improved* 
The Climatology & Environmental Protection Section 
1 December 1?UU LIST OF ATTENDANCE 
lo Viritors:- 
Capto Lo- Lo Adamkiewitz, Naval Medical Research Institute 
Lto Colo To Fo Hatch, Armored Medical Research Laboratory 
Commander F. Co Houghton, Medical Department, Uo S. Navy 
Surgeon Ho F« Fraser, Industrial Hygiene Research Laboratory 
Lto C. Ro Spealman, Naval Medical Research Institute 
Lto C. Taylor, Wright Field 
Dr, Ho So Belding. Harvard Fatigue Laboratory 
Dr, H. F. Blum, Naval Medical Research Institute 
Mr*. Gerald C. Bristow, Uo So Weather Bureau 
Dr0 Co Fo Brooks, Blue Hill Meteorological Observatory 
Dr® Ao C« Burton, National Research Council of Canada 
Dr0 Dana Coraan, John Hopkins University 
Dr« Richard Day, Climatic Research Laboratory 
Dr„ Lyman Fount, Textile Foundation, Bureau of Standards 
Dr0 Goldthwaite, Personal Equipment Laboratory, Wright Field 
Dr0 Milton Harris, Textile Foundation, Bureau of Standards 
Dr0 Ellsworth Huntington, Yale University 
Dr, Robert Go Stone, Array Air Forces 
Mr» Herbert Co So Thom, U. So Weather Bureau 
Dr» Co Wo Thornthwaite, Uo S0 Agriculture Department 
MTo Marvin VanDilla, Climatic Research Laboratory 
Dr0 Samuel VanValkenburg, Clark University 
Commander A» R0 Behnke, Naval Medical Research Institute 
2 o QQMG Representativest- 
Colonel Georges F0 Doriot, Director Military Planning Division 
Lto Colo Do Bo Dill, Assistant for Product Analysis 
Major Ro Mo Ferry, Test Section 
Dr0 F* Ro Wulsin, Test Section 
Dr0 Lo To Williams, Textile Section 
Major Paul Ao Siple, Climatology & Environmental Protection Sec* 
Major Weldon Fo Heald, » » » « 
Dr0 Jesse Ho Plummer, M * ** ** 
MrSo Margaret I0 Cochran M H it w 
Mrso Elizabeth Schickele M H “ •• 
Mr0 Malcolm Murray ** “ * 11 
Mr0 David Ho Miller u 11 n * 
Miss Rose Sachs, '• 11 h « 
Mrso Jane Westbrook u M M M 
MTo John P0 Bader M • « n CLIMATIC INDEX 
Minutes of Meeting, 25 August 1944 
The meeting was called to order at 1015 by Major Paul A. Siple, who 
introduced Colonel Georges Fa Doriot. 
COLONEL DORIOTt- We are very happy to have you. We are also very proud. A 
group such as this is distinguished by its intelligence, and 
the war has called upon you to use that intelligence in helping 
us provide adequate clothing and equipment for at least seven 
million seven hundred thousand men. Other sources furnish 
their products to a limited number only. Only a limited number, 
for example, use 150 millimeter guns which ordnance furnishes; 
the same is true of the other Corps, but every person in the 
Array will benefit or suffer according to how quickly the 
Quartermaster does its work. There has been, in the past, no 
systemized body of knowledge which concerned the food, cloth- 
ing and shelter for the human being. I must look to you to 
see that the small knowledge which already exists is increased 
and developed so that the Military Planning Division will be 
able to furnish far better items than have heretofore been 
available. I understand that you cannot chart the course 
very accurately, but the wavy line of the progress must be 
determinable within certain boundaries. In clothing for cold 
weather, we have made progress. Our knowledge of hot weather 
clothing is, however, still very limited; and I feel quite 
distinctly that we have little or no knowledge on the subject 
of wet cold. We have a man in the nude. We have to dress him, and we can do anything we want. We are now beginning to 
realize that something can be done to keep his body healthy 
and efficient. Industry will follow the direction of our know- 
ledge, There is much still to be accomplished* This is no 
time to shorten the research program* The war in Europe may 
be progressing beyond our hopes, but the scientific research 
of the Quartermaster must progress with unslackened speed 
regardless of when the war may end. 
Major Siple then thanked Colonel Doriot and introduced Lto Col* D* 
B. Dill, 
COLONEL DILL*- In view of the introduction by Colonel Doriot, there is little 
left for me to say except to reinforce what he has said and to 
emphasize particularly one statement he made* This is certain- 
ly a time to continue research rather than to consider plans 
for curtailment. Do you know that the Navy considers every 
battleship and every aircraft carrier to be essentially a 
research project? I have not heard of any immediate trend to 
discontinue the construction of those craft. 
Another argument which was implied in what Colonel Doriot 
said is that no project ever reaches a state of perfection. 
It is also a fact that a longer time may be required to pro- 
gress from BO# perfection to 90# perfection, than was required 
to gain the original 80# in the first place. The difference 
between 80 and 90# may mean the difference between success and 
failure in a military operation. There are then two fields in 
which we must work, first, to spread new ideas, and secondly, to further perfect items in which the Quartermaster is 
% 
interested. 
Our Canadian friends have recently initiated a system at 
these meetings which we would do well to follow, (1') No meet- 
ing of this sort should be adjourned without a definition of a 
further course of work; (2) no meeting should be adjourned 
without definite assignment of future work, nor without a date 
when at least a portion of the work is to be completed. 
MAJOR SIPLEt- The specific problem confronting us is the development of an 
index which will tie laboratory tests together with the experi- 
ences in the field, We are searching for a quantative means of 
determining adequate quantities of clothing, beds and shelter 
and for a way in which these can be plotted on maps* The 
laboratories have given us certain factors. They have worked 
out those factors with care and in great detail. The Quarter- 
master is confronted with the groups of men in the field whose 
comments are apparently at variance with the laboratory ideas* 
This difference is probably due to a group of variables which 
cannot be ideally measured in a laboratory where sunlight, 
high wind velocity and many other factors are by necessity 
absent; therefore, there should be some reliable means of extra- 
polating from the laboratory tests to the knowledge which has 
been accumulated in the field throughout the years. There is 
not enough time during war and there is too much danger in 
waiting until after supplies have reached a region to determine 
whether or not supplies are adequate f.or the time and place* 
We must be able to predict that the clothing and equipment will be completely adequate under normal conditions so that under 
subnormal conditions little or no danger is encounteredo 
For this reason, we have asked together today an extensive 
group of physiologists, physists and climatologist so that 
three portions of this study may be brought together; the 
climatic conditions as they are known by the climatologists; 
the reaction of man's body as it is known by the physiologists; 
and between them the physical laws of heat transfer through 
clothing* We have chosen as the temporary chairman of our 
meeting today, Dr* Jesse H* Plummer, who is a physicist from 
the glass industry* He has studied this problem deeply so as 
to find laws through the medium of Physics for integration be- 
tween laboratory and field* 
In this endeavor, we have several objectivesr 
(1) The construction of a comparative index with which to 
compare different climatic strains in all parts of the world* 
With such an index, we could map the world for the effect of 
climate on human beings* These maps would not only show the 
type of clothing needed, but would predict where trouble might 
be encountered* We know, rodghly, where we have jungle and 
desert, but the intensity of the strain under which man's life 
may be endangered is still generally unknown* 
One way of measuring the climatic strain can be obtained 
from a thermal analysis* We know that the body produces heat 
and that for life to be sustained this heat must be lost at an 
average rate equal to the cate of production, otherwise the body temperature will steadily rise or fall until death occurs0 
The heat produced by the metabolism must then be equal to the 
sum of the heat lost by conduction through the clothing, con- 
vection from unclothed areas, radiation from the clothing and 
skin, and evaporation from the body surface or wet portions of 
the clothingo 
Not all of these factors are always losses. Under condit- 
ions of high temperature and in the sunshine, it is quite 
possible for the body to gain heat through convection, conduct- 
ion and radiation. The essential feature, however, is that in 
order to maintain a constant body temperature all of the heat 
which is produced or carried into the body by exterior condit- 
ions mast be lost. 
This provides us with a means of calculating an index of 
climatic strain, as we can measure quite accurately the quan- 
tities of heat transferred through the various channels. For 
instance, if the climatic conditions and the clothing have 
been defined, we may calculate the heat production that is re- 
quired in order to maintain a balance. On the other hand, if 
the heat production and the climatic conditions are defined we 
may calculate the amount of clothing that is required to keep 
a man in equilibrium. 
As the critical danger always lies in extreme conditions, 
we suggest the use of two indices. The hot weather index may 
be defined as the limits of work which men may safely accomplish 
without raising their temperature. For cold conditions, the index may be defined as the amount of clothing necessary to 
maintain equilibrium in standing men* Another -way of defining 
a cold weather index would be the amount of insulation required 
to provide eight hours of comfortable sleep0 
In this way, we could map the entire world and these maps 
would show the danger zones where severe heat strain may occur, 
as well as damp cold areas where trench foot would be prevalent. 
These maps would not be expected to evaluate precisely the 
strain on any given individual but we do expect them 1~ rk 
the areas of the w ’Id where the maxilurn protection must oe 
provided for everyone* In addition, they will furnish a quan- 
tative estimate of the strain involved. Any individual, how- 
ever, may feel more- or less strain o;r require more or less 
protection than that estimated. 
In this way, we can map the entire world, and these maps 
will show the danger areas where severe heat strain might occur 
as well as the damp cold areas where trench foot would be pre- 
valent. 
(2) The construction of clothing designed to make the most 
efficient use of the various avenues of heat loss under natural 
conditions. The indices provides a means of weighing these 
different avenues, and these in turn will, provide accurate in- 
formation -as to how the clothing should be constructed. In the 
past we have designed clothing as if it were to solve a single 
problem; but if we are aware that, in one section of the world, 
the problem of human heat tolerance is 90$ radiation and only 
10$ wind, then clothes can be so designed as to take the gieatest possible advantage of these two factors. 
(3) From a human standpoint, we are also interested in 
the single effect of different types of heat loss registered 
by a single sensation in the human body. The psychological 
sensations of disagreeable cold, pleasant comfort and oppress- 
ive heat are important to the efficiency of the man even 
though the danger point may not be reached. 
Our goal today is to establish an index which is satis- 
factory to the physiologist, which follows physical laws, and 
which can be used by the geographers and climatologists. 
If there is time later in the afternoon, it may be poss- 
ible to discuss the formation of a meteorological instrument 
which would register the same kind of heat stress which is 
felt by man. The Weather Bureau cannot establish a human test 
ing laboratory at all of its locations, but it could give us 
some measure in a heat flow term which would represent the 
combined stress. 
Since we cannot weight the single sensation on the human 
body until we have analyzed its four causes, we have divided 
the agenda into four parts* convection, conduction, radiation 
and evaporationo Following the review of each, we have asked 
for particular discussion of the problems by various members 
present — but we are hoping that everyone will be free to 
comment, criticize and suggest. 
At this point, I should liteto turn the meeting over to 
Dr, Plummer, SECTION I - CONVECTIVE HEAT TRANSFER: 
DR« PLUMMER:- The first topic on the program is the discussion of ti * in- 
fluence of convection upon the heat losses from the human body* Winslour 
Herrington, and Gagge* have studied the effect of -wind velocity upon 
convection and found that the convective heat transfer was proportional 
either to the wind velocity or to the square root of the velocity* 
Unfortunately, the experiments were based upon a relatively small range 
of air movement* and at high wind velocities there is a considerable 
difference in the values obtained from the two fomnia. 
To generalize Winslow, Herrington, and Gagge‘s results so that they 
may be applied with confidence to high wind velocities, it is necessary 
to assume that the convective losses from the body are the same as those 
from a cylinder whose diameter may be found by comparison with physio- 
logical data. 
Upon examining the literature within the last ten years, it is 
evident that there is a considerable amount of confusion existing in 
the relationship between convection and wind velocity. Some investi- 
gations show the square root law to be valid, others require different 
powers of wind velocity such as the 0,55 power, 0,6 power, O.06 power, 
or even higher powers. 
Within the last five years, much of this confusion has been 
eliminated through the application of dimensional analysis to the sur- 
Gagge, Herrington and Wipslow, The American Journal 
of Physiology;** 1937 face coefficients of heat transfer. To use this method in the present 
case, the assumption is made that the film coefficient of heat transfer 
is some function oft 
The cylinder, diameter D 
The thermal conductivity of air K 
The wind velocity V 
The density of air p 
and the specific heat of air Cp 
The viscosity of air /t 
H = *(D.VvVkK.CP) 
The unknown function may be expanded in terms of an exponential 
series. }-j = A, ( D°' V Cpf' ) + 
(1) ' ~ 
A2( D°2MbyCz Kdz/?e2 C fz 
Each of these terras is of the forms 
A ( D°VV Kd/CPf) 
In which the d,b,c,d,e,f, are dimensionless constantse Each of the 
terms in the right hand side of this equation must have the same 
net dimensions as the terms in the left hand side of the equation. 
Each of the variables may be expressed in terms of the five 
fundamental dimensions: 
Mass - m Time - T 
Length — L Temperature - t 
Quantity of heat - Q 
The dimension of the diameter is simply L. The dimensions of 
velocity is length per unit time or .L. Of viscosity is jn„ Of the 
T LT 
density is m Of the specific heat is Q 
mt 
Of thermal conductivity is 
Lit Equating the dimensions-of the general term to the dimensions 
of h gives the equation: 
J_= f-U b l-BL.) * (-£-) d (-!*-] 8 flf f 
Lait L It; \lt ) vut 1 v l» / / \ mt / 
This relation is identical to 
+ e-f jj3+b-c-d-3e + 2 -|—b-c-d+i Qd+f-i 
which can only be satisfied if each of the exponents is equal to 
Oo 
c £ e - f r 0 
d4b“C-d-3e42crO 
-b“C“d|lrO 
-d-fjlsO 
d|f-lr 0 
These five simultaneous equations in six unknowns cannot be com- 
pletely solved, but a, b, c, and d may be found in terms of e 
and f0 
This solution is: 
a as -1 + c 
b — c 
c ~ 4 f 
d s 1 - f 
The general term in the series then takes the form: 
AD"l+e V>“e+' K'-y CPf 
and equation (1) may be rewritten as: 
n(^)e"(c-F)f’ 
Recent studies have shown that * x x r\ -i ± r\ a 
fi =T2=f„ = 0.3 to 0.4 
so for air the terras [ V* n may be considered constant and 
included in the value of the constants» Equation (1) then becomess 
V-EAjyf)” 
The term HD is known as Nusselt's number and *Pvp~ is called 
K h- 
Reynold’s number,, McAdams has published a summary of the work of 13 
different workers in the field of convective heat transfer and shows 
that the relation between these two numbers is a smooth continuous 
function,, 
The equation t ( 
(2) = | + .407 + .00123 
fits McAdams1 curve with a maximum error of less than 5% between the 
values of Reynold’s number 100 and 25,000., For the present purposes, 
this is the complete range since small values of Reynold's numbers 
occur only with very small diameters or extremely small wind velocit- 
ieso 
This equation is in the form which would be expected from 
dimensional analysis and consequently should very closely express 
the way in which surface coefficients are effected by such variables 
as wind velocity, temperature, and diameter of cylinder,, Unfort- 
unately, it is not a simple equation to work with, but it may be 
readily solved by graphical means# 
Solving equation (2) in this way for diameters of 1, Uy 6, and 
12 inches, and for temperatures of 0 and 120°F«, a set of curves 
can be developed which show the relationship existing between con- 
vective heat transfer and wind velocity for various diameters and 
temperatures (Fig# 1)# It is obvious that the diameter plays a 
very important part and also that the effects of temperature, while STANDARD CROSS SECTION 
ENGRAVING 320 5X5 TO THE HALF INCH 
CLIMATOLOGY ft ENVIRONMENTAL PROTECTION SEC. 
RESEARCH A DEVELOPMENT BRANCH O.Q. M.Gl 
CONVECTIVE HEAT TRANSFER 
Between atmosphere and cylinders of 
various diameters of surface temperatures 
of 0°F and I20°F- Kg.cal./M*/hr./°F at vari- 
ous wind velocities. 
FIGURE I 
Original Version-18 JUNE 1944 appreciable, may be neglected in any but the most precise analysis* 
By taking a cross plot of this last set of curves and showing con- 
vective heat transfer as a function of diameter for specific values 
of the wind velocity, the effective diameter of the human body may 
be found from the work of Winslow, Herrington, and Gagge* The best 
agreement occurs when the diameter of the nude human body is chosen 
as 3 inches* Within the range of experimental wind velocities used 
by Winslow, Herrington, and Gagge, the points fit the 3 inch curve 
with an accuracy of approximately 2%o Upon extrapolating the 
physiological data to higher wind velocities, the difference may be 
of the order of 30$* Figure 2 shows the convective heat transfer 
and thermal resistance for cylinders of varying diameter, including 
the three inch* The result of temperature differences has here 
been averaged over the range likely to include the human body* 
Radiation is not included* 
To compare this data with Burton’s, a correction to the con- 
vective heat transfer must be added to account for the radiation • 
lost from the surface* Assuming black body conditions, this is 
equivalent to adding a constant term of 2*65 kilogram calories per 
degree F, to the total convective loss* Upon converting the con- 
ductance to resistance in do value, the agreement with Burton’s 
data is reasonably good* In the range of wind velocities from \ 
mile per hour to 20 miles per hour, the deviation, in general, is 
only *05 do or less* The maximum variation is found at J mile 
per hour where the deviation rose to *08* 25-8367-300 
CLIMATOLOGY Or ENVIRONMENTAL PROTECTION SacIIoa- RtMOrch O Dal Bronch, aQ.MjT 
.Resistance: #gj||ldR 
FIGURE 2 
ill convective; heat transfer : 
AND THERM A- IffSISrflNCE 
Fpfe f DIAMETERS 
Wind Velocity ini lM/hr 
Heat Transfer 
" TER ”1 TEMf’ERAliURE 'WFLRENtpr 
(vaovff hr BEiow THE BODY 
STANDARD CROSS SECTION 
ENGRAVING 320 5X5 TO THE HALF INCH DISCUSSION 
DR, BURTON:- In some calculations I made in Toronto based only on my own 
dimensions, I found the average diameter to be 7 cm. 
DR, PLUMMER:- I am glad you mentioned that for the value of 3 inches we 
found was so small that we were rather disturbed about it. 
DR, THOM:- May I make a comment? In some experiments we made, the 
radiation factors were extremely important. It probably will be 
much more important in the human body because of the difference 
in temperature between the body and the outside air. Hfhen the 
gradient between the body and the air is increased, the radiation 
factor mist be altered. 
DR, PLUMMER:- This is perfectly correct, but for a limited temperature 
range, the radiation factor may be considered constant without intro- 
ducing an appreciable error. 
DR, BURTON:- In a recent conference here on standardization of methods, 
o_ 
I showed that, with a change in external temperature from 70 F, to 
-40°F, the change in the radiation factor is almost exactly com- 
pensated for by the change in convection, I think that we may take 
a standard curve and neglect the effect of temperature for all 
practical purposes. Do you agree? 
DR. PLUMMER}- I do. Certainly the error involved is less than the 
experimental error in practical measurements. 
COL, HATCHThe present discussion concerns only transverse air flow. 
As the transverse velocity is diminisned, a longitudinal velocity, 
caused by the temperature difference between the body and the air, 
will begin to be effective. At what transverse velocity does the vertical movement cause a change in the results, and how can you 
combine the effect of the two velocities? 
DR. PLUMMER:- Only additional experiments could provide a complete 
answer. Equation 6 is valid for transverse velocities as low as 
0.1 miles per hour. Below this, it departs appreciably. Since we 
are primarily interested in outdoor conditions, lower velocities were 
not considered. I believe that the effect of the transverse velocity 
is 10 to 12 feet per minute or less. 
CONDUCTIVE HEAT TRANSFER AND CLO VALUES 
Dr. Plummer then introduced Mrs. Margaret lonides Cochran. 
MRS. COCHRANt- For the benefit of our visitors who may be more or less 
unfamiliar with the scientific study of clothing, I should like to 
* 
define a do unit. The do unit was first described by Drs. Qagge, 
Burton, and Bazett in an article in in 1939» A do 
serves the purpose of establishing a unit of insulation for the 
human body which can be used by physiologists, clothing experts 
and housing engineers. It is a resistance unit similar to an ohm 
in electricity. One do is defined as the amount of clothing 
necessary to keep a man comfortable at normal indoor winter con- 
ditions, or, to be more precise, at a temperature of 70°F with 
relative humidity less than 50% and almost still air. The number 
of do necessary for any other condition varies with the amount of 
heat which the man's body is creating, the temperature of the out- 
side air, and the wind velocity. 
In laboratories •when do measurements are taken, the meta- 
bolic rate of the man is gauged by determining the heat lost from 
£■ 
See Appendix 2 the skin, the amount of heat lost by warming the air which the man 
breaths, and the amount of heat lost by evaporation from the skin 
surface and from the lungs* 
Since the do is a physical unit of heat resistance, the 
value of clothing may be determined by a simple calculation; 
measuring the thicknesses, calculating the resistances, and adding 
them. 
This method is illustrated by these two charts. Figure 3, 
’♦Combat Uniform 3 Clo11, and Figure 4, "Arctic Uniform 4 Clo". We 
call these the thickness charts* I should like to point out that 
these particular charts are more an illustration of method than a 
statistical analysis of thS way in which clothing fits various sub- 
jects* Only one or two men were measured in making these charts* 
tfery careful measurements were taken of the circumference of 
a man in the nude, and at each stage of his dressing* These cir- 
cumferences were then converted to radii* The difference between 
the nude radius and the clothing radii gave the thickness of the 
layers plus the included air at each stage. The textiles were 
also measured for their thickness by a precise instrument, --to 
thicknesses were taken for each material; (l) the greatest possible 
thickness without any pressure, and (2) the thickness at 1 pound 
per square inch of pressure. (Occasionally arbitrary adjustments 
were necessary to take into consideration the extra thickness of 
pockets, binding, and findings.) 
In construction of the graph, we measured first the full 
radius of the outside layer since this was the absolute maximum ARCTIC UNIFORM-4 CLO 
FIGURE 3 
ORIGINAL = FE B. 1944 
Thlt EDITION = 24 JULY 1944 
CLIMATOLOGY 8r ENVIRONMENTAL PROTECTION Section-Reseorch 0r Dev, Branch, O.Q.M,G~ 
KEUFFEL & ESSER C9 NEW YORK 
24-0838B-2001 COMBAT UNIFORM - 3 CLO 
FIGURE 4 
ORIGINAL* FEB. 19 44 
CLIMATOLOGY a ENVIRONMENTAL PROTECTION Section_Research a Dev. Branch', O.Q.M.6, 
THIS EDITION * 24 JULY 19 44 
*4-99285- 200 of the thickness of the clothing, The difference between this 
outermost radius and the radius of the next layer of material 
represents the space available for the textile plus the included 
aii*0 Wfren the space between layers was smaller than the optimum 
thickness of the clothing, then compression was apparent at some 
point beneath. If the space were greater than the possible thick- 
ness of the material, it was obvious that the full benefit of the 
insulating value of the material was present plus the amount of 
dead air for which there was room, (If this dead air between layers 
exceeded ,2 of an inch, the additional air was judged to be in- 
efficient, since above that amount convection currents will set in 
and reduce the insulating power of the air. For example, notice 
the large inefficient spaces of the trouser legs,) 
■When the bar graph for each part of the body was finished, 
the total efficient thickness of air and clothing was added to- 
gether, One-fourth inch of air and material is approximately 
equal to one do. This gives the do value which would be present 
if the material and air were covering a flat plate. 
After the diagram was complete, two corrections had to be 
made in estimating the adequacy of the clothing. The first was 
the correction for insulation loss due to the increase in sur- 
face area provided by the varying size4 cylinders. This is a 
form of the law of diminishing returns. Extra clothing layers 
cannot give proportionally greater insulation. If a small stove 
is put in a small storeroom, it will heat the room sufficiently. 
If, however, it is put in a large circular storeroom, the room will not be heated even though it is filled to the ceiling with 
soft woolo This is because the radiating surface from which the 
heat is lost increases more rapidly in proportion to the radius 
of the insulation,, 
The same is true in the body. As extra layers are added, the 
area of their surface increases. This is obvious when one realizes 
how much more material is needed to make a shirt than an 
and how much more still to make a coat. As a result of this in- 
creasing size, the efficiency of each additional layer is decreased. 
The seller the cylinder, the more rapidly the surface area in- 
creases in proportion to the square of radius and the greater the 
decrease of efficiency as additional layers are added. Figure No, 5 
shows the relationship of effective insulation to surface area. Two 
and one-half inches of insulation around the torso would be 80$ 
efficient; whereas, the same over the hands would be only 40$ 
efficient, besides being impractical for dexterity. These correct- 
ions for surface area are shown as the efficiency and inefficiency 
figures on the charts. This gives the figures listed in the 
column under do values, which represent the local insulation pro- 
vided for each part of the body. 
The second correction made is due to the varying loss of heat 
from different parts of the body? The feet, for example, lose 
only 7% or the total body heat while zhe torso loses 36£, The 
value of the weighted figures is shown in the column under total 
contribution. 
If should be noted that the clothing indicated here gives 
•Vr 
See Appendix 3 STANDARD CROSS ‘SECTION 
ENGRAVING 320 5X5 TO THE HALF INCH 
21-98118-200 
CLIMATOLOGY AND ENVIRONMENTAL PROTECTION SECTION 
RESEARCH AND DEVELOPMENT BRANCH 
0. Q. M. 6 - WAR DEPARTMENT 
FIGURE 5 fairly adequate protection for all parts of the body, except for 
the face, Very different effects will be found if any portion of 
the body is inadequately protected. 
The final column of figures is the contribution which the 
clothing over each part of the body makes as the whole. Labora- 
tory measurements have shown the arctic uniform to be approximately 
4 clo, IWhen the figures in the final column are added, it will be 
seen that with the measurement of thicknesses, the uniform appears 
to be 4«13 clOo In the same way, the laboratory 3 clo uniform is 
calculated to be 3«»19 clo. 
A greater variation than this between laboratory measurements 
of conductance and these calculations of resistance might, of 
course, be expected to occur if measurements were made on more 
subjects. 
By means of this method of estimating clothing insulation as 
an alternate to precise physiological tests, a number of advantages 
are obtained other than its short cut measurements. Some of the 
advantages over cold chamber metabolic clb testing are as follows: 
(a) To make a quick and simple estimate of the insulation 
value which any garment contributes to a given assembly. 
(b) To determine the thermal balance of an assemo±y of 
clothing for the purpose oi correcting points which are too 
tight or too loose to give optimum protection. Also to 
indicate where additional thickness may be added to improve 
insulation with a minimum increase in weight. 
(c) To .nyaluate the loss of local insulation at pressure 
points. (d) To evaluate the component parts of lined garments. 
(e) To provide a suitable means of making a measurement 
analysis of a large group of soldiers to determine the ade- 
quacy of garment sizing. 
It is suggested that the application of this method might 
bring to light other interesting differences in insulation such 
as is provided by the front and back of the jackets due to the 
presence of numberous pockets and findings. 
In order to use the do values for an index, it is necessary 
to correlate them with climatic conditions. Figure No, 6 rtClo 
Values11 shows the temperature along the side and the activity or 
the heat produced by the body across the top. This chart is 
plotted for an average wind of 5 miles an hour. From it, one may 
determine what do is necessary to keep a man in thermal equilibrium 
for various activities between sleeping and marching at 4 miles per 
hour at any given temperature if the clothing and atmosphere are 
dry. For use in the index, it seems probable that the best activity 
to select would be one which would cover such activities as truck 
driving, standing at guard duty, and standing with occasional 
shifting of feet. Naturally, if this man begins to walk fast, he 
will have to remove some layers of his clothing; nevertheless, it 
is far more necessary that he be well protected at a low activity 
than at a high. If he is forced to lie still in a fox hole with 
this clothing, his endurance will be limited by a time factor; 
although lack of wind will give him considerable added protection. 
The range of activities cited here (between 65 and 75 
Kg, Cals/M^/hr) has the additional advantage in that they can be 21-98 I 18-200 
KEUFFEL & ESSER C8, NEW YORK 
iiiilMUESj 
CLIMATOLOGY AND ENVIRONMENTAL PROTECTION SECTION 
RESEARCH AND DEVELOPMENT BRANCH 
0. Q. M. 6. WAR DEPARTMENT 
FIGURE 6 
Origlnol Version 15 MARCH 1944 
This Edition = 21 JULY 1944 
HONI dIVH 3H1 01 SXS 02£ 9NIAVU9N3 
N0U03S ssoao ayvoNvis correlated with the Climatic Zone Maps* In this range, one addit- 
ional half do is needed for each 9°F drop in average air tempera- 
ture* The Climatic Zone Maps are so designed that the temperature 
range of each zone is 18°F or 10°C* For precise purposes of cloth- 
ing distribution, half do lines should also be drawn on the 9' °F 
temperature lines* 
DISCUSSION 
DR, BURTON:- An extension* of the report on limits of thermal insulat- 
ion (Climatic Research Laboratory, Report No* 76) might be made 
to include the effect of increasing surface area on total insulat- 
ion of the air, as well as of the clothings This shows the 
limitations of insulation on surfaces of small radii of curvature 
to be even more drastic than has been supposed. Unless the out- 
side diameter exceeds a certain value, adding an insulation layer 
may even increase, rather than decrease, the heat loss. This 
critical condition could hold for the fingers in very still air. 
It is possible that thin gloves of poor insulating material 
actually made the hands colder* This idea never applies to hand- 
gear in greater air movements* For precise measurements, account 
should be taken of this connection in do determination on gloves, 
and caution should be taken not to interpret results in hand 
calorimeters, with very still air, as indicating the practical 
usefulness of thin inner gloves in the field* The importance of 
* 
This discussion is now published in N,R.C* Canada, S,P0Co 
Report Noo 174o using the best possible insulating material (such as Aerogel) for 
handgear should be emphasized, 
DR. BELDINGi- I feel that the Clo value charts issued by this section 
must be used rather cautiously. They are probably quite accurate 
for low activity rates, but when the rates of work become high, 
sweating occurs, at least localized sweating, and the evaporative 
heat loss mist be taken into consideration. This has not been 
done in the present tolerance time figures. 
DR. PLUMMERYou are quite correct, we have not taken into account the 
evaporative heat losses in calculating tolerance times regardless 
of the rates of activity. We would like to do so, but unfortunately 
have had no data which we could use for this purpose. In spite of 
this, however, we think that the tolerance times as calculated at 
present are a reasonably good approximation and are somewhat on 
the conservative side because they are based on a total loss of 
40 or BO Kg. Cal. per square meters. 
Local sweating is primarily an unbalanced situation, i,e,, one 
portion of the body is generating more heat than necessary and 
other parts of the body are probably generating less heat. We 
would very much like to have some information concerning the 
quantity of heat output per unit area for different parts of the 
body as a function of the activity. This would give us informa- 
tion with which to calculate the effects of unbalanced clothing 
conditions', and it would also permit us to take into considera- 
tion the evaporative heat loss and then the calculation of toler- 
ance times. DR, BSLDINGOf course, the do equation cannot be taken with great 
precision. In applying the equation which Burton originated to 
human subjects, we have found that there is a! variation of 10 to 
15$ between different subjects on the same day and also between 
the same subjects on different days. This whole matter is dis- 
cussed in a revised edition of the Harvard Fatigue Report No. 19, 
dated 3 August 1944* 
DR, BURTON:- Is it not possible that some of this variation is due to 
the way that the clothes fit? 
MAJOR SIPLEx- In the early stages of this work two years ago, many 
physiologists believe that any type of clothing index would be 
impractical because of the great difference between human beings. 
Further study of the factors governing heat loss shows that many 
of these variables are external. The same man may not put on his 
clothes in just the same way two days in succession, and the same 
clothes wi3J. not fit two different men just alike; as a result, 
there will be considerable variation in the distribution of dead 
air space and pressure points from time to time. MRS a COCHRANS'- In report No. 76 from the Climatic Research Laboratory to 
which Dr. Burton referred, the do value per inch was taken as the 
maximum for dead air space. This value is, 1 believe, 4*7 do to the 
inch. However, I should like to ask Dr. Burton whether with the in- 
clusion of textiles this figure would not drop to about 4 do to the 
inch? 
DR. BURTONt- 4 do per inch seems to me an acceptable estimate. It is the 
value we takfe for calculations of dead air and clothing. 
EVAPORATION 
Dr. Plummer then introduced Dr. Fourt of the Bureau of Standards to 
speak on the subject of "Evaporation*. 
DR. FOURTjr- We tried two different kinds of experiments at Dr, Plummer's re- 
quest. The first of these concerned the effect of wind on the evaporat- 
ion from a completely wet cylinder. The observed rates of evaporative 
cooling are shown on Figure 7 in - (E) per millimeter 
vapor pressure difference, (p) are plotted against wind speed (V) in 
miles per hour. The upper curve shows the results for a wet surface 
without any cover. It is distinctly curved, rather than linear with 
wind velocity, Powell* studied the evaporation from completely wet 
cylinders of different diameters, in air streams of different speeds. 
These are shown in Figure 8, His equation may be writtent 
E/P a 35.1 V .6 
D.4 
When D is the diameter in centimeters» For the diameter of the 
*Trans. Inst, Chem. Eng., 18, 36 (1940), Relationship of evaporation rate to wind velocity, for fabrics having the 
air permeabilities shown at the ends of the lines. E/P = Kg.cal/lr per n. 
vapor pressure difference. Air permeability = ft3/ft? min at pressure « 0.5 inch 
water. 
FIGURE 7 mkmmwhh 
FIGURE 8 
Original Version « 23 JULY 1944 
CLIMATOLOGY a ENVIRONMENTAL PROTECTION SEC. 
RESEARCH a DEVELOPMENT BRANCH 0. 0. M. 6. artificial sweating man, 20„4 centimeters, this reduces to - 
E/P - 10o5 V*6 
The observations at the higher speeds lie 15% above Powell's values 
but follow the same general trend® Perfect agreement should not be 
expected, because Powell was concerned only with the sides of the 
cylinders, while these experiments included evaporation from the 
flat top® 
Qagge, Herrington and Winslow, American Journal of Hygiene, 26, 
84 (1937) have given a different type of equation for the effect of 
air movement on evaporative cooling from a man with completely wet 
skin, which may be written E/P a 2®S £ 1®0 V® This may apply better 
than Powell's at low air movement, since it includes the effect of 
natural convection, but it falls 15% too low at 10 miles per hour® 
The other type of experiment which we have done concerns the 
evaporation from a wet skin through dry clothing® A cylindrical 
fabric cover was held at an average distance of 0®7 centimeter from 
the wet blotting paper® Under these conditions, the rate of evapora- 
tion depends on the air permeability of the fabric, as shown in the 
charts (Figure 9)« Air permeability is expressed in cubic feet of 
air passing through 1 square foot of fabric per minute, at a pressure 
difference across the fabric equal to 0®5 inch water® In addition 
to air permeability, the size of the cover, or the amount of air 
trapped between cover and skin makes a difference, as shown in the 
chart (Figure 10). For any fabrics of low permeability, such as 
herringbone twill or poplin, these size factors are of as much in- 
fluence as the permeability factor® Effect of wind on evaporation (E/P = kg hr per ram vapor 
pressure difference). 
Fabric Air Permeabilitv 
■■ ■■■■ ■ ■ — ■ i. ■■■»■■ ■ ■ ■,■■■— ..i■,, u 
Palm Beach 91 
Coat 4* shirt + underwear 66 
6 oz. khaki 45 
JO cloth 0,88 
Water permeable cellophane 0*00 
FIGURE 9 2 
Effect of wind on evaporation (E/P = Kg cal/m hr per mm vapor 
pressure difference) for covers differing in size. 
Material Air Permeability Tight Loose 
uadius Radius 
ft3/ft2 min at cm cm 
0.5 in water 
Muslin 98 11.0 11.8 
Herringbone twill 13 11,3 11*9 
Poplin d 11.0 12.2 
FIGURE 10 The combined effect of wind and air permeability can be analyzed 
in an empirical way, for the range of air speeds up to 10 miles per 
hour, and fabric permeabilities up to 500, neglecting small variations 
in size„ The chart (Figure 11) shows the increase in evaporation per 
unit wind speed, plotted against air permeability of fabric«, Various 
empirical relations can be fitted to this, but the one of present 
choice is a linear relationship which does not go through the origin,, 
The fact that there is an increase in evaporation with increasing 
wind, even with zero air permeability, should be expected, since 
part of the resistance to evaporation lies in the air outside the 
fabrico The equation for the combined effects of air movement and 
fabric permeability is 
S/P - 3 i (0o3 j- o004 A) V 
in which A is the air permeability„ The charts show that the experi- 
mental uncertainty is such that a difference in air permeability 
of about 30 is needed to demonstrate a difference between fabrics„ 
For the purpose of mapping the effect of climatic factors, it 
must be remembered that there is a big difference between the rates 
of evaporation from bare, wet skin and from clothed skin0 The 
differences between these physical experiments and the reactions of 
a real man should also be pointed out„ The physical experiments deal 
with a 100$ wet cylinder, or with this covered by dry clothing„ It 
is very seldom that the extreme condition of 100$ wet skin is reached„ 
Experiments at the Pierce Laboratory* have shown that the sensation 
*Winslow, Herrington, & Gagge, A0S„H<,VoEo Transactions, 44* 179 (1939) Observatlons ; o 6*4 niles/hr, 
• 10 miles/hr. 
nir Permeability min. at pressure = 0.5 in. water 
Empirical eouations connecting increase in evaporation per unit wind 
speed (A&/PV = Kg cal/nr hr per mm. v.p, difference per mile/hr. wind) with air 
permeability. A, 
nine a is for A E/PV = 0.09 A0»5 
iAne b is for A E/PV - 0.25 (A/30 1)0-75 
.bine c is for Ae/PV = 0.3 (A/75 + 1) * 0.3 + 0.004 A 
broken lines indicate deviation from line c. 
FIGURE II of discomfort increases with increase in wetted area, and that above 
75% wetted area is unpleasant. However, the clothing does not remain 
perfectly dry, and, since wet clothing resembles wet skin in rate of 
evaporative cooling, a real man presents a situation intermediate be- 
tween the perfectly wet surface and the wet surface covered by dry 
clothing. These experiments show that the extreme cases can be des- 
cribed by two different types of equations: for wet skin or wet 
clothing, Powell's equation; for dry clothing, a modified form of 
Gagge’s equation. 
DISCUSSION 
DR, BURTONr- The systematization of the information regarding evaporation 
from the body is in a manner analogous to the system of Clo units 
for thermal insulation. It is not necessary to invent a new Unit 
other than that already used by Dr. Goodings and by Dr. Fourt, 
namely, the Equivalent centimeters of dead air1*, Incidentially, 
I suggest that "dead air" be used instead of '♦still air" to avoid 
confusion with the use of '♦still air” to denote that in a room with- 
out ventilation. Here convection currents make it very far from the 
"dead air'1 in a fabric or in the small dish of the experimental 
measurements, Th® fundamental equation of vapor transfer is: 
Cals/Sq o M,/Hr, by _ * _ s 
evaporation “* .1 a / x3 
R 
Where and ?2 are the vapor pressures of the skin and outside air 
in millimeters of Hq, and R is the resistance to passage of vapor in 
cms of dead air. By a fortunate coincidence, it turns out that in 
normal indoor conditions with normal clothing, the total resistance R is about 1.7 cms of dead air0 Of this, about 1 cm. is in the 
clothing, and 0o7 cms8 in the outside air. In a wind the latter 
may fall to as low as 0.2 cms. The analogy with the thermal in- 
sulation normal clothing in do units is complete. It is to be 
noted that a total up to 17 cms0 of resistance to vapor could be 
tolerated before the inactive subject became uncomfortable. This 
indicated how far one could go with a protection impermeable suit 
before it became uncomfortable. 
DR# PLUMMER:- Thank you Dr0 Burton0 We had not thought of calculating 
thermal transfer by vapor pressures in terms of resistance# That 
is a most useful addition# 
We are most grateful to Dr. Fourt of the Textile Foundation for 
the assistance he has given us in studying evaporation. For includ- 
ing the evaporative heat transfer in the index, wo suggest the graph 
as illustrated in Figure 12. The upper curved line on this graph 
shows the heat transfer from any bare surface irrespective of whether 
that surface is the nude skin or the clothing surface so long as it 
is entirely wet. Heat transfer can then be measured in 
per millimeter vapor pressure difference between the surface and the 
atmosphere for any wind velocity. This corresponds to the upper 
curved line as shown in Dr. Fount's diagram. Figure No. 7. For zero 
wind velocity, this also corresponds to the experiments made by 
Winslow, Herrington, and Gagge. When the figures taken from this 
line have been added to or subtracted from the corresponding figures 
for convection for any given atmospheric condition, the result 
should be the limits of safe activity which a man can endure without storing additional bodily heat0 
It is obvious, however, that men often become distinctly uncomfort- 
able long before they have reached the limits of safe activity,, Winslow 
Herrington, and Gagge* have measured these limits of comfort in terms of 
percent of wetted area of the human body„ Using a fabric of low air per- 
meability such as Herringbone twill and replotting from the graphs shown 
by Dr, Fount, we have drawn three straight lines near the bottom of the 
chart, Noo 120 Reading from top to bottom, these represent respective 
ly (a) 100$ wetted skin surface covered with one dry layer of herring- 
bone twill, (b) 75$ wetted skin surface covered with one layer of dry 
herringbone twill, (c) 25$ wetted skin surface covered with one layer 
of dry herringbone twill0 Summer underclothes arc included in the 
normal costume, the permeability of the material is sufficiently high 
to make no difference in the transfer factors0 
For the purpose of demarkating efficient military service it may 
be necessary to plot 2 lines for every hot climate; one with the limits 
of safe activity, and another with a 75$ wetted area or an extremely 
unpleasant line, since in some climates extreme unpleasantness and 
hence decrease of efficiency is apparent under normal daytime condit- 
ions even though the threshold of danger rarely occurs, whereas in 
other climates unpleasant conditions may be reached at a temperature 
and vapor pressure only slightly below those of critical danger,, 
Until the limits of danger are reached, there will be, of course, 
a considerable time when the body is not all wet nor the clothing all 
*Rcprint from The American Journal of Hygiene, Vol„ 26, No0 1, 103-115, 
July, 1937o dryn Adjustments for these periods could be made but since their variat 
ions are so numberous, it seemed more reasonable to make the estimates 
which we have shown0 
then are our suggestions for the evaporation factors to be 
included in the index„ 
The meeting was adjoined for lunch at 1300 hours© 
-27b— IIH 
tittiipMS: 
FIGURE 12 
CLIMATOLOGY a ENVIRONMENTAL PROTECTION SEC. 
RESEARCH 8 DEVELOPMENT BRANCH 0. Q. M. G. 
Original Version > 23 JULY \S44 The meeting was reconvened by Major Siple at 1430 hours. 
Dr. Plummer then introduced Mrs, Elizabeth Schickele, 
RADIATION 
MRS, SCHICKELE:- In considering radiation, particularly out-of-doors, we 
discover that radiation exchange bears some resemblance to good 
conversation - it is strictly a reciprocal affair. Is is almost 
impossible, out-of-doors, to vary the flow from one source without 
at the same time varying that from another. As an example, step- 
ping out of the sun to the shade of a tree changes the amount of 
sunlight falling on the body, but that is not the whole of it. It 
also affects the radiant exchange between body and ground, and the 
extent of the reradiation: of the body to space. Possibly other 
factors are also affected. The terms of the radiation exchange 
equation are evidently interdependent - a change in one may cause 
change in many or all of the others. 
This is one of three threads which run as a theme through 
this discussion. The second thread concerns the necessity of in- 
cluding radiation gains and losses in calculations of heat loss 
out-of-doorso Evaporation notes have sometimes been taken as the 
sole measure of heat transfer under these conditions. The third 
thread, a corollary of the first two, considers the changes in 
radiation exchange as surface temperatures change. This may well 
act as a compensatory device to form a kind of insulating layer 
which decreases the effective radiation load. These may appear 
to be elementary propositions, radiation exchange, however, although 
complex in practice, is relatively simple in theory. As Dr. Plummer stated, this complexity of factors, this hand- 
ling of the numerous variables, poses a nice problem in maneuvers. 
It is literally true that almost everything under the sun affects 
radiant transfer out-of-doors. Most of the factors affecting cli- 
mate- the position of the body; nature of the terrain; materials 
of the clothing- these include some of the most important. 
There are five sources of radiant heat exchange between the 
body and its environment - (1) solar radiation, (2) diffuse 
radiation from the sky, and (3) and (4-) two types of radiation 
from the ground. Reradiation from sun and sky is diffusely re- 
flected from the ground at unchanged wavelengths, In addition, 
the ground will radiate according to the fourth power of its 
absolute temperature. At these long wavelengths, both ground 
and body may be considered as black bodies - that is, emissivity 
and absorptivity equal to unity. Out-of-doors, the radiation of 
the body to cold space ($) must be included in the calculations. 
The radiant exchange may therefore be expressed as- 
Z - Zo * 2h * Zg + h - Zs 
Where Z « Net radiant exchange - total radiant heat stress 
on body 
Z0 = Direct solar radiation 
2h - Diffuse sky radiation 
Zj - Reflected radiation 
Zf, - Ground radiation 
o 
2S = Radiation from the body to the sky reduced by 
incoming radiation from the atmosphere We begin with the solar constant, which is the amount of solar 
energy which falls per minute on one square centimeter outside the 
atmosphere. The general accepted figures is 1,94 Cals/M^/min, 
y 
This is depleted and modified somewhat as it passes through the 
atmosphere. Scattering will be caused by gaseous molecules, water 
vapor, and dust. Absorption will occur due to ozone, C02, water 
vapor, etc. The effective length of path through the atmosphere 
varies with the secant of the zenith angle of the sun, being twice 
as great when the sun is 60° from the zenith as when the sun is 
overhead. 
Scattering of solar radiation by air and water vapor, and 
absorption by water vapor, for various angles of the sun, as 
determined by latitude, season, and time of day, are taken direct- 
ly from the data of the Smithsonian Institution. (Smithsonian 
Physical Tables, Table 686, page 555, Bth revised edition). Ozone 
absorption cuts off transmission of the solar specturm at 2.9, 
but the loss in intensity is small in this range, of the spectral 
intensity curve. 
Water vapor is the principal absorber of radiation in the 
infra red. The effect is so marked that solar radiation received 
at normal incidence is on the average higher in the winter When 
the air is dry than the summer. The highest solar radiation ever 
recorded in Washington occurred on a February day when the tempera- 
ture dropped suddenly to the lowest point in twenty years. 
Particles of dust, being large, are generally considered to 
scatter light independently of wave length. As dust content of the air is difficult to estimate, it has been disregarded in the 
calculations., This seems to be a reasonable procedure, as we are 
most interested in maximum stress. Actually, our calculations run 
five or six percent higher than recorded measurements of solar 
radiation at Washington. Independent measurements here estimate 
that "average11 dust content lowers solar radiation by about 6%, 
Measurements of the albedo of human skin indicated that 
blonde skin reflects A3% of solar radiation, brunette skin some- 
what less, and negro skin about 16$. As measurements on military 
cloths by Dr. Aldrich for Dr. Wulsin give figures of A0% to 50%, 
the transmission is included in the absorption figures, since it 
is small, from 0 to 5%, and is absorbed close to the surface, 
(This recalls the fact that radiation cannot always be considered 
as entirely a function of the surface. The most apague material 
becomes translucent if thin enough, and the most transparent 
material becomes apague with sufficient thickness.) An average 
between absorption of blonde skin and herringbone twill has been 
used here. 
Now for the geometry involved in determining the amount of 
direct solar radiation falling on the human body. For a person 
standing up, it will be least when the sun is overhead and will 
increase as the sun descends in the sky. On the other hand, the 
stress on the prone body will be greatest for an overhead sun, 
and will decrease as the sun descends. We have used profiles of 
body area measured by Dr, Harold F, Blum, to whom I am indebted 
for his valuable cooperation. An average figure for diffuse sky radiation is 15% of direct 
solar radiation, the range in Washington, on the average, running 
from 10% in winter to 20% in summer0 We have taken three percent- 
ages as representative, 5% for very dry air, 15% for average air, 
and 20% for moist air0 A consideration of the geometry shows that, 
in this case, the amount of radiation received is independent of 
the position of the bodyD When lying down, one-half of the body 
received radiation from half the sky (considering the body as a 
flat-two-sided affair). If the body is considered to be a many 
sided prism, or, if you will a cylinder, the same relationship 
holds. 
Since the reflection of radiation by the terrain depends on 
the albedo of the surface, it is unfortunate that most albedos 
have been measured photometrically, A reflectivity of 25% for 
desert sand, measured over the entire spectral range, is employed 
as the basis of our calculations, once again a maximum figure. 
If the ground is flat, the erect body will receive approximately 
half the radiation emitted by unit area. This may be demonstrated 
mathematically, it being sufficient to note at this time that the 
sides of the body are exposed to half the solid angle through 
which radiation passes, • 
(Discussion of the chart of total solar radiation falling 
on the human body followed. It was suggested that 130 Kg,Cals/ 
Vp/hr, be taken as an average value for the total solar load in 
clear weather. It was pointed out that for position of the sun 
not far from the zenith (an average summer noon position) the variation with varying moisture content of the air is small0 It 
must be remembered that this is a maximum, based on clear weather, 
dust free air, high reflectivity of ground surface, and low re- 
flectivity of clothing or skin surface„) 
Direct radiation from the ground may be treated in the same 
manner as the radiation diffusely reflected by the earth’s sur- 
face, the one divergence from this procedure being due to the 
fact that both emitter and receiver are now treated as black 
bodieso The ground temperature which determines the intensity 
of radiation may theoretically reach 200°F, although the recorded 
upper limit is 180o Desert sands reach 140 to 180, and even dry 
grass normally attains a temperature of 110° to 125°F in the sun, 
with occasional readings of 150°F, with green grass running about 
20° cooler, according to Dr„ Brooks« Moisture content of the 
ground surface certainly affects the temperature - indeed, the 
high temperature of rocks in the sunshine may be attributed to 
their dryness„ 
Water vapor, a powerful absorber of infra red radiation, is 
even more effective in this region of very long wave lengths« 
(Chart indicates how much is completely absorbed),, As a matter of 
fact, its action cannot be ignored even in the small amounts which 
occur in the radiation path between the body and its surroundings„ 
The average amount of moisture in the air may account for a re- 
duction of as much as Indoors as well as out, the absolute 
amount of water vapor present must be considered,, 
Unquestionably, the most difficult radiation flow to handle 
practically ia that of the body to cold outer space. The outward 
33 radiation of the body amounts to 216 the net 
radiation exchange of the body being this figure reduced not 
only by incoming radiation from the sources already discussed, 
but also by radiation from that highly variable unknown quantity, 
the atmosphereo Although the radiation to space of the body it- 
self has not been studied, the nocturnal radiation of the atmos- 
phere has received a great deal of attention. Extrapolation of 
results made on instruments at air temperature yield a tentative 
figure of 90 lost from the body to the sky, clear 
weather, vapor pressure about' 13 (fairly average humidity condit- 
ions) skin temperature 96°F0 This is quite independent of all 
radiation at shorter wave lengths, coming in from the sun, either 
direct or diffused as sky radiation. Indoors, where walls and 
ceiling temperatures, approximate body temperatures, the radiant 
exchange is small. Merely stepping out-of-doors on a clear night, 
when there is no incoming solar radiation to balance it, causes a 
sharp increase in heat loss; this after a time becoming minimized 
by the reduction in surface temperature of skin or clothing. In- 
crease in temperature and moisture content of the air decreases 
the net loss from the body, to a point where the exchange is almost 
zero in heavy clouds. 
Radiation is a surface phenomen, and as has been previously 
mentioned, any change in incoming radiation tends to change sur- 
face temperatures, thereby causing further adjustment in the ex- 
change. This mechanism may, on occasion, operate to minimize the 
radiant heat load on the body. Little *is known of the temperature of clothing surfaces« The 
Smithsonian Institution is making preliminary measurements at the 
present time. When there are completed, they may be applied to 
the study of heat transfer through clothing to the skin, and a 
more complete picture obtained for sunshine conditions. CLIMATOLOGY ft ENVIRONMENTAL PROTECTION S'Ctio* 
RESEARCH R DEVELOPMENT BRANCH — O.Q.M.O. 
FIGURE 13 
FCnaii;:!SOi-AR HEAT LOfilD 
Latitudei off Dose rver at Mias immer moon 
mmmmmjm 
ilir'suN' ANEisSilli 
ORIGINAL VERSION - 8 AUGUST 1944 RADIANT HEAT EXCHANGE 
BETWEEN ERECT HUMAN BODY 
AND GROUND FOR LONG 
WAVE LENGTH RADIATION 
Kg. cals./MVhr. 
FIGURE 14 
Ground Wormer Than Skin Temperoture.{96° F) 
Read upper row of figures for Ground Temperatures. 
Ground Cooler Than Skin Temperature. (91° F) 
Read lower row of figures for Ground Temperatures. 
CLIMATOLOGY a ENVIRONMENTAL PROTECTION SEC. 
RESEARCH a DEVELOPMENT BRANCH O.Q.MG- 
8MOB35-iiCO DISCUSSION 
DR. HAROLD F. BLUM?- It seems to me that what we need is a lot of measure- 
ments we do not have. Unless we could go on to the desert and make 
measurements simultaneously of all these factors, we can not hope to 
get a balance sheet or to say very much about what the actual load is. 
For purely illustrative purposes, a thermodynamic balance sheet 
is presented for a hypothetical set of conditions, namely; sun at 
zenith, temperature of the terrain 60°C, ambient air relatively dry 
and at a temperature somewhat above that of the body, the man erect 
marching at 3 miles per hour. The evaporation factor is based on 
the loss of 882 gms. of water per hour, an average figure obtained 
by Adolph for men walking on the desert. Convection and conduction 
losses are assumed to be small because the temperature of the 
t 
ambient air is near that of the body, but represent an unknown value. 
The radiation values are those calculated in this paper. 
Kilogram Calories Per Hour 
Metabolism £265 
Total solar heat load 4-234 
Long wavelength radiation 4-128 
exchange with terrain 
Long wavelength radiation -128 
exchange with heavens 
Evaporation —506 
Convection and conduction £ ? 
Total 
The close over all balance obtained is fortuitous, as is the exact 
balance between radiation from the terrain and to the heavens. Had the ground temperature been taken as 10° lower or the assumption made that 
the sun had warmed the clothing to a temperature 10° higher than that 
chosen, the balance would be considerably upset« It should be pointed 
out that for a man at rest, the long wavelength radiation exchange 
would be more important relative to the metabolism, and it might be 
interesting to explore other'possibilitiesc 
The evaporat on factor must adjust itself to achieve a balance 
if the body temperature is not to rise0 Hence it must be expected to 
vary as the other factors shift with the conditions, and when the 
magnitude and variability of the other factors are considered, it 
does not seem surprising that Adolph and his coworkers should have 
obtained different values for evaporative heat loss under the various 
conditions they explored, nor that these values display the general 
consistency they do0 
The whole problem of radiant exchange with outdoor surroundings 
is, thus, quite complex and cannot be accurately simulated in an 
enclosed roora0 Moreover, all these factors render physiological 
measurements out of doers subject to considerable variability, not 
only insofar as the solar heat load is concerned, but with regard 
to the heat load as a whole <■ 
SUMMARY 
DRa PLUMMERr- In the previous discussion we have covered as thoroughly as 
possible all of the avenues of heat loss normally available to the 
human bodyD Equilibrium can only occur if the heat production is 
equal to the heat loss, and this may be used to provide an index or 
indices which may be used to evaluate climatic stress0 For cold weather conditions we may use as an index the insulation requirements 
to provide equilibrium when the activity, temperatures, wind velocities, 
etCo, are known. Any scale of activity may be chosen, but two specific 
vones appear to be the most desirable. For normal daylight conditions, 
7$ Kilogram Calories has been chosen because men in the Army spend a 
considerable portion of their time working at this level. An index set 
up on this basis, however, would not be adequate for night conditions as 
the metabolic rate of the sleeping men is very much lower.* Consequently, 
it seems that two indices are necessary, and on the basis of previous 
discussions the insulating value of the clothing required to maintain 
equilibrium may be calculated. An example for day is shown on the map 
of Central Europe, which shows the clothing required for winter day- 
light conditions for various parts of the country. 
. The situation is very much more complex, however, in the tropical 
or high temperature as it is not possible to control heat 
-oss by the mere removal or addition of extra clothing. In many of 
these places a certain amount of clothing must be worn as a protection 
against other factors of the environment, such as mosquitoes, jungle 
vegetation, etc. As the clothing requirements are fixed by other con- 
ditions and the environmental conditions are also fixed by the locality, 
the only variable which remains is the rate of activity. We have chosen 
as an index of climatic stress the maximum activity which may be per- 
mitted in a given environment without causing an increase in the stored 
heat within the body. This work is not a comfort index, but represents 
the maximum conditions in which men may be expected to woric indefinitely. 
An index based upon comfort and 
mapping according to the index see Appendix II. AVERAGE CLOTHING REQUIREMENTS FOR JANUARY 
Based on the Mean Monthly Temperature; Wind Velocity of 5 
M.P.H., and in Dry Shade. Calculated to Maintain Continuous 
Comfortable Protection for Men Standing Around (76 Kg. Cals. 
M2/Hr. 
Insulation Effective Limiting 
Clo Insulation Temperaturs 
Values Thickness °P. 
(inches) 
2.00 to 2.50 0.50 to 0.63 46 to 37 
2.50 to 3.00 0.63 to 0.75 37 to 28 
3.00 to 3.50 0.75 to 0.88 28 to 19 
3.50 to 4.00 0.88 to 1.00 19 to 10 
4.00 to 5.00 1.00 to 1.25 10 to -7 
5.00 to 6.00 1.25 to 1.50 -7 to -23 
34-06715-800 inefficient discomfort could also be calculated by using a wetted 
area of the body surface of 25$, and 75$ respect!vely0 
In calculations of maximum activity, we have been forced to 
eliminate the effect of radiation,, Data is available for so few 
» 
parts of the world that we can only calculate an index on a basis 
of convection, conduction, and evaporation. The calculations of 
radiation can be used to estimate the possible effect of the 
radiant heat load. The index as we use it excludes radiation, 
but in all cases it must be borne in mind that radiation may add 
a very definite heat load and its effects must be considered in 
those localities in which the maximum permissible activity begins 
to approach normal activities. 
As a comparison of the results achived with an index of this 
type, we have compared our index of various activities with the 
work of the Pierce Laboratory, the A.SeH,VcE, Laboratory, and 
Dr0 Robinson’s recent work. 
The comparison of the index with Pierce Laboratory results 
is shown in Figure 15» It is interesting to note that the limit 
of endurance calculated by the index (equilibrium conditions) 
lies in regions of slightly more severe conditions than those 
indicated by the Pierce Laboratory,, In terras of temperature 
differences, however, the index is within 1° of the Pierce Labora- 
tory figures for all vapor pressures. For the limit of comfort, 
the index is within lj° of the Pierce Laboratory results for all 
vapor pressures. 
In making this comparison, certain assumptions have been 
necessary, and all of the assumptions used in calculating the index VAPOR PRESSURE mm. Hg. 
FIGURE 15 
COMPARISON OF INDEX WITH 
PIERCE LABORATORY RESULTS 
ASSUMPTIONS; 
(Index) 
Wind Velocity 20 Ft./min. 
Clothing None 
Activity 50 Kg. col./Mf/hr._ 
Convection 3" Cylinder 
Radiation 2.6 Kg. cal./M^/hr./p 
Wetted Area 100%, 25% 
CLIMATOLOGY ft- ENVIRONMENTAL PROTECTION Sicllon-RtMorch ft D*«, Branch, 0-O.HJi. 
#8-11788-800 are listed in Figure 15o A slight change in wind velocity would affect 
the slope of the lines, and also a small change in the percent of wetted 
area would appreciably affect the position of the lines0 However, the 
agreements seem remarkably good0 
Figure 16 shows a comparison of the limiting comfort line as derived 
from the index with the ASHVE effective temperatures * Again, because of 
lack of data, it has been necessary to make certain assumptions, and these 
assumptions are listed on the chart,, It will be seen that the limiting 
comfort line becomes very close to an effective temperature of 71° line 
by a change in the wind velocity figures „ Considering the absence of 
exact data and also that the ASHVE experiments demarcate a zone of com- 
fortable sensation through which a line has been drawn according to a 
probability curve, this figure likewise shows good agreement between the 
index and experimental figures0 
In figure 17 we have shown a comparision of the index with the 
experimental work of Dr0 Sid Robinson recently published in Report No„ 120 
Here the index lines represent the limiting conditions of temperature 
and vapor pressure for different activities at wind velocity figures 
used in Dr„ Robinson’s experiments,, It will be seen that the agreement 
\ 
for activity of 190 Kilogram Calories and 125 Kilogram Calories is 
excellent, although the agreement is not quite so good as for activities 
of 50 Kilogram Calories„ 
Figure 18 shows a comparison made in the same way of the index 
with Dr„ Robinson’s experiments on nude men. Here the qualitative agree- 
ment is quite good, but the quantitative agreement leaves something to 
be desired„ Unfortunately, at the present time we are not able to FIGURE 16 
COMPARISON OF LIMITING COMFORT 
LINE AS DERIVED FROM INDEX WITH 
ASHVE EFFECTIVE TEMPERATURES 
ASSUMPTIONS; Wind Velocity 20 Ft. /min. 
('nd'xl Wetted Area 25% 
Clothing I Clo 
Activity 50 Kg. cal./M*/hr. — 
Convection 3" Cylinder 
Radiation 26 Kg. cal./M1/hr./°f 
EFFECTIVE T E MPE R ATU RE = E f f. Temp. 
CLIMATOLOGY 8r ENVIRONMENTAL PROTECTION S Action-Rtworeh * Dtv. Broncti, 0.0.M-G. FIGURE 17 
COMPARISON OF INDEX WITH 
ROBINSON'S DATA FOR CLOTHED MEN 
ASSUMPTIONS: 
(Index) 
Wind Velocity 2mi./hr. 
Clothing 0.5 Clo reduced to 0.1 Clo by sweat 
Activity 190-125-50 Kg. cal./MVhr. 
Convection 3" Cylinder 
Radiation 2.6 Kg. cal./M2/hr./°F. 
Wetted Area 100 % 
0 =ROB INSON 
CLIMATOLOGY Or ENVIRONMENTAL PROTECTION Section-Research ft Dev. Branch, O.O.MJL 
8<5- 1 22 ft ft- 200 FIGURE 18 
COMPARISON OF INDEX WITH 
ROBINSON'S DATA FOR NUDE MEN 
ASSUMPTIONS: 
(Index) 
Wind Velocity 2 mi./hr. 
Clothing None 
Activity 190-125-50 Kg.calVMVhr. 
Convection 3" Cylinder 
Radiation 2.6 Kg. cal./MVhr./°F 
Wetted Area 100% © = ROBINSON 
CLIMATOLOGY tr ENVIRONMENTAL PROTECTION SutlM- RMMreh * D«* Bronch, OOJAfi- explain the difference0 
The proposed formula for mapping the index is as follows? 
Io Cold Weather Index?— 
A0 Equilibrium index for standing men*^ 
1 do = 3o09 (Ts - Ta) 
M - S - (E * A) ” a 
in which M is 75 
and S is 0 
Bo Index for 8 hours comfortable sleep 
Equation as above, except that - 
M -» 40 and 
S “ 5 XgCals/l^/hr 
II. Hot Weather Index?- 
Maximum Metabolism - Evaporative Heat Loss £ Convective 
♦ Heat Transfer, £ Radiation 
in which Radiation is generally omitted, but its possi- 
bilities should never be excluded0 
DISCUSSION 
COLONEL HATCH:- As far as the index is concerned, from the present discussion, 
I gather that this is based purely on equilibrium conditions* At Fort 
Knox our experiments have been based' instead upon the ability of a nan 
to perform a definite amount of work for a four-hour period* How would 
you expect these results to tie in with an equilibrium index? 
■a-1 
A tentative explanation of this difference will be furnished in a 
future paper 
*2 
For explanation of symbols see Appendix 2 together with further details 
of correlation with other experiments* DR, PLUMMER ?- In developing such an index, it is almost axiomatic to first 
attempt to solve the problem for equilibrium conditions and then modify 
the solution for short period conditions. From the purely theoretical 
side, I would think that we would be able to relate the equilibrium 
index to an index for four-hour periods, or any other perids, if we knew 
definitely the quantity of heat storage that could be permitted. We 
would also have to know what skin temperatures and rates of sweating 
would be possible during this period of time as a change of 1 or 2 
degrees in skin temperature increases the possible evaporative cooling 
quite appreciably. We would be very glad to have any data on either 
time, period, or equilibrium tests as, unfortunately, there is very 
little available with which we may check our results,. 
DR, BURTONi~ I feel that at present the calculation of the tropical 
’’Index’* is far from reliable. The excellent work of Dr, Plummer snd 
Mrs, Schickele has given us the value of the heat absorbed from solar 
radiation in but how should this be included in the 
index? There is an ’’efficiency factor” by which it must be mulitiplied 
before it is added to the metabolic heat, since the insulation of cloth- 
ing protects a man from receiving all the heat that is absorbed on the 
surfaces of the clothing. Also, the very important drop in physiological 
efficiency of evaporation when evaporation takes place from the surface 
of clothing instead of directly from the skin is not included, A fur- 
ther difficulty is that for the values of prevailing wind velocity, 
which so greatly affect the calculation of the index, one could take 
only the values supplied by the meteorologist. These are usually taken 
on top of a tall pole and might have little relation to those affecting a man in the jungle0 
DR, PLUMMER*— I don’t agree that the calculation of the tropical index is 
far from reliable. For mapping purposes, we calculate the index on a 
basis b>f convective and evaporative heat transfer at relatively low 
wind velocities, generally of the order of two to three miles per 
hour. This wind velocity is so low that an active man may readily 
produce it through his own motions, whereas the resting or sitting 
individual will have, naturally, a much lower metabolic rate and 
consequently not require as high a loss. Furthermore, the purpose of 
the index is not necessarily to indicate the relative ease of per- 
forming work, but is primarily expected to point out the danger 
areas of the world where maximum protection is required. Also, we 
expect, through a quantitative study of heat losses, to obtain a 
more accurate understanding of the type of protection required. We 
are only too ready to admit that a great deal remains to be done, but 
we do feel that an index as derived from the present work is at least 
a good first approximation. As more data becomes available, we will 
be glad to modify or correct the results. 
At present we are unable to incorporate radiation in the index, 
primarily because of the lack of data and also because of the 
variability of conditions. We feel that the tropical index should be 
used primarily on a basis of convection plus evaporation, but bearing 
in mind that the radiant heat load may add a definite quantity. We 
have attempted to evaluate this load and calculate the probable limits. 
*A theoretical analysis of the efficiencies referred to and their 
consequences is now being written by Dr, Burton* APPENDIX I 
The original purpose of the meeting was to present the basic Xav/s 
of heat transfer as applied to the human pody by physicists and physio- 
logists to a group of meteorologists, climatologists, and geographers© 
Unfortunately, the meeting fell behind schedule in the late afternoon 
and too little time remained to give the climatologists an opportunity 
to make preliminary comments on the formula or on the problem of the 
application of these physical laws to climatic data for mapping pur- 
poses© Also the transcript of this part of the meeting was too in- 
sufficiently kept to permit complete reconstruction© Major Heald pre- 
sented some of the basic problems, followed by various overall random 
comments by various meteorologists, climatologists, and geographers 
present* 
Just as it was frequently necessary in the establishment of the 
index to set forth assumptions, it will be necessary for the clima- 
tologists to assume certain average values of climatic elements before 
they will be able to apply the index to mapping techniques© Tempera- 
ture is constantly in fluctuation, as well as wind, humidity, fnd solar 
radiation© Each climatic element introduces a problem, because average 
values cannot give a complete picture© In the tropics the human being 
is most concerned with the maximum heat, the radiation, humidity, and 
low wind speed© In the cold regions, the body is under greatest stress 
when the temperatures are lowest and the wind is strongest© 
Mean or average monthly weather conditions fail to reflect the 
average worst condition© To show only the average worst conditions would give a distorted impression for it can only express the actual 
stress that would occur for a brief period„ It is probable that plot- 
ting of stresses will require the use of average values with some 
method used to show the average daily range„ 
Considerable experimentation will be necessary before a suitable 
technique can be developed for mapping0 The climatologists in the 
Office of the Quartermaster General are now beginning this and 
it is hoped that others will also apply their thoughts to the 
application of the index,, It is expected that the meteorologists, 
climatologists, and geographers present at the meeting, as well as 
others concerned, will meet later to consider in detail the appli- 
cation of the index to mapping techniques0 
Anticipating many of the problems which will arise in mapping the 
index of climatic stress, the climatologists of the Climatology and 
Environmental Protection Section have summarized some of the trouble- 
some factors-that may appear: 
TEMPERATURE 
Whether mean maximum, average, or mean minimum temperature data should 
be utilized,, 
Whether any employment should be made of the frequency ranges of 
temperatures 0 
EVAPORATION 
The deficiencies of relative humidity data as it is published6 
Difficulties of determining vapor pressures from available data0 
Whether the minimum or maximum vapor pressure should be used. 
What consideration must be given to variations of vapor pressure0 WIND VELOCITY 
A means of extending the scattered material that is available. 
Whether the mean wind speed has any significance. 
Reduction of wind speed from anemometer level, and associated 
assumptions as to Austausch and its variations. 
RADIATION 
Rapid calculation of the zenith angle of the sun, considering diurnal, 
annual, and latitudinal variation,, 
Extending the sparse radiation measurements that have been made, and 
utilizing them„ 
Substitution of data on duration of bright sunshine for radiation 
values e 
Substitution of data on mean cloudiness for radiation data, 
* 
Difficulties of using data on either sunshine duration or mean 
cloudiness, 
Assumptions of the temperature of the ground and vegetation. 
GENERAL 
The major problem involved in employment of the mean to represent 
climatic elements that have large diurnal, seasonal, and aperiodic 
variations 0 
The increase of this problem in geometric progression when single 
climatic elements are brought together in indices of two, three, or 
four componentso 
The group of problems involved in converting observational data from 
the location where instruments are exposed to the environment of the 
soldiero 
The general difficulties resulting from lack of observations of 
certain elements over large arease APPENDIX II 
Basic Information Necessary for Determining Clo Values 
lo The metabolic do equation as originally developed by Drs. Gagge, 
Burton, and Bazett is as follows: 
Clo Value Required for Complete Comfort ss 
3q09 (Ts - Ta) 
M - S - (E i A) " Ia 
"Where M a Metabolic heat in KgCals/M^/hr 
S a Bodily Heat Debt 
E a Total heat lost by evaporation from body and lungs 
A ss Heat lost by warming the inspired air 
T3 cs Temperature of the skin in °F 
Ta a Temperature of the ambient air in °F 
Ia a Resistance of the still air in clo units 
20 Metabolism as a Function of Activity?- The heat created by the 
body under various activities is generally accepted as follows? 
Activity Metabolism in 
Kg o Cals/M*/hr 
Sleeping 4-0 
Sitting still 50 
Truck driving or standing still 75 
Slow walking 100 
Marching at 3 miles an hour 150 
Marching at 4 miles an hour 200 
Heavy activity such as mountain 300-600 
climbing or ditch digging 
3o Time and Clo Values:- The original formula as given above only 
positc the Clo Value necessary to keep a man in equilibrium so that he 
is losing the same amount of heat as his body creates„ It often happens, 
however, that a man may be inadequately clothed for the temperature at 
which he finds himself, even though his clothing is well-balanced over all portions of his bodye His endurance of cold will then be limited by a 
time factor, which is technically known as the tolerance time0 
Obviously it is not always necessary to provide clothing which will 
keep a man comfortable indefinitely0 If he is to stand guard duty for 
four hours only and is certain of a warm room in which to regain his lost 
heat afterwards, he need have far less protection than a man who is going 
to drive a truck for eight hours at the same temperature* For mapping 
purposes, we have assumed that indefinite protection is necessary at a 
low activity, such as truck driving, if the temperatures chosen are the 
monthly average of the daily mean0 It is not necessary, however, to 
map indefinite protection for sleeping bags* Eight hours at average 
minimum temperatures is quite sufficient* 
Graphs illustrating tolerance times as a function of activity, do 
value, temperature, and wind velocity are given* These are based on 
the equation - Time x Intensity equals a Constant* The original 
formula was applied to unbalanced conditions, where the footgear was 
inadequate compared to the other garments* The plottings made were 
checked with data on tolerance time received both from the Climatic 
Research Laboratory and from the Harvard Fatigue Laboratory* Tolerance 
time under such conditions follows the locus of a point on various 
cooling curves where the average skin temperature of the foot falls a 
certain specified number of °F (for example from 89°F to 55°F)0 
This formula was extrapolated to make it more usable for general 
metabolic h'eat loss rather than for local cooling time curves as 
follows• 
Time - Heat Loss x Resistance 
K Temperature Difference The following assumptions have been made: 
a0 That the clothing is equally adequate all over the 
body, i0e0 that there are no local cooling points0 
bo The total heat debt of 80 was taken as 
the limit of endurable cold0 This is thought to be a con- 
servative estimate since much greater losses have been re- 
corded at various laboratories0 However, because no cloth- 
ing is completely balanced and because susceptible subjects 
need to be protected, it was thought best to assume a con- 
servative losso The value of I4.O KgoCals, was taken as the 
total loss which a man might endure while still remaining 
asleep 0 This is based on a statement made in the Harvard 
Fatigue Laboratory Report No0 19 and is corroborated by the 
Climatic Research Laboratory's records of the length of 
time during which a man may remain comfortable in a sleeping 
bago 
Co The same amount of basic heat loss may be withstood 
over any period of time0 This is probably the case, but the 
data to substantiate it is not available» It is possible 
that for low activity the sharp gradient of extreme cold may 
make a loss of 80 Calories unendurablee For this reason the 
curves have not been plotted for the first hour® 
do Tolerance times can also be computed from the basic 
do chart (Figure 9, following page lU) by taking the length 
of exposure and dividing it into the total number of 
KgoCals/M2 of stored body heat to be lost before.reaching 
the limit of cold tolerance0 (80 KgoCals/M2 is assumed to 
be a safe amount to be lost for men who are awake and I4O 
KgoCals/M2 is assumed to be the total number which a sleep- 
ing man can lose without being awakened by the cold®) 
For example, to compute the length of time for which 
a U do suit could provide adequate protection at -5°Fo for 
a man sitting still - 
(1) Subtract the number of KgoCals/M2 which he is 
producing (i0e0 £0) from the number which he 
should produce in order to keep in equilibrium 
at -£°Fo (io60 90)o This gives the difference 
of k0 KgoCals/Mv^1*0 
(2) Since a total loss of 80 is assumed 
to be the limit of safety, it follows that the 
tolerance time will be 80 4 kD, or two hours* c0 If tne tolerance time and temperature are known, the 
do value of the clothing assembly can be computed in a 
similar manner0 
fo If the tolerance time and do value are known, the 
temperature can be computed at which the man is in thermal 
equilibrium, or the limits of tolerance at other temperatures 
may be determined0 ACTIVITY - 40 KG. CALS./w2/h»: 
SLEEPING 
HEAT LOSS- 40 KG. CALS./m2 
h titt afir E5e bS" la 
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wnwou- COM MG EFF CtENCY 3EPE <DS LlPOf Tfi E AliOUK T OF 
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- 
UP(IN; 1 US JMAFr FCR Al AC IVtT f. Of 40 «L CftUS,/K Al 10 
A tEAT DEiiT 0 r40 KG. CAL < ./M* ■ _LL _L Hi: 1L 
Originol Version* JUNE 1949 
This EDITION - FEB. 1944 
CLIMATOLOGY B ENVIRONMENTAL PROTECTION-Saa. 
Raaasreh B Oa.alopaiaat BroaeN-OAM.#. 
lt.N11t.IM ACTIVITY - 50 KG. CALS./M2/hr, 
SITTING STILL 
HEAT LOSS - 80 KG, CALS, /m2 
JHF -OUR TEMPERATURE LINES 
IGIVEljl FOI? EACH CLO VALUE 
Represent wind velocities 
OF 30/12 AND 2-yrrnrp-tr- 
TTDLERANCL TIME iN HO. JR!3~ 
; | THE TEMPERATURE j WHICH ft MAfJ wjlTHStANDi 
WITHOUT LOSING | EFFICIENCY DEPENDS |UPOh| THE AMOUNT OF] 
jHE DEGREE PF ACTIVITY AND j THE| DUftATldN Off 
EXPOSURE. 
THE RELATIONSHIP BETWEEN THESE .CToks isj SHOWN 
UPON TjHIS pHARfT FOR AN ACTIVITY Ofj 5 0YG. qALS/M'/h-, AND 
A HEATi DEBT OF 80 KG. ICALS./M'I I 
Original Var»lon«juHE 1943 
this Edition -FEB. 1944 
HONI dIVH 3HI 01 SXS 032 0NIAVa0N3 
Cllmotology a Environmental Protection_Sec. 
Research 8 Development Branch — O.Q.M.G. STANDING 
ACTIVITY — 75 Kg. Cal./MVhr. 
Heat Loss = 80 Kg. Cal./w* 
KEUFFEL a ESSER C8. NEW YORK 
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L 5EM ESEJs K?+i3 ifaO) atlC 
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without losing eff cieulor;: speeds: jpon ; -7Hs;aMDONT:w n 
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jh'-jtfAr : OEftT QA80 
Original Vtrsion* JUN€ 1943 
Thl» EDITION » FEB 1944 
CLIMATOLOGY 8 ENVIRONMENTAL PROTECTION Stction 
Research ft Development Branch. 0.0.M.6. SLOW WALKING 
ACTIVITY - 100 Kg. cals. / M2/ hr. 
HEAT LOSS - 80Kg. cals. / M2 
KEUFFEL & ESSER C8 NEW YORK 
ilpRANGE lii: wipRSil 
KEUFFEL & ESSER C2. NEW YORK 
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Original Version • JUNE 1943 
Thl» Edition ■ FEBRUARY 1944 
CLIMATOLOGY & ENVIRONMENTAL PROTECTION SECTION 
RESEARCH & DEVELOPMENT BRANCH 0. 0. M. 6. 
25-13523-250 APPENDIX III 
The proportionment of heat loss from various parts of the body 
is normally taken from the DuBois figures as follows? 
Forehead 2<>5% 
Occiput 3c$% 
Trunk 3610% 
(precordium 9%) 
(scapula 9%) 
(abdomen 9%) 
(kidney 9%) 
Upper thigh 9o0% 
Lower thigh 9»0% 
Leg (calf) 13o0% 
Foot 7 o0% 
Upper arm 7 »0% 
Forearm 7 »0% 
Hand $0Q% 
TOTAL 100o0%