Clothing Test Methods, Edited by L.H. Newburgh (Physiological Tests) and Milton Harris (Physical Tests) of Subcommittee on Clothing of the National Research Council (U.S.A.) (1945)

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

PART I Physiological Tests

MEASUREMENT OF SKIN AND CLOTHING TEMPERATURES L. P. Herr>ington Among the methods now in use by various workers are: a. resistance thermometers, b. thermocouples attached to the skin or clothing with adhesive tape or sewn onto the clothes, and c. thermocouples soldered on thin copper discs and held in place by means of harnesses. * With proper precautions, all these methods are satisfactory for measuring relative changes of surface temperatures on exposure to heat or cold. Junction wires should be as fine as is consistent with mechanical strength, but no heavier than #30 gauge. Capillary circulation must not be disturbed by pressure of junc- tions against the skin. It is desirable to check all methods against readings of a radiation thermopile under conditions that are suitable to thermopile use. 1 Thermopiles should be provided with a thermocouple for measuring the temperature of its cold junctions. Good results may be obtained by the use of a long thermocouple junction, made of 40 gauge copper-advance wire and cemented onto the thermopile junctions, after coating with duco or some other insulating mate- rial. For high temperature work at least 10 surface-temperature measurements are necessary to obtain a fair average skin temperature for the whole body. On ex- posure to cold more readings are necessary because of the steep temperature gradients over the body's surface. Instructions for construction, calibration and correct use of thermocouples and radiation thermopiles will be found in "Temperature: Its Measurement and Con- trol in Science and Industry," Reinhold Publishing Corporation, 330 West 42nd St., New York, 1941. 1. We have found that cheap and convenient oencopile iB subject, at low temperatures, to calibra- tion changes of considerable order. For this reason we use a double "reference bath" and calibrate for a 10°F. difference between baths on every measurement. We believe the effect is probably due to moisture changes in the internal parts of pile which probably are less im- portant in a precision'constructed instrument.

CALCULATION OF THE HEAT DEBT A. C. Burton 1. Introduction In the "Clo determination" of the insulating value of clothing it is necessary to know the heat that passes through the clothing by radiation plus con- vection. This quantity divided into the temperature gradient across the clothing gives the insulation. A direct calorimeter measures the total heat loss, and from this the heat loss by evaporation, E Cals/Sq.M./Hr. , obtained from the weight loss of subject plus clothing, may be subtracted to give the quantity de- sired. However, where such a calorimeter is not available, recourse is had to indirect calorimetry. The total heat loss must be equal to the heat produced, M Calories/Sq.M./Hr. , plus any heat given up by the body tissues in falling to a lower average temperature, D Cals/Sq.M./Hr. This is by agreement known as the "Heat Debt" acquired by the body, since it must be made good to restore the body to normal temperature. The quantity used in the Clo determination is then (M + D - E) Cals/Sq.M./Hr. 2. Calculation of D The heat debt D is equal to the thermal capacity of the body times the fall of average body temperature TA . i.e., D = W.S. TA (l) where W is the weight, and S the average specific heat of the body tissues. As a first approximation TA was taken to be the same as the drop of deep body tempera- ture (say deep rectal temperature) TR . However, it was recognized that this might lead to very serious errors since a large proportion of the body is at a much lower temperature than the deep tissues, and skin temperature changes were often not at all correlated with changes in rectal temperature. The first intensive attempt to obtain a better approximation by using also the change of skin tempera- ture was in 1935. (i.) F°r complete explanation and details the reader is referred to that paper. It was there shown that the average temperature of the tissues could be expressed by the equation: TA = AJ.T! + A2T2 + A3T3 + ---- (2) where Ti, T2, T3, etc., were temperatures measured at various points in the body, and Ai, A2, A3 were coefficients derived by physical considerations of shape and size of the appropriate body parts, and of the nature of the gradients of tempera- ture within the tissues. The method of calculating these coefficient for any desired temperature points is given in the paper referred to. Some of the results are given in the table below:

CLOTHING TEST METHODS Table 1 Value of Coefficients in Formula for Average Body Temperature Position where Position where temp, was measured Coeff. temp, was measured Coeff. Rectum 0.59 Skin of trunk 0.09 Mouth 0.05 Skin of head 0.02 Skin of lower leg 0.07 Skin of upper arm 0.0? Skin of thigh 0.12 Skin of lower arm 0.03 If fewer temperature points are desired, the temperature of any point omitted is assumed to be midway between that of the points proximal and distal to that point, and the coefficient appropriate to the omitted point is divided equal- ly between these two points and added to their coefficients. 3. Average Surface Temperature Merely for convenience in calculation, formula (l) can be re-cast into the form: TA = AO.TB + ASTS (3) where TB is an "average surface temperature" calculated from the original formula as TB = B2T2 + B3T3 + (4) (The new coefficients B2, B3, etc., are, of course, merely the old coefficients A2, A3, etc., divided by AB). In this way it was predicted that in this form the best partition of coefficients would be likely to be: TA = 0.64 TR + 0.36 TB (5) It was then shown by analysis of 40 one-hour periods where both indirect and direct calorimetry was made, that for these periods the statistically best partition was: TA = 0.7 TR + 0.3 TB (6) However, any value between 0.6 and 0.75 for the first coefficient gave satisfactory results. The improvement over the use of the rectal temperature above in calculat- ing the heat debt was very marked. Subsequently, Hardy and DuBoIs found that a partition of 0.8 TB + 0.2 TB gave the best results for their data.(2_) The Pierce Laboratory adopted a coef- ficient very similar to that given here. (3.) It was pointed out that necessarily the best partition would be different for different individuals, whether obese or slim and might also vary with the state of vasodilation and constriction. The best "mixing coefficient" must either be chosen by valid statistical- methods on a number of results for simultaneous direct and indirect calorimetry, or a "universal" value be adopted as the best available approximation for all cases. It is recommended that the coefficients TA = TB + TB (7)

CALCULATION OF THE HEAT DEBT be adopted for such "universal" use, the average surface temperature TB to be calculated from the skin temperature points measured according to the method out- lined in the paper referred to. (The values used in the work at the Cold Chamber, No. 1 Clinical Investigation Unit, R.C.A.F., Toronto, are: Te = 5 (Ttrunk + Tthigh ) + 0.18 T1eg + 0.15 TUpper arm) Average Surface Temperabure • It must be emphasized that the average surface temperature T is calculat- ed according to the weight of tissue represented by any temperature point, not ac- cording to the surface area it represents. The coefficients (B in Eq. 4) are quite different from those pertaining to a "surface area average" of skin tempera- ture. In the Clo determination the gradient across the clothing and the surround- ing air is taken as (average skin temperature - air temperature). The average skin temperature in this part of the calculation should, to be precise, be separate- ly calculated on an area rather than a weight basis. However, the average sur- face temperature rarely changes by more than 4 or 5 degrees C. in even an extreme experiment while the total gradient will be 50°C. or more in experiments at 0°F. (-18°C.). Thus the difference in the final result if the average "weight" skin temperature is used, in this part of the calculation, instead of the average "surface" skin temperature, is likely to be insignificant. On the other hand, to'use a "surface" rather than a "weight" average skin temperature in the calculation of heat debt may introduce very serious errors. For example, each hand represents only 1.8$ by weight of the whole body, but 2.5$ by surface area. (4_) Since the temperature of the hands may change a very great' deal compared to the change of other parts, use of the wrong formula may greatly overemphasize the contribution of the hands to the total heat debt, and destroy the usefulness of the inclusion of skin temperature in the calculation of heat debt. Value of Specific Heat In the calculations an average specific heat of 0.83 was assumed, based on values of Pembrey (5_). It was shown for the data used in the original calcula- tions that any value between 0.70 and 0.90 gave almost as good results, but 0.83 actually gave the best results. This is the only direct determination, to our knowledge, of the average specific heat of the whole body. It is recommended that the value of 0.83 be used for the specific heat of the body, until a further experimental determination on the whole human body suggests another value. REFERENCES (l) Burton, A. C., J. Nutrition £, 261, 1935- (2_) Hardy, J. D., and E. R., DuBois, J. Nutrition 15_, 477, 1938. (_3_) C. E. A. Winslow, A. P. Gagge and L. P. Herrington, Am. J. Physiol. 127, 505, 1939. (See page 511) (4) E. R. DuBois, Arch. Int. Med. 17, 863, 1916. (5_) Pembrey, Animal Heat, Schafer's Textbook of Physiology, Vol. 1, p. 838, 1898.

12 CLOTHING TEST METHODS where 0.30 x liters oxygen consumption per hour represents the excess of weight of C02 expired over 02 taken in at an R.Q. of 0.88, and 0.58 is the heat of vaporization. The underwear and socks are worn during the weighings because very little body heat loss is occasioned when moisture is evaporated at the skin and recon- densed in the layers of clothing next to the skin; the error in weighing a man with this much clothing for estimation of E8 is therefore considered to be less than when the calculation is made from stripped weights. On the other hand if the weighings are made with the subject fully dressed it is known that 1/2 to 2/3 of the insensible perspiration may be recondensed in the outer layers of the clothing. The exact part that this recondensation plays in the thermodynamics of the insulating system is not clearly understood; it is probably small when the subject is at rest in the cold, but may be considerable under other conditions, and certainly merits further study. Alternatively EI may be approximated from a knowledge of total hoanly ventilation since we have shown that with our respiration tubes the inspired air is cooled to within a degree or two of the temperature of the cold room, and since it is known that at ambient temperature below freezing the absolute moisture content of air is very small. We have also shown that air is expired at 33°C. regardless of environmental temperature, at least down to -40°. Saturated air at 33°C. contains 0.0353 grams of water per liter (0.0353 g. H20)x (0.58 Cal. heat of vapor)x (liters vent, per hr. STP dry) x 1.18 S.A. 0.0242 x (liters vent, per hr. STP dry) , / 2 A . —... _ r **• = Cals/m /hr. heat of vaporization of moisture from lungs, , where the factor 1.18 is used to convert volume of ventilization STP dry to 33°C. wet. E8, the heat lost through vaporization of the insensible perspiration, may be estimated at 6.3 Cals/m2/hr. if a suitable sensitive balance is not available for weighing the subjects. This figure was arrived at from a study of over a hundred records obtained on numerous subjects who were exposed in somewhat inade- quate clothing in our cold room. It will be noted that 6.3 Cals/m2/hr. represents only 19 grams of moisture for a man of average size, and since we have demonstrat- ed that the underwear does not usually gain moisture in these exposures, it is obvious that the figure of 30 grams per hour usually given as the amount of hour- ly insensible perspiration in normal environments does not apply for subjects who are resting in an. environment somewhat too cold for their state of dress. A,, the calories dissipated per square meter of body surface in warming the inspired air, may readily be calculated. (T. exp. air - T. insp. air)x0.00031x (ventiliation in liters/hr/STP) '" '~ "" """" S.A. " " " where air temperatures are given in Centigrade; and 0.00031 = (1.293 g./liter specific gravity of air) x(0.00024 Cal/g. specific heat of air). Alternatively, EI + A may be read directly from Fig. 3 when the "Ventila- tion" and the "Temperature of Inspired Air" are known. When this nomogram is used "Calories Heat Loss via Lungs" should be divided by body surface area to obtain Ei + A.

EVALUATION OF THERMAL INSULATION PROVIDED BY CLOTHING 19

20 CLOTHING TEST METHODS FIGURE 3 °c • 1 • • LINE CHART FOR DETERMINING '50^ L_55 1000— r50 -45 HEAT LOSS VIA LUNGS (WARMING ^5~ ^-50 ^--45 950- 900— AIR AND VAPORIZING WATER) FROM -4Ch r-40 850- 1-40 • oc 800— :35 PULMONARY VENTILATION AND _35J TEMPERATURE OF THE INSPIRED = --35 J--30 r-25 750- 700— -30- h-20 -30 AIR, ASSUMING FULL SATURATION • 650- r-15 OF THE AIR WITH WATER ~25~ - 600— -25 L-IO 550- -20- r-5 5OO- -20 rogc -15- • - 5 < 450- • Q. »~ -15 Hog : CT 1-400— -10- "I5E 0 (/) (/) 350- Z -20 Z S 1 D -5- , 1- —25'*" • j300- -10 : O ^ : u > -9 • -30 tr Z - </) - 8 0- : D O 250- ; H Jj O - -7 r35j • -J -J • o! • ^200- H - -6 ^-40 2 LJ 190- Id 5- u > 180- I _ -5 • ITOn • (/) -45 160- U . I50H o: - -4 I40H O 130-j •i — ! - 10- -50 ^^ 120-j 3 o -3 100^ J • -55 . "C- -CF

MOISTURE LOSS AND MOISTURE EVAPORATED L. P. Herrington These are estimated from successive weighings of subjects, a) clothed, b) naked and c) naked and dried with a towel, when there is visible perspiration on the skin. The following quantities may be computed from these readings: Moisture secreted = weight loss of naked subject after drying + weight of C02 produced - weight of 02 consumed. Moisture loss = weight loss of naked subject without drying, + C02 - QZ. Moisture evaporated = weight loss of clothed subjects + C02 - 02. Under ordinary conditions with subjects at rest, the correction C02 - 02 amounts to less than 5 grams per hour, but it may become significant during muscular work. Moisture in Clothing Clothing absorbs not only liquid sweat, but also moisture evaporated from the skin, increasing in weight without containing any liquid water. It is desira- ble to standardize the initial moisture content, and measure the change during the experiment. The initial water content can be standardized for a given series Of experiments by exposing the clothing for at least 8 hours to moving air of known relative humidity and temperature. The equilibrium moisture content is more sensi- tive to changes in relative humidity than to changes in temperature. The follow- ing measurements are needed: Conditioned weight = weight after exposure to the reference atmosphere of moving air for at least 8 hours. The clothing should be well opened. Heavy clothing may require longer exposure. The conditioned weight will be somewhat greater if the clothing dries from a previously wetter state than if it absorbs moisture during the conditioning. Any relative humidity below 80$ can be used as a reference standard. Standard conditions for textile testing are 65% +_ 2% relative humidity, 70°F. + 10°F. Water uptake = weight at end of experimental period - conditioned weight. This will check with the difference bebween moisture evaporated and moisture loss, except for drying during the period of weighing. Such drying can be reduced by enclosing the clothing in tarred metal boxes or other air-tight containers while weighing. Dry weight = constant weight reached after drying in a ventilated oven at 105°C. If it is not convenient to dry the whole mass of the clothing, samples of the fabrics, taken in the proportion which they constitute of the total weight, can be conditioned in the reference atmosphere along with the clothing, and dried separately. , weight of absorbed water rf Regain = —-0 ———-——— as %. dry weight of cloth Knowing the dry weight and the regain corresponding to the reference condi- tion, the water uptake during the experiment can be roughly divided between ab- sorbed water and liquid water, if the clothing is made of one kind of fiber. The 21