tion of air movement and ambient temperature
and during heat exposure it is, in addition, a
function of ambient humidity. Table I shows

‘Taste I.—The relationship of skin temperature at toler-
ance to the exposure conditions. Skin temperature
is a function of air movement and humidity as well
as ambient temperature.

Ambient Conditions Final Skin
Dry Bulb Vapor Pressure Air Movement ‘Temperature

°C CF) mm Hg ft/min °C (°F)
4.0 (25) 16 <88 21.8 (71.3)
—4.0 (25) 16 440 17.6 (68.6)
4.4 (40) 3a <88 28.8 (74.8)
4.4 (40) 31 440 21.4 (70.5)
4.4 (40) 31 880 19.0 (66.2)
15.6 (60) 66 <88 28.2 (83.0)
15.6 (60) 6.6 440 25.7 (78.2)
15.6 (60) 66 880 28.9 (75.0)
37.8 (100) 40.4 264 36.5 (97.7)
37.8 (100) 48.7 264 38.1 (100.6)
48.3 (110) 19.6 264 36.1 (97.0)
43.3 (110) 49.1 264 38.7 (101.7)
42.8 (109) 63.6 264 40.8 (105.5)
48.3 (119) 448 264 38.0 (100.4)
48.9 (120) 50.5 264 39.5 (103.2)
48.3 (119) 719 264 41.2 (106.1)
60.0 (140) <20 40 88.9 (102.0)
TL (160) * <20 40 40.2 (104.4)
98.3 (200)* <20 40 40.8 (105.4)
112.8 (235) * <20 40 41.9 (107.4)

* Data of Blockley’.

final skin temperature for some representative
hot and cold exposures. It is apparent that for
a given dry bulb temperature during cold expo-
sure final skin temperature is lower with higher
air movements. As would be expected, skin tem-
perature is lower when ambient temperature is
lower. During exposure to high temperature in-
creasing humidity and air movement increase
final skin temperature at a given ambient tem-
perature. Increasing ambient temperature with-
out increasing humidity or air movement also
increases final skin temperature.

Tolerance times were determined for all of
those exposures during which the subjects were
terminated before the scheduled time was com-
plete. Table II lists tolerance times for a variety
of exposures. These times varied from hours for
the mild exposures to about 20 minutes for the
most severe hot or cold exposures. These data
show that tolerance time is not determined solely
by dry bulb temperature; air movement and
humidity also have an influence on tolerance.

Tapre II.—The relationship of tolerance time to the
exposure conditions. Tolerance time is a function
of air movement and humidity as well as ambient

temperature. ‘Tolerance times are given to the
nearest five minutes.
Ambient Conditions

Dry Bulb Vapor Pressure Air Movement Tolerance
°C (°F) mm Hg ft/min ‘Time minutes
4.0 (25) 16 <88 >120
—4.0 (25) 16 440 40
11 (30) 24 440 80
—1.1 (30) 24 880 60

4.4 (40) 31 <88 >120

4.4 (40) 3.1 440 >120

4.4 (40) 81 880 80
15.6 (60) 66 <88 >120
156 (60) 66 440 >120
15.6 (60) 66 880 >120
37.8 (100) 40.4 264 >120
87.8 (100) 48.7 264 60
43,3 (110) 19.6 264 >120
43.3 (110) 49.1 264 60
42.8 (109) 63.6 264 20
48.3 (119) 448 264 65
48.9 (120) 50.5 264 45
48.3 (119) 9 264 20
60.0 (140) <20 40 90
T11 (160)* <20 40 70
93.8 (200) * <20 40 35
112.8 (235)* <20 40 25

* Data of Blockley’.

We noted the fact that tolerance time and
change in skin temperature are related to the
several environmental factors in the same way.
For example, increasing the humidity during
exposure to a hot environment increases the
total change in skin temperature and decreases
the tolerance time. During cold exposure, in-
creasing the air movement at a given temperature
increases the total change in skin temperature
and decreases the tolerance time.

Figure 2 shows tolerance time plotted against
final skin temperature for all exposures. Final
skin temperatures in the approximate range
87.8° C. (100° F.)-21.1° C. (70° F.) are asso-
ciated with tolerance times of 120 minutes or
greater. Tolerance times less than 120 minutes
are obtained when skin temperatures are greater
than 87.8° C. or less than 21.1° C. and the de-
crease in time is proportional to the increase or
decrease in skin temperature. Figure 2 indicates
that tolerance time will be essentially “zero”
when skin temperature approaches 46.1° C.
(115° F.) and 15.6° C. (60° F.). The upper
value, 46.1° C. agrees well with studies showing



. Adolph, E. F. and G. W. Molnar.

. Blockley, W. V. and J. Lyman.

. Buettner, K.

REFERENCES

“Exchanges of.
heat and tolerances to cold in men exposed to out-
door weather.” Am. J. Physiol. 146:507, 1946.

“Studies of human
tolerance for extreme heat. III: Mental perform-
ance under heat stress as indicated by addition and
number checking tests.” AF Tech. Rep. No. 6022,
1950.

“Effects of extreme heat on man.”
JAMA 144 :732-738, 1950.

. Goldman, R. F., E. B, Green and P. F. Iampietro.

“Tolerance of hot wet environments by resting men.”
J. Appl. Physiol. 20 :271-277, 1965.

. Hardy, J. D. Ch. I in Physiological Problems in

Space Hxploration (J. D. Hardy, ed) Charles ©.
‘Thomas, Springfield, Ill, 1964.

. Iampietro, P. F. “Prediction of skin temperature
of men in the cold.” J. Appl. Physiol. 16:405-408,
1961.

. Iampietro, P. F., D. BE. Bass and B. R, Buskirk.

“Heat exchanges of nude men in the cold: Effect of
humidity, temperature and windspeed.” J. Appl.
Physiol. 12 :351-356, 1958.

8.

10.

u.

13.

14.

Iampietro, P. F. and E. R. Buskirk. “Effects of
high and low humidity on heat exchanges of lightly
clothed men.” J. Appl. Physiol. 15:212-214, 1960.

. Iampietro, P. F., W. D. Chiles, E, A, Higgins and

H. L. Gibbons. “Complex performance during ex-
posure to high temperature.” Aerospace Med.
40 1331-1385, 1969.

Iampietro, P. F., V. Fiorica, E. A. Higgins, M. Mager
and R. F. Goldman. “Exposure to heat: Comparison
of responses of dog and man.” Int, J. Biometcor.
10:175-185, 1966.

Tampietro, P. F. and R. F, Goldman.
men working in hot, humid environments.”
Physiol. 20:73-76, 1965.

“Tolerance of
J. Appl.

. Iampietro, P. F., R. F. Goldman, E. R. Buskirk and

D. E. Bass, “Responses of Negro and white males
to cold.” J. Appl. Physiol. 14:798-800, 1959.

Webb, P. Ch. 8 in Temperature, Its Measurement
and Control in Science and Industry (J. D. Hardy,
ed.) Reinhold Publishing Corp. New York, N. Y.,
1963.

Wyndham, 6. H.
tures in man’s temperature regulation.”
Physiol. 20 :31-36, 1965.

“Role of skin and core tempera-
J. Appl.


A relationship between skin temperature at
ten minutes of exposure and skin temperature
at the tolerance limit is depicted in Figure 3.
When environmental conditions are essentially
thermally “neutral” for the seminude, resting
mean skin temperature does not change during
the course of the exposure and therefore skin
temperature at ten minutes of exposure (Ts, )

is the same as final skin temperature (Ts, ). As
the environmental conditions deviate from the

“neutral” situation, Ts, and Ts, deviate from
the neutral T, (33.8° C., 93° F.).

When subjects are exposed to cold environ-
ments T, | is always higher than Ts, However,

as the conditions become more extreme, and tol-
erance time decreases, T, | approaches the Ts,

value. When the conditions are so severe that
tolerance time is ten minutes, then Ts, will

equal T, . The same situation occurs when sub-
jects are exposed to hot environments except that

°c
46.1

oF
us

43.3 X = Data of Blockley

40.6 7105

37.8100

35.0795

32.2790
Tg F 532.3574 - 18.2000 (S19)

29.4485 +.2282 (Tg, J*.0008 5,.)°

26.7780

10-MINUTE SKIN TEMPERATURE

23.9775

212770

18.3

7O 75 80

15.6

Tg_*- 35.05 +137
SF Ti

85 90 95 100 105,

to 5

18.3 21.2 23.9 26.7

29.4

32.2 35.0 37.8 40.6 43.3 46.1

FINAL SKIN TEMPERATURE

Ficure 3. The relationship between final skin temperature (at tolerance) and skin temperature at 10 minutes of

exposure.

5

Dashed portion of curves are extensions beyond the limits of the data (Data of Blockley, 2).



that the thermal pain threshold is around 45.6° C.
(114° F.). These studies indicate that the toler-
ance limit is achieved within seconds to a minute
or two when surface temperature reaches
45° C3538, The lower limit (15.6° C.) is not as
simple to define. In an earlier study* we showed
that tolerance time was 60 minutes when skin

temperature was 17.2° C. (63° F.). Estimates
of time below this skin temperature indicated a
tolerance of about 20 minutes when skin tempera-
ture reached 15.0° C. (59° F.). Therefore, it
appears that the value 15.6° C. in the present
paper for “zero” tolerance may be about two
degrees too high,

°c oF
48.97120

N
N

X = Data of Blockley

43.34

37.84

32.27

26.77

FINAL SKIN TEMPERATURE

2l.27

15.65

HHONS
NX

F100

90

r80

L50 :

10.0-
° 20

40 60

80

100

120

140

TOLERANCE TIME, MINUTES

Ficure 2. The relationship of tolerance time during exposure to hot and cold environments to the final skin tem-

perature achieved.
ley, 2).

Dashed portion of the curves are extension beyond the limits of the data (Data of Block-


fore, a cubic expression was derived which would
take this fact into consideration. This expression
has essentially the correct values for the “neutral”
T, and for T; to =T., at both the hot and cold

extremes. This equation is also indicated in

Figure 3.

We have established that final skin tempera-
ture and tolerance time are related and we have
shown that skin temperature at ten minutes of
exposure is related to skin temperature at the
tolerance limit. Therefore, skin temperature at
ten minutes can be used to predict tolerance time
for both hot and cold exposures. Figure 4, which
is patterned after Figure 2 shows the relationship
of T, 4» € tolerance time. If T, to is between
the limits of 25.0° C. (77° F.) and 364° C.
(97.5° F.) tolerance time is at least 120 minutes.
Beyond these limits tolerance time decreases in
proportion to the increase or decrease in Ts,

values. Tolerance time would decrease to ten
minutes when T, _ increases to 43.3° C. (110° F.)

a0
or decreases to 16.4° C, (61.5° F.).

The very good agreement between skin tem-
perature and tolerance time is remarkable be-
cause several criteria were used to determine
tolerance including subjective evaluations as well
as several objective measures. It would thus ap-
pear that skin temperature is the one physiologi-
cal measure which responds to all environments
in a predictable and sensitive manner, at least
under the conditions of these studies. This meas-
ure can be a very useful tool to those who have
an interest in the effects of the thermal environ-
ment on man’s ability to perform in, and tolerate
physiologically, that environment. More work is
required to determine the effects of workload,
clothing, equipment and other factors on this
prediction model.



TECHNICAL REPORT STANDARD TITLE PAGE

T. Report No. 2. Government Accession No. 3. Recipient's Catalog No.
FAA-AM-71-4

4, Title and Subtitle > 5. Report Date

USE OF SKIN TEMPERATURE TO PREDICT TOLERANCE TO January 1971
THERMAL ENVIRONMENTS 6. Performing Organization Code

7. Author's) 8. Performing Organization Report No,

P. F. Tampietro

9. Performing Organization Name ond Address 10. Work Unit No.
FAA Civil Aeromedical Institute
P. 0. Box 25082 11. Contract or Grant No.

Oklahoma City, Oklahoma 73125

13. Type of Report and Period Covered

12. Sponsoring Agency Name ond Address

Office of Aviation Medicine OAM Report
Federal Aviation Administration
800 Independence Avenue, S. W. 14. ‘Sponsoring Agency Code

Washington, D. C. 20590

15. Supplementary Notes

This study was done under Task No. AM-F-69-PHY-32.

16. Abstract

Skin temperature is a sensitive index of the effect of the thermal environment
on the seminude man. Skin temperatures and tolerance times from several studies
have been utilized in an attempt to establish a relationship between 1) final skin
temperature and tolerance time and 2) skin temperature during the early minutes of
exposure and final skin temperature, The number of subjects during each exposure
ranged from five to ten. Exposure temperatures ranged from -4 to 113°C (25° to
5°F). Air movement ranged from about 50 to 880 ft/min. Many criteria were used
to fix tolerance time; for hot exposure we used T, = 102.5, HR = 180 beats/min,
nausea, etc.; for cold exposures we used toe temperatures below 4.4°C (40°F) and
subjective evaluations. A relationship exists between final temperature and toler-
ance time and between final skin temperature and skin temperature at ten minutes
of exposure. Final skin temperature (at tolerance) in hot and cold environments
can be predicted from the skin temperature at ten minutes. Tolerance time may also
be estimated from the ten minute skin temperature.

17, Key Words 18. Distribution Statement
Tolerance, Heat, Cold, Human, Thermal Availability is unlimited. Document may
Exposure, Skin Temperature, Prediction be released to the National Technical
of Tolerance Information Service, Springfield,

Virginia 22151, for sale to the public.

4

19.” Security Classif. (of this report) 20. Security Classif. (of this page) Ti. No. of Pages | 22, Price
Unclassified Unclassified 8 $3.00

Form DOT F 1700.7 (8-69)







°c
48.97

°F
120

43.37

37.87

IO-MINUTE SKIN TEMPERATURE

X= Data of Blockley

32.2790 e
é
e
26.7+80 t
a
21.2770 e e
aa
a
. a
15.6760
100450 i 1 1 1 1 i
ie) 20 40 60 80 100 120 140

TOLERANCE TIME, MINUTES

Fioure 4. The relationship of skin temperature at 10 minutes of exposure to tolerance time.

Dashed portions of

the curves are extensions beyond the limits of the data (Data of Blockley, 2).

Ts
10
time is ten minutes. The dashed portions of the
curve represent extrapolations beyond the: avail-
able data. Figure 3 also indicates that the rela-
tionship between T, to and T, is essentially

(75°

is always lower than Te, until tolerance

linear for the range Ts, =93.9° C.

F.) —37.8° C. (100° F.). An expression was de-
rived to fit the data so that T, | could be caleu-

lated from T, within this range. The regres-

sion is shown in Figure 3. However, as indicated
above, the ratio Ts, /T;, approaches unity as

tolerance time approaches ten minutes. There-


decision of a physician. These criteria were
applied either singly or in any combination. For
cold exposures we used toe temperature 4.4° C.
(40° F.), exhaustion, or the decision of a physi-
cian. In the event the tolerance limit was not
reached, the exposures were terminated at 120
minutes or longer.

Il.

Skin temperature responds rapidly and sensi-
tively when an individual is exposed to an en-
vironment warmer or colder than a “neutral”
environment. Figure 1 shows mean skin tem-
perature plotted against time for a number of
representative exposure conditions. We pointed
out in an earlier paper that during exposure to

Results and Discussion.

hot environments at least 75% of the total change
in skin temperature occurred during the first 15
minutes of the exposure’. Subsequently, we
examined data from other studies we had per-
formed in cold environments and established
that essentially the same degree of change took
place during the first ten minutes of exposure.
This characteristic of the rapid change in skin
temperature was mentioned by Adolph in 1946+
when he pointed out that equilibrium mean skin
temperature during exposure to cold was nearly
established after ten minutes of exposure.

The second characteristic of the change in skin
temperature is that the final skin temperature is
a function of the exposure conditions. Final
skin temperature during cold exposure is a fune-

X= Data of Blockley
shi (235)
112.8 (235) /<20
43.37 110 93.3 (200) /<20
w 711 (i160) /<20
us 37.8 (100)/48.7
5 s7etioo 37.8(100)/40.4
a. ° *
ir —*. ‘
rs 37.8(100)/34.|
a 4
: 32.2+90
ty 15.6 (60) /< 88
_,'5. a
Z 267480 15.6(60)/440
S 26.778 —e- ©
(7p)
“1 (30) 7¢ggy—e 15.6 (60)/880
21,2+70 -1,1(30)/440
-1.1(30)/880
15.6 +60 ! ; ; ;

0 20

40

60 80 100 120

TIME, MINUTES

Ficune 1. The relationship of skin temperature to time during exposure to hot and cold environments.
tative conditions are illustrated.

2

Represen-
(Data of Blockley, 2).


USE OF SKIN TEMPERATURE TO PREDICT TOLERANCE
TO THERMAL ENVIRONMENTS

I. Introduction.

The effects of the environment on man have
been receiving a great amount of attention dur-
ing the last several years. Because of advanced
technology in aviation and space activities, more
interest is being generated concerning the effects
of the thermal environment on man, The two
areas of interest in aviation activities center
around performance capabilities and physiologi-
cal tolerance, especially in hot environments,
such as those presented during failure of the
ventilation system of high performance aircraft.
What has been needed is a definitive means of
predicting performance capabilities and. tolerance
times of people in hostile environments. In our
laboratories we have recently completed two
studies evaluating performance during time-
temperature profiles simulating air conditioning
failure in-flight aboard a high-altitude, high-
speed aircraft. A single-parameter predictive
index would have facilitated the study through
simplification and would have obviated multiple
temperature measurements. This paper repre-
sents an attempt to use a single physiological
criterion to predict tolerance time in all thermal
environments,

The possibility of using a single physiological
measure to predict tolerance time for humans in
all thermal environments has long intrigued
workers in the field. Attempts to use deep body
temperature, skin temperature, sweat rate, heart
rate, and oxygen consumption as indexes have
allowed only partial success in predicting toler-
ance. During exposure to hot environments,
heart rate, sweat rate and deep body temperature
have been used with varying degrees of success
as predictors of tolerance while heat production,
skin temperature and deep body temperature
have been used during cold exposures. Perhaps
the single’ measure which has shown the most
promise over a wide range of thermal environ-
ments has been deep body temperature.

Many workers have shown rectal temperature
to be very sensitive to increases in environmental
temperature but not as sensitive to decreases in
ambient temperature'’. During exposure to cold
environments, rectal temperature actually in-
creases during the first 30 or 40 minutes of ex-
posure’,

Adolph, in the mid-1940’s recognized that skin
temperature was a sensitive measure of the effect
of cold environments in man. Later, we showed
that skin temperature could be predicted for a
wide range of cold environments and that there
was a relationship between final skin temperature
and tolerance time®.

The purpose of this paper is two-fold: (1) to
show that skin temperature is a reliable and
sensitive measure of the effect of hot and cold
environments on man, and (2) to show that skin
temperature during the first minutes of exposure
can be used to predict final skin temperature and
tolerance time.

II. Methods.

Data from studies conducted over several years
in the author’s laboratory‘ *4? and in other lab-
oratories? have been used for the present paper.
Subjects in these studies were used for a variety
of purposes, but all were lightly clothed or semi-
nude and all were wired for the measurement of
skin temperatures. Subjects (5 to 10 per environ-
ment) were exposed usually in groups, but some-
times singly, to environments which ranged in
temperature from ~4° C. (25° F.) to 118° ©.
(235° F.), in air movement from about 50 to
880 ft/min and in vapor pressure from less than
20 mm Hg to about 72 mm Hg. Only group
means are used in this paper. Tolerance was
established according to a variety of criteria.
For termination of hot exposures, we used rectal
temperature 39.2° C. (102.5° F.), heart rate 180
beats/min, nausea, hyperventilation tetany or the