(101.1° F.)) both heart rate and rectal tempera-
ture were increasing rapidly ‘at the end of the
30-minute exposure.* Although heart rate began
to decrease almost immediately, rectal tempera-
ture continued to climb for about 10 minutes
after the chamber temperature began to lower.
Thus, it is conceivable that an additional 15-20
minutes at an effective temperature of 38.4° C.
would have caused an explosive rise in either or
both of these parameters with the possibility of
the collapse of the subject. In addition, certain
other factors became more prominent with in-
creasing time at high temperature. These are
concerned with the discomfort of handling hot,
thermally conductive objects, and the mechanical
effects of sweat in the eyes or on the hands.
Figure 4 shows that finger temperature was 42.1°
C. during exposure to 71.1° C. The pain thresh-
old is usually considered to be about 45° ©.
(118° F.), and one subject in our study com-
plained of considerable discomfort due to contact
with hot metal parts of the headphone set.

At an Effective Temperature of 35° C. (which
corresponds to our 60.0° C. test), Lovelace and
Gagge’ show the recommended limit of exposure
to be about 90 minutes. However, it should be
noted that the peak heart rate under this tem-
perature condition was fewer than 10 beats/min.
less than under the higher temperature condition
at the corresponding point in time. Although
rectal temperature was somewhat lower at the
end of the 30-minute exposure at 60.0° C. than
it was at 71.1° C., rectal temperature continued
to climb in the Phase I experiment until about
the time the chamber temperature had returned
to normal.

The data collected with the complex perform-
ance device used in this study are probably more
applicable to questions of aircrew performance
during exposure to high temperature than those
obtained with the tasks in most of the recent
studies. First, our tasks assess functions that are

*In order to show our data on the chart constructed
by Wing (Fig. 5), we converted the parameters of our
conditions to effective temperatures according to the

equation: ET=
107.5 (DB-WB) + 623 WB
3 + DBWB
where DB and WB are, respectively, dry bulb and wet
bulb temperatures in degrees Fahrenheit. Thus, our
effective temperatures were, in degrees Centigrade (0°
F.), 18.9 (66.0), 85 (95.0), and 88.4 (101.1).

12

intuitively involved in aircrew activities in the
sense that it is difficult to see how the man could
perform his aircrew duties at his normal level of
competence if important decrements showed up
in any of these functions. Second, and perhaps
more important, the task combinations we used
require time-sharing in the exercise of different
psychological functions. And time-sharing seems
more to characterize the role of the aircrewman
in advanced aircraft. Experiments in which
single tasks are performed (as is the case in most
of the related research), not only do not provide
a measure of this important aspect of behavior
but also such tasks permit much more of an op-
portunity for the subject “to muster his reserves”
and, thus, counteract any adverse effects of tem-
perature by increased application to the task at
hand. Further development of the rationale
supporting this position can be found in a paper
by Chiles, Alluisi, and Adams.?

The results of this study indicate that complex
performance is unimpaired for 30 minutes at
60.0° C. However, this statement must be quali-
fied in view of the fact that the first subgroup of
10 subjects tested at this temperature did show
decrements on the tracking task.

For a moderate level of workload, performance
was not impaired during the first 5 minutes at a
temperature of 71.1° G., and, when this same task
combination appeared again after 15 minutes at
temperature, performance was still not impaired.
However, during the second 5 minutes at tem-
perature, both manual performance and mental
performance suffered, with mental performance
also showing decrements under a somewhat lighter
workload during the third 5 minutes at tempera-
ture. The time figures just cited do not include
the time required to raise the chamber tempera-
ture to the test level, 5 minutes and 8 minutes
for the lower and higher temperature conditions
respectively.

Although we interpret our data to indicate that
performance is unimpaired for 5 minutes at
71.1° C., caution should be exercised in making
extrapolations. The necessity for caution arises
from the fact that the absence of decrements
during the first 5 minutes at temperature may
have been an artifact of the experimental design.
Had the more complex, heavier workload condi-
tion (condition B) been presented first, decre-
ments might very possibly have occurred imme-
diately. Similarly, the decrements in arithmetic


Freure 1—Complex performance device.

The forcing function for the tracking task is
generated by selecting “at random” from among
eleven possible voltages—five minus voltages, five
plus voltages, and zero volts, The selection is

a

eaais

(See text for identification of components.)

carried out by a stepping switch actuated once
each 4 seconds, the various contacts of the switch
being wired to the 11 positions of a voltage di-
vider by reference to a table of random numbers.



Nn

i

a

REFERENCES

. Brocktey, W. V. and Lyman, J.: Studies of Human

Tolerance for Heat. IV Psychomotor Performance
of Pilots as Indicated by a Task Simulating Aircraft
Instrument Flight. AF Tech, Rep. No, 6521, Wright-
Patterson AFB, Ohio, 1951.

Cums, W. D., Autursr, E. A., and Apams, 0. S.:
Work Schedules and Performance During Confine-
ment. Human Factors 10: 143, 1969.

. Crocker, J. F., and Warrz, ©. R.: A Heat Pulse

Oven for Study of Human Heat Tolerance. WADD-
Tech Rep, 60: 733, 1960.

. Fortanno, G., BarMacn, J. E. and Coaxtey, J. D.:

The Effects of Ambient and Body Temperatures Upon
Reaction Time. SDC Report R-151-1-13 ONR Wash-
ington, D.C., 1948.

Haner, F.: Ch. V in Physics and Medicine of the
Upper Atmosphere (C. 8. White and O. O. Benson,
Eds.) University of New Mexico Press, Albuquerque,
1952.

16

6. Logs, M. and JeanrHeau, G.: The Influence of Nox-
ious Environmental Stimuli on Vigilance. J. Appl.
Psychol. 42: 47-49, 1958.

Loverace, W. R., II and Gacax, A. P.: Aero-Medical
Aspects of Cabin Pressurization for Military and
Commercial Aircraft, J. Aeronautical Sciences 18:
143, 1946.

Perrer, R. D.: Extreme Warmth and Sensormotor
Coordination, J. Appl. Physiol. 14: 383-386, 1959.

9. TercuNer, W. H. and Wenrxamp, R. F.: Visual
Motor Performance as a Function of Short Duration
Ambient Temperatures, J. Exp. Psych. 47: 447-450,
1954,

Wing, J. F.: A Review of the Effects of High Am-
bient Temperature on Mental Performance. AMRI-
TR-65-102, Wright-Patterson AFB, Ohio, 1965.
‘Wine, J. F. and Toucustong, R. M.: The Effects of
High Ambient Temperature on Short Term Memory.
AMRL-TR-65-103, Wright-Patterson AFB, Ohio,
1965.

A

10.

11.


140

1307

HEART RATE
(beats per minute)

°C

38.1 +100.6

37.7 4

37.5 4

37.3 4

RECTAL TEMPERATURE

37.14

37.9 7100.3

T T TT T T T T T T T T

SOLID LINES = PRE AND POST EXPOSURE
BROKEN LINES = EXPERIMENTAL PERIOD

peelenge

. oy
Tape yt
At
ra

jet
¥

PeSeoterton, — oT p. 909 MPH. reopen SyT 1

O—0 = 23.8 °C (75°F)
B— 8 =60.0°C (I140°F)
S—4 =71.1°C (160°F)

99.9

99.6 Anadods L
peeteeteng pert

jee TTD roqrepenpootoey,

“preprey: |

Le a Ss GS SS ON CL SN SS GS OS GN GO jj

798.8

O 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 64 68 72 76 80 84
TIME (minutes)

Frourr 8—Heart rate and rectal temperature during exposure to 23.8, 60.0 or 71.1° ©. Values are means with stand-

ard error shown at six-minute intervals.

Body surface temperatures (Fig. 4) increased
rapidly during the first minutes of exposure to
heat and then remained level or increased slowly
during the remainder of the exposure. At 71.1°
C., forehead temperature reached 40.7° C. (105.8°
F.) ; hand temperature was 40.2° C, (104.4° F.) ;

and finger temperature was 42.1° C. (107.8° F.).
At 60.0° C., skin temperatures, in the same order
were 39.2° C. (102.5° F.), 38.9° C. (102.0° F.),
and 40.9° C. (105.6° F.). During exposure to
23.8° C., all temperatures were unchanged.


of the light until the switch was actuated to turn
the light off.

The discrimination reaction time task consists
of two lights located on the lower right corner of
the panel (designated as D in Fig. 1) and two
telegraph keys located immediately below the
lights. The left light and key are green; the
right light and key are red. The subject is re-
quired to use his left hand in responding to this
task and to keep that hand on a third “ready”
key (located on the table just to the left of center
near the front edge) except when responding to
this or one of the other tasks. The subject de-
presses the green key in response to a green light
and the red key in response to a red light. Sig-
nals are presented at a rate of approximately
two/minute. Two basic time measures were re-
corded on this task and a third measure was de-
rived from the first two. Time was measured to
the nearest 1/100th second from the onset of a
red (or green) light until the subject lifted his
hand from the ready key. The elapsed time from
the onset of a light until the depression of the
appropriate response key was also measured.
From these two measures—reaction time and
total time—a third measure was derived by sub-
tracting the first from the second to yield an
index of movement time.

These five tasks are presented in three different
combinations so that the levels and natures of the
workloads imposed on the subject can be varied.
The first combination, designated as condition A,
consists of the tracking task, simple reaction time
task, discrimination reaction time task, and meter
monitoring. The second combination (condition
B) consists of those tasks constituting condition
A plus the mental arithmetic task. And the
third combination (condition C) is the same as
condition A except that the arithmetic task is
substituted for the tracking task. During all
conditions, the subjects respond only to the track-
ing task and the simple reaction time task with
the right hand; they respond to all other tasks
with the left hand and are instructed to keep the
left hand on the ready key when not responding
to one of these tasks.

Environmental Chamber. The chamber in
which the performance console was located and
all of the training and testing were carried out
was 10 feet long, 8 feet wide, and 8 feet high.
The interior was illuminated by a single 300

watt light bulb located in the center of the ceiling.
The subject sat on a padded, wooden chair with
his back toward both the entrance door and the
viewing window located beside the door. He was
dressed in a short-sleeved, loose shirt, trousers,
shoes and socks.

The temperature of the chamber was controlled
by two methods. The primary system provided
a convective input that controlled air temperature
directly. However, this system by itself was in-
capable of achieving the desired temperature
rises as rapidly as was required. Therefore, an
auxiliary system of six, 5 kw. radiant heaters was
used to bring the temperature up to the specified
value. Once the temperature had stabilized, only
one or two auxiliary heaters were typically re-
quired to maintain equilibrium. Control of hu-
midity was completely automatic. The convective
system produced a continuous flow of turbulent
air varying between 50 and 100 ft./min. at the
subject position at all temperatures.

The temperature conditions used were as
follows:

Phase I—60.0° C. (140° F.); vapor pres-
sure 13.6 mm. Hg, relative hu-
midity 9.1%
Phase II—71.1° C. (160° F.); vapor pres-
sure 19.9 mm. Hg. relative hu-
midity 8.5%

Phase IIT—23.8° C. (75° F.); vapor pres-
sure 2.6 mm. Hg, relative hu-
midity 12.0%

The temperature conditions of Phase III were
maintained during training and during the pre-
and post-exposure baseline periods of Phases I
and II.

Temperature was monitored by means of an
air probe located just above and to the right of
the subject’s head. Subsequent checks showed
that the Globe temperature at the level of the
subject’s trunk approximated the air temperature
(Fig. 2).

Procedure. Twenty subjects served in Phase I
of the experiment which involved a 30-minute’
exposure to a temperature of 60° C. The sub-
jects reported to the Laboratory the afternoon
before they were to be tested. They were given
a brief indoctrination as to the purposes of the
experiment, the conditions to be used, and the
safety precautions being taken. They were then



The output of this circuit, which is a series of
step-function changes in voltage, is modified by
an operational amplifier circuit into which is
built a lag circuit and two stages of integration
before being displayed to the subject. The dis-
turbances are programmed independently for the
two axes so that the dot appears to the subject
to wander about the display at random. The
polarity of the voltages applied to the stick are
such that forward movement of the stick causes
the dot to move down and movement of the stick
to the right causes the dot to move to the right.
The output of the stick goes through one stage
of integration before being added to the output
of the forcing function generator; thus, from the
subject’s point of view, he is not manipulating a
simple position control.

Four measures were recorded of the subject’s
performance of the tracking task: integrated ab-
solute error in the horizontal and the vertical
dimensions (taken independently) and integrated
error squared in the horizontal and vertical di-
mensions (also taken independently). From the
subject’s point of view, error is the deviation of
the dot from the intersection of the two axes
scribed on the plastic overlay. These measures
were recorded at the end of each minute of per-
formance; thus, because of the time required to
read and reset the scoring integrators, four 1-
minute samples of performance were measured
for each 5 minutes of tracking. However, the
subject had no way of knowing that there were
brief periods during which his tracking perform-
ance was not being measured.

The mental arithmetic task is presented to the
subject by means of three in-line projection dis-
plays designated as B in Figure 1. A two-digit
number appears in the first window and, simul-
taneously, a buzzer sounds to alert the subject.
The subject notes and remembers the number and
acknowledges seeing it by pressing a button im-
mediately below that window. The first number
then disappears and a two-digit number appears
in the second window and the buzzer again
sounds. The subject acknowledges this number
in a similar manner whereupon that number also
disappears. The subject is instructed to add this
number to the first and remember their sum. A
two-digit number then appears in the third win-
dow; the subject is instructed to subtract this
number from the sum of the first two numbers.
He enters his answer into two columns of push-

buttons designated as B, in Figure 1. He is also
instructed that, as soon as he has entered his
answer, he is to push a button immediately above
the “tens” answer column to indicate that his
answer is complete. Problems are presented on
this task at a rate of approximately three/
minute. Performance was measured in terms of
percentage correct and the time (to the nearest
1/100th second) from the appearance of the third
number until the subject pushed the “answer
complete” button.

The meter monitoring task is presented to the
subject by means of the two meter displays desig-
nated as C in Figure 1. The normal condition
for the two displays is for the two pointers to be
at rest in the horizontal position; the left meter
points to the 3 o’clock position, the right to 9
o'clock. Introduction of a “signal” results in the
drifting of one of the pointers either up or down
through an angle of approximately 20 degrees.
The subject indicates that he has detected a meter
signal by pushing the appropriate button (desig-
nated C, in Figure 1); he pushes the left button
for the left meter and the right button for the
right meter. A correct response “freezes” the
pointer in its current location and illuminates an
amber-colored light above the affected meter, thus
giving immediate feedback to the subject. A
signal, if undetected, produces the maximum 20-
degree deflection in approximately 8 seconds, at
which time it rather quickly returns to the normal
position. This return to normal is of sufficient
attention value that subjects often notice it and
are made aware that they have missed a signal.
Signals are introduced at a rate of approximately
1.5 signals/minute. The meter affected and the
direction of the deflection (up or down) is se-
lected unsystematically. Performance was meas-
ured in terms of the response time to the nearest
1/100th second and the number of signals de-
tected.

The simple reaction time task requires the sub-
ject to respond to an amber-colored light located
on the lower left corner of the panel (designated
in Fig. 1 as D) by depressing a push-button lo-
cated in the top of the control stick for the track-
ing task; the response extinguishes the light.
Signals are presented on this task at a rate of
approximately one signal every two minutes. The
performance measure used was the time elapsed
(to the nearest 1/100th second) from the onset




given a description of the tasks and were told
how to perform them. The first training trial
consisted of 15 minutes of performance with five
minutes of each of the task combinations in the
sequence A, C, B. After a short rest, this was
followed by 15 minutes of performance of the
combinations in the sequence A, B, C. After
another rest period, the subjects performed for
30 minutes (A, B, C, A, B, C); another rest
period followed and then this 30-minute sequence
was repeated.

Subjects reported to the Laboratory at approxi-
mately 8:30 on the morning of the test. The first
20 minutes were spent in attaching the physiologi-
cal recording electrodes to the subject and in
verifying the adequacy of the electrode place-
ments for recording purposes. The subject was
then equipped with a handtowel tied comfortably
around his forehead to serve as a sweatband.
Preliminary exposures had shown that profuse
sweating could be expected and, as a result, vision
would likely be interfered with. Inasmuch as
the purpose of the experiment was to examine
the integrity of performance functions, it was
decided that such a readily preventable effect of
the heat should not be permitted to interfere with
the primary interest of the research. Figure 2
shows the protocol for the experiment. The first
15 minutes were devoted to collecting baseline
data and involved the three performance condi-
tions in the sequence A, B, C. Beginning with
the 16th minute, the chamber heat sources were
activated and the temperature was stabilized at
60° C. by the end of the 20th minute. During
the period when the temperature was increasing,
subjects performed on task combination B, the
heaviest workload condition. The period at tem-
perature consisted of two repetitions of the A,
B, and C sequence. At the end of the 50th minute
the process of lowering the temperature began
so that it would return to normal (23.8° C.) by
the end of the 65th minute; during this period
of decreasing temperature, the subjects again
performed on task combination B. Upon reach-
ing normal temperature, the subject began a
15-minute period of post-exposure testing, after
which the run terminated.

During Phase IT, 11 of the 20 Phase I subjects
were tested during a 32-minute exposure to
71.1° C. The afternoon before the test, the sub-
jects came to the Laboratory for 45 minutes of
refresher training. The following morning, the

subjects were tested according to the same basic
schedule with the exception that, since it required
7 to 8 minutes to reach the higher temperature,
the 15-minute baseline period was followed by
10 minutes of performance of condition B. Thus,
the total time at temperature was approximately
32 minutes, and the total period of testing was
85 minutes.

A new sample of 10 subjects was tested in
Phase III. These subjects were given the same
training as the subjects in Phase I and were
tested according to the schedule used in Phase IT
except that the temperature was maintained at
23.8° C. throughout the 85-minute test period.

Ill. Results.

Physiological Responses. Rectal temperatures
during the Phase I experiment (60° C.) increased
0.3° C, (0.5° F.) to a peak of 37.7° C. (99.9° F.)
which was reached approximately on the first
reading made after the chamber temperature had
returned to “normal.” As shown in Figure 3,
rectal temperature did not begin to rise until 10
to 20 minutes after chamber temperature began
to increase. Rectal temperatures during Phase IT
(also shown in Fig. 3) rose 0.6° C. (11° F.)
and reached a peak of 38.05° C. (100.5° F.). As
jin Phase I, the peak rectal temperature occurred
during the post-exposure period. It had virtually
reached the peak approximately 10 minutes after
the air temperature began to decrease and stayed
at about that value until about 5 minutes after
the chamber temperature had reached normal.
During Phase IIT (23.8° C.) rectal temperature
decreased 0.2° C. (0.4° F.) to a value of 37.2° C.
(99.0° F.) during the course of the run.

Heart rate (Fig. 3), during exposure to 60.0° C.
reached a mean peak of 114 beats/min.; the high-
est value was recorded during the last minute of
heat exposure, ie., just before the temperature
began to decrease. Peak heart rate during expo-
sure to 71.1° C. was 1382 beats/min. with the
peak occurring during the first minute of the
period during which the temperature was low-
ered. In both Phases I and II, heart rate began
to increase as soon as the chamber temperature
began to rise, and in both experiments, heart rate
had returned to essentially pre-exposure levels
by the end of the run. During the Phase IIT
experiment, heart rate remained essentially un-
changed during the entire run.



AM 69-10

COMPLEX PERFORMANCE DURING EXPOSURE TO
HIGH TEMPERATURES

P. F. Iampietro, W. D. Chiles, E. A. Higgins,
H, L. Gibbons, A. Jennings, J. Vaughan
(with the technical assistance of
G. Funkhouser and R. Lewis)

Approved by Released by
J. Ropert Ditz, M.D. P. V. Siecen, M.D.
Cuter, Civin ArroMEDICAL Feperat Arr Surcron
Instrrore
June 1969

Department of Transportation

FEDERAL AVIATION ADMINISTRATION
Office of Aviation Medicine



Performance Measures. The Wilcoxon matched-
pairs, signed-ranks (two-tailed) test was used to
evaluate the differences between the performance
during a given 5-minute interval at temperature
and the 5-minute interval during the baseline
period for the corresponding task combination.
Thus, two tests were made for each of the major
tasks (tracking [Table 1] and arithmetic [Table
2]), and three tests were made for each of the
monitoring tasks (simple reaction time, discrimi-
nation reaction time, and meter monitoring
[Table 3]).

It was apparent from the data that the learning
asymptote had not been reached on several of the
tasks prior to the beginning of the experimental
run of Phase I. This is seen in the solution time
measure on the arithmetic task; for both per-
formance conditions (B and C), response times
were shorter during the first subinterval at tem-
perature than during the baseline period, and
response times during the second subinterval at
temperature were shorter than those for the first
subinterval at temperature (Table 2). There is
also a suggestion of such a trend in the moni-
toring tasks, but in this case, there are some re-
versals and the decreases are generally less pro-
nounced (Table 8).

Phase I—This portion of the experiment was
carried out in two parts, each portion involving
a different sample of 10 subjects. The first
sample of subjects showed significant decrements
on two measures. Integrated absolute error in
the horizontal dimension was greater (P<.05)
during both the first and second subperiods at
temperature under task condition A (tracking
plus monitoring), and reaction times to the red
light in the discrimination reaction time task
were significantly longer (P<.05) during both
subperiods at temperature under task condition
A. However, several of the other time measures
showed significant improvements at temperature.
Response times to the green light were signifi-
cantly shorter during the first subperiod at tem-
perature under task condition C but not during
the second subperiod (P<.05). Response times
to the amber light were significantly shorter
(P<.05) during the first subperiod at tempera-
ture under condition B but at no other time.
Solution times for the arithmetic task were sig-
nificantly shorter for the second subperiod at
temperature under task condition B (P=.05),
during the first subperiod for task condition C

10

(P=.05) and for the second subperiod for task
condition C (P<.01). It was the contradictory
nature of the finding of improvements on several
measures and decrements on others that led to
the testing of the second group of 10 subjects at
60° C.

The second group of subjects showed neither
decrements nor improvements as a function of
exposure to the elevated temperature condition.
And, when the data from both groups were com-
bined, the overall effects of temperature were not
significant; these data are summarized in Tables
1, 2, and 3, columns 1, 2, and 3.

Phase II—All of the subjects who served in
Phase I were asked to serve as subjects in the
Phase II experiment. The data of the 11 sub-
jects who volunteered for this second experiment
are presented in Tables 1, 2, and 3, columns 4, 5,
and 6. - Significant decrements were found on
two of the tasks. Integrated absolute error in
the horizontal dimension of the tracking task
showed a significant increase (P<.02) during
the first subperiod at temperature under task
condition B, and approached significance (P<.10)
during the second subperiod. As shown in col-
umn 6 of Table 1, the amount of error during the
second subperiod was greater than the error dur-
ing the first subperiod at temperature; a change
in the performance of one subject produced the
apparent discrepancy between the two subperiods.

Integrated error squared in the horizontal di-
mension showed a significant increase (P<.05)
during both subperiods at temperature under
task condition B.

The other task to show significant effects of
exposure to a temperature of 71.1° C. was the
arithmetic task. Under task condition C, signifi-
cantly fewer problems were solved correctly dur-
ing both the first (P<.05) and second (P<.01)
subperiods at temperature. Under condition B,
the number of problems solved was fewer than
during baseline for the first subperiod at tem-
perature (P<.05) but not during the second
(.10>P>.05); however, under this task condi-
tion, the percent correct was numerically poorer
during the second subperiod than during the first
(column 6 versus 5, Table 2).

None of the response time measures were sig-
nificantly affected by the exposure to 71.1° C.

In all cases at both temperatures, performance
during the 15-minute post-experimental baseline


T ——T
oc | er
42 + 107.6 l pokes ower hy 4
Pw ae ‘
1” -2-f-a- 8g
Ww 40+104.0 k A Testers, 4
« Pod
> ay
kb r
£ 36 +100.4 if 4
w Ag
g H /
ii 36+ 969 I i 4
F t
o in a0 -0-9-0,0-9-0-0-9-O-0,
E 347 93.3 olelooy t ths ane hes O0n OO J
i
Ww £ t
oO a
Z 32+ 897 ' 4
ire
s
soy asof tT SOLID LINES= PRE AND POST EXPOSURE |
BROKEN LINES « EXPERIMENTAL PERIOD
20+ 62.4 4
40 + 104.0 o pant
104. me" \ 4
& ak Dep Teer . a,
aw er ee \
® 3e+004 y =e ON 1
p=) ye
E aos ‘.
& ie, BX
& 36+ 969 ad . 4
a /
= mai “re*tees,
347 93.3 if 6 4
10-9-0-0-9-0-0"9-0-0-9.9.0-9-0-
3 1S prac eee One One O00 S08 OAS O08 taneee|
Rpghaotee,
/ 4
= 327 6974S s o—0 = 23.8°C (75°F)
. 60.0°C (140°F)
30+ 86.0 O—4 = 71.1 °C (160°F) 4
a + + + —t + +
oe
% 40+104.0 Oe a cool % ‘Q 4
q geerterneteeetty LS
5 Z ‘ x
Wi 38+100.4 B 4 4
= a. S
B Nf
36+ 969 pet! 4
Gg Qo 0-2-0 02-0-0-9-0-0-9-00 Q-0-0-9-0-0-9-0-0-9-0-0-9-0-0-D-1
G 347 933 4
a
6
w

FA a OO
0 4 8 12 16 20 24 2632 36 40 44 48 52 56 60 64 6872 76 80 84
TIME (minutes)

Ficure 4—Forehead, hand and finger temperatures during exposure to 23.8, 60.0 or 71.1° C, Values are means with
standard error shown at six-minute intervals.



TEMPERATURE

°c
724

68 4

S
@

367

327

284

244

oF
161.7

154.4

147.2

140.0

132.8

125.6

18.4

Wd

1040

96.9

20°

Solid lines —Proposed Profiles
Dotted lines----Room Air Temp.
Dashed lines—— Globe Temp.

4 1 ae or os 1 | os oes a | pj i it — oo

o 4 8 2

16 20 24 28 32 36 40 44 48 52 56 60 64 68 72 76 80 84
TIME (minutes)

TaTeltelseloelalsaplclalslclalalelaltsalc!

Schedule of performance tasks sequence for the 23.8° C (75° F) and the 71.1°C
(160° F) exposures.

TaTelectTelaltelclateatctealealepltaleltc!

A= Tracking,

Schedule of performance tasks sequence for the 60.0° (140° F) exposure.

B= Tracking, monitoring,
arithmetic.

C = Monitoring,

monitoring. arithmetic.

Figure 2—Protocol of experiment. Proposed and actual air temperature profiles (23.8°, 60.0°, 711° C.) are indicated
as well as black globe temperature, Task combinations are indicated by A, B, C. Each task combination was
performed for five minutes. Baseline data were collected during pre-exposure period.

6


4.9° C. (108° F.) and 450° C, (113° F.) re-
spectively. Testing continued until the subject
showed signs of approaching his physiological
tolerance limit as indicated by an unacceptable
rise in rectal temperature. The mean times to
tolerance were 61 minutes, 29 minutes, and 21
minutes respectively. Blockley and Lyman state
that error began increasing abruptly approxi-
mately 8 to 12 minutes before the runs were
terminated. Error was measured as a composite
involving accuracy of holding altitude, heading
and airspeed. Pepler* used a one dimensional
tracking task of pointer alignment during two
30-minute exposures to a temperature condition
of 46.6° C. (115.9° F.) db/40.6° C. (105° F.)
wh, a condition said by Pepler to yield an effec-
tive temperature equivalent to the 93.3° C. condi-
tion used by Blockley and Lyman. A significant
increase in error was reported to appear at 5 to
6 minutes after the beginning of the period and
a marked rise in error occurred at approximately
20 minutes.

Based on the data summarized by Wing and
those just outlined, the effective temperature to
which a man can be exposed for a period of 30
minutes without some impairment in his perform-
ance may be as low as 29.4° C. (85° F.) (Teich-
ner) or as high as 37.8° C. (100° F.) (Blockley
and Lyman).

In any event, the studies cited here, as well as
those reviewed by Wing, suffer from two major
deficiencies with respect to the problem of setting
a maximum temperature figure for commercial
aircraft operations. First, the subjects used in
the studies were young, healthy, and (in at least
some cases) acclimatized to high temperatures.
Second, the tasks (with the exception of the
Blockley and Lyman study) in no way approxi-
mated the range of activities required of a crew-
member in operating an aircraft. In particular,
the requirement for time-sharing a variety of
tasks was not included in these studies, a fact
which substantially decreases the applicability of
the resultant data. Although the procedure used
by Blockley and Lyman involved a complex task
(flying a Link trainer), the scoring method was
somewhat lacking in precision.

Clearly, additional research is required if the
allowable temperature/time profile for commer-
cial aircraft operations is to be accurately speci-
fied. The purpose of the study reported here is
to make a contribution toward filling the gaps in

our knowledge of this problem area by (1) exam-
ining two additional temperature conditions in
the range suggested by the literature to be criti-
cal; (2) using a sample of subjects who are both
trained as pilots and representative of the age
range of commercial airline pilots; and (3) re-
quiring performance of a complex task designed
to assess functions involved in operating an air-
craft and requiring the exercise of those functions
in a time-shared manner.

Il. Methodology.

Subjects. The subjects used in all phases of the
study were FAA Aeronautical Center male em-
ployees who volunteered to participate in a high
temperature study in response to an item in the
Center information bulletin. No attempt was
made to select the subjects according to number
of hours flown, type of rating, or physical char-
acteristics, except that all subjects held private
or commercial pilot’s licenses and all held current
Class II or III Medical Certificates. The total
number of subjects was 30; their ages ranged
from 30-51.

Physiological Measures. The physiological
parameters monitored (in each case at 2-minute
intervals) were : rectal temperature via thermistor
probe and YSI Telethermometer; heart rate by
chest electrodes and Grass Model 5C recorder;
and skin temperature by a Honeywell Elektronic
16 recorder with thermocouples on forehead, tip
of index finger, and back of hand.

The complex performance device, shown in
Figure 1, was designed to measure performance
of five tasks. These are: two dimensional com-
pensatory tracking, mental arithmetic, meter
monitoring, discrimination reaction time, and
simple reaction time.

The tracking task is presented to the subject
on a CRT display 434 inches in diameter (desig-
nated as A in Fig. 1). Intersecting horizontal
and vertical lines etched into a clear plastic over-
lay define the two principal axes. The controlled
element is a dot of light approximately 1 mm.
in diameter. Control is exercised by manipula-
tion of a hand control stick (designated as A, in
Fig. 1). The stick gain is such that movement
of the stick approximately 25° from vertical is
sufficient to move the dot off the face of the dis-
play. A 15° movement of the stick is sufficient
to compensate for the maximum displacement
that the forcing function can produce.


performance quite possibly would also have ap-
peared immediately had condition B or C been
presented first. Putting both of these possibili-
ties together suggests that the effects of tempera-
ture are dependent upon both the workload and
the nature of the task. This inference receives
support from the fact that none of the simple
tasks (reaction time and meter monitoring)
showed an effect of temperature.

The absence of an effect of temperature on
tracking in the vertical dimension is interpreted
to be the result of the fact that cross-coupling
between tasks is much less likely to occur in the
vertical than in the horizontal dimension. Spe-
cifically, when the subject is required to respond
on one of the other tasks while tracking, he must
reach with his left hand. In the case of the dis-
crimination reaction time and the arithmetic
tasks, the response involves rapid movement of
his hand across the panel to points in front of
the tracking control stick. Especially in making
responses to these two tasks, there is a tendency
for the subject to shift his body laterally. Since
the subject can anchor his arm firmly on the arm
rest and, thus, virtually preclude movement of
his arm in the fore/aft dimension, such lateral
movements of his body are much less likely to
result in inadvertent inputs to the vertical dimen-
sion than to the horizontal. This implies that a
major effect of temperature on manual perform-
ance is a decrease in the ability of the subject to
decouple movements of the two arms.

The return of performance to the pre-exposure
baseline levels during the post-exposure period
is interpreted to mean two things. First, it sug-
gests that the obtained effects were real effects of
temperature and not a result of fatigue. And
second, it suggests that the effects of temperature
are acute and that recovery of performance is
fairly rapid. The main contribution of the Phase
III experiment is that it lends support to the
first of these interpretations. Namely, the sub-
jects tested for the same time period at normal
temperatures (23.8° C.) showed neither increases
nor decreases in their performance.

Figure 5 shows Wing’s chart, slightly modi-
fied, with the results of the present study in-
cluded. The curve labelled “Wing” was con-
structed by Wing based on his studies** and those
of several other investigators. It shows the low-
est values of temperature and exposure time at
which statistically significant decrements were

18

observed in the performance of mental tasks.
Since the present study involved a task complex
requiring the time-shared exercise of several
psychological functions, it would be expected that
our results would fall below and to the left of
Wing’s curve as they do. Several additional
factors may have contributed to the position of
our hypothesized curve. For example, our sub-
jects were older than those used in the typical
study; they were not acclimatized to heat, and
they probably were not in as good physical con-
dition as the subjects in the previous studies. All
of these factors would tend to decrease the time
for which unimpaired performance could be main-
tained.

As with any performance study conducted
under laboratory conditions, there are problems
in extrapolating the results to the real world.
Broadly speaking, these problems lie in two cate-
gories; one is concerned with the applicability
of the performance functions measured to the
job the man carries out in the operational situa-
tion; the other is concerned with the procedures
attendant to the testing.

With respect to the first category of problem
we would argue that the task complex provided
an adequate (though admittedly limited) sam-
pling of the things the man does in the course of
performing his real world work assignments, and
we will not repeat arguments presented earlier
in the paper in support of our position. In any
event, this problem category is most critical when
decrements are not observed.

The problems arising from the procedures used
are much more involved, are, ultimately, much
more a matter of experimenter judgment, and,
hence, are much more subject to disagreements
in interpretation. Recognizing this caveat, sev-
eral factors combine to suggest that the times for
which performance was found to be unimpaired
in this study should be regarded as liberal rather
than conservative with respect to generalizing to
an aircraft emergency. The main reason is that
the sequence of events which were to occur in this
experiment was clearly understood by the sub-
jects. And, perhaps more important, they knew
(if they thought about it) that the very nature
of conducting research of this sort dictates that
a subject not be placed in a situation in which
there is serious reason to believe that his safety
or health are being compromised. They also knew
that they could leave the chamber any time they



Tau 1.—Tracking Performance

Work-} 60.0° C. 711° C. 23.8° C.
Measure load
B 1 2 B 1 2 B 1 2

Horizontal Absolute A 43.26 | 44.78 | 47.38 43.34 | 46.64 | 45.23 46.76 | 49.04 47,44
Error B 85.01 | 84.31 | 85.66 71,23 | 78.38% 79.01% 66 | 82.57 80. 49
Horizontal Error A 9.9) 9.94] 12.11 8.79 | 10. 9.48 10.20 | 12.25 8.64
Squared B 35.37 | 35.73 | 38.67 24.51 | 28.88*) 29.68*]/ 38.38 | 32.19 31,23
Vertical Absolute Error A 64.96 | 66.60 | 65.06 69.81 . 66.07 84.34 | 79.34 79.02
B 85.42 | 82,16 | 86.33 77,47 | 79.96 2. 96.53 | 98.44 94,81

Vertical Error Squared A 14.81 15.19 | 15.43 15.19 | 15.64 | 15.38 . 19.11 19. 68
B 30,31 27.32 | 32.06 22.52 | 25.32] 27.64 33.79 | 37. 31,19

*P <.05

TasLe 2.—Arithmetic Performance

‘cores are in volts with a different arbitrary scale for each measure, B—baseline; 1—first period at temper-
cond period at temperature.

Work-| 60.0° C. 711° C. 23.8° C.
load
B 1 2 B 1 2 B 1 2
Solution Time (Seconds) | B 5.20) 4.76| 4.61|) 4.18] 4.12] 3.72]) 5.08] 4.64] 4.00
c 474] 4.69) 4:37] 3.97] 4:02] 3.95]] 4.73| 4.42| 4.14
Percent correct B | 88.05| 87.47] 86.96 || 95.76 | 90.30%, 89.70 || 87.16 | 93.24] 89.93
Cc | 89.40 | 86.90] 89.56 |} 93.94 | 87.88%] 87.88%) 86.30 | 85.91 | 89.26
*P<.05 9 *P<.01 ¥
Note: B—baseline; 1—first period at temperature; 2=second period at temperature.
‘Tanue 3.—Monitoring Performance Mean Response Times (Seconds)
Work- 60.0° C. TLIC. 23.8° C.
load
B 1 2 B 1 2 B 1 2
Red Light z 68 v6 TOI 762 v61 750 764 739 768
Reaction Time B {74 270 67 175 163 270 {71 179 173
c 15 270 166 165 161 13 {71 268 174
Red Light A 147 146 48 144 149 147 146 $52 349
Movement Time B 152 139 136 154 : 156 +60 169 137
c 156 166 $60 158 153 £60 167
Green Light A 165 161 159 $61 156 14 156 159
Reaction Time B £80 72 177 136 158 158 v7 169
c 168 78 270 172 159 263 169 162
Green Light A 144 152 143 143 143 138 248 145
Movement Time B 178 159 164 150 152 152 153 151
c 260 153 54 161 170 145 156 0)
Amber Light A 1:09 99 | 1.03 |) 1.12 193] 1:06 1110 1.07
Reaction Time B 119 97 | 1142) 1122) 1.08 197 121 1,05
c 1132} iz] 119]) 155] 112) 1.02 Vit 1,13
Meter Detection A 2.70 2.59 2.92 2.68 2.78 2.61 2.49 2.59
Time B 3.28| 3.29| 3.41 || 2.89) 2 3115 297 3.00
c 3.17} 3.22] 2.93]/ 3.:01| 298! 2.91 276 3.05

Note: B=baseline; 1=first period at temperature; 2—second period at temperature.

15



COMPLEX PERFORMANCE DURING EXPOSURE TO HIGH
TEMPERATURES

I. Introduction.

A number of advances achieved during the past
two decades in the field of aviation and space
flight have led to an increased requirement for
more precise information concerning the effects
of elevated temperatures on man’s performance
capabilities. For the most part, the questions
raised by these advances stem directly from the
increased speeds of which aircraft and space ve-
hicles are capable. Although normal operation
of aircraft does not entail exposing the man to
very great heat loads, in emergency situations
cabin temperatures may rise to extreme values if
the cooling system should fail and adequate
back-up cooling capability is not provided. Tech-
niques that are adequate to provide temporary
or even long-term protection to individual crew-
members (e.g., a ventilated suit) are not feasible
for passenger-carrying aircraft and certainly not
applicable to commercial operations.

The potential temperature problems become
extreme in the supersonic transport in which the
safety and (at least to some extent) the comfort
of 200 or more people must be protected. The
U.S. SST has been designed to fly in the regime
of 1,875 m.p.h. and 70,000 feet.. Under these
conditions, the surfaces of the plane can achieve
steady-state temperatures of 260° C. (500° F.)*.
Clearly, this implies a significant weight penalty
(for insulation and cooling) if the interior of the
aircraft is to be maintained at temperature levels
that will neither impair the performance of the
crew nor endanger passengers whose states of
health have in no way been certified. The critical
question is, how much of this weight penalty
must be duplicated to cover the possibility of
failure of the primary cooling system? The an-
swer to this question must be applicable, not only
to aircrew of rather diverse composition with
respect to age and general physical condition, but
also to the general population including the very
old, the very young, and the infirm. However, to

keep the magnitude of the problem within man-
ageable proportions for research purposes, we
will be concerned here only with aircrew per-
formance.

A number of previous investigations have
yielded data that are relevant to the problem as
herein defined. Wing’ has reviewed those studies
in which the primary or exclusive emphasis was
on mental performance; the conclusions of his
review are shown graphically in Figure 5, and
they will not be discussed further at this point.
A similar review is not available for motor per-
formance, and, therefore, we shall cover that topic
briefly.

Forlando, Barmach, and Coakley+ have re-
ported a study in which simple reaction time
showed no decrement after 6 hours under a tem-
perature condition of 47,.2° C. (117.0° F.) db/
29.4° C. (85.0° F.) wb (dry bulb/wet bulb).
Similarly, Loeb and Jeantheau® found no signifi-
cant loss in performance on a task of monitoring
20 dials over a 3-hour period under a heat stress
that was allowed to vary between 43.3° C. (110.0°
F.) and 51.6° C. (124.9° F.) (wet bulb not speci-
fied). Crocker and Waitz* found reaction time
to be slower during a 15-minute exposure to
149° C. (300° F.) and “low humidity.” How-
ever, they indicated that they felt the decrement
to be too small to be of any practical importance,

Tracking tasks have generally proven to be
somewhat more sensitive to the effects of high
temperatures. Teichner® measured performance
on a pursuit rotor during a 30-minute trial at
effective temperatures of 21.1° C. (70° F.), 29.4°
C. (85.0° F.) and 37.8° C. (100.0° F.). He found
a significant drop in time-on-target at the two
higher temperatures. Blockley and Lyman*
measured the performance of subjects in flying a
repetitive, 4-minute pattern in a Link trainer at
three temperatures: 71.1° C. (160° F.), 93.3° C.
(200° F.) and 112.9° ©, (235° F.) ; the estimated
effective temperatures were 37.8° C. (100° F.),



ACKNOWLEDGMENTS

The authors thank the subjects who experienced some discomfort during
exposure to the hot environment.

Qualified requesters may obtain Aviation Medical Reports from Defense Documentation
Center. ‘The general public may purchase from Clearinghouse for Federal Scientific
and Technical Information, U.S. Dept. of Commerce, Springfield, Va. 22151.


period was statistically equivalent to that during
the pre-experimental baseline period.

Phase III—The performance of the subjects in
the Phase III experiment (entire period at 23.8°
C.) was generally inferior to that of the subjects
in Phases I and II. This is seen in Tables 1, 2,
and 3, columns 7, 8, and 9. Of particular import-
ance is the fact that the performance of the Phase
III subjects was poorer than that of the Phase I
and II subjects during the baseline, pre-exposure
period, though not significantly so. There were
no effects of time at work on any of the measures
for these subjects; there were neither improve-
ments nor decrements.

Iv.

The conditions of our study were chosen to be
within the physiological tolerance limits of the
subject, and the biomedical data suggest that such
was the case. However, there are important
reservations to be considered if any extension of
these exposure times is to be contemplated. For
example, the recommended physiological limit
shown in Figure 5 (curve labelled “Lovelace and
Gagge”) indicates that at an effective temperature
of 38° C. (100° F.) to 39° C. (102° F.), the toler-
ance time is approximately 40 minutes and the
marginal physiological limit is only 90 minutes
(curve labelled “Taylor”). At our higher tem-
perature (an effective temperature of 384° C.

Discussion.

°C oF
48.97120

46.1 +115

Taylor
43.4 +110

40.6 7105

37.8 +100

35.0 +95

N

THIS STUDY

EFFECTIVE TEMPERATURE

32.2 790

29.5 +85

1 4 1 1

Unimpaired Complex Performance

Marginal Physiological Limit
(Imminent Collapse )

T T T T T

Lovelace and Gagge
Recommended Physiological Limit

‘a

Unimpaired Mental Performance
it 1 1 1 1

30 60

90

120 150 180 210 240

EXPOSURE TIME (minutes)

Figure 5—Physiological and performance limits in hot environments (modified from Wing”).

11



felt themselves to be in any danger. Thus, it
seems clear that an important factor that must
be weighed (and that factor is virtually impos-
sible to produce in the laboratory) is the implied
threat of the emergency situation to the survival
of the crewman and his passengers. The extent
to which this additional source of stress would
contribute to or compound the problem cannot
be specified, but its potential for interfering with
performance cannot be denied.

Counterpoised against this problem is the fact
that the human operator has many times demon-
strated himself to be capable of tremendous feats
when the successful execution of his duties and
his life and the lives of others are threatened.
There is virtually no way of stating which of
these two factors is more important, but the case
for cautious extrapolation is clearly established.

v.

The research reported here involved a three-
phase experiment on the effects of elevated tem-
peratures on complex performance. In Phase I,
20 subjects were tested during a 30-minute expo-
sure to a temperature of 60° C. (140° F.) anda
vapor pressure of 13.6 mm. Hg; this corresponds
to an Effective Temperature of 35° C. In Phase
II, 11 of the 20 subjects used in Phase I were
exposed to a temperature of 71.1° C. (160° F.)
and vapor pressure of 19.9 mm. Hg (an Effective
Temperature of 384° C.). Phase III which
served as a control condition for possible fatigue
effects, involved 10 subjects tested under normal
temperature conditions; the temperature was
23.8° C. (75° F.) and the vapor pressure was
2.6 mm. Hg (an Effective Temperature of 18.9°
C.).

The performance tasks were combined in three
different ways to provide three different perform-
ance conditions varying in terms of the level and
nature of the workload. Level A involved two
dimensional, compensatory tracking, discrimina-
tion reaction time, simple reaction time, and meter
monitoring. Level B consisted of adding a
mental arithmetic task to the tasks of Level A.
And Level C was the same as Level B but with-
out the tracking task. The training of the sub-
jects for the Phases I and III experiments
involved 90 minutes of practice the afternoon
before the test run—30 minutes on each of the
three levels of workload. The subjects who
served in Phase II were given 45 minutes of re-

Summary and Conclusions.

14

fresher training the afternoon before the Phase
TI test.

Data samples were taken every 2 minutes
throughout the three phases on rectal tempera-
ture, heart rate, and skin temperature (recorded
at the forehead, tip of the index finger, and the
back of the hand). The subjects were equipped
with a sweatband to preclude the possibility of
easily preventable, direct visual effects of sweat.

The physiological effects of the temperature
exposures were those typically found in this type
of experiment.

Performance effects were observed. only under
the 71.1° C. condition; arithmetic scores and
tracking error in the horizontal dimension both
showed decrements. The tracking decrements oc-
curred only under workload condition B; the
arithmetic decrements occurred under both work-
load levels B and C.

The following conclusions are drawn:

1. Unimpaired performance can be maintained
for a period of 5 minutes at a temperature of
711° C. (160° F.) and a vapor pressure of 19.9
mm. Hg. However, in a strict interpretation of
the results, it must be specified that this conclu-
sion holds only for light to moderate workloads
involving psychomotor performance.

2, Decrements in psychomotor performance
(tracking) and mental performance (mental
arithmetic) when these functions are performed
in a time-shared manner, will occur fairly quickly
after exposure to 71.1° C. and a vapor pressure
of 19.9 mm. Hg. Because of the specific experi-
mental design used, this experiment does not
permit ruling out the possibility that decrements
with these task combinations will occur imme-
diately upon reaching temperature.

3. Performance is unimpaired during a 30-
minute exposure to a temperature of 60.0° C.
(140° F.) and a vapor pressure of 13.6 mm. Hg.
However, decrements were observed in tracking
performance with the first subgroup of 10 sub-
jects tested at this temperature though not with
the second subgroup nor were there significant
decrements when the data of the two groups were
combined.

4. From the methodological point of view as
regards research on environmental stress, the re-
sults of this study support the use of multiple
tasks requiring the time-shared performance of
different psychological functions and permitting
the presentation of different levels of workload.