performed, followed by an ascent at 3,000 ft/min
to the predecompression altitude.

The decompression runs consisted of 10 cycles
of performance on the coordinator, cycle 16
through 25 (cycles 1 through 15 being the train-
ing session). Decompression occurred immedi-
ately following the presentation of the stimulus
lights for the 10th trial of the 22nd cycle. The
subject was unaware as to when in the run
the decompression would occur, nor was he aware
of the total number of cycles in the run. Until
the subject completed cycle 22, the chamber re-
mained at the decompression altiude and then de-
scended to ground level at 3,000 ft/min.

Decompression runs were filmed at 24 frames/
sec with a camera driven by a synchronous motor.
The camera view included the coordinator dis-
play panel, the altitude-warning light, a large
sweep-hand timer, an altimeter, and a clear view
of the subject’s head, shoulders, and hands. By
means of frame counting, a chronology accurate
to %4 second was determined for the following
events:

. Onset of decompression.

. Activation of the altitude-warning light.

. Subject’s hands leave controls.

. Subject’s hands return to controls.

. Start of coordinator trial immediately
preceding event #3.

. Completion of coordinator trials follow-
ing event #4.

oP wpe

2

IIL. Subjects.

The subjects for the study were 16 active male
aircrewmen, 9 of whom were pilots, the remain-
ing 7 being either navigators or flight engineers.
Their mean age was 34.7 years, the range being
from 26 to 47 years of age. The average flight
time for the group was 3,633 hours, and the range
was from 500 to 9,000 hours. All of the 16 sub-
jects had received physiological training and
were currently so qualified.

The subjects received training on the Scow
coordinator, consisting of 15 cycles of 25 trials
each. The performance times for the training
cycles for each subject and the cycle means are
presented in the Appendix. Figure 2 is a plot of
mean performance time per cycle and is taken to
indicate that by the eighth cycle the preponder-
ance of improvement in performance time had
occurred. These results are interpreted as indi-

45

8
a
&
2 35
=
2 _~
= 30)
w ee
Zz — Nee
a2
g
icy
2.0)
12345 67 8 9 10 Il 12 13 14 15

TRAINING CYCLE

Ficure 2. Mean time over 15 training cycles on Scow
coordinator, 16 aircrewmen.

cating that the coordinator task was sufficiently
learned in the training session to qualify it as
an index of the performance effects of decompres-
sion. In instances where the training session and
the decompression were run on the same day, a
minimum of 1 hour separated the two.

IV. Results.

Mean interruption time (N = 18)*, which is
the time elapsed from warning light through
donning and the return of both hands to the con-
trol, was found to be 11.40 seconds. The mean
time (N = 14)* that the operator’s hands were
off the controls was 10.44 seconds. The differ-
ence between these two values, 0.96 second, repre-
sents reaction time to the red warning light. It
is well to note that our attention is not directed
at, mask donning itself, for, although donning
is what necessitates the interruption, it is felt
that the crucial time to be measured is the time
taken away from the primary task, These values
correspond to the findings of Bennett* in his
experimental study of 42 in-flight aircraft decom-
pressions. Bennett presents grouped data on the
distribution of time to recognize depressurization
and to complete mask donning grouped by 5-
second intervals. A mean time for his data was
calculated by the present authors, by using the
interval midpoint, and was found to be 11.9 sec-
onds for the 42 pilots. Although in most in-
stances the mask was donned within 4 to 6 sec-

*Due to clouding of chamber and noise of decompression,

some data were lost, and one subject anticipated the warning
light and started donning early.



REFERENCES

1, Barron, ©. I,, and Coox, T. J.: Effects of variable de-
compressions to 45,000 feet. Aerospace Med. 36:
425-430, 1965.

2, Hanxs, T. G.: Human factors related to jet aircraft,
in Sexzs, 8. B., and Berry, C. A., eds., Human Factors
~ in Jet and Space Travel. Ronald Press, N.Y., 1961.

8, Barron, ©. 1, Corus, D. L, and Coox, T. J.: Ob-
Servations on simulated 12 second decompressions to
82,000 feet. J. Avia. Med., 29: 564-574, 1958.

4, Bryan, A. C.: Rapid decompression in transport air-
craft. RCAP Rept. IAM 58/8, Instit. Aviat. Med.,
RCAF, Toronto, Canada, 1958.

5, Berry, C. A.: Human qualifications for and reactions
to jet flight, in Seurs, 8. B., and Berry, C. A., eds.,
Human Factors in Jet and Space Travel. Ronald
Press, N.Y., 1961.

6. Bancrort, R. W., and Smmons, J. G.: Rapid decom-
pression up to 60,000 feet wearing the standard
oxygen mask. Aerospace Med., 35: 208-211, 1964.

7. Fryer, D. I.: Consequences of loss of cabin pressure,
in collected papers on Aviation Medicine, AGARD,
NATO, Butterworth, London, 1955.

8. Bewnert, G.: Reactions and performance of pilots
following decompression, Aerospace Med., 32: 134-136,
1960.


DECOMPRESSION

|.

|
2.
eee —~ aT —~

TERMINAL
DECOMPRESSION
ALTITUDE

41,000 FEET

Nez

35,000 FEET
2.50 N=3

3.50 |

3.00 30,000 FEET

~..
Neo

2.50 |

3.50
3.00
2,50

27,000 FEET

eaenaaN

Nes —+
3.50 |

3,00
2.50

25,000 FEET

prwi tis

18 19 20 21 22 23 24 25

fo
CYCLE 16 I7

Fieure 5. Cycle times before and after decompression
for the five decompression altitudes.

formance to yield a percent of baseline figures—
the higher the value, the slower the postdecom-
pression performance. These figures are shown
in Figure 6, with postdecompression altitude
plotted against percent of performance decre-
ment or amount of slowing. The number of |

8

8

o

&

&

8

3
&

Altitude in thousonds

POST DECOMPRESSION PERFORMANCE, "% OF BASELINE
a

SY 4 35 30 2728

5 80) 35 «AD «4550 BS Pounds er sq.in
DECOMPRESSION ALTITUDE IN THOUSANDS OF FEET, SCALED BY PSL

Fiaure 6. Performance decrement in percent of base-
line time for 25 trials following decompression for
the five decompression altitudes.

cases at each altitude does not permit establish-
ing a relationship; however, the data indicate a
trend toward greater performance decrement as
decompression altitude rises.

A further analysis was performed to ascertain
more precisely the temporal extent of the per-
formance decrement. This analysis of the per-
formance data utilized the methods of quality
control, with the human operator representing
a process, which is regarded as and is subject to
perturbations causing output to vary. A cer-
tain range of variations is regarded as acceptable
or within normal limits, but should the measure
fall outside these the process is regarded as “out
of control.” In this instance of timed perform-
ance measures, only one side of the control limits
may be regarded as crictical, the other or lower
limit representing exceptionally rapid perform-
ance. Quality-control charts for each subject
are presented in Figure 7, with the quality-
control limits based on the 50 trials immediately
prior to decompression. The operator was re-
garded as being “in control” if his mean of 5
successive trials fell within 8 standard deviations
of his predecompression mean of 50 trials, which
represented approximately the 0.01 level of confi-
dence. The overall mean trial-completion time
was 0.11 minute or about 6 seconds; therefore,
each set of five trials represents behavior within
approximately a 30-second interval.

27,000 FT.

° 41,000 FT. 30,000 FT.

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Fieure 7. Quality-control limit charts, limits equal 3
standard deviations of baseline mean of 50 trials.



onds, from a time-and-motion point of view,
this merely represents one element in a chain of
events. The start of the chain is the warning
stimulus, and its completion is the return of the
operator’s hands to the controls. As indicated
above, the mean interruption time (11.40 sec-
onds) is approximately double the time for mask
donning itself. These data are presented sche-
matically in Figure 3.

WARNING HANDS OFF SOLUTION
LIGHT CONTROLS OF PROBLEM
96 10.44 >
' 1 !
t
t 11.40 H

Vv
21.92

IMMEDIATE LOSS 21.92 — NORMAL AVE (6.64) = 15.28

Ficure 3. Operator-response time in seconds to
decompression.

For a two-operator crew, individual operator-
interruption times will be less than crew-inter-
ruption times in instances where a coordinated
crew response following depressurization is nec-
essary. In such a case, the crew’s return to
the task will be a function of the slowest re-
sponding operator, as is illustrated in Figure 4.
Thus, for all of the possible unique pairings of
operator interruption times, the slowest time is
treated as the time for the pair. The mean in-
terruption time for such pairings for the data
was found to be 14.22 seconds.

The above analysis does not take into account
the immediate postdecompression effects upon the

INDIVIDUAL
INTERRUPTION
PILOT TIME A Bc OD
A 20 - 20 20 20/3x20+ 60
B 15 x - 15 15 ]2x15= 30
c 10 x x = 1] 1x 10= 10
D 5 x x x - 10x0= 0
4[50 6 [100
MEAN

INDIVIDUAL TIME 12.5 CREW TIME 16.7

Figure 4, Example illustrating derivation of two-operator
team-response times.

operator’s proficiency but merely indicates the
magnitude of the gap in performance. There is
a distinct slowing down in operator performance
following decompression. In this group of sub-
jects, the average time to complete a trial prob-
lem under normal conditions was 6.64 seconds,
while the average time on the trial immediately
following decompression was 10.52 seconds (this
trial time is calculated from the moment the
operator’s hands return to the controls), or about
58% slower. The difference between normal and
postdecompression response times (10.52 and 6.64
seconds), 3.88 seconds, when added to the mean
interruption time of 11.40 seconds, yields an
estimate of 15.28 seconds for the total time loss
during the period immediately following decom-
pression, as depicted in Figure 3.

The data represented in Figure 3 are average
times, and it is felt that more emphasis should be
placed on the distribution of interruption times
or total time loss, Based on the present sample,
Table 1 presents the cumulation proportion of
‘Taste 1, Distribution of operator total time loss following

decompressions.
Total time loss

Percent operators (seconds)
10 9.9
25, 13.0
50 16.6
x) 20.1
90 23,8
95 25.1
99 28.6

operators for various lengths of total time loss.
These data indicate, for example, that an allow-
ance of approximately 25 seconds loss from the
operator’s primary task will encompass 95% of
the population of operators. This figure of 25
seconds represents the time loss due to donning
and the slowing of performance immediately fol-
lowing decompression.

The performance-decrement effects of the de-
compression are not limited to the first 20 to 30
seconds but are found to persist over some 8 to
4 minutes. This time represents the approxi-
mate period required to complete the decom-
pression block of trials, block 22, as shown in
Figure 5. For some subjects, these effects per-
sisted into block 23. The performance decre-
ment observed on the postdecompression series of
25 trials for the five decompression altitudes of
25,000, 27,000, 30,000, 85,000, and 41,000 feet was
calculated by dividing predecompression per-


APPENDIX

Performance Time per Subject per Training Cycle.
Scow Coordinator

Cycle Number

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* Recording system malfunction.



AM 66-10

EFFECTS OF DECOMPRESSION ON OPERATOR
PERFORMANCE

William F. O’Connor, Ph. D.
George E. Pendergrass

Approved by Released by
ae [USagek 0
J. Rosert Diiiz, M.D. P. V. Srecet, M.D.
Cuter, Civ, Arromepican InstiTuTE Feperat Ar Surcron
April 1966

FEDERAL AVIATION AGENCY

Office of Aviation Medicine





Taste 2. Incidence of performance deviations following decompression outside control limits

during 10 sets of five trials each, 16 aircrewmen operators where + = slow deviation and — = fast deviation
Set No.
Altitude Subject No.
1 2 3 4 5 6 7 8 9 10
41,000 9 + + - +
1 + + -
35,000 18 + +
15 + + -
uw + +]t]4]44]- +
30,000 13 + _ - - -
10 + - - -
7 + + + -|-
6 + - -
2 a +
27,000 4 + + +
8 + + +] +
7 + - -
25, 000 14 + - + -
5 tlt] - f+] 4 -|[-
3 +] + tft] -
Totals + 15 6 4 6 3 5 2 5 4 0
- 0 0 3 3 0 1 3 4 3 7

Table 2 presents the data for all subjects, indi-
cating when, on a basis of indivdualized norm or
process data, their postdecompression perform-
ance was outside the three standard deviations of
the mean limits. For the first set of five trials,
15 of 16 are abnormally slow, and for the first
five sets of five trials, 81 of the 37 are outside
the limits and represent slower times. On the
other hand, the sets 6 through 10 split closely,
16 slow and 18 fast. Testing this difference
between the first five sets and second five sets
yields a x? of 12.06 (1.d.f, P = 0.001). Thus, it
would appear that operator performance is sig-
nificantly slowed through the first 25 trials (five
sets) following decompression, or for approxi-
mately 2-14 minutes. There are insufficient data
here to draw conclusions concerning differences
that may be associated with the various terminal
decompression altitudes.

IV. Discussion and Conclusions.

The various analyses indicate impairment of
the operator’s rate of performance for 2 to 4
minutes following rapid decompression with some
suggestion that the severity of effects increases

with increase in decompression altitude. The
operator’s total time lost from his primary task,
at the point of decompression where donning is
required, has a mean value of some 16 seconds,
while the 95th percentile falls at about 25 sec-
onds.

Application of these results to the environment
of the commercial air carrier involves a number
of extrapolations. For one, the task involved is
not piloting, but rather a continuous self-paced
serial-coordination problem. This possesses the
advantage of permitting a degree of quantifica-
tion of performance not feasible with an\actual
aircraft or aircraft simulator. On the other hand,
the subjects employed were all current with re-
spect to physiological training, whereas no re-
quirement exists for such training for air-carrier
pilots, though many have had previous exposure
as military pilots. Hence, it is felt that this
study presents evidence that the effects on per-
formance are much more extended than merely
the 5 to 6 seconds consumed by mask donning.

Further work suggested by this study includes
obtaining control data on performance follow-
ing decompression with mask on throughout.


Ficure 1. Scow complex coordinator.

the right column containing the response lights.
The latter are illuminated singly by movement of
the appropriate control. Successful completion
of a trial occurs when the subject has concur-
rently positioned his controls to effect a match
between stimulus and response lights for all
four quadrants. This concurrent match must be
held for approximately 0.5 second before the
next set of stimuli are presented by a revolving
programming drum. Stimuli for a given quad-
rant were presented in a random order, except
for the restriction that the same stimulus light
could not appear two trials in a row. The pro-
gramming drum presented 25 sets of four stimuli
patterns (trials), constituting a cycle. At the
base of the display panel is an interval timer that
can be preset any time up to 15 seconds. It resets

when each problem is successfully completed. If -

the subject does not complete the problem in the
preset time, there are two red lights on the co-
ordinator forward of the hand controls that are
lighted and remain on until the subject success-
fully completes the problem. The appearance of

the red sweep hand at the vertical and the sub-
sequent appearance of the red “overtime” lights
provide the subject with feedback on his per-
formance. During training, the latency of the
red lights was progressively shortened as the
subject improved, the settings being adjusted for
a red-light frequency of occurrence of approxi-
mately one-third.

An Esterline Angus event recorder recorded
response time for a correct solution to each of the
four stimulus elements, the time to complete a
trial, and the occurrence of the red “overtime”
lights. Performance scores were the time to com-
plete a cycle of 25 trials, which was measured in
minutes and hundredths of minutes of the re-
corder,

The experiments were conducted in an altitude
chamber equipped with an accumulator and a
“butterfly”-type rapid-decompression valve. Each
subject was briefed on the chamber-flight profile
before each experimental run. The level-off alti-
tudes following the decompression were 25,000,
27,000, 80,000, 35,000, and 41,000 feet. Each sub-
ject was decompressed to one of these altitudes.
The predetermined starting altitude was calcu-
lated using 8.66 psi pressure differential.‘ Decom-
pression times were determined by a combination
of the Haber-Clamman and Fliegner equations.
Times varied from 10 to 47 seconds to simulate
a partial and total pressure loss through a hole
266 sq in. in area; ie. the approximate size of
the current jet air-carrier window.

Each subject was fitted with a quick-donning
mask of a type (Puritan Sweep-On) currently
used aboard civil jet passenger aircraft. The sub-
ject was briefed and practiced mask donning until
he and the experimenter were satisfied with his
donning proficiency. The subject was instructed
to start donning immediately after he detected
the appearance of a red-stimulus signal light in
the center of the coordinator display panel. This
warning light was triggered by a mercuric ba-
rometer as soon as the chamber’s simulated alti-
tude reached 14,000 feet following decompression,
comparable to the cabin-pressure warning-light
system found in civil air carriers. Following
the donning of his mask, the subject was in-
structed to resume the performance task as
quickly as possible. A qualified altitude-chamber
specialist accompanied the subject. At the out-
set of the decompression, an ear-sinus check was


EFFECTS OF DECOMPRESSION ON OPERATOR PERFORMANCE*

I, Introduction.

Rapid decompression represents, even to the
most experienced pilot, a highly demanding
emergency situation that must be dealt with
quickly and appropriately. With commercial
passenger aircraft there is the additional problem
of effecting a descent rapidly enough to avoid
possible harm to the passengers. Evidence exists
that even with instructions and demonstrations
not all passengers will successfully don their
masks It has been estimated that, following a
decompression at the higher operational altitudes,
a descent to 18,000 feet should be completely ac-
complished within 4 minutes to avoid permanent
neurological injury to those who may be unpro-
tected.?

Experienced and physiologically trained pilots
have been observed to manifest greater variabil-
ity and a degradation in the quality of their
performance following decompression.» ** Tak-
ing into account these and other considerations,
it has been recommended by Berry® and Hanks*
that in jigh-altitude passenger-aircraft opera-
tions above 25,000 feet at least one pilot be on
oxygen at all times. (Current FAA regulations
call for one pilot to be on oxygen when at or
above 41,000 feet.) In this manner, the immedi-
ate effects of the transition to oxygen and the
time lost in mask donning would be avoided.
Recent work ° reports no significant psychomotor-
performance degradation following rapid decom-
pression to 60,000 feet while wearing a standard
oxygen mask.

The present study was performed to provide
more quantitative estimate of degradation of
pilot performance following decompression and
the extent to which a decompression with mask
donning interrupts the task of piloting.

Mask-donning time is not equal to the total
pilot-functioning time loss following decompres-

* Opinions and conclusions drawn are those of the authors
and are not to be construed as necessarily reflecting the poli-

cies or practices of the Office of Aviation Medicine or the
Federal Aviation Agency.

sion, and it, of course, does not reflect degrada-
tion of performance attributable to decompres-
sion. Pilot-functioning time loss is time that
is taken away from the piloting task by mask-
donning. This total time loss can be broken
down into reaction time to the donning stimulus,
actual time to don, and the time consumed re-
orienting to the interrupted task. Consideration
of the total time loss becomes critical for flight
safety, since rapid aircraft decompressions almost,
always call for immediate action on the part of
the crew.? The distinction being made here is
between the time needed for self-protection and
the time consumed before functioning can resume.

A second consequence of decompression is its
effects on the quality of performance. In addi-
tion to marked shifts in oxygen uptake and
cardiac function, there is also expansion of gases
in the abdomen and lungs.’ All of these factors
appear to contribute toward degradation of post-
decompression task performance.

The present study is aimed at assessing under
mask-donning conditions the task-interruption
time (pilot-functioning time loss) associated with
decompression and extent of performance decre-
ment following decompression.

IL. Procedure.

The objectives of the study called for a con-
tinuous task that would permit quantification
of the subject’s performance output. A modifica-
tion of the Mashburn coordinator, the Scow com-
plex coordinator shown in Figure 1, was em-
ployed as the performance task. This task re-
quires the subject to match a pattern of four
light stimuli by the concurrent positioning of
four controls (two foot pedals and two hand-
control levers). The four light stimuli are
presented by a display that has four quad-
rants, each of the quadrants representing a
control. Within a given quadrant, there are
two vertical columns of five lights, the left
column containing the stimulus lights and



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