The same protocol for testing was followed as for Phase
Il, except that during the initial testing (masks 3-I, 3-II,
and 3-III) for Phase III, only subjects with high tidal
volumes were studied.

Results and Discussion

Mask 3-11, which had only the punched holes in the valve
flapper, did not prove to be any more efficient than previous
designs. Masks 3-I and 3-III ameliorated the problem of the
rebreather bag collapsing but did not provide an adequate
reduction to the buildup of C02.

One reason that the C02 continued to build up in these
masks could be that the reduced resistance at the valve into
the rebreather bag was not accompanied by a concomitant
reduction in the resistance of the escape valve at the distal
end of the rebreather bag. Thus, there was an inadequate
amount of air moved out to the ambient atmosphere. To reduce
the resistance of the valve at the distal end of the
rebreather bag, the loading spring was removed and one-half
the length cut off before replacing it. This additional
modification was made on both the first and third designs
described above, now designated as mask 3-I-4 and mask 3-III-
4, respectively. They were tested with both high and low
tidal volume subjects.

The results of the tests with these two modified masks
are presented in Table VIII (for mask 3-I-4) and Table IX
(for mask 3-III-4). The results present mixed findings.
With both masks, one low tidal volume subject exhibited
acceptable results at the 5 L/min, BTPS, flow both at rest
and with exercise. However, good results were obtained with
the low tidal volume subjects before any modifications were
made. Most of the unacceptable results were caused by
unsatisfactory pC02 levels. There were no instances of the
rebreather bag collapsing with the mask that had the surface
area of the exhalation valve into the rebreather bag
increased by 27 percent (mask 3-I-4).

CONCLUSIONS

Results to date indicate that the continuous-flow
passenger mask to which a rebreather bag is added still has
the potential for providing protection from smoke and fumes
for the wearer. However, the system must have appropriately
balanced resistance and appropriately sized valve openings.
This critical balance has not yet been achieved for subjects
with a wide range of breathing patterns and with large tidal
volumes.

14


3 min of data collection during the exercise portion of the
The flows required for properly functioning masks

tests.

TABLE IL

Minute Volumes (L/min) of Subjects Under a 50-Watt Workload

Subject No.

ee

ROMY HDAURwWN HE

MEAN

23.31
23.31
23.31
28.63
27.72
27.20
19.14
20.72
23.89
22.45

23.97

Minute 2

Minute

25.47
25.61
26.19
29.92
29.36
26.33
21.30
24.89
24.32
23.60

25.70

4

Minute 6

28.84
26.91
27.20
30.64
29.21
27.20
22.30
21.01
24.46
23.46

26.12

while subjects were at rest are given in TABLE III. These
data confirm those of the first study.

effect on flow requirements.
the STPD flows.at each altitude to BIPS flows.

Altitude had little
This is evidenced by converting

The mean BIPS

flows ranged from 5.29 L/min at ground level to 5.58 L/min at

21,500 £t.
TABLE IIL
Acceptable Flows (L/min,STPD) - No Exercise
Subject Altitude
Number Ground Level 8,000 ft 14,000 £t 21,500 £t
1 4.77 3.12 2.14 1.69
2 4.09 3.12 3.21 1.69
3 4.09 3.12 2.41 1.69
4 4.09 3.12 2.41 1.69
5 4.09 4.16 3.21 2.26
6 4.09 3.12 2.81 1.98
7 4.09 3.12 2.41 1.69
8 4.09 2.60 2.01 1.69
10 4.09 4.16 2.81 1.98
1l 4.09 2.60 2.01 1.69
Mean, STPD 4.12 3.22 2.57 1.81
Mean, BIPS 5.29 5.39 5.56 5.58




LIST OF FIGURES

Figure Page

1. Photograph of subject wearing passenger mask
with rebreather bag added (front view). ..... 4

2. Photograph of subject wearing passenger mask
with rebreather bag added (side view) ...... 5

3. Schematic drawing of passenger mask modified by
the addition of a rebreather bag. . . « «2 sae 6



Results of Tests of Mask 3-1-4

TABLE VIII

Oxygen Flow (L/min, BTPS)

8,000 ft 14,000 ft 21,500 ft
Condition 5 6 7 5 6 7 5 6 7
Without Exercise
Subject 1-L * - - * - - * - -
7-L * - - * - - * - -
2A-L coz cog * eee eee
3A-H McO2 - - MCO2 - - Og - -
8-H * - - * - - * - -
21,500 ft 14,000 ft 8,000 ft
Condition 5 6 7 8 9 5.7 8 9 5 6 7 9
With Exercise
Subject 1-L * - - - - * - - - * ~ - -
7-L cop - = Coz - - = = # - = = C02
2A-L - C02 - = C2 - = = C2 = = = C02
3A-H - - - C02 - - - = C02 - - - C02
8-H * - - - cOp * - - - C02 COg *
Legend: * indicates acceptable results.
- indicates no measurements made.
C02 indicates unacceptable carbon dioxide level.
MCO2 indicates marginally acceptable carbon dioxide level.
-H indicates a high tidal volume subject (greater than 1.5 L).
-L indicates a low tidal volume subject (less than 1.5 L).

15



REFERENCES

1.

Consolozio CF, Johnson RE, Pecora LJ. Physiological
measurements of metabolic functions in man, p.196. New
York: McGraw-Hill, 1963.

deSteiguer D, Saldivar JT. An Analysis of potential
protective breathing devices intended for use by
aircraft passengers. Report No. FAA-AM-83-10.
Washington, DC: Federal Aviation Administration, Office

of Aviation Medicine, 1983.

17



pCO2 Values for Subjects While Using

TABLE VI

Redesigned Masks ~ Without Exercise

8,000 ft 14,000 ft 21,500 ft

Exercise Oxygen Oxygen Oxygen

Tidal Flow Flow Flow
Subj. Volume (BTPS/ pco2 (BTPS/ pco2 (BTPS/ pco2

No. (L) STPD) (mm_Hg) STPD) (mm_Hg) STPD) (mm_Hg)

2 1.03 5.0/3.0 1 5.0/2.3 1 5.0/1.6 1
4 1.22 5.0/3.0 2 5.0/2.3 1 5.0/1.6 1
5 1.32 5.0/3.0 2 5.0/2.3 1 5.0/1.6 1
7 1.38 5.0/3.0 1 5.0/2.3 1 5.0/1.6 1
1 1.43 5.0/3.0 2 5.0/2.3 1 5.0/1.6 1
9 1.59 5.0/3.0 2 5.0/2.3 8 5.0/1.6 6
3 1.80 5.0/3.0 8 5.0/2.3 8 5.0/1.6 3
8 1.88 5.0/3.0 15 5.0/2.3 11 5.0/1.6 2
6 1.98 5.0/3.0 19* 6.0/2.8 8 6.0/2.4 3

* pCO2 too high, BIPS flow increased for next altitude.

12


—

Figure 1. Photograph of subject wearing passenger mask with rebreather
bag added (front view).


EVALUATION OF A PASSENGER MASK MODIFIED WITH A
REBREATHER BAG FOR PROTECTION FROM SMOKE AND FUMES

INTRODUCTION

It is now possible to provide protection from smoke and
fumes for both flight deck and cabin crewmembers, with the
same system that is designed to provide protection from
hypoxia. Technical Standard Order, TSO-C99, that was issued
June 27, 1983, defines the standards for protective breathing
systems that will serve this purpose. The TSO specifies
maximum permissible contaminant leaks of 5 percent or less for
the mask, and 10 percent or less for the goggles, or 5
percent cr.less for a full-face mask.

Providing protection for passengers from smoke and fumes
is more complicated than for crewmembers. There are several
complex questions which must be answered. Some of the
questions asked concerning a device for passenger protection
are: (i) Could the continuous-flow oxygen mask be adapted to
provide this protection? (ii) Would a separate mask or other
device be required? (iii) Since smoke could contain irritant
gases, is it necessary to provide protection to the eyes, or
is protection for the respiratory system, where fumes could
be more life threatening, adequate?

Also, several steps are being proposed at this time to
reduce the probability of uncontrolled in-flight fires; e.g.,
the addition of fire-blocking material to seat cushions,
automatic fire extinguishers at lavatory trash bins,
installation of smoke alarms at possible ignition sites, and
additional hand-operated portable fire extinguishers.
Considering these steps and the history of relatively
infrequent occurrences of in-flight uncontrollable fires, is
it necessary or economically feasible to develop additional
breathing protection for passéngers?

Table I presents a 10-year history of incidents
involving smoke and fumes in the cabin or cockpit. Over this
period, the number of incidents averaged just over 20 per
year. On the average, about 13 per year were serious enough
to warrant an emergency landing. Over this time, there were
24 fatalities. Twenty-three were from the Air Canada
accident at Cincinnati (June 2, 1983). In a separate
incident, one passenger set himself afire in a lavatory; it
was determined that he died from carbon monoxide and smoke
inhalation, not from burns. There were 3 passengers with
serious injury (hospitalization); 17 passengers, 2 flight
deck crewmembers, and 11 flight attendants exhibited minor
smoke inhalation injury. There were also five flight deck
crewmembers who suffered eye irritation without smoke
inhalation. Even though it is apparent that the number of
incidents of smoke or fumes in flight is small, the manner of





pCO2 Values for Subjects While Using

TABLE VII

Redesigned Masks - With Exercise

8,000 ft 14,000 ft 21,500 ft
Exercise Oxygen Oxygen Oxygen
Tidal Flow Flow Flow
Subj. Volume (BTPS/ pcog (BIPS/ pco2 (BIPS/ pco2
No. (L) STPD) (mm Hg) STPD) (mm Hg) STPD) (mm Hg)
2 1.03 5.0/3.0 5 6.0/2.8 2 7.0/2.3 1
4 1.22 5.0/3.0 2 5.0/2.3 1 5.0/1.6 4
5 1.32 5.0/3.0 11 5.0/2.3 5 5.0/1.6 1
7 1.38 5.0/3.0 3 5.0/2.3 1 5.0/1.6 1
1 1.43 5.0/3.0 1 5.0/2.3 4 5.0/1.6 2
9 1.59 6.0/4.2 11 6.0/2.8 19 5.0/1.6 8
3* 1.80 7.0/4.8 10 8.0/3.7 20 6.0/2.0 16
8% 1.88 9.0/6.0 11 9.0/4.2 16 6.0/2.0 23
6x* 1.98 9.0/6.0 1 10.0/5.1 1 8.0/2.4 7

* Less than 1 min recorded before pCO? reached
rebreather bag collapsed.

** Rebreather bag collapsed before pC0O2 reached

13

unacceptable value or the

unacceptable value.



These further evaluations are herein reported; tests
were conducted using a standard passenger mask with a
rebreather bag added (Figures 1, 2, and 3). The major
advantages of this system are: (i) It is a single system for
protection from both hypoxia and fumes that would require
only one stowage site and one set of donning instructions,
and (ii) it would be relatively inexpensive (about $5) to
retrofit an existing mask. The major disadvantages are: (i)
It provides no protection for the eyes; (ii) it would require
engineering modifications for some aircraft to activate the
oxygen flow at normal cabin altitude pressures; and (iii)
although the cost of the bag itself is modest, engineering
modifications could be expensive and it could involve some
additional stowage space involving additional cost. These
follow-on studies were conducted in three phases.

PHASE IL
Methods

As originally designed, and as reported (2), this device
worked quite well when the subject was seated quietly at
ground level with oxygen flows of about 5 L/min, STPD, which
is about 6 L/min, BIPS (Body Temperature Pressure Saturated).
To test the device further, a workload of 50 watts was
imposed to increase test subjects' respiratory exchange rate,
since, on occurrence of an emergency, respiratory minute
volume may increase due to anxiety or increased physical
activity.

Subjects were required to pass a physical examination
prior to minute volume determinations under exercise
conditions. Accepted subjects reported at a later date for
altitude tests. On the test day, they were given
instructions on ear~- and sinus~clearing techniques.
Following this, an ear/sinus check was conducted by taking
the altitude chamber to 6,000 ft equivalent altitude and
returning to ground level at 3,000 ft/min. If test subjects
could not clear their ears/sinuses readily, they were
considered unsuited for the test. Subject 9 was disqualified
at this point. If successful, they were fitted with chest
electrodes for EKG and heart rate monitoring. The EKG was
monitored on an electrocardiograph (Burdick EK-5A), and a
simultaneous trace was continuously recorded on a polygraph
(E & M Physiograph). The heart rate was also monitored on a
heart rate meter that continuously averaged the preceding
four beats (Burdick CSS-61). Subjects then put on a crew
mask with a demand oxygen regulator and pedaled an ergometer
set to impose the 50-W workload for a 10-min period. During
this time, air samples were drawn from the mask for
determining oxygen, nitrogen, and carbon dioxide levels. A
respiratory mass spectrometer (Perkin Elmer MGA-1100) was
used as the analytical instrument for measuring respiratory
gases. It provided on-line analyses for oxygen, nitrogen,



Technical Report Documentation Page

T. Report No. 2. Government Accession No. 3. Recipient's Catalog No.

DOT/FAA--AM-85- 10

4. Title and Subtitle 5. Report Date
EVALUATION OF A PASSENGER MASK MODIFIED WITH A October 1985
REBREATHER BAG FOR PROTECTION FROM SMOKE AND FUMES 6. Performing Orgonization Code

8. Performing Organization Report No.

7. Author's) EE, A. Higgins, J. T. Saldivar, P. J. Lyne,
and G. E. Funkhouser

9. Performing Organization Name and Address 10, Work Unit No. (TRAIS)
FAA Civil Aeromedical Institute
P.O. Box 25082 11. Contract or Gront No.

Oklahoma City, Oklahoma 73125

13. Type of Report and Period Covered

12. Sponsoring Agency Name ond Address
Office of Aviation Medicine
Federal Aviation Administration
800 Independence Avenue, SW. 14. Sponsoring Agency Code
Washington, D.C. 20591

15. Supplementary Notes
Research leading to preparation of this report was performed under tasks
AM-B-84-PRS-71 and AM-B-85-PRS-71.

16. Abstract
A series of experiments were conducted in an altitude chamber at ground level,

8,000 ft, 14,000 ft, and 21,500 ft, both with and without exercise, to evaluate

the potential for providing protection from smoke and fumes for airline passengers
while wearing a standard continuous-flow passenger mask modified by the addition

of a rebreather bag. It was determined that it would provide increased protection
for those individuals who had tidal volumes of 1.5 L or less. However, it would
not function properly for those individuals who had tidal volumes greater than

1.5 L. Either the carbon dioxide levels were too great (above 15 mm Hg partial
pressure) or the rebreather bag collapsed. These results indicate that the addition
of the rebreather bag to the passenger mask has the potential for providing protec-
tion from smoke and fumes, but the system must have appropriately balanced valve
resistances and appropriately sized valve openings. This critical balance has not
yet been achieved for those individuals with large tidal volumes.

4A

« Sabon S
é ? Labora, o Shh ayy som
— Pte & fe & P we Alice

‘ oe ce

Av

17. Key Words 18, Distribution Stotement
Passenger Masks Document is available to the public
In-Flight Fires through the National Technical
Protective Breathing Equipment Information Service, Springfield,
Smoke and Fume Environment Virginia 22161.

19. Security Clessif. (of this report) 2. Security Clossif. (of this page) Bi No. of Pages | 22, Price

Unclassified Unclassified 22

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized



Inhalation valve from the oxygen reservoir

~- Exhalation valve to the rebreather bag
Inhalation valve from the rebreather bag
Exhalation valve to ambient from rebreather bag
Inhalation valve to rebreather bag from ambient

1

wAoOOwD>
'

Figure 3. Schematic drawing of passenger mask modified
by the addition of a rebreather bag.


Pa /

Figure 2. Photograph of subject wearing passenger mask with rebreather
bag added (side view).



death in the fatality cases during this 10-year period
indicates that there is a potential problem which warrants
investigation.

TABLE I

Ten-Year History of Incidents Involving
Smoke or Fumes in Cabin or Cockpit*

Total

Emergency No Emergency Unknown Number of
Year Landing Made Declared Status Incidents
1974 9 2 7 18
1975 11 1 4 16
1976 14 1 7 22
1977 1l 8 2 21
1978 13 2 2 17
1979 19 3 2 24
1980 17 4 0 21
1981 9 7 1 17
1982 10 5 5 20
1983 17 9 4 30
TOTAL 130 42 34 206

*Source: The Civil Aeromedical Institute's Cabin Safety
Data Bank.

In an earlier study conducted at this laboratory (2),
several potential protective breathing devices for passenger
use were tested for efficiency. One of the most promising
was a standard passenger oxygen mask modified to incorporate
a rebreather reservoir in addition to, but separate from, the
oxygen reservoir. All prior tests for this device were
conducted at ground level (about 1,300 ft at Oklahoma City)
with subjects seated, without exercise. Under these
conditions, it was determined that a sustaining oxygen flow
of about 5 L/min, STPD (Standard Temperature Pressure Dry),
would be required to provide oxygen and carbon dioxide levels
within acceptable limits. It was recommended that additional
studies be conducted at altitude to further verify the
suitability of this device.


TABLE IX

Results of Tests of Mask 3-III-4

Oxygen Flow (L/min, BTPS)

8,000 ft 14,000 ft 21,500 ft
Condition 5 6 7 5 6 7 5 6 7
Without Exercise
Subject 2-L * - - x - - * - -
4-L * - - * - - * - -
3-H * - - * - - * - -
5-H * - - * - - * - -
6-H * - - * - - * - -
21,500 ft 14,000 ft 8,000 ft
Condition 5 6 7 8 9 5 7 8 9 5 6 7 9
With Exercise
Subject 2-L coz - C02 - C02 - - = 02 - - - co2
4-L kA - = - koe 8 - * - - -
3-H co2 - - - C02 - = C02 - co2 cO2) - *
5-H R= eee BO - = = - co2 - =
6-H MBC - - - - MBC - - - cO2 MBC - -
Legend: * indicates acceptable results.
- indicates no measurements made.

C02 indicates
BC indicates
MBC indicates
~H indicates
-L indicates

unacceptable carbon dioxide level.
collapse of rebreather bag.

rebreather bag moving toward collapse.
a high tidal volume subject (greather than 1.5
a low tidal volume subject (less than 1.5 L).

16

L).


Table

Il.

IIl.

Iv.

vi.

VII.

VIII.

IX.

LIST OF TABLES

Ten-Year History of Incidents Involving Smoke and
Fumes in Cabin or Cockpits. ». 1. 1. 2 ss ee eee

Minute Volumes (L/min) of Subjects Under a
50-Watt Workload. . 1. 1. 1 2 ee ee ew ee ew we

Acceptable Flows (L/min, STPD) - No Exercise. ..
Attempted Flows (L/min, STPD) - With Exercise . .

Respiratory Data for Study of Redesigned Mask
with Rebreather Bag . . 2. 1 1 ee ee ww eee

pCO2 Values for Subjects While Using Redesigned
Masks ~ Without Exercise. ............

pCOy Values for Subjects While Using Redesigned
Masks - With Exercise . . 2. 1. 6 2 4 ee ee eee

Results of Tests of Mask 3-I-4. .......246.

Results of Tests of Mask 3-III-4. ......4..

iv

10

12

13
15
16


When subjects increased their minute volumes by
exercise, the device would not function properly, even with
flows up to 11.28 L/min, BIPS. It appears that the cause of
the malfunction is the inability of the valve into the
rebreather reservoir to accept the increased flow. Only a
portion of the exhaled air enters the rebreather bag, and the
balance of each breath escapes around the outer edges of the
mask. Also, the mask seals to the face better with
inhalation than with exhalation. Thus, with only partial
filling of the rebreather reservoir during exhalation and a
more efficient emptying of the bag during inspiration, the
volume of the reservoir declines with each succeeding breath
until the reservoir bag is collapsed and the subject is
unable to draw in any expired air. Additionally, incomplete
filling of the reservoir does not allow any escape of the air
through the distal end of the bag, therefore preventing the
dilution of carbon dioxide. Table IV lists the flow for each
subject during exercise at each altitude. Subjects 8 and 11
are the only ones for whom some adequate flows were attained.
As shown in Table II, these two subjects were among those
with the lowest minute volumes when exercising.

TABLE IV

Attempted Flows (L/min, STPD) - With Exercise

Subject Altitude

Number Ground Level 8,000 ft 14,000 ft 21,500 ft
1 8.18* ee aK **
2 8.18* 6.24% 4.82* 3.11*
3 6.81* 5.20* 4.02* 2.82%
4 ae 6.24% 4.82* 3.39%
5 ** ** ** 3.39%
6 *K ** ** 3.39%
7 8. 86* 6.76* 5.22* 3.39%
8 8.86 6.24% 4.82 3.66
10 8.86* 6.76* 5.22* 4.22%
11 8. 86* 6.24% 4.42 3.11

* Maximum flow attempted - not adequate.

** Unable to collect sufficient data for flow determination.

PHASE Il.

Methods

Two new designs of the mask with a rebreather bag were
considered in Phase II. One design, which had a reduced-
volume rebreather bag, did not function any better than the
original design, and detailed testing was not conducted for
it. The other design had the inhalation valve removed from
the distal end of the rebreather bag so that ambient air



excessively high and therefore unacceptable levels. Oxygen
flows were considered as too high if they exceeded 7 L/min,
BIPS, because the increase in cylinder drainage rate could
cause the supply to be depleted too rapidly. As can be seen
in this table, the tidal volume was a much more critical
measurement than was the minute volume.

Table VI presents the flows and the pCO? (partial
pressure of carbon dioxide) values for the subjects during
rest. The upper limit for an acceptable pC02 is 15 mm Hg.
Only subject 6, who had the highest tidal volume, produced an
unacceptable pC02 when oxygen flows were limited to 5 L/min,
BIPS. When the flow was increased to 6 L/min, BTPS, pCO,
fell within acceptable values for Subject 6.

Table VII presents the same data for subjects during
exercise. Those with the lower tidal volumes had
satisfactory pCO levels with low oxygen flows. Those with
high tidal volumes had unacceptable pCO09 levels with the
exception of subject 6, for whom the rebreather bag collapsed
before high pCO levels were reached.

As with the first series of tests, it appears that when
tidal volumes were high, the exhalation valve into the
rebreather bag was not able to accommodate the high volume of
air, and a part of the air escaped around the edge of the
mask instead of into the rebreather bag. However, during
inhalation, the mask has a better fit to the face, and the
emptying of the bag is more efficient than the filling. This
has two deleterious results. First, it does not allow enough
air to enter the rebreather bag to force air out through the
distal valve and, thus, allows the CQ, to build up. Second,
with the inefficient filling, and efficient emptying of the
rebreather bag, the rebreather bag will eventually collapse.

PHASE IIL
Methods

To alleviate the suspected problem of restricted flow,
possibly caused by, an undersized exhalation valve into the
rebreather bag or an exhalation valve with too great a
resistance, three further modifications were made to the
Phase II design. The first modification (identified as mask
3-I) was to increase the diameter of the valve opening,
thereby increasing the surface area of the opening by 27
percent. The second modification (mask 3-II) was
accomplished by punching four holes in the valve flapper.
This allowed a 27-percent increase in total opening. The
third modification (mask 3-III1) was accomplished by punching
the four holes in the valve flapper as was done for the
second modification, in addition to increasing the surface
area of the opening by 15 percent.

11



TABLE OF CONTENTS

Page
Abstract 2. 6 6 6 6 6 6 ee ee ee ww we we ee ee i
Acknowledgment . 2. 6 6 ee ee ee ee ee ee ee ee ii
Table of Contents. . . 6 ee ee ee ee ew we ee ew we ew) GGG
List of Tables «1. 6 6 ee 6 ee ee ew we ew we we ew iv
List of Figures. . 2. 6 «6 ee © ee ew ee ee ee v
INTRODUCTION . «1 6 ee eo oe ee ee ee ee ee we ew 1

PHASE Le. ee ee es 3

Methods. «6 6 6 6 6 ee ee ee we we we we ee ee 3
Results and Discussion . . 1 1 + 6 2 ee ee ee we 7

PHASE IL. wee ee ee ee 9

Methods. « «© 6 6 + es ee ee ee ew we we ee ew 9
Results and Discussion »« « «+ s+ + s+ ee ee ee eee 10
ll

PHASE

Iil.

Methods. . 2. 6 6 ee ee ew ww ew we ww ee ee 11
Results and Discussion . . « «+ + © © © © © © ew wo ew 14

CONCLUSIONS. «© 2 6 6 © 6 ee ew we we we ww ww we ee 14

REFERENCES « «6 6 6 6 ee ee ee we we ew ww ee 17

iii



ACKNOWLEDGMENT

The authors wish to acknowledge the excellent support given
by Mr. Charles Valdez, Mr. David Hehmeyer, Mr. James Whitley,
and Mr. Harold Nelson. In addition to operating the altitude
chamber, they also provided subject monitoring inside the
chamber during all altitude exposures.

We also appreciate the assistance of Mr. Fenton Winters,
Mr. Lee Forrest, and Mr. David Dyer for photographic
documentation of the tests.

Also acknowledged is the support of Clifton Brooks, M.D., and
the staff of the Aeromedical Clinical Branch in providing
physical examinations for all subjects and for medical
monitoring during the tests.

di


and carbon dioxide of each breath. A sample volume totaling
60 mL each minute was continuously drawn from the masks for
gas analysis. Digital readouts for these gases provided
continuous monitoring. A Honeywell Model 1858 fiber-optic
oscillograph was used to produce high-speed analog recordings
of the gas analyses from the mass spectrometer. After the
exercise period, the mask was removed and subjects were given
a 5-min rest period. Tests were terminated early if the
heart rate exceeded 120 beats per minute for 1 minute or a
transient peak heart rate exceeded 125 beats per minute.

Subjects then began the test with the passenger mask.
Chamber-qualified FAA personnel accompanied test subjects
during all chamber tests. The observer assisted the subject
in obtaining a "best fit" of the passenger mask and
ascertained that the correct sampling tube to the nose cone
of the mask was in place. First, tests without exercise were
conducted at ground level, 8,000 ft, 14,000 ft, and 21,500
ft. Oxygen flow to the mask was increased in increments of
1 L/min, BTPS (converted to STPD for altitude), until the
rebreather bag remained distended and the end inspiratory
partial pressure of carbon dioxide did not exceed 15 mm Hg
pressure. After an adequate flow was established, 3 min of
data were collected, and the chamber was taken to the next
higher altitude. After the completion of the data-collection
period at 21,500 ft with the subject at rest, data collection
with the subject exercising was begun. While still at the
maximum test altitude, subjects pedaled the ergometer at the
50-W load. The same two criteria were applied as for the
rest condition to establish the correct flow. If the C02
level (percent of carbon dioxide) was too high, the flow was
increased. However, if the flow was inadequate to prevent
the rebreather bag from collapsing, we were unable to
increase the flow quickly enough to reinflate the bag unless
the subject stopped exercising. After each exercise period,
subjects were given a 5-min rest period before collecting
data at the next lower altitude. These data were collected
in reverse altitude order; i.e., first at 21,500 ft, then at
14,000 ft, then at 8,000 ft, and finally at ground level.

Results and Discussion

Table II presents the minute volumes of the test
subjects during the second, fourth, and sixth minutes of
exercise on a bicycle ergometer set for 50 W and 50 rpm,
during the pretest trials. This workload increased the
minute volume to an average of 26.12 L/min during the sixth
minute of exercise. Resting minute volumes for healthy
adults will usually range from 3 to 10 L/min, with a mean of
about 8 L/min (1).

Only 2 of the 10 subjects were able to maintain
permissible oxygen and carbon dioxide levels to obtain a full



would not enter at this site, and the plastic seals were
replaced with soft rubber seals to improve the seal of the
rebreather bag to the mask. The same procedures were
followed for the testing of this design as for those tested
in Phase I, except that the verification testing at ground
level was eliminated.

Results and Discussion

Table V presents the minute volumes, respiratory rates,
and tidal volumes of subjects when they exercised on the
bicycle ergometer at the 50-W workload. When tidal volumes
were 1.59 L or higher, the masks did not function well.
Either the buildup of carbon dioxide was unacceptable, the

TABLE V

Respiratory Data for Study of
Redesigned Mask with Rebreather Bag

Minute Volume Respiratory Rate Tidal Volume
Subject with Exercise with Exercise with Exercise
Number (Liters) (Breaths/min) (Liters)
2 23.6 23 1.03
4 22.0 18 1.22
5 18.5 14 1.32

6 17.8 9 1.98

For those subjects above the line, the redesigned mask worked
well, requiring flows of only 5 to 6 L/min, BIPS. For those
subjects below the dividing line, the redesigned mask did not
work, Either the required flows of oxygen were too high, the
buildup of carbon dioxide was unacceptable, the rebreather
bag collapsed, or a combination of the failure criteria
occurred.

rebreather bag collapsed, or a combination of these failures
occurred, even when oxygen flows were increased to

10