DOT/FAA/AM-00/6

U.S. Department

of Transpor tation

Federal Aviation

Administration

Robert P. Garner

Richard E. Murphy

Civil Aeromedical Institute

Federal Aviation Administration

Oklahoma City, Oklahoma

Steve S. Donnelley

Soldier Systems

U.S. Army Aberdeen Test Center

Aberdeen Proving Ground, MD 21005-5059

Ken E. Thompson

Kevin L. Geiwitz

Automotive Instrumentation Team

U.S. Army Aberdeen Test Center

Aberdeen Proving Ground, MD 21005-5059

February 2000

Final Report

This document is available to the public

through the National Technical Information

Service, Springfield, Virginia 22161.

Testing the Structural

Integrity of the Air Force’s

Emergency Passenger

Oxygen System at Altitude

Office of Aviation Medicine

Washington, D.C. 20591
NOTICE

This document is disseminated under the sponsorship of

the U.S. Department of Transportation in the interest of

information exchange. The United States Government

assumes no liability for the contents thereof.
i

Technical Report Documentation Page

1. Report No. 2. Government Accession No. 3. Recipient's Catalog No.

DOT/FAA/AM-00/6

4. Title and Subtitle 5. Report Date

Testing the Structural Integrity of the Air Force's Emergency Passenger

Oxygen System at Altitude

February 2000

6. Performing Organization Code

7. Author(s) 8. Performing Organization Report No.

Garner, R.P.1, Murphy, R.E.1, Donnelley, S.S.2, Thompson, K.E.3, and

Geiwitz, K.L.3

9. Performing Organization Name and Address 10. Work Unit No. (TRAIS)

1

FAA Civil Aeromedical Institute, P.O. Box 25082, Oklahoma City, OK 73125

11. Contract or Grant No.

2

Soldier Systems, U.S. Army Aberdeen Test Center

3

Automotive Instrumentation Team, U.S. Army Aberdeen Test Center

Aberdeen Proving Ground, MD 21005-5059

12. Sponsoring Agency name and Address 13. Type of Report and Period Covered

Office of Aviation Medicine

Federal Aviation Administration 14. Sponsoring Agency Code

800 Independence Ave., S.W.

Washington, DC 20591

15. Supplemental Notes

16. Abstract

The chemical bond attaching the elastic neck seal to the body of the protective breathing equipment (PBE)

procured by the U.S. Air Force as an emergency passenger oxygen System (EPOS) was alleged to be

inadequate to allow the PBE to perform as intended at altitude. To test this possibility, EPOS units were

collected from Air Force Bases and systematically tested at altitude. The Civil Aeromedical Institute was

requested to participate in the testing through the FAA Office of the Inspector General and the U.S. Air

Force's Office of Special Investigations due to the Institute’s longstanding expertise in the area of PBE.

Eighty-four of the EPOS units collected were divided into four groups of 21. Since the PBE in question

were of relatively recent manufacture, three of the four groups were artificially aged. Altitude testing was

conducted in a hypobaric chamber at a simulated altitude of 40,000 feet above sea level. An EPOS unit

from each of the "aged" groups was placed on one of the four mannequin heads that were instrumented for

monitoring pressure, temperature, and atmospheric gas concentrations. The EPOS units were activated at

altitude with the primary data collection continuing for a minimum of five minutes after activation. The

neck seal/hood interface did not fail on any of the 84 devices during altitude exposure. A destructive test

series conducted on an additional 16 EPOS units indicated that an internal pressure approximately six times

that observed at altitude was required to result in structural failure of the EPOS units. Based on the data

collected in the performance of these tests, the neck seal/hood body interface bond utilized in the

construction of these devices is sufficient to allow the PBE to perform as intended at altitude.

17. Key Words 18. Distribution Statement

Protective Breathing Equipment, Emergency Passenger

Oxygen System, High-Altitude Destructive Testing

Document is available to the public through

the National Technical Information Service,

Springfield, Virginia 22161

19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price

Unclassified Unclassified 11

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

1

TESTING THE STRUCTURAL INTEGRITY OF THE AIR FORCE’S EMERGENCY

PASSENGER OXYGEN SYSTEM AT ALTITUDE

INTRODUCTION

An emergency aboard an aircraft can require individual protection from hypoxia, smoke, and fumes.

Generally, this type of protection can be offered

through the availability of protective breathing equipment (PBE), commonly referred to as a “smoke

hood.” PBE devices have been designed for both

aircraft passengers and crew. It is recognized that

crewmembers require the protection offered by PBE

to successfully complete their assigned tasks in emergency situations. Performance standards for

crewmember PBE call for specific functional capabilities and have been relatively well defined (1, 2, 3,

4). The net safety benefits in providing PBE to

passengers aboard commercial transport category aircraft are a subject of debate (5). Although some

guidelines have been created (6), no governing body

currently mandates or regulates “smoke hood” type

devices for transport category aircraft passengers.

However, due to the potential benefits of the devices

in certain circumstances, many private and military

organizations have made the decision to equip their

aircraft with PBE for passengers.

The United States Air Force Air Mobility Command recognized the need for a readily accessible,

portable, passenger protective system to supply passengers with oxygen and protect them from the effects of smoke and toxic fumes. After an extensive

evaluation and testing of available devices suited for

passenger protection, a “smoke hood” type of device

was chosen by the Air Force. The device is manufactured by the Essex PB&R Corporation. The United

States Air Force calls the device the Emergency Passenger Oxygen System (EPOS). During the delivery

cycle for the devices ordered by the Air Force, the

production facility was relocated from Elkton, Maryland, to Edwardsville, Illinois. The quality of the

construction of the EPOS came into question after

the relocation of the manufacturing facility in terms of

a Qui Tam lawsuit filed on behalf of the government.

It was hypothesized that the relocation of the

manufacturing from the original production facility

(OPF) to a new production facility (NPF) resulted in

flaws in the assembly process. Specifically, the hypothesis holds that the attachment between the neck

seal and hood body of the units from the NPF are not

able to withstand the forces generated if the Victim

Rescue Units (VRU) were activated in a manner, and

at an altitude, consistent with its intended use. To

examine this possibility, VRU units from both the

OPF and NPF were tested. The Civil Aeromedical

Institute was requested to participate in the testing

through the FAA Office of the Inspector General and

the U.S. Air Force’s Office of Special Investigations

due to their longstanding expertise in the area of PBE.

The purpose of the testing was to evaluate the

capabilities of a PBE neck seal and hood shell attachment. The goal was to address a very specific aspect

of the VRU design and the associated manufacturing

processes. Emphasis was placed on the investigation

of the influence of aging on the device’s capabilities

to provide adequate protection during an emergency

involving altitude exposure. The devices tested were

the Essex VRU provided to the Air Force as a Passenger Smoke and Fume Protective Device (PSFPD),

designated herein as the EPOS.

METHODS

Emergency Passenger Oxygen System:

The 84 EPOS tested at altitude had been previously distributed to United States Air Force bases.

The Air Force’s Office of Special Investigations had

collected the test devices from Charleston AFB in

South Carolina, Travis AFB in California, Dover

AFB in Delaware, and McGuire AFB in New Jersey.

The experimental design of the tests was balanced, in

that each test group contained equal numbers of

EPOS units from the bases and manufacturing
2

locations. Only those EPOS units that had not been

removed from the original packaging were used for

the tests making up this study.

Artificial Aging: The EPOS devices in question

were manufactured relatively recently. It is possible

that the neck seal bonds in the new systems are

functional but might deteriorate with age. Therefore

an attempt was made to artificially age them. A higher

incidence of failures among the aged devices would

indicate that the neck seal bond was insufficient.

Three groups of EPOS units were artificially aged.

Aging consisted of placing each group in an environmental chamber for a period of one week at temperatures of 50°C, 65°C, and 80°C. These groups were

designated Aged1, Aged2, and Aged3, correspondent

with the temperature range. The relative humidity of

the environmental chamber was maintained at 25%.

A fourth group served as a non-aged control.

Altitude Testing: Altitude testing was conducted

in a hypobaric chamber at a simulated altitude of

approximately 40,000 feet above sea level. A total of

84 EPOS units were tested.

The test setup consisted of a mannequin head

mounted on a wooden stand. The interior of the head

was hollow. Three polypropylene tubes were channeled through the mannequin base and the interior of

the head emerging in the area of the mouth and nose

for data collection purposes. This setup allowed data

collection from inside the EPOS without the risk of

compromising its structural integrity. Figure 1 shows

the mannequin head setup.

A metal disk screwed to the wood of the base sealed

the interior of the mannequin head from the ambient

environment. A pressure relief valve that opened at

25 mmHg was mounted in the metal disk. A test rack

was built that held four mannequin heads outfitted in

this manner. The arrangement allowed four EPOS

devices to be tested during each hypobaric chamber

decompression. An EPOS from each of the “aged”

groups was tested during each of the 21 decompressions, and test items from each group were rotated

onto the different mannequin heads during the tests.

Testing consisted of opening the EPOS immediately prior to the altitude test. Care was taken not to

activate the oxygen system. Activation of the oxygen

system normally consists of the neck of the hood

being pulled open so the EPOS can be placed over the

user’s head. A small clip seals the oxygen canister

before activation. The clip is attached via a string to

a plastic bulb on the side of the EPOS opposite the

oxygen canister. When the user pulls open the neck of

the EPOS for donning, the clip is pulled away from

the oxygen canister, allowing the flow of oxygen. The

tests required the EPOS to be activated at altitude.

Therefore, the plastic bulb of the string system normally used to activate the oxygen canister was carefully removed. The EPOS was then placed on one of

the four mannequin heads. A cord running from

outside the chamber was tied to the string that normally activated the oxygen flow when pulled. This

arrangement allowed the EPOS to be activated from

outside the chamber once the desired pressure level

was achieved.

Once the four EPOS test units were in place, the

chamber was closed and evacuated to a simulated

altitude of approximately 42,000 feet at a rate of

5,000 feet per minute. The oxygen system was activated after two minutes at the maximum altitude

obtained. A 15-second interval was allowed between

activation of each device. Changes in gas concentrations were collected in 15-second segments using a

mass spectrometer (Perkin-Elmer, MGA-1100). A

rise in oxygen concentration indicates that oxygen

Figure 1. Mannequin head and base setup used for

testing EPOS at altitude.
3

was being released into the EPOS. Of primary interest was the pressure change within the EPOS after

activation at altitude. It was hypothesized that the

expansion of ambient air trapped in the EPOS hood

coupled with activation of the oxygen system at

altitude, would result in failure of the chemical bond

between the neck seal and the hood body.

Pressure changes were measured using OMEGA

PX-140 pressure transducers. Temperature changes

in the EPOS were monitored using thermocouples.

Gas concentrations were followed for a total of 5

minutes at altitude. The chamber was then held at

altitude for an additional 2 minutes before being

returned to ground level. Upon return to ground

level, the EPOS were removed from the mannequin

heads and carefully checked for any structural failure,

particularly in the area of the neck seal and hood

body. After the spent hoods were removed and

checked, the next set of four EPOS units was tested.

Data signals from the measurement transducers

were collected using an Advanced On-Board Computer System (ADOCS). The ADOCS is a computerbased data acquisition system developed by the

Aberdeen Test Center for applications at Aberdeen

Proving Grounds. The data were saved as a text file

and later analyzed using either a computer spreadsheet (Microsoft ExcelTM) or the LabVIEWTM data

acquisition and analysis software (National Instruments).

Destructive Tests: Two sets of tests were performed at ground level. These were conducted in the

Protection and Survival Laboratory at the Civil Aeromedical Institute. The first set consisted of activating

a subset of four EPOS units and monitoring pressure

changes at ground level for comparison with values

observed after activation at altitude. In the second set

of tests, an air compressor was used to distend the

EPOS until the unit failed structurally. These tests

were anticipated to indicate the pressure and failure

pattern of the units when stressed beyond their structural capacity.

RESULTS

There is no way to specifically determine the

extent that the aging process conducted in this study

was effective. Care was taken in administering the

process to mimic conditions in the laboratory that are

used in equipment specifically designed for aging (7).

However, none of the vacuum seals of the EPOS

packaging were disrupted by the attempt at artificial

aging. Therefore, the influence of airflow and humidity on the EPOS itself must be considered minimal. The elevated heat in the environmental chamber

must be considered the primary determinant of artificial aging of the materials and manufacturing processes.

Eight-four devices were tested at an altitude of

approximately 40,000 feet above sea level. There was

not a failure of the neck seal/hood interface in any of

the tests. The pressure level inside the hood after

activation at altitude increased, on average, 3.5 mmHg

(i). It took approximately 1 minute for this value to

be reached. This increase is less than would be anticipated based on release of gas into a fixed volume. The

test setup could lose oxygen through leakage from

around the neck of the mannequin, sampling by the

mass spectrometer, and diffusion through any small

leaks in the test configuration. Another contributing

factor is that the pressure increase in the EPOS

attenuates flow rate of oxygen out of the cylinder.

Oxygen concentration did rise in the EPOS in all of

the tests (Figure 3). Nitrogen levels within the devices fell, consistent with the increase in oxygen

concentration. The level of nitrogen remaining in the

EPOS suggests that the flow was sufficiently restricted to prevent the total washout of nitrogen by

the oxygen from the storage canister.

Pressure changes within the EPOS (n=4) activated

at ground level are presented in Figure 4. The average

pressure change observed was 1.6 mmHg and occurred approximately 2.5 minutes after activation. As

expected, PBE activation at altitude resulted in greater

internal pressure. The pressure change at altitude
4

Average Internal Pressure Change After Mask Activation at Altitude

Time (minutes)

Pressure (mmHg)

Figure 2. Summary of pressure changes associated with activation of passenger emergency oxygen

system at approximately 40,000 feet simulated altitude. The values represent the mean + standard

deviation for a sample of 4 devices.

developed more quickly than when EPOS devices

were activated at ground level. A subset of four

devices from each aged group was tested in the

destructive test series. The average pressure required

to rupture the PBE was 17.8±1.3 mmHg with no

statistically significant differences existing among

the four groups (Figure 5). This pressure level is

approximately six times the change observed at altitude. No consistent pattern was observed in the failures.

DISCUSSION

A key component in conducting these tests was the

attempt to artificially age the EPOS. Accurately conducting an artificial aging test is a complex task (8, 9).

Although studies related to artificial aging of materials have become more plentiful in recent years, the

variety of materials from which the EPOS is

constructed does not allow a definitive analysis of

aging. The approach used in this study was to use an

aging protocol that would allow treatment differences to be identified, even though a specific time

value could not be reliably placed on the treatments.

Aging is commonly recognized as the changes

occurring in an entity over a period of time. Accelerated or artificial aging is a procedure that is designed

to indicate in a relatively short period of time what

will happen to materials over a period of years in

storage. There have been numerous studies investigating factors that make artificial aging most consistent with the normal aging process. Most of the test

methods are ultimately based on van’t Hoff’s principle, which describes the effect of temperature on

the rate of chemical reaction (10). It has been found

that the effect of heat is similar to that of natural

aging under average conditions. Other factors such as
5

Figure 3. Changes in oxygen concentration inside the EPOS after activation at altitude. The last 5 data points

collected (10 seconds) of each 15-second collection interval are presented. Each data point in the graph

represents the average of the 21 EPOS units making up the “aged” group.

Time (seconds)

RControl D Aged1 ¢ Aged2  ̈ Aged3

humidity and airflow can also influence the artificial

aging process (7). The challenge in the process is

matching appropriate changes in environmental conditions to bring about changes consistent with the

natural process in the material(s) being tested.

Due to the vacuum packaging, heat was the only

variable that could have characteristically aged the

EPOS. The complexity of the materials and adhesives

in manufacturing the devices does not allow assignment of specific time periods to the aging exposures

used in this study. However, it is assumed that the

temperature differences among the three artificial

aging scenarios were sufficient to make the test characteristically different from each other. It appears

that two alternatives need to be considered since none

of the bonds failed during the altitude tests. The

chemical bond between the neck seal and hood body

did not deteriorate as a result of the heat increases. If

that were the case, natural aging would not be anticipated to significantly alter the bond during the lifespan

of the device. The other explanation is that the

artificial aging did not last long enough to have an

effect on the hood body/neck seal bond.

However, this position must be considered in the

context of recognized approaches to artificial aging.

The Food and Drug Administration and others have

accepted a 14-day exposure to 55°C and 70-90%

relative humidity as being roughly equivalent to 1

year of ambient real-time aging (11). Based on this

estimate, the 80°C treatment used in this study may

represent natural aging of 4 to 6 years. It could be

more or less than this due to the dependence of heat

aging on both the materials and the nature of the

chemical bond (9). The complexity of these interactions makes a definitive time equivalent impossible

to achieve.

Oxygen (%)
6

Figure 4. Summary of pressure changes associated with activation of passenger emergency oxygen system

at ground level. The values represent the mean + standard deviation for a sample of 4 devices.

Average Internal Pressure Change After Mask Activation at Ground Level

Pressure (mmHg)

Time (minutes)

There are valid arguments on both sides of the

debate over aircraft passenger use of equipment designed to provide protection from smoke and fumes

in addition to hypoxia protection. Based on experiences and circumstances anticipated on Air Force

aircraft, the decision was made to provide protective

breathing equipment as a means of smoke protection

for the passengers. The minimum acceptable performance requirements the Air Force set forth were

high. They wanted a device that could be donned in

20 seconds. It could not interfere with hearing and

vision or the physical mobility of the wearer. The

ability to evacuate the aircraft or perform emergency

duties must be maintained. Fire protection was required for the head and neck. Inflight, the Air Force

wanted 15 minutes of smoke and fume protection

coupled with hypoxia protection equivalent to the

“Dixie cup” style of continuous flow passenger oxygen mask commonly found aboard civilian airliners.

All of these features were to be contained in a package

that fit the existing storage space aboard aircraft,

weighed less than 2 pounds, and cost under $200.00.

A Sources Sought Synopsis regarding the anticipated

off-the-shelf procurement of a EPOS and meeting

announcement for all interested vendors was published in the Commerce Business Daily on February

24, 1993.

The Air Force used numerous resources in evaluating the PSFPD submitted for consideration. There

was an extensive evaluation of all of the devices. Both

positive and negative aspects of each were weighed in

the context of Air Force requirements. The decision

was made to procure the PSFPD manufactured by

Essex PB&R Corporation. The production facilities
7

Figure 5. Average pressure increase immediately prior to structural failure in a subset of devices from each

of the aged treatment groups. The mean + standard deviation is represented. The pressure level results in

distension of the elastic neck seal material to a diameter of 2.5 to 3.5 feet, which extends the hood body well

above the head of the wearer.

Average Internal Pressure at Failure

Treatment Group

Pressure (mmHg)

for the device were moved after the contract had been

signed with the Air Force. If quality was maintained,

it does not appear that a change in manufacturing

point within the continental United States is of

significance. However, the competence of the NPF

was challenged in the courts. This action may have

been a function of problems with the bond between

the hood shell and neck seal of units that were

original manufacturer DuPont, or there may have

been other factors involved. Regardless of the basis of

the complaint, the decision was made to investigate

the performance of the hood body/neck seal bond.

Results from the tests conducted on the devices

that had been previously delivered to the Air Force

indicated that the neck seal/hood interface would

remain bonded, consistent with the intended use of

the EPOS. Furthermore, destructive testing on a

subgroup of devices indicated that it only took a

small percentage of the internal pressure resulting in

structural failure to distend the rubber neck seal to an

extent that the EPOS became functionally useless

due to visual obstruction. Improvements in protective capabilities, donning, and design may some day

make passenger protective breathing equipment

consistent with the safety goals of organizations

throughout the world of aviation. Performance, comfort, and other characteristics of the EPOS tested in

this study could be improved. However, the results of

the tests strongly suggest that the structural integrity

of the device exceed any functional demands placed

on it by the wearer.
8

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1. SAE Aerospace Standard 8047. Performance standard for cabin crew portable protective breathing

equipment for use during aircraft emergencies.

Available from the Society of Automotive Engineers, Inc., Department 331, 400 Commonwealth

Drive, Warrendale, PA 15096.

2. SAE Aerospace Standard 8031. Personal protective devices for toxic and irritating atmospheres:

Air Transport Crewmembers. Available from

the Society of Automotive Engineers, Inc., Department 331, 400 Commonwealth Drive,

Warrendale, PA 15096.

3. Technical Standard Order (TSO) - C116.

Crewmember Protective Breathing Equipment.

Federal Aviation Administration. Aircraft Certification Service, Washington, DC.

4. Technical Standard Order (TSO) - C99. Protective Breathing Equipment. Federal Aviation

Administration. Office of Airworthiness, Washington, DC.

5. Speitel, L. and Hill, R.G. Study of benefits of

passenger protective breathing equipment from

analysis of past accidents. FAA Technical Center

Report DOT/FAA/CT-88/03. March 1988.

6. EUROCAE ED-65. Minimum operational performance specification for passenger protective

breathing equipment.

7. Spetz, G. Recent developments in heat aging tests

and equipment. Polymer Testing 15: 381-95, 1996.

8. Bille, H. and Fendel, H. How to do hot air aging

tests properly: A survey of influencing parameters

and practical guidance on dealing with them.

Paper presented at the 143rd Meeting of the

Rubber Division, ACS, at Denver, Colorado.

May 1991.

9. Woo, L., Palomo, J., Ling, M.T.K., Chan, E.K.

and Sanford, C. Shelf-life prediction methods

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March/April 1996.

10. Atkins, P.W. Physical Chemistry (3rd ed), New

York, W.H. Freeman, pp 221-23, 1986.

11. Brillhart, M. Windau, J. and Bonutti, P. The

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