Scott Emergency Escape Breathing Device Evaluation for Use by Aircraft Cabin Crew and Passengers

N. A. MARTIN and J. R. POPPLOW, M.D., M.S.

Defence and Civil Institute o f Environmental Medicine, Downsview, Ont., Canada

MARTIN NA, POPPLOW JR. Scott emergency escape breathing device evaluation for use by aircraft crew and passengers. A viat. Space Environ. Med. 1987; 58:747-53.

The Scott Emergency Escape Breathing Device (EEBD) was evaluated for use in Canadian Forces (CF) transport/passenger aircraft in provldlng smoke protection durlng emergencies and in preventlng hypoxia during cabln decompression at hlgh altitude. Five human subjects wearing the EEBD were subjected to decompresslon from 2,438 m (8,000 ft) to 9,753 m (32,000 ft) in approximately 15 s followed by a free fall to 7,010 m (23,000 ft) in a challenge gas atmosphere of 5,000 ppm of carbon monoxide (CO), where they performed moderate exercise (80 W output) on a blcycle ergometer. Very llftle In- leakage of CO was observed when the neck seal was malntalned. Hood atmosphere was measured at 97% oxygen at 7,010 m, which resulted in an arterial oxygen saturation (Sao2) of 97%. Temperature in the hood rose to as high as 45.5"C but the subjects were able to function normally. The EEBD is effective In provldlng noncockplt aircraft crew with smoke protection, adequate vlsion, and hypoxia prevention for at least 15 mln In the event of a fire, smoke, or decompresslon emergencies at altitudes up to 7,0~0 m fol- lowing a brief exposure to 9,753 m.

E SCAPE FROM a fire- or smoke-filled aircraft is often difficult or impossible when passengers or

crew are incapacitated from the effects of the smoke, carbon monoxide, cyanide gas, etc. The Air Canada DC9 disaster at Cincinnati is a prime example. I f a

This manuscript was received for publication in April 1986. The revised manuscript was accepted for publication in August 1986.

Send reprint requests for DCIEM Pub. No. 86-P-34 to Lt. Col. J. R. Popplow, Director, Medical Life Support Division, Defence and Civil Institute of Environmental Medicine, 1133 Sheppard Ave. West, P.O. Box 2000, Downsview, Ont., Canada M3M 3B9.

source of uncontaminated air were available for even 2 min in such a situation, lives could often be saved. The Medical Life Support Division (MLSD) of The Defence and Civil Institute of Environmental Medicine (DCIEM) evaluated the Scott Emergency Escape Breath- ing Device (EEBD) to determine the degree of protection it would provide passengers and crew during escape from fire- or smoke-filled aircraft, and to test the device at altitude to determine if it would provide sufficient hypoxia protection for in-flight emergencies.

The EEBD (Fig. 1,2) was initially developed for the United States Navy for emergency egress from a smoke- filled environment below decks on large ships. It is a Teflon-coated fibre#ass cloth hood inside a "Kynol" fabric hood, with a clear polyamide window and a thermoplastic urethane neck seal. The hood acts as a counter-lung to the user's respiratory system. Attached at the nape is a sodium chlorate candle oxygen generator with a lithium hydroxide and molecular sieve scrubber. As shown in Fig. 3, the generator powers a venturi to provide a total recirculated flow of 55 L . m i n -1 (ATP) through the hood and scrubber. This arrangement ensures delivery of oxygenated air to the user and removes carbon dioxide, excess moisture, and any trapped par- ticles. To use, the actuating pin is pulled for generator start and the hood is donned over the head. The EEBD has an advertised operating life of 15 rain while providing an oxygen flow of 5.5 L-min -].

Our literature search revealed that the most compre- hensive data available on this device were three test reports (1,4,5) by the manufacturer which, unfortunately, did not provide all of the details we required. The in- hood atmosphere had been tested for carbon dioxide but not for oxygen content. The in-leakage test depended

USING SCOTT EEBD IN A I R C R A F T I M A R T I N & P O P P L O W

on only the subject's report of having smelled or tasted the challenge aerosol during a 3-min exposure. The high temperature test was limited to operating the EEBD in ambient temperatures after a hot soak. The carbon monoxide measurement test did not use the complete EEBD.

Fig. 1. EEBD test setup showing sampling lines.

METHODS AND MATERIALS

Subjects: Six subjects, four male and two female volunteered to participate in this phase of the study. They were selected to provide a distribution in size, particularly neck circumference. The relevant anthro- pometric data are shown in Table I (2,3).

Test Methods: Testing was carried out in four phases: gas production analysis, high-temperature operation, in- leakage measurement, and high-altitude operation. Each test was performed with five new hoods to assess reliability. A pressure test on the hoods to determine seam leakage was not considered necessary.

Gas production analysis determined volume produced, oxygen purity, and generator operating time. Each hood was mounted on a hollow mannequin head and, after the generator was activated, the gas produced was evacuated through a Tygon tube to a 200-L mylar bag. The gas was analysed using a Bio-Marine OM300 analyser calibrated with a "zero gas," with 95% oxygen, and with ambient (21% oxygen) air. The gas from the bag was sampled and passed over a Rexnord oxygen sensor and the results were recorded on a Pedersen strip-recorder. Samples were also tested on a Taylor oxygen analyser to confirm the Rexnord sensor results.

PULL TO ACTUAl E ~OXYGEN ~ . R~NG 1 GENERATO. /___ ::L/EF

_ _ FX~ GEN ~ / V E N T U R I NO~LE I '

HOOD

TO HOOD ~ ~ - -

HOOD EXHALATION ~b,-

VENT VALVE

\ F,LTER ~-"-SCRUBBE R

Fig. 3. EEBD schematic.

Fig. 2. EEBD showing septal neck seal.

TABLE I. SUBJECTS' ANTHROPOMETRIC DATA.

Subject

No. M/F

Head Circumference Neck Circumference*

cms. Percentile** cms. Percentile**

A M 57 30 38 25 B F 56 75 33 50 C F 54.5 37 29 1-5 D M 57 30 41 75 E M 57 30 36 5 F M 56 12 38 25

* Note: The measuring tape is held in a plane perpendicular to the long axis of the neck. The circumference of the neck is measured just below the bulge of the thyroid cartilage ("Adam's Apple"). ** Canadian Forces Personnel (5,6).

USING SCOTT EEBD IN A I R C R A F T - - M A R T I N & P O P P L O W

High-temperature operation was tested to simulate a fire/smoke emergency. The hollow mannequin head was mounted in a DCIEM environmental oven which had been reheated to 80"C. A temperature probe and a Tygon sampling line were sealed to the head and routed through the oven wall to a cooler coil, then to a thermometer, and finally to a Rexnord oxygen sensor. Temperatures inside the hood and of the gas sample being extracted were noted and manually recorded. A Pedersen recorder was used to note the sensor output. A new EEBD hood was then placed on the mannequin head, the generator was activated and the readings were recorded. No attempt was made to evaluate the hood on a human subject in a very hot environment because of possible hazards to the subject.

In-Leakage Measurement: To evaluate the protection afforded by the EEBD against toxic gases, it was necessary to measure the leakage into the hood under simulated conditions. Five subjects, three male and two female, were utilized for this phase. The subject for each test run entered the DCIEM hypobaric chamber, at ground level, and was seated on a bicycle ergometer. Heart rate was continually monitored by ECG wave form using a standard three-lead system. The subject breathed 100% oxygen through a standard oxygen mask while the chamber was flooded with and maintained at a 5,000 ppm concentration of carbon monoxide (CO). A mixing fan ensured even distribution in the chamber. The subject then started the oxygen generator of the EEBD, held his breath, discarded the oxygen mask, donned the hood and started pedalling the ergometer at 80 W output. The observer ensured that the neck seal fitted properly with no clothing interference. CO was chosen as the challenge gas because of its ease of detection in very low concentrations. The concentration was chosen in consultation with our biomedical section specialist as being safe over the exposure period. Gas from inside the hood was sampled through ports in the EEBD face window close to the mouth, as seen in Fig. 1, and these gases were routed outside the chamber to CO and oxygen sensors calibrated with 500 ppm CO and 100% oxygen, respectively. The CO and oxygen levels were recorded on strip charts. The test continued until the subject heard the EEBD generator begin to slow. The subject then removed the hood and quickly exited the chamber. Alveolar air samples were taken before and after the run to determine carboxyhaemo- globin (COHb) rise.

Hypoxia Protection: The capability of the EEBD hood to provide hypoxia protection at altitude was tested using subjects exposed to a simulated pressure altitude of 9,753 m (32,000 ft) followed by a descent at 1,524 m-min-, (5,000 ft-min-0 to hold at 7,010 m (23,000 ft).

The subject's arterial oxygen saturation (Sao0 was monitored continually with a Hewlett-Packard H- P47201A ear oximeter and the heart rate was monitored by the ECG. The subject and the inside observer prebreathed 100% oxygen for 30 min prior to the test. The subject then sat on the ergometer and the oximeter probe was mounted on the ear and recalibrated. A standard ear/sinus check was completed and the chamber altitude raised to 2,438 m (8,000 ft). The subject activated the generator, held his breath, removed the

oxygen mask, donned the EEBD hood and resumed breathing. If the ear oximeter sensor probe was not properly positioned, it provided an "Off Ear" warning light which was continually monitored. When an "Off Ear" indication occurred, the subject and observer attempted to reposition the sensor. If this was unsuc- cessful after 5 min, the run was aborted, as the remaining generator running time would not have been adequate as a test period. When the sensor was correctly positioned, the chamber was decompressed in approxi- mately 15 s to 9,753 m. The subject's Sao: was closely monitored and the minimum level allowed before termination was 70%. After approximately 30 s at 9,753 m, a simulated emergency descent at 1,524 m. min -~ was established and the chamber stabilized at 7,010 m. The subject then began to exercise on the ergometer and continued until the EEBD generator began to slow. When the EEBD was exhausted, the subject held his breath, removed the hood and donned the oxygen mask. The chamber was then brought to ground level pressure and the subject exited.

RESULTS Gas Analysis: The results of the gas analysis showed

that approximate 120 L of gas were produced from each generator run. Analysis of the gas inside the hood showed approximately 65% oxygen content after 1 min of operation, 87% after 2 min, 95% after 3 min, and a steady state level of 95-100% at about 6 min. The peak oxygen levels recorded from different runs were 95-100% (Fig. 4). These results were confirmed by the Taylor analyser using bagged samples taken at 5-rain intervals. The rate of increase in oxygen level was the same in each sample. The running life of the generators ranged from 15.5-17.5 min, at which time the oxygen percentage in the sample dropped sharply. The tem- perature inside the hood (maximum 45.5"C) and the temperature for the gas being sampled were recorded at 30-s intervals (Table .II).

High-Temperature Operation: In the 80"C environ- ment, the EEBDs operated normally, producing the same oxygen content rise rate and achieving the same concentration levels as in the other tests. The operating life ranged from 14.5-17 min, and the gas sample during the running period was 90-100% oxygen, with the peak above 97% in all runs (Fig. 5). The maximum temperature recorded inside the hood was 74.8"C.

In-Leakage Measurement: In the 5,000 ppm CO atmosphere ground-level in-leakage test, the oxygen levels again started at 18-20% and rose rapidly reaching at least 70% in 1 min and 87% after 2 min, with one exception. The oxygen level in subject C (Fig. 6) failed to reach 75%, and the CO levels rose immediately at the start and peaked at 1,600 ppm (Fig. 7). The run was terminated at this point due to the abnormally high CO level. The CO levels measured in subject D were also higher than expected and peaked at 700 ppm. Although the oxygen level was 85% or better, the run was terminated at 7.5 min due to this CO level (Fig. 8,9). Post-run alveolar air samples confirmed these termination decisions, revealing an 8.8% carboxyhae- moglobin (COHb) in subject C, a non-smoker, and 16% COHb in subject D, a smoker. Because of the

U S I N G S C O T T EEBD IN A I R C R A F T m M A R T I N & P O P P L O W

Fig. 4. Oxygen productlon--cold (21~

100-

9O-

80-

TO-

Laboratory Test-Gas Analysis

Time (minutes)

Fig. 5. Oxygen productlon--hot (s0"c).

100-

90-

8o-

7 o -

~_6o- ~,~o

30-

20-

10-

o

EEBD Hot Operation-Oxygen Content

Time (minutes)

TABLE II. AMBIENT AND UNDER-HOOD TEMPERATURES---GROUND LEVEL RUNS.

Ambient Temperature Hood Temperature (*C) (At Subject (*C) Time

Elapsed) Minimum Maximum Minimum Maximum [min]

A 21.4 21.4 22.7 34.8 (4:00) B 19.2 22.7 20.8 41.5 (15:00) C 18.7 19.9 20.6 28.4 (4:30)* D 19.6 23.1 23.6 36.3 (7:30)* E 20.0 21.8 23.2 45.5 (17:30)

* Run aborted before completion

high readings, the CO level in the chamber was reduced to 1,000 ppm for subject E. Post-run alveolar air samples from this subject showed no rise in COHb. The relative temperatures taken during the run, shown in Table III indicate again the conditions inside the hood.

Hypox ia Protection: The first three test runs had to be terminated before the rapid decompression because the oximeter probe was displaced during hood donning and could not be properly repositioned. After resolving this problem, four runs were successfully completed. The subjects' arterial oxygen saturation was maintained

above 97% during the sudden decompression and subsequent exercise at 7,010 m. Subject C, who had the smallest neck, did not complete the altitude run because of the oximeter problem mentioned. Following problem resolution, subject B, who had the next to smallest neck, did complete the run, and the observed oxygen levels were not lower than those of other subjects, as might have been expected (Fig. 10,11). The temperatures inside the hood increased with time, as mentioned previously. The max imum recorded temper- ature was 45.5~ after 17 min in an ambient temperature of 21.3~ Despite the relatively high temperatures inside the hood, no subject complained of unacceptable heat levels during the test run, even while exercising. Tests at higher ambient temperatures with human subjects were not done and personal communicat ions with the USAF School of Aerospace Medicine cautions that internal hood temperatures in excess of 60~ were recorded during their tests.

Vision and Communicat ion: Although the subjects could generally see well through the clear hood window, such small details as the numbers on the ergometer speedometer were blurred and unreadable. This problem was caused primarily by the crease in the centre of the window where the hood had been folded in its

USING SCOTT EEBD IN AIRCRAFF--MARTIN & POPPLOW

Oxygen Levels, Subject C 100-

Fig. 6. A poo r neck seal f rom a small neck c i rcumference (29 cm) al lowed s o m e di lut ion.

9 0 -

8 0 -

70 -

6 0 -

(1) ,J 5 0 -

x ~ 4 0 - o

3 0 -

20 -

10-

Time (minutes)

Fig. 7. A poo r neck seal f rom a small neck c i rcumference (29 cm) a l lowed a rapid CO In-leak.

1500 -

E O. t-~ 1000

._i 0 500 c~

0

CO Levels, Subject C

(Chamber CO Level : 5238 + 50 ppm.)

I i I I 1 2 3 4

Time (minutes)

Fig. 8. A poo r neck seal f rom improper h o o d posi t ion slightly low- ered the Sao2.

100-

90-

80-

70-

-J 5o- g

( ~ 4 0 -

30-

10-

0

Oxygen Level, Subject D

Time (minutes)

container. There was no noticeable misting of the facepiece/window during the trials, even though one subject experienced heavy facial perspiration due to the heat. Hearing was difficult for the subject because of generator noise inside the hood (the generator discharges into the hood near the subject's right ear). Speech from

inside the hood to an external observer was equally difficult.

DISCUSSION

The slightly shorter operating life observed during the

751

USING SCOTT EEBD IN A I R C R A F T - - M A R T I N & P O P P L O W

Fig. 9. A poor neck seal from improper hood position allowed some CO in-leak.

A 600

O~ --I ~ 400

0 0

0

CO Levels, Subject D

Time (minutes)

Fig. 10. Typical Sao2 levels ob- served.

100 - 90- 80-

70-

~ 50 ~ g ~ 40 -

30 -

20-

10-

0

Oxygen Levels, Subject B

Time (minutes)

Fig. 11. Typical CO levels s e r v e d .

5~- 4 ~ - ~ 3~- 3~-

oh- ~ 2~o- 200- 100 -

i r I I I

Time (minutes)

TABLE III. AMBIENT AND UNDER-HOOD TEMPERATURES--ALTITUDE RUNS.

Subject Ambient Temperature Hood Temperature (*C) (At

(*C) Time Elapsed)

Minimum Maximum Minimum Maximum [min]

A 21.0 25.3 23.1 30.4 (10:00)* B 21.7 24.4 21.0 3 0 . 5 (10:00)* C 20.1 24.3 21.9 38.5 (16:45) D 19.2 25.5 21.4 40.0 (16:30) E 18.9 26.2 23.1 41.4 (17:00) F 19.2 24.0 21.9 38.7 (16:30)

* Run aborted before completion

EEBD operation at high temperature agrees with results by the manufacturer (4), who explains that generator reaction is accelerated as the temperature increases, which results in increased oxygen production over a shorter time.

Only two of the five subjects experienced significant hood in-leakage. There was a limited volume of gas

available as a "counter lung" when the hood was on the head, and the partial collapse of the hood with each breath was thought to be the reason for the observed in-leakage. This point was especially valid for subject C, whose very small neck of 29 cm circumference did not fill the seal's minimum circumference of 33 cm. Nevertheless, the hood maintained 60% or better oxygen concentration even with this gross leakage, although the CO challenge gas quickly built up in the hood. The high leakage rate experienced by subject D (Fig. 9) was unexpected, and was probably due to the hood not being squarely positioned on the head. If the neck seal is pulled up and prevented from forming an airtight seal around the neck, a large in-leakage may develop. During an emergency, the wearer would be unaware of a loose neck seal, and so no attempt was made to improve the seal during these tests.

During the hypoxia protection runs, the low pressure inside the EEBD hood in operation relative to the gas sampler mounted outside the chamber, precluded direct sampling of the gas being breathed by the subject. As

USING S C O T T EEBD IN A I R C R A F T - - M A R T I N & P O P P L O W

a result, the blood oxygen saturation, continually mon- itored throughout the run, was the only check on the percentage of oxygen being received by the subject. The problems in donning the hood without disturbing the ear oximeter were greater than anticipated, but a redesigned suspension and moleskin skullcap helped considerably. Although subject C, with the smallest neck, could not complete the altitude run because of CO build-up, the positive results of subject B's run indicate that neck size is not a great problem with respect to hypoxia during high-altitude exposure. The high blood oxygen concentration levels were maintained by the EEBD and confirm its effectiveness in preventing hy- poxia. Heat build-up of 24"C in 17 min inside the hood was judged acceptable in ambient temperatures of 20~

CONCLUSIONS

From the results obtained during this evaluation, the following conclusions were drawn:

a. The consistency of the results indicates that the testing methods were reliable;

b. The Scott EEBD operated as advertised and generated oxygen of 95-100% concentration for 14.5-17.5 rain. Concentrations inside the hood worn by a human subject rose from an ambient 20% to 75% in approximately 70 s, then to the near-100% level until the generator was exhausted;

c. The Scott EEBD performance at 80"C was comparable with its performance at ambient temperatures, except that the generator operating life was shortened slightly with increased tem- perature;

d. In-leakage in a hostile breathing environment was minimal using subjects whose neck circum- ference was greater than 33 cm. For subjects with smaller necks, in-leakage was much greater but, in a life-threatening situation, this factor should not prejudice use of the EEBD;

e. The EEBD was able to prevent hypoxia in crew members for 15-17 min following a simulated typical accidental decompression of a pressurized aircraft. It must be noted, however, that crew functions could be impaired due to the loss of visual acuity and hearing impairment. For these reasons, it should not be considered for crew members, such as the cockpit crew, who require a high degree of visual acquity; and

f. Although the use of the EEBD created some discomfort and minor distress in the users because of high temperatures, the device per- formed well, proving its ability to save lives in the given circumstances.

REFERENCES

I. Duvall C, Laehinger N. Scott performance demonstration of Scott's EEBD for use in protecting tlight attendants during smoke emergencies. Scott Engineering Report No. ER 1185, October 1982.

2. McCann C, Noy I, Rodden B, Logan O. 1974 Anthropometric Survey of CF Personnel. DCIEM Report No. 75-R-1114, August 1975.

3. MacDonald GAH, Sharrard KA, Taylor MC. Preliminary anthropometric survey of Canadian Forces women. DCIEM Technical Report No. 78X20, July 1978.

4. Harwood V, Nettleland LG. Scott performance demonstration test report. Scott Engineering Report No. ER 1081, April 1976.

5. Harwood V, Netteland LG. Scott performance demonstration test report. Supplement to Report No. ER 1081, December 1976.