Report of Investigations 9650

Performance Comparison of Rescue Breathing

Apparatus

Nicholas Kyriazi

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES

Public Health Service

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

Pittsburgh Research Laboratory

Pittsburgh, PA

October 1999
International Standard Serial Number

ISSN 1066-5552
CONTENTS

Page

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Introduction ................................................................................... 2

Description of apparatus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Biomarine BioPak 45 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Biomarine BioPak 60 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Biomarine BioPak 240 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Draeger BG-174A ............................................................................ 5

Draeger BG 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Litton LITPAC II . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

MSA Custom 4500 II Air Mask ................................................................. 8

MSA Chemox . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

MSA McCaa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Sabre SEFA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Scott Rescue-Pak . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Siebe Gorman Aerorlox . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Siebe Gorman Proto Ten . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Survivair LP-120 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Test apparatus and experimental procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Results and discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Biomarine BioPak 45 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Biomarine BioPak 60 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Biomarine BioPak 240 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Draeger BG-174A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Draeger BG 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Litton LITPAC II . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

MSA Custom 4500 II Air Mask . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

MSA Chemox . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

MSA McCaa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Sabre SEFA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Scott Rescue-Pak . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Siebe Gorman Aerorlox . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Siebe Gorman Proto Ten . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Survivair LP-120 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

ILLUSTRATIONS

1. Biomarine BioPak 45 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2. Biomarine BioPak 45 schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

3. Biomarine BioPak 60 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

4. Biomarine BioPak 60 schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

5. Biomarine BioPak 240 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

6. Biomarine BioPak 240 schematic ............................................................... 5

7. Draeger BG-174A ........................................................................... 6

8. Draeger BG-174A schematic .................................................................. 6

9. Draeger BG-174A canister schematic ............................................................ 6

10. Draeger BG 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

11. Draeger BG 4 schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
CONTENTS—Continued

Page

12. Litton LITPAC II . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

13. Litton LITPAC II schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

14. MSA Custom 4500 II Air Mask ................................................................ 8

15. MSA Custom 4500 II Air Mask schematic ........................................................ 8

16. MSA Chemox . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

17. MSA Chemox schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

18. MSA McCaa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

19. MSA McCaa schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

20. Sabre SEFA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

21. Sabre SEFA schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

22. Scott Rescue-Pak . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

23. Scott Rescue-Pak schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

24. Siebe Gorman Aerorlox . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

25. Siebe Gorman Aerorlox schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

26. Siebe Gorman Proto Ten . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

27. Siebe Gorman Proto Ten schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

28. Survivair LP-120 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

29. Survivair LP-120 schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

30. Breathing and metabolic simulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

31. Durations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

32. CO2 levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

33. Differences between average and minimum inhaled CO2 levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

34. O2 levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

35. Temperatures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

36. Breathing pressures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

37. Pressure swings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

38. Breathing pressures during high-work-rate intervals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

TABLES

 1. Rescue breathing apparatus tested . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

 2. Means of average values of monitored physiological parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT

breaths/min breaths per minute L/min liter(s) per minute

ft foot (feet) min minute(s)

hr hour(s) mm H2O millimeter(s) of water pressure

kg kilograms(s) psi pound(s) per square inch

L liter(s) EC degrees Celsius

L/breath liter(s) per breath % percent
PERFORMANCE COMPARISON OF RESCUE BREATHING APPARATUS

By Nicholas Kyriazi1

ABSTRACT

A performance comparison of 14 rescue breathing apparatus was undertaken as an assessment of past and

present worldwide technology. Rescue breathing apparatus are self-contained, closed-circuit breathing

apparatus used for entry into areas having atmospheres that are immediately dangerous to life and health.

Apparatus tested were the Biomarine BioPak 45, 60, and 240; the Draeger BG 4 and BG-174A; the Litton

LITPAC II; the MSA Custom 4500 II Air Mask, Chemox, and McCaa; the Sabre Selected Elevated Flow

Apparatus (SEFA); the Scott Rescue-Pak; the Siebe Gorman Aerorlox and Proto Ten; and the Survivair

LP-120. The apparatus were tested on an automated breathing and metabolic simulator at the Pittsburgh

Research Laboratory of the National Institute for Occupational Safety and Health (NIOSH). Physiological

parameters monitored during the testing were average inhaled CO2 and O2, minimum inhaled CO2, inhaled wetand dry-bulb temperatures, and peak inhalation and exhalation breathing pressures. The metabolic demand

on the apparatus was 1.35 L O2/min for most of the test with two 5-min intervals of 2.5 L O2/min, the first

beginning 10 min into the test and the second beginning 10 min before the end of the rated duration of the

apparatus. Results presented include apparatus service life and test-averages of monitored physiological

parameters. Schematic drawings and photographs of the apparatus are also included.

The Draeger BG-174A and BG 4 had the highest durations—295 and 291 min, respectively. The BG 4 had

the lowest minimum inhaled CO2 levels, attesting to the effectiveness of its CO2-absorbent canister. The Sabre

SEFA had the lowest average inhaled CO2 levels, due mostly to the apparently low-dead-space mask and

nose cup. The MSA Air Mask, the only open-circuit device tested, had the lowest wet- and dry-bulb

temperatures, with the liquid-O2-source Siebe Gorman Aerorlox having the next lowest temperatures. The only

apparatus with a CO2-absorbent not in a packed-bed design, the BG-174A, had the lowest exhalation pressures.

The BG 4 had the highest level of positive pressure, with the Biomarine BioPak 60, Survivair LP-120, SEFA,

and Litton LITPAC II nearly as high. The BG 4 had the lowest pressure swing, with the SEFA a close second.

1

Biomedical engineer, Pittsburgh Research Laboratory, National Institute for Occupational Safety and Health, Pittsburgh, PA.
2

INTRODUCTION

In the event of a fire or explosion in underground coal

mines, the air is likely to be irrespirable because of toxic gases

or the absence of O2. For this reason, all underground coal

miners in the United States are required to have access to

emergency escape breathing apparatus. Performance

comparisons of such apparatus have been published by the

author [Kyriazi and Shubilla 1984; Kyriazi 1996]. In order to

recover the mine after a fire or explosion, or to rescue trapped

miners, mine rescue teams use long-duration, closed-circuit,

self-contained breathing apparatus for respiratory protection.

These are commonly called rescue breathing apparatus (RBA),

or entry, versus escape, apparatus.

In an effort to compare the performance of presently used,

commercially available apparatus and those that have been used

in the past, models of each type, which were either bought or

borrowed, were tested on an automated breathing and metabolic

simulator (BMS) [Kyriazi 1986]. Testing on a BMS enabled

the apparatus to be evaluated with identical and repeatable

inputs unlike human-subject testing. Although little attempt

was made to analyze the designs of the apparatus, an apparatus

designer can evaluate the effectiveness of the designs, which are

shown in schematic form, by comparing the performance

results. Consumers can use the performance results to help

decide which apparatus best suits their needs.

DESCRIPTION OF APPARATUS

All of the apparatus tested are similar in their basic

functions, which are to provide O2 to, and absorb CO2 produced

by, the user. The standard parts of the breathing apparatus

coming into contact with the user's exhaled air are the face

mask, breathing hoses, CO2-absorbent canister, and breathing

bag. O2 is stored in the apparatus as either a solid (potassium

superoxide (KO2)), a liquid, or a gas. The CO2 absorbents used

were lithium hydroxide (LiOH), calcium hydroxide (CaOH),

sodium hydroxide (NaOH), or a combination of these usually

simply poured into a canister (packed-bed design).

In general, exhaled air is channeled through the exhalation

breathing hose to the CO2-absorbent canister where the user's

CO2 is absorbed, and then to the flexible breathing bag. It is

stored there until it is drawn through the inhalation hose and

into the user's lungs upon inhalation. In most compressed-O2

apparatus, the O2 flows at a constant rate to the breathing bag

and is supplemented at times of higher O2 consumption by a

demand valve triggered by either low bag volume or a threshold

inhalation pressure. In contrast, when O2 consumption is lower

than the constant flow, the breathing bag fills to capacity and

begins venting to ambient through a relief valve triggered by

either high bag volume or a threshold exhalation pressure.

Table 1 lists the apparatus tested. A description of each

apparatus follows.

Table 1.—Rescue breathing apparatus tested

Apparatus

Rated

duratio

n,

hr

Country of

origin Gas supply Weight,kg

Biomarine BioPak 45 . . . . . . 0.75 U.S.A. . . . . . Compressed O2 . . . . 7.7

Biomarine BioPak 60 . . . . . . 1 U.S.A. . . . . . Compressed O2 . . . . 11.4

Biomarine BioPak 240 . . . . . 4 U.S.A. . . . . . Compressed O2 . . . . 17.7

Draeger BG-174A . . . . . . . . 4 Germany . . . Compressed O2 . . . . 15.8

Draeger BG 4 . . . . . . . . . . . 4 Germany . . . Compressed O2 . . . . 13.5

Litton LITPAC II . . . . . . . . . . 2 U.S.A. . . . . . Compressed gas . . . 13.6

MSA Air Mask . . . . . . . . . . . 1 U.S.A. . . . . . Compressed air . . . . 16.0

MSA Chemox . . . . . . . . . . . 1 U.S.A. . . . . . Chemical O2 . . . . . . 6.1

MSA McCaa . . . . . . . . . . . . 2 U.S.A. . . . . . Compressed O2 . . . . 17.7

Sabre SEFA . . . . . . . . . . . . 2 U.K. . . . . . . . Compressed O2 . . . . 16.0

Scott Rescue-Pak . . . . . . . . 4 U.S.A. . . . . . Compressed O2 . . . . 15.9

Siebe Gorman Aerorlox . . . . 3 U.K. . . . . . . . Liquid O2 . . . . . . . . . 13.4

Siebe Gorman Proto

Ten . . . . . . . . . . . . . . . . . . .

3 U.K. . . . . . . . Compressed O2 . . . . 15.0

Survivair LP-120 . . . . . . . . . 2 U.S.A. . . . . . Compressed O2 . . . . 10.0
3

Figure 1.—Biomarine BioPak 45. Figure 2.—Biomarine BioPak 45 schematic.

BIOMARINE BIOPAK 45

The BioPak 45 (figures 1-2) is a compressed-O2, closedcircuit apparatus with a disposable CO2-absorbent canister. It

was certified by the National Institute for Occupational Safety

and Health (NIOSH) in 1973 as a 45-min unit when the

O2 cylinder is filled to 2,100 psi (at room temperature). The O2

is delivered to the user at a rate of 3.6 L/min at ATPD (ambient

temperature and pressure, dry) with no demand valve. The CO2

absorbent is a form of soda lime (mostly calcium hydroxide).

Unlike most of the other apparatus tested, the BioPak 45 is

worn on the chest rather than the back. The face mask is

equipped with a speaking diaphragm. The low-pressure alarm

sounds at approximately 25% of capacity.

Exhaled air travels past the exhalation check valve in the

face mask, through the exhalation hose, through the CO2-

absorbent canister, and into the breathing bag. Air is inhaled

from the bag, through the inhalation breathing hose, past the

inhalation check valve, and into the face mask. There is an

optional coolant ring that surrounds the CO2-absorbent canister.

BIOMARINE BIOPAK 60

The BioPak 60 (figures 3-4) is a compressed-O2, closedcircuit apparatus with a refillable CO2-absorbent canister. It

was certified by NIOSH in 1978. It was certified again in 1988

as a positive-pressure device after that classification was added

in 1985. It contains approximately 170 L of O2 if filled to the

recommended cylinder pressure of 2,250 psi.2

 A constant flow

of 1.9 L O2/min (ATPD) plus a volume-activated demand valve

constitute the O2-delivery system. The relief valve is also

volume-activated. The CO2 absorbent is Sodasorb, a form of

 2

All volumes, unless otherwise noted, are listed at standard temperature and

pressure, dry.

soda lime. The low-pressure alarm sounds at approximately

25% of capacity.

The user exhales into the face mask containing both

inhalation and exhalation check valves, through the exhalation

hose, through the CO2-absorbent canister, and into the breathing

bag consisting of a spring-loaded, rigid diaphragm and a

flexible sleeve. The CO2-absorbent canister and breathing bag

are contained within the breathing chamber, as Biomarine calls

it. Upon inhalation, the air is drawn from the breathing bag

through the inhalation hose and check valve, and then into the

face mask. An anoxia-prevention valve, located in the

exhalation hose at the point that it enters the breathing chamber,

blocks exhalation flow unless opened by pressure provided by

the O2 cylinder. This prevents use of the apparatus unless the

O2 cylinder is opened and pressurized. It also signals the user

when the cylinder is empty by preventing exhalation into the

circuit.

The flow path through the breathing chamber is relatively

complex. The exhaled air enters an inlet plenum between the

CO2-absorbent canister and a solid plate separating it from the

breathing bag. The O2 constant flow enters the circuit at this

point, also. The exhaled air then travels through the absorbent

to an outlet plenum formed by the canister and the lid of the

breathing chamber. The exhaled air is then routed around

coolant rings containing sodium phosphate crystals, through

slots around the circumference of the housing, and into the

breathing bag.

The spring-loading on the diaphragm results in a positive

static pressure in the breathing circuit. The term "positivepressure" is derived from this feature. When the user demands

more air than is contained in the breathing bag, the diaphragm

presses against a demand valve, which causes O2 to flow into

the bag. The flow of O2 from the bypass valve is delivered to

the bag at a location on its circumference. If more air is exhaled

into the breathing bag than it can hold, the diaphragm presses

against a relief valve and vents the excess volume.
4

Figure 4.—Biomarine BioPak 60 schematic.

Figure 3.—Biomarine BioPak 60.
5

Figure 6.—Biomarine BioPak 240 schematic.

Figure 5.—Biomarine BioPak 240.

BIOMARINE BIOPAK 240

The BioPak 240 (figures 5-6) is a compressed-O2, closedcircuit apparatus with a refillable CO2-absorbent canister. It is

NIOSH-certified (1985) as a 4-hr apparatus and is separately

certified (1986) as a positive-pressure device. The fiberglasswrapped aluminum O2 cylinder contains approximately 535 L

of O2 at the recommended fill pressure of 3,000 psi at room

temperature. The BioPak 240 has a constant O2 flow of

1.65 L/min ATPD plus a volume-activated demand valve. The

relief valve is also volume-activated. The CO2 absorbent is

called Rexsorb, a form of soda lime. The low-pressure alarm

sounds at approximately 25% of capacity. Over the main

viewing area, the face mask has a double lens, which is intended

to minimize fogging.

The user exhales into the face mask containing the inhalation

and exhalation check valves, through the exhalation hose,

through the canister, and into a breathing bag. The configuration of the CO2-absorbent canister/breathing bag

component is the same as that of the BioPak 60. Upon

inhalation, the user draws air from the breathing bag, through a

heat-absorbent canister, and then through the inhalation hose

and check valve back to the face mask.

DRAEGER BG-174A

The BG-174A (figures 7-8) is a compressed-O2, closedcircuit apparatus with a disposable CO2-absorbent canister. It

is the most widely used long-duration closed-circuit breathing

apparatus in the world. Originally certified in 1966 by the

former U.S. Bureau of Mines (USBM) as a 2-hr apparatus, it

was NIOSH-certified in 1975 as a 4-hr apparatus. The O2

cylinder contains approximately 395 L of O2 at the

recommended fill pressure of 3,135 psi at room temperature.

The BG-174A has a constant flow of O2 of 1.5 L/min ATPD

plus a pressure-activated demand valve. The relief valve is also

pressure-activated. The CO2 absorbent is NaOH suspended in

.

.
6

Figure 8.—Draeger BG-174A schematic.

Figure 9.—Draeger BG-174A canister schematic.

Figure 10.—Draeger BG 4.

a crisscross, corrugated-screen bed (figure 9) designed to

prevent the NaOH from melting into a solid mass during use

The user exhales into the face mask, through the exhalation

hose, past the exhalation check valve, through the CO2-

absorbent canister, and into the breathing bag. Upon inhalation,

the user draws air from the breathing bag, through the valve box

and inhalation check valve, through the inhalation hose, and

back to the face mask.

The face mask includes a wiper that removes condensation

from the inside of the lens. A preflushing device operates when

the O2 cylinder is opened and fills the breathing bag with

approximately 6 L ATPD of O2, purging the circuit of a large

quantity of N2. If the user's O2 consumption rate is higher than

the O2 constant flow rate and the circuit contains a large

Figure 7.—Draeger BG-174A.

.

quantity of N2, the O2 concentration in compressed-O2 apparatus

can fall to subambient levels before the demand valve is

activated.

DRAEGER BG 4

The BG 4 (figures 10-11) is a compressed-O2, closed-circuit

apparatus with a disposable soda lime CO2-absorbent canister
7

Figure 11.—Draeger BG 4 schematic.

Figure 12.—Litton LITPAC II.

It has been NIOSH-certified four times (1995) as both a 3- and

4-hr apparatus and a standard- and positive-pressure apparatus.

The 4-hr, positive-pressure version of the BG 4 was tested using

the same O2 cylinder as that used for the BG-174A, which has

the same recommended fill pressure of 3,135 psi at room

temperature. The 3-hr version comes with a fiberglass-wrapped

cylinder. The BG 4 has a constant flow of O2 of at least

1.5 L/min ATPD plus a volume-activated demand valve. The

relief valve is also volume-activated and purges exhaled air

before it enters the CO2-absorbent canister. The face mask is

the same as that used with the BG-174A.

The user exhales into the face mask, through the exhalation

check valve and breathing hose, through the CO2-absorbent

canister, and into the spring-loaded breathing bag. Upon

inhalation, the user draws air from the breathing bag, through

the heat-absorbent canister, the inhalation hose and check valve,

and back to the face mask. The heat-absorbent canister works

by routing inhalation air around a chamber containing a large

cylinder of ice inserted just before use, formed in a separate ice

mold.

LITTON LITPAC II

The LITPAC II (figures 12-13) is a positive-pressure,

compressed-gas (39% O2), closed-circuit apparatus with a

refillable, CO2-absorbent canister. It was certified by NIOSH

in 1994 as a 2-hr, positive-pressure apparatus. Its targeted
8

Figure 13.—Litton LITPAC II schematic.

Figure 14.—MSA Custom 4500 II Air Mask.

Figure 15.—MSA Custom 4500 II Air Mask schematic.

market is mainly the fire service and other users who require

positive pressure even at high work rates. These users desire

durations longer than open-circuit apparatus can provide, but do

not want high O2 levels in the breathing circuit. This apparatus

was designed to pass the anticipated National Fire Protection

Association 1984 standard for closed-circuit apparatus.

The two gas cylinders contain 1,036 L ATPD of gas when

filled to 4,500 psi. The LITPAC II is a demand-only apparatus

with approximately 20% of each breath coming from the

cylinders through a positive-pressure-biased demand valve

regulator. The same portion of exhaled air is vented out of the

circuit on every exhalation through a pressure-biased

exhalation/relief valve. This strategy spares the CO2-absorbent

to some extent and provides cooler breathing air, but requires a

large quantity of supply gas. If one considers that open-circuit

apparatus draw 100% of each breath from the gas supply versus

approximately 4% for typical closed-circuit apparatus, this

apparatus can be seen as a cross between open- and closedcircuit.

The user exhales into the face mask, through the exhalation

breathing hose, into an exhalation/relief valve assembly

containing a check valve and a relief valve, both of which are

spring-loaded. The exhaled air then either exits the circuit via

the relief valve or enters the scrubber inlet bag. The air that

enters the scrubber inlet bag then passes through the CO2-

absorbent canister into a scrubber outlet bag, then into the

pressure vessel bag, which encases the two compressed-gas

cylinders. A small fourth bag made of thicker material,

functioning more as a duct, connects the pressure vessel bag

with the regulator. Inhalation draws air from the breathing bags

and the gas cylinders. The gas from the cylinders enters the

regulator through an injector nozzle, creating negative pressure

in the regulator, which draws air in from the breathing bags,

functioning as a sort of power-assist. This combination gascylinder/breathing-bag air is then drawn through the inhalation

breathing hose and back into the face mask.

MSA CUSTOM 4500 II AIR MASK

The Air Mask (figures 14-15) is a positive-pressure,

compressed-air, open-circuit apparatus with a belt-mounted

regulator. It is NIOSH-certified (1988) as a 1-hr apparatus. It

contains approximately 2,300 L of air that is delivered to the

user on a demand-only basis. As in all open-circuit apparatus,

every inhalation draws air from the air cylinder and every
9

Figure 16.—MSA Chemox.

Figure 17.—MSA Chemox schematic.

exhalation is vented to ambient. The face mask used for the

performance comparison did not have the nose cup accessory.

MSA CHEMOX

The Chemox (figures 16-17) is a chemical-O2, closed-circuit

apparatus with a disposable KO2 canister. It was certified by

the USBM in 1946 as a 1-hr breathing apparatus. Because it

was certified for less than a 2-hr duration, it was considered an

auxiliary rescue apparatus. It has seen extensive use from 1946

to the present as the primary U.S. Navy shipboard firefighting

apparatus progressing from the A-1 model to the presently used

A-4. The early models had no chlorate candles and differed in

the design of the breathing bag, relief valve, and the mechanism

and procedures for loading. The U.S. Navy calls the device the

OBA, short for O2 breathing apparatus. Like the BioPak 45, it

is worn on the chest rather than the back.

KO2 not only absorbs CO2 but also produces O2, so that a

separate O2 source is not needed. The new KO2 canisters

contain sodium chlorate "candles," which provide a quick

source of O2, permitting the apparatus to be worn immediately.

Otherwise, the KO2 needs three or four exhaled breaths, which

provide not only the H2O and CO2 required for the chemical

reactions, but also sufficient initial volume in the breathing bag

to permit self-contained use of the apparatus. Since there is no

O2 cylinder and gauge to indicate quantity of O2 remaining,

a timer is provided that informs the user how long the apparatus

has been in use. This allows for only a rough estimate of

remaining duration, however, since KO2 is strictly demandresponsive. KO2 overproduces O2 relative to human CO2

production such that the breathing bag is always full and

continually venting O2 through the volume-activated relief

valve. Earlier models had a manually activated relief valve.

The model tested was the A-4 with an automatic relief valve and

canisters containing chlorate candles.

Exhaled air goes through the exhalation check valve and

hose, through a passageway down the middle of the KO2

canister, up through the chemical bed, and is channeled to the

bottom of one breathing bag, sweeping over the inner surface of

the bag to a connecting tube terminating at the top of the other

breathing bag. Upon inhalation, the air is drawn from the

bottom of the second breathing bag, through the inhalation

breathing hose and check valve, then back into the face mask.

MSA McCAA

The McCaa (figures 18-19) is a compressed-O2, closedcircuit apparatus with a refillable CO2-absorbent canister that is

integral with the apparatus frame. It was originally approved by

the USBM in 1925 as a 2-hr apparatus and is permitted by

NIOSH to be used indefinitely as long as it is maintained in an

approved condition. The O2 cylinder contains approximately

243 L ATPD of O2 when filled to 1,985 psi at room

temperature. The McCaa does not have a constant flow of O2;

the demand valve regulator is activated by bag volume. The

relief valve is functionally combined with a saliva trap release

in the face mask and is manually activated. The CO2 absorbent

is called Cardoxide, which consists mostly of CaOH.

The user exhales into a face mask or a mouthpiece, through

an exhalation check valve and hose, through the CO2-absorbent

canister, to the 8-L breathing bag. Inhaling draws air from the

breathing bag, through a large plenum formed by the entire case

housing that serves as a heat radiator, and through the inhalation
10

Figure 18.—MSA McCaa.

Figure 19.—MSA McCaa schematic.

Figure 20.—Sabre SEFA.

hose and check valve in the face mask or the mouthpiece.

A face mask without a nose cup was used in this testing.

This device is no longer used to any extent. It is claimed that

this apparatus is positive-pressure with a static head pressure of

about 6 mm H2O. This claim is made by Grove [1941], but the

breathing circuit pressure does not remain positive during

inhalation and would certainly not qualify as positive-pressure

by present standards.

SABRE SEFA

The SEFA (Selected Elevated Flow Apparatus) (figures 20-21) is a compressed-O2, positive-pressure, closed-circuit

apparatus with a refillable CO2-absorbent canister. It

was approved by the U.K. Health and Safety Executive in 1985

as a 2-hr apparatus in its low-flow mode, with a constant flow

of O2 of 5 L/min ATPD. In its high-flow mode—10 L/min

ATPD—it is certified for 1-hr duration. It contains 750 L

ATPD of O2 at a pressure of 3,000 psi at room temperature. It

has no demand valve. The pressure-activated relief valve is

located upstream of the canister, venting exhaled air before it

has been cleansed of CO2 or enriched with O2. The CO2-

absorbent canister is filled with SEFAsorb, consisting mostly

of CaOH.

The user exhales into the face mask, through an exhalation

check valve and hose, through the CO2-absorbent canister, and

through a heat exchanger to the 6-L breathing bag, consisting of

a spring-loaded, rigid diaphragm connected to a flexible sleeve.

Inhaled air is drawn from the bag, through the inhalation

breathing hose and check valve, then back to the face mask.

The heat exchanger functions in tandem with the ambient-air

chamber containing the breathing bag. The volume in the

ambient-air side of the chamber increases when the breathing

bag decreases, during inhalation, drawing ambient air through

two check valves in the panel separating the chamber from the

O2 cylinder compartment. Upon exhalation, the breathing bag

volume increases, forcing the ambient air in the chamber out

through the outside and core of the wetted heat exchanger,

drawing heat—through the evaporation of the water as well as

direct conduction—from the hot exhaled air passing in the

opposite direction through the middle plenum of the heat

exchanger on the way from the canister to the breathing

chamber. Two relief valves in the panel separating the ambient

air chamber from the O2 cylinder compartment permit ambient

air in the chamber to escape if exhalation pressure becomes

too high.
11

Figure 21.—Sabre SEFA schematic.

Figure 22.—Scott Rescue-Pak.

SCOTT RESCUE-PAK

The Rescue-Pak (figures 22-23) is a compressed-O2, closedcircuit apparatus with a disposable CO2-absorbent canister. It

is NIOSH-certified (1975) as a 4-hr apparatus. The O2 cylinder

contains 435 L ATPD at a pressure of 1,980 psi at room

temperature. A constant O2 flow of 1.5 L/min ATPD is

augmented by a volume-activated demand valve. The relief

valve is also volume-activated and dumps exhaled air from the

breathing circuit before it enters the CO2-absorbent canister.

The CO2 absorbent is LiOH.

Exhaled air passes through the exhalation check valve and

breathing hose, through the CO2-absorbent canister, and into the

breathing bag, which consists of a rigid diaphragm attached to

a flexible sleeve. Air is inhaled from the breathing bag, through

the inhalation breathing hose and check valve, then back to the

face mask. The relief valve is activated by the movable

diaphragm of the breathing bag, but channels the excess volume

from the exhaled column of air just before it enters the CO2-

absorbent canister. This feature conserves both the absorbent

and the O2 supply, since the vented exhaled air has not yet been

cleansed of CO2 nor enriched with O2.

SIEBE GORMAN AERORLOX

The Aerorlox (figures 24-25) is a liquid-O2, closed-circuit

apparatus with a refillable CO2-absorbent canister. It is

NIOSH-certified (1973) as a 3-hr apparatus. It is filled with

3 kg of liquid O2 and provides a flow of between 6 and 12 L

O2/min to the breathing circuit. The pressure-activated relief

valve continually vents the excess volume of breathing air in the

circuit. The CO2 absorbent is 8-12 mesh Protosorb, a soda lime

that is mostly CaOH. 
12

Figure 23.—Scott Rescue-Pak schematic.

Figure 24.—Siebe Gorman Aerorlox.

Figure 25.—Siebe Gorman Aerorlox schematic.

Exhaled air is channeled through a check valve in the face

mask through the exhalation breathing hose, through the radial

CO2-absorbent canister, around the liquid-O2 dewar (called an

evaporator), which cools the air on its way to the breathing bag.

The moisture that is condensed from the air as it passes over the

evaporator collects in the breathing bag. The inhaled air is

drawn from the breathing bag around the evaporator again, then

through the inhalation breathing hose and back to the face

mask, through the nose cup, which contains two inhalation

check valves. The O2 flows from the evaporator into the

breathing bag.

SIEBE GORMAN PROTO TEN

The Proto Ten (figures 26-27) is a compressed-O2, closedcircuit apparatus with a refillable CO2-absorbent canister. It

was certified by the USBM in 1968 as a 3-hr apparatus. The

cylinder contains 400 L ATPD of O2 when filled to 2,840 psi at

room temperature. A constant O2 flow of 1.5 L/min ATPD is

provided and augmented by a pressure-activated demand valve.

The relief valve is also pressure-activated. The CO2 absorbent

is Protosorb, a soda lime composed mostly of CaOH.

Exhaled air from the face mask passes through the exhalation

hose and check valve through the radial CO2-absorbent canister

housed in a metal shell, which also contains an inverse

breathing bag, a heat-absorbent canister, and a warning whistle.

The breathing circuit air is contained within the metal shell and

contacts the exterior of the breathing bag, the interior of which

is open to ambient. Air is inhaled from the shell interior,

through a metal tube connected to the heat-absorbent canister,

through the inhalation check valve and hose, and back to the

face mask.

The inverse breathing bag design results in the breathing

circuit air contacting the metal shell, enabling heat to be
13

Figure 26.—Siebe Gorman Proto Ten.

Figure 27.—Siebe Gorman Proto Ten schematic.

radiated to air in a plenum vented to ambient. A chamois cloth

jacket covers the exterior of the metal shell. The jacket is

wetted from water coming from the ice melting in the heatabsorbent canister, which is wicked through a hole in the

canister to two positions on each side of the surface of the shell.

The water in the chamois jacket evaporating to ambient cools

the surface of the metal shell. Heat is transferred to ambient

also through the breathing bag, which pulls ambient air into it

with each breath. A sponge at the bottom of the inside of the

metal shell, under the CO2-absorbent canister, holds the water

released by the chemical reaction.

SURVIVAIR LP-120

The LP-120 (figures 28-29) is a prototype, compressed-O2,

closed-circuit apparatus with a refillable, LiOH CO2-absorbent

canister. It is NIOSH-certified (1987) as a 2-hr apparatus. The

O2 cylinder contains 240 L ATPD at a pressure of 3,000 psi.

O2 is delivered on a demand-only basis by a positive-pressurebiased, pressure-activated, demand valve. The relief valve is

also pressure-activated. The apparatus functions as a positivepressure system, but was not submitted for certification under

that category because of the use restrictions for pure-O2

apparatus in the positive-pressure, closed-circuit apparatus

category.
14

Figure 28.—Survivair LP-120.

Figure 29.—Survivair LP-120 schematic.

Figure 30.—Breathing and metabolic simulator.

The user exhales into the face mask, through the exhalation

breathing hose, past the exhalation check valves, and into the

exhalation breathing bag. Some of the exhaled air passes

through the CO2-absorbent canister and heat-absorbent

canister, into the inhalation breathing bag. When the user

inhales, some of the air is drawn from the inhalation breathing

bag and some from the exhalation breathing bag, across the

CO2-absorbent and heat-absorbent canisters. The inhaled air

continues through the inhalation check valves and breathing

hose, then back to the face mask. The dual-breathing bag

design splits the breathing pressures of the CO2-absorbent

canister between inhalation and exhalation rather than only on

exhalation.

The heat-absorbent canister contains LiNO3, a phase-change

material that is formulated to melt at about 27 EC.

TEST APPARATUS AND EXPERIMENTAL PROCEDURE

Unlike human subjects, the BMS used in this study (figure 30) elicits a constant and repeatable metabolic demand on

the breathing apparatus. Human-subject testing of a breathing

apparatus is similar to evaluating the output of a black box with

an unknown input. Use of the BMS provides a known input.

The BMS simulates O2 consumption and CO2 production, reproduces humanlike waveforms, and heats and humidifies the

inhaled air.

The metabolic work rates used in this study are:

Work rate 1

VO2 (O2 consumption) ' 1.35 L/min

VCO2 (CO2 production) ' 1.10 L/min

Ve (ventilation) ' 30 L/min

Vt

 (tidal volume) ' 1.67 L/breath

RF (respiratory frequency) ' 17.9 breaths/min

Qpeak (peak flow rate) ' 67 L/min (exhalation)

 ' 83 L/min (inhalation)
15

Work rate 2

VO2 (O2 consumption) ' 2.50 L/min

VCO2 (CO2 production) ' 2.50 L/min

Ve (ventilation) ' 54.8 L/min

Vt

 (tidal volume) ' 2.45 L/breath

RF (respiratory frequency) ' 22.4 breaths/min

Qpeak (peak flow rate) ' 115 L/min (exhalation)

 ' 149 L/min (inhalation)

Most of the test consisted of work rate 1 with the addition of

two 5-min intervals of work rate 2, the first beginning 10 min

into the test and the second beginning 10 min before the end of

the rated duration of the apparatus. This was done not only to

evaluate performance at a higher work rate, but also to

determine if this performance is maintained as the apparatus

nears depletion.

The physiological parameters measured were average inhaled

concentrations of CO2 and O2, minimum inhaled CO2, end-ofbreath inhaled wet- and dry-bulb temperatures, and inhalation

and exhalation peak breathing pressures. Measure-ments were

calculated over a two-breath period and averaged each minute.

Test-averages were derived from the minute-averages, including

the two high-work-rate periods. At least five tests were run on

each apparatus.

The levels of the physiological parameters considered to be

acceptable here are:

Average inhaled CO2 <4%

Average inhaled O2 >15%

Wet-bulb temperature <50 EC

Exhalation pressure <200 mm H2O

Inhalation pressure >&300 mm H2O

The average inhaled gas concentrations include the

contribution of any dead space in the face mask or hoses.

(Dead space is that apparatus volume containing exhaled air that

will be reinhaled.) All measurements were made at the mouth

of the headform except the wet-bulb temperature, which,

because of the configuration of the wet-bulb thermocouple

[Kyriazi 1988], was placed at the back of the neck of the

headform.

The wet-bulb temperature reflects both temperature and

humidity. The wet-bulb temperature is the temperature actually

perceived by the wearer with the wet human respiratory tract

functioning essentially as a wet-bulb thermometer.

A test was terminated when the O2 supply was exhausted, if

average inhaled CO2 reached 10%, or if average inhaled O2 fell

below 15%. A depleted O2 supply is the preferred termination

mode since this can be determined by the user without the aid

of instrumentation. Termination under the other conditions is

undesirable because the safety of the user may be compromised.

In some cases, average inhaled CO2 level was permitted to

exceed 10% because the O2 supply was nearly exhausted, and

the test was permitted to continue until complete exhaustion.

RESULTS AND DISCUSSION

Table 2 lists the means of the test-average values of each

physiological parameter for each model of apparatus.

Figures 31-38 graphically illustrate the results of table 2.

Figure 33 shows the differences between the average and

minimum inhaled CO2, which can be interpreted as some

indication of quantity of apparatus dead space. If there were no

dead space and the minimum inhaled CO2 remained at a steady

level from beginning to end of inhalation, average and minimum

inhaled CO2 would be equal. The greater the dead space, the

higher the difference between the two values. It is not

surprising, therefore, that the two apparatus with no face mask

nose cups (MSA Air Mask and McCaa) have the highest deadspace values. A small difference between the wet- and dry-bulb

temperatures, shown in figure 35, indicates that the air was

humid; a large difference means dry air. Pressure swing, as

depicted in figure 37, is the combination of inhalation and

exhalation breathing pressures.

The duration obtained from a compressed-O2 apparatus is

entirely dependent upon how much O2 is contained in the

cylinder. Filling compressed-O2 cylinders rapidly to high

pressures results in the heating of both gas and cylinder. If

filled exactly to the recommended pressure, the final pressure

after cooling will be below this level, requiring additional

filling. Final cylinder pressures varied based on filling

procedures and ambient temperatures, with some settling below

and some above the manufacturer's recommended pressure.

The durations listed in table 2 for gaseous-O2 apparatus were

those actually attained, with the standard deviations reflective

of the arbitrary differences in fill pressures, and the estimated

durations for the apparatus if their storage vessels had been

filled to their recommended levels.

In addition to the numerical results, discussions of unusual

or notable behavior and/or comments about the testing follow

the table and figures.
16

Table 2.—Means of average values of monitored physiological parameters (standard deviations)

Apparatus

Duration, min

Cause of

termination

Average

inhaled

O2, %

Average

inhaled

CO2, %

Minimum

inhaled

CO2, %

Exhalation

pressure,

mm H2O Average of

all tests

At recommended

fill

pressure

Biomarine BioPak 45 . . . . . 51 (3) 51 Empty 80 (1) 1.7 (0.3) 0.8 (0.3) 46 (3)

Biomarine BioPak 60 . . . . . 80 (2) 80 Empty 88 (1) 0.8 (0.1) 0.1 (0) 82 (3)

Biomarine BioPak 240 . . . . 264 (6) 264 High CO2 87 (2) 1.4 (0.1) 0.6 (0.1) 69 (1)

Draeger BG-174A ....... 295 (9) 298 Empty 62 (6) 1.2 (0.3) 0.4 (0.2) 26 (4)

Draeger BG 4 .......... 291 (17) 299 Empty 90 (2) 1.3 (0.1) 0 (0) 44 (1)

Litton LITPAC II . . . . . . . . . 138 (15) 130 Low O2 25 (1) 1.0 (0.2) 0.1 (0.1) 51 (1)

MSA Custom 4500 II

 Air Mask . . . . . . . . . . . . . 62 (4) 66 Empty 19 (1) 1.8 (0) 0.1 (0) 63 (1)

MSA Chemox . . . . . . . . . . 70 (4) — Empty 76 (3) 3.6 (0.8) 3.0 (0.9) 93 (5)

MSA McCaa . . . . . . . . . . . 130 (10) 137 Empty 60 (8) 4.0 (0.5) 1.6 (0.4) 42 (4)

Sabre SEFA . . . . . . . . . . . 174 (3) 176 Empty 87 (2) 0.5 (0.1) 0.1 (0) 39 (1)

Scott Rescue-Pak . . . . . . . 265 (18) 293 Empty 73 (4) 1.1 (0.2) 0.3 (0.2) 42 (3)

Siebe Gorman Aerorlox . . . 228 (8) 216 Empty 96 (1) 1.0 (0.1) 0.1 (0) 51 (1)

Siebe Gorman Proto

Ten . . . . . . . . . . . . . . . . . .

 130 (13) — Empty 45 (17) 1.5 (0.6) 0.9 (0.7) 33 (3)

Survivair LP-120 . . . . . . . . 141 (7) 137 Empty 63 (8) 1.6 (0.1) 1.0 (0.1) 58 (3)

Apparatus

Inhalation

pressure,

mm H2O

Highdemand 1

exhalation

pressure,

mm H2O

Highdemand 2

exhalation

pressure,

mm H2O

Highdemand 1

inhalation

pressure,

mm H2O

Highdemand 2

inhalation

pressure,

mm H2O

Inhalation

wet-bulb

temperature, EC

Inhalation

dry-bulb

temperature, EC

Biomarine BioPak 45 . . . . . . &27 (2) 73 (10) 72 (9) &46 (7) &45 (3) 34 (0) 35 (1)

Biomarine BioPak 60 . . . . . . 6 (2) 112 (2) 119 (1) &18 (2) &28 (2) 34 (1) 36 (1)

Biomarine BioPak 240 . . . . . 0 (3) 87 (1) 99 (3) &31 (1) &39 (6) 32 (1) 34 (1)

Draeger BG-174A ........ &26 (5) 47 (4) 70 (9) &45 (2) &56 (3) 36 (1) 39 (1)

Draeger BG 4 . . . . . . . . . . . 8 (2) 55 (3) 53 (2) &6 (2) &13 (3) 32 (1) 34 (1)

Litton LITPAC II . . . . . . . . . . 0 (1) 56 (2) 57 (2) 0 (3) &12 (4) 29 (2) 31 (2)

MSA Custom 4500 II

 Air Mask . . . . . . . . . . . . . . &20 (2) 66 (1) 68 (1) &41 (3) &44 (3) 14 (0) 18 (0)

MSA Chemox . . . . . . . . . . . &27 (2) 141 (8) 164 (13) &65 (3) &73 (3) 22 (1) 32 (1)

MSA McCaa . . . . . . . . . . . . &42 (4) 90 (7) 121 (16) &70 (1) &141 (74) 34 (1) 38 (1)

Sabre SEFA . . . . . . . . . . . . 0 (1) 54 (2) 56 (2) &23 (2) &25 (1) 34 (1) 35 (1)

Scott Rescue-Pak . . . . . . . . &33 (2) 78 (5) 92 (9) &58 (2) &68 (5) 35 (1) 38 (1)

Siebe Gorman Aerorlox .... &26 (1) 92 (2) 87 (1) &62 (2) &58 (1) 16 (0) 20 (1)

Siebe Gorman Proto Ten . . &70 (17) 66 (5) — &101 (8) — 30 (3) 31 (1)

Survivair LP-120 . . . . . . . . . 2 (3) 84 (3) 84 (3) &8 (4) &12 (4) 34 (1) 35 (1)
17

Figure 31.—Durations.
18

Figure 32.—CO2 levels.
19

Figure 33.—Differences between average and minimum inhaled CO2 levels.
20

Figure 34.—O2 levels.
21

Figure 35.—Wet-bulb (WB) and dry-bulb (DB) temperatures.
22

Figure 36.—Breathing pressures.
23

Figure 37.—Pressure swings.
24

Figure 38.—Breathing pressures during high-work-rate intervals.
25

BIOMARINE BIOPAK 45

This apparatus is no longer being manufactured, and the

apparatus tested was of advanced age. This was not particularly

evident except for one peculiarity that surfaced after several

tests had been performed. Either or both of the check valves in

the face mask began to leak. Exhalation check valve leakage

causes exhaled air in the exhalation hose to be reinhaled,

effectively increasing the dead space and causing the average

inhaled CO2 to incrementally rise in value. Inhalation check

valve leakage permits exhaled air to enter the inhalation hose.

This high-CO2 air is then reinhaled, again effectively increasing

the dead space and causing the average inhaled CO2 to

incrementally rise in value. When the check valves leaked,

average inhaled CO2 values were approximately 3.5% compared

with approximately 0.9% when they sealed properly. If this

problem were to occur in actual use, a user would respond to

the higher level of CO2 by increasing his ventilation rate, which

would result in the valves sealing better, thereby lowering the

CO2 level.

During the high work periods, the valves seemed to begin

functioning again, with average inhaled CO2 levels dropping.

Presumably, the higher ventilation rates forced the valves to seat

properly. At the manufacturer's suggestion, newer check valves

from the face mask of the BioPak 240 were installed in the

BioPak 45 face mask. These check valves sealed properly

during the test performed immediately after their installation.

After sitting over a weekend, however, they warped. This was

discovered after the next test again showed high average inhaled

levels of CO2. The manufacturer later informed PRL that the

check valves from the two apparatus were not identical.

Biomarine then sent a new set of apparatus-specific check

valves, which functioned properly in the remaining tests.

BIOMARINE BIOPAK 60

During the two periods of work rate 2, both the demand and

relief valves were activated, indicating that the tidal volume

(volume of a breath) was larger than the volume of the

breathing bag. This is wasteful of the cylinder gas.

BIOMARINE BIOPAK 240

Throughout its rated duration, the average inhaled CO2 of

the BioPak 240 remained low and the O2 high. Every test,

however, was terminated due to high CO2 (10%), with an

average duration of 264 min with at least 600 psi left in the

cylinder. High CO2 level is not a positive indicator of end-oflife, i.e., it is not easily evident without instrumentation. A user

would increase his ventilation rate at higher values of CO2 and

would increasingly desire to remove the apparatus. Ideally, the

scrubber would be oversized relative to the quantity of available

O2. It could be that the manufacturer counts on a certain

amount of outleakage of O2 in normal use due to imperfect face

mask sealing. In these tests, the face mask was sealed with

putty to the headform with no leakage.

As with the BioPak 60, during the high-work-rate intervals,

both the demand valve and relief valve were activated with each

breath, which wastes cylinder gas. Possibly this is intentional,

since reducing the gas supply brings it closer in capacity to that

of the CO2-absorbent canister.

DRAEGER BG-174A

The BG-174 had the lowest exhalation pressure of any

apparatus tested here. This is due mostly to the CO2 bed design,

which suspends the chemical absorbent in a wire mesh rather

than a packed bed.

DRAEGER BG 4

This apparatus had the lowest minimum inhaled CO2 of any

apparatus tested, including the open-circuit MSA Air Mask,

testifying to both the efficiency of the canister and the fact that

its face mask included a nose cup. In the Air Mask tests, the

lack of a nose cup resulted in the nonzero minimum inhaled

CO2 level measured. In addition, the BG 4 had the lowest

absolute pressure swing—exhalation and inhalation peak

pressures combined—of any apparatus tested in this study.

LITTON LITPAC II

In the LITPAC II, the low-pressure alarm sounds at

approximately 25% of capacity and continues until the cylinders

are empty. Users should remove the apparatus when the alarm

ceases because O2 drops immediately thereafter. Although the

user's manual states that it becomes difficult to inhale when the

cylinders are empty, it was found that O2 fell below 15% before

inhalation pressure increased significantly. This occurred only

after the low-pressure alarm stopped sounding, however.

Although this apparatus was designed so that face mask

pressure never becomes negative relative to ambient, very shortduration inhalation pressure spikes occurred on every breath,

eventually becoming negative toward the end of the test. These

are the values measured and reported, but the inhalation face

mask pressures, excepting these spikes, were ap-proximately

20 mm H2O, remaining well above ambient even during the

high-demand intervals. Although the reported positive-pressure

performance of the LITPAC II is comparable to the Draeger

BG 4 and Survivair LP-120 in being among the best performing

apparatus during the high-demand intervals, measuring average

inhalation pressures instead of peak inhalation pressures would

undoubtedly improve the measured performance of this

apparatus over that of the others.
26

MSA CUSTOM 4500 II AIR MASK

Very short-duration negative inhalation pressure spikes of

approximately &15 mm H2O occurred on every breath with this

apparatus, but the inhalation pressure during most of the

inhalation was approximately 15 mm H2O. During the highdemand intervals, initial spikes of approximately &45 mm H2O

were followed by diminishing oscillations, with pressure

stabilizing at approximately %20 mm H2O. As with the

LITPAC II, measuring average inhalation pressures instead of

peak inhalation pressures would better reflect actual user impact

since, in the event of a breathing circuit leak from ambient, the

degree of in-leakage depends upon both the level and duration

of the negative pressure.

It was somewhat surprising that the minimum inhaled CO2

level was not zero for an open-circuit apparatus. This can be

explained, however, by the fact that the face mask did not have

a nose cup. Nose cups not only reduce the face mask dead

space volume, reducing the average inhaled CO2 level, but are

also designed without remote corners so that CO2 is swept

cleanly at once from the contained space rather than trickling

out a little at a time which seems to have happened here. Since

the cylinder air contained no CO2, this is the only possible

explanation for a nonzero minimum inhaled CO2 level.

MSA CHEMOX

 Except for the Aerorlox, which has a cold O2 source, and

the open-circuit Air Mask, the Chemox provided inspired air

with the lowest wet-bulb temperature of any apparatus tested.

There was a large difference between wet- and dry-bulb

temperatures, indicating relatively dry air. The low wet-bulb

temperature is attributed to the inherently dry air produced by

KO2, causing heat of evaporation to be drawn from the

respiratory tract. The low dry-bulb temperature can be

attributed to the design feature of the apparatus that forces air

to sweep over the inner surfaces of the exposed breathing bags

from one end to the other, maximizing heat exchange with the

cooler laboratory environment. Of course, in a warmer

environment, this feature would be less effective and, with

rising ambient temperature, would begin to add heat to the

breathing-circuit air.

On the negative side, the CO2 and breathing resistance levels

were high. The second, 5-min, high-workload interval,

beginning at 50 min, usually brought average inhaled CO2 up to

10% and beyond. Since substantial recovery occurred after this

interval, the test was permitted to continue, but CO2 continued

to rise after this recovery. Since the breathing bag volume was

rapidly decreasing as average inhaled CO2 levels reached 10%,

the test was not terminated until the breathing bag was empty.

High inhaled CO2 concentration is not considered a positive

indicator of end-of-life, nor desirable. A person would likely

have removed the apparatus by the time CO2 levels reached

10%. It should be noted, however, that the apparatus passes the

standard U.S. Navy step test.

The performance of the Chemox is extremely dependent on

the KO2 canister, as might be expected. The canister determines

the O2 production and CO2 absorption and greatly influences

temperatures and exhalation pressure. Only inhalation pressure

is related more to the rest of the apparatus than to the canister.

The performance of the Chemox is, therefore, naturally

dependent on the formulation of KO2 used in the canisters.

Canisters from three batches of KO2 were used randomly in this

study, with CO2 and pressure seeming to be particularly batchsensitive, and temperature and O2 appearing to be less so.

On one apparatus from an old batch of canisters, the chlorate

candle pull cord slipped out of the firing pin, requiring the

candle to be activated by pulling the pin out with pliers.

Assuming that under normal circumstances this action would be

taken while still in good air, this is not considered to be a

dangerous defect.

MSA McCAA

In order to test the McCaa, because of its aging and deteriorating parts, we had to have the O2 cylinders hydrostatically

tested and combine the good parts of two apparatus to make one

functional unit. The regulator of one apparatus malfunctioned

and caused a downstream O2-supply line to burst. The CO2-

absorbent canister of the other apparatus, which is integral with

the entire frame and body, had its lower screen excessively

clogged with hardened absorbent. Because of this, after 20 to

40 min of use, the breathing pressures approximately doubled.

The pressures remained at that level for the duration of the test.

The visibly cleaner canister screen of the second apparatus did

not experience this phenomenon and was used for all recorded

tests.

The termination mode was low bag volume in every test,

although average inhaled CO2 levels were high in general, due

in part to the lack of a nose cup in the face mask, and in two

cases reached 10% in the second 5-min, high-work interval.

The test with the longest duration, 144 min, reached average

inhaled CO2 levels of 10% at 135 min.

The demand valve was activated generally once every three

breaths at the start of the tests. Later in the tests, as the pressure

in the O2 cylinder fell, the demand valve was activated

generally once every two breaths. Near the ends of the tests,

the demand valve was activated every breath. This

phenomenon is attributed to the delivery of more O2 than

demanded at first, then less overdelivery as cylinder pressure

decreased. The large variation in pressures experienced in the

second, 5-min, high-work interval is believed to be a result of

variations in the cylinder pressures. Lower cylinder pressure

seemed to cause the demand valve to be less responsive,

resulting in greater inhalation pressure. With higher cylinder
27

pressure during the second 5-min high-work interval, the

inhalation pressure averaged in the &80 mm H2O range; with

lower cylinder pressure, this value increased to &250 mm H2O.

SABRE SEFA

The SEFA was tested at the low-flow (5 L/min) regulator

setting. Even the "low" O2 flow rate, however, was much

greater than the test O2 consumption rate, so that the relief valve

was activated on every breath. This characteristic spares the

CO2-absorbent canister by dumping high-CO2 air, and ensures

a high concentration of O2 throughout the test. The SEFA had

the lowest average inhaled CO2 of any apparatus tested, as well

as the lowest difference between average and minimum values,

indicating low face mask dead space. The SEFA also had the

lowest exhalation peak pressures of any positive-pressure

apparatus.

SCOTT RESCUE-PAK

This apparatus is no longer being manufactured, so new

CO2-absorbent canisters were unavailable. The CO2-absorbent

canisters used for the Rescue-Pak varied in condition from

questionably sealed to positively sealed, but all were past the

recommended use date by nearly 2 years. LiOH does not

degrade with age, however, so all the canisters were used.

Although there was variation between individual canisters, all

of them maintained very low CO2 levels.

Two Rescue-Paks were tested. Five tests were run on one

and three on the other. The data from both apparatus were

combined since the differences between them were negligible.

The O2 cylinder fill requirement was from 1,800 to 2,000 psi.

This low pressure enabled them to be filled from standard 4.5-

ft-tall cylinders. Since we did not yet have an O2 pump on site,

this expedited testing. As the supply cylinder was depleted,

however, less O2 was available to the apparatus cylinders,

resulting in less duration and more variation in duration than

would be seen if each cylinder had been filled by a pump to a

targeted pressure. The average cylinder pressure achieved was

approximately 1,780 psi on the first seven tests. The last test

was with a cylinder at 2,000 psi filled by a pump. This test

lasted 297 min compared with an average of 260 min for the

first seven tests, with a standard deviation of 11 min. The

average inhaled CO2 concentration for the last test was only

.01% higher than the average of the first seven tests indicating

that the extended duration resulted in no CO2 breakthrough.

The demand valve was usually activated during the tests, but

did not seem to add to the inhalation pressure, probably because

it is volume-activated, rather than pressure-activated.

SIEBE GORMAN AERORLOX

The most difficult challenge in testing this device was

obtaining the liquid O2 and filling the device. Once the

apparatus had been filled, however, it became the simplest

device to test. It has no demand valves, regulators, or gauges.

It was certainly the coolest closed-circuit apparatus tested and

had the highest O2 concentration due to the high O2 flow rate of

6-12 L/min, which mostly exited the relief valve.

The Aerorlox is no longer being manufactured, but Siebe

Gorman will make custom replacement parts if desired for its

remaining users.

SIEBE GORMAN PROTO TEN

This apparatus presented many obstacles to testing; some

parts were missing while others had deteriorated, compromising

performance. It is no longer being manufactured and Siebe

Gorman had no spare parts. The inhalation check valve could

not be located; a Rudolph 1800 check valve was used in its

place. The metal frame of the apparatus, containing the CO2-

absorbent canister, the breathing bag and the heat-absorbent

canister, had a crack in a weld joint which had to be repaired.

The bypass valve kept opening on its own and had to be

screwed down shut. We could not locate the ice mold to form

a block of ice for the heat-absorbent canister, so small ice cubes

were used instead. The most serious problem, however, was

found after six tests had been performed. It was discovered that

the O2 supply lines were leaking along their entire lengths and

could neither be repaired nor replaced. This resulted in a large

quantity of the O2 supply being lost to ambient, preventing the

3-hr-rated apparatus from attaining its intended duration. This

means that the CO2-absorbent canister was never pushed to its

limit and that, in general, late test performance was not

observed and averaged in with the early test data; this resulted

in favorably biased average performance results. Given all

these problems, the apparatus would not have been included in

this study at all were it not for its unique design.

The test averages were calculated from the best four tests, all

of which still suffered from one or more problems,

compromising their validity to some extent. All the durations

were short due to the leaky O2-supply hoses, and some of the

tests suffered from random activation of the bypass valve before

it was permanently shut off. Durations ranged from 116 to

148 min. The first two tests had average inhalation pressures of

&55 mm H2O compared with &85 mm H2O for the last two tests.

This might be explained by differing use of the demand valve

or by an actual change in performance characteristics after

reassembly for cleaning. There were also large variations in

both average and minimum inhaled CO2 levels for unknown

reasons.

The warning whistle is located inside the breathing circuit,

presumably to make use of the O2 vented from it when

activated. Unless the user is working at a very high O2

consumption rate, however, most of this O2 is simply vented to

atmosphere after the volume able to be contained in the

breathing circuit is exceeded. Further, the sound made by the

whistle is severely muffled by its placement inside the shell,

compromising its intended purpose.

The areas in which the Proto Ten excelled were the

exhalation pressure and both wet- and dry-bulb temperatures.
28

The temperatures would have been higher had the durations

been longer, however. The low exhalation pressure was,

presumably, the result of the low bed depth of the radial

canister. It would not likely have changed much with longer

durations.

SURVIVAIR LP-120

Four prototype apparatus were delivered to the USBM as

part of the contract to develop a low-profile, lightweight, 2-hrrated rescue breathing apparatus. Only one of the prototypes

was used in the performance comparison so as to ensure that

performance variation was a reflection of replaceable

components rather than different apparatus, since the prototypes

were all hand-built and not from a machine-tooled, assembly

line.

The relief valve was originally placed in the exhalation

breathing bag and was volume-activated. Our prototype, of a

later design, had a pressure-activated relief valve in the face

mask. This design, however, vented large volumes of air from

the breathing circuit at high work rates. Between 30 and 40 L

of air were vented during the first, 5-min, high-work-rate

period. This resulted in severely reduced durations; therefore,

the relief valve was plugged in subsequent tests. Since a relief

valve serves little purpose in demand-only apparatus, this

modification was considered an acceptable tradeoff in order to

permit full evaluation of the apparatus.

SUMMARY

The Draeger BG-174A and BG 4 and the Scott Rescue-Pak

had the highest durations. The Biomarine BioPak 240 contains

more O2, but the lower-capacity CO2-absorbent canister does

not permit its full use; average inhaled CO2 concentrations

reached 10% at 264 min with 600 psi remaining in the cylinder.

The BG 4 had the lowest minimum inhaled CO2 levels, attesting

to the effectiveness of its CO2-absorbent canister. The Sabre

SEFA had the lowest average inhaled CO2 levels, due mostly

to the apparently low-dead-space mask and nose cup.

Peculiarly, the face mask used on both the BG 4 and the

BG-174A behaved differently on each apparatus, exhibiting

higher dead space characteristics on the BG 4 than the

BG-174A. Apparently, there is some interaction between the

mask and the apparatus. The impact of having no face mask

nose cup to reduce the quantity of reinhaled CO2 is shown by

the large difference between the average inhaled and minimum

inhaled CO2 levels in both the MSA McCaa and

Air Mask. In fact, the Air Mask, with a completely CO2-free

inhalation source of breathing gas, had a nonzero minimum

inhaled CO2 level. This is due, presumably, to the exhaled CO2

trapped in the recesses of the face mask, trickling out during the

entire inhalation but never being completely washed out.

The Air Mask had the lowest wet- and dry-bulb

temperatures, which is not surprising because it is an opencircuit device. The liquid-O2-source Siebe Gorman Aerorlox

had the next lowest temperatures. The only apparatus with a

CO2-absorbent not in a packed-bed design, the BG-174A, had

the lowest exhalation pressures. The BG 4 had the highest level

of positive pressure, with the Biomarine BioPak 60, Survivair

LP-120, SEFA, and Litton LITPAC II nearly as high; the

Air Mask and the LITPAC II would have been higher if the

short-duration, inhalation-pressure spikes had been ignored.

The BG 4 had the lowest pressure swing (36 mm H2O), with the

SEFA a close second (39 mm H2O).

ACKNOWLEDGMENTS

The schematic drawings in this report were done by Richard Roth, Marion Molchen, and John Pozzuto, Pittsburgh Research

Laboratory. For larger size schematic drawings, please contact the author.

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Kyriazi N [1986]. Development of an automated breathing and metabolic

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IC 9110.

Kyriazi N [1988]. Fast-response wet-bulb thermocouple. J Int Soc for

Respiratory Protection 6(3):12.

Kyriazi N [1996]. Performance comparison of second-generation oxygen

self-rescuers. Pittsburgh, PA: U.S. Department of Energy, RI 9621.

Kyriazi N, Shubilla JP [1984]. Performance comparison of oxygen selfrescuers. Pittsburgh, PA: U.S. Department of the Interior, Bureau of Mines,

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