Self-Contained Self-Rescuer Field Evaluation: 

Fourth-Phase Results 

By Nicholas Kyriazi and John P. Shubilla 
U.S. Department of the Interior 

Mission Statement 

As the Nation's principal conservation agency, the Department of 

the Interior has responsibility for most of our nationally-owned 

public lands and natural resources. This includes fostering 

sound use of our land and water resources; protecting our fish, 

wildlife, and biological diversity; preserving the environmental 

and cultural valuesof our national parks and historical places; and 

providing for the enjoyment of life through outdoor recreation. 

The Department assesses our energy and mineral resources and 

works to ensure that their development is in the best interests of 

all our people by encouraging stewardship and citizen participation in their care. The Department also has a major responsibility 

for American Indian reservation communities and for people who 

live in island territories under U.S. administration. 
Report of Investigations 9499 

Self-Contained Self-Rescuer Field Evaluation: 

Fourth-Phase Results 

By Nicholas Kyriazi and John P. Shubilla 

UNITED STATES DEPARTMENT OF THE INTERIOR 

Bruce Babbitt, Secretary 

BUREAU OF MINES 
International Standard Serial Number 

ISSN 1066-5552 
CONTENTS 

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

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

Acknowledgments .................................................................... 2 

Experimentalprocedure ............................................................... 2 

Resultsanddiscussion ................................................................ 3 

CSE ........................................................................... 8 

Draeger ........................................................................ 8 

MSA ........................................................................... 9 

Ocenco ......................................................................... 10 

Conclusions ........................................................................ 10 

ILLUSTRATIONS 

1 . CSEunits ....................................................................... 2 . Draegerunits .................................................................... 3 . MSAunits ....................................................................... 4 . Ocencounits ..................................................................... 

TABLES 

1 . Self-contained self-rescuers received for evaluation ......................................... 2 . BMSmetabolicworkload ............................................................ 3 . Human subject workloads in treadmii tests .............................................. 4 . Wilcoxon rank-sum test results ........................................................ 5 . CSE CO, breakthrough times ......................................................... 6 . Draeger CO, breakthrough times ....................................................... 7 . MSA CO, breakthrough times ........................................................ 8 . OcencoCO, breakthroughtimes ...................................................... 
UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT 

"C degrce Celsius L/min liter per minute 

h hour min minute 

kg kilogram mm H,O millimeter of water (pressure) 

L liter pct percent 
SELF-CONTAINED SELF-RESCUER FIELD EVALUATION: 

FOURTH-PHASE RESULTS 

By Ntchobs ~yriazi' and John P. ~hubilb* 

ABSTRACT 

A joint effort by the U.S. Bureau of Mines (USBM) and the US. Mine Safety and Health 

Admiitration (MSHA) was undertaken to determine how well self-contained self-rescuers (SCSR's), 

deployed in accordance with Federal regulations (30 CFR 75.1714), held up in the underground 

environment with regard to both physical damage and aging. This report presents fmdings regarding 

laboratory-tested SCSR's in the fourth phase of testing from 1989 to 1993. The SCSRYs were tested on 

human subjects and on a breathing and metabolic simulator (BMS). These results indicate that most 

of the apparatus, if they pass their inspection criteria, perform as expected except units with manufacturing defects. However, when the apparatus are carried in and out of the mine daily and stored at 

the working section, they may suffer abuse. Physical signs of abuse, unless extremely obvious, are 

frequently not detected by the miners or mine operators. In addition, some apparatus collected for this 

study had not been returned to the manufacturer in a recall effort for correction of a manufacturing 

defect. In both cases, the apparatus would have presented problems in emergency use. Recommendations include improved training in inspection procedures and better enforcement of recall notices. 

'~iomedical engineer. 

'~ngineerin~ technician. 

Pittsburgh Research Center, U.S. Bureau of Mines, Pittsburgh, PA. 
INTRODUCTION 

On June 21, 1981, coal mine operators in the United 

States were required to make available to each underground coal miner a self-contained self-rescuer (SCSR). 

The regulations (30 CFR 75.1714) require that each 

person in an underground coal mine wear, carry, or have 

immediate access to a device that provides respiratory 

protection with an 0, source for at least 1 h, as rated by 

the certifying agencies, the National Institute for Occupational Safety and Health (NIOSH) and MSHA. The 

USBM is involved with MSHA in a long-term, in-mine 

evaluation of SCSR's now deployed in underground coal 

mines. In this study, MSHA's responsibility is to identify 

the participating mines and to procure from those mines 

the SCSR's to be tested. The USBM replaces those 

SCSR's with new apparatus and tests the SCSR's in its 

laboratories. The objective of this long-term program is 

to evaluate the in-mine, operational durability of SCSR's. 

Of utmost concern is the successful performance of any 

SCSR that passes its manufacturer's inspection criteria. 

The USBM is interested only in apparatus that pass their 

inspection criteria. Such apparatus are relied upon to 

function successfully in an emergency. Apparatus that fail 

inspection criteria are expected to be removed from 

service. 

ACKNOWLEDGMENTS 

The authors thank Don Peiffer, physical scientist, participation in this study amongst commercial underApproval and Certification Center, Mine Safety and ground coal mines. 

Health Administration, Triadelphia, WV for soliciting 

EXPERIMENTAL PROCEDURE 

This program involves testing approximately 100 SCSR's 

in each phase of the study. This report describes findings 

in the fourth phase of testing occurring from late 1989 

through early 1993. Testing was conducted using a BMS 

and human subjects on a treadmill. 

The SCSR's tested were manufactured by CSE Corp., 

Draegerwerk AG, Mine Safety Appliances Co., Inc. 

(MSA), and Ocenco, Inc. and were sampled according to 

estimated market share (table 1). The sampling was modified to ensure that at least 10 SCSR's from each manufacturer were sampled for each phase of the program, 

90 pct using thc BMS and 10 pct with human subjects. 

Table 1.-Self-contained self-rescuers received for evaluation 

Apparatus Quantity Quantity 

inspected tested 

CSE AU-9A1 .................... 20 19 

Draeger OXY-SR 60B ............. 26 26 

MSA 60-min SCSR ............... 12 12 

Ocenco EBA 6.5 ................. 45 45 

Total ....................... 103 102 

Some apparatus were not tcstcd bccausc of failure to 

pass inspection criteria or because of a manufacturing 

defect preventing testing. 

The 0, constant-flow rate is checked on compressed-0, 

apparatus; the NIOSH-required flow is 1.5 L/min at ambient temperature and pressure, dry (ATPD). 

All apparatus are checked for leak-tightness after opening. The leak test used is that recommended for the CSE 

AU-9A1 by the manufacturer; this test is identical to the 

one required by Draeger for the BG-174 rescue breathing 

apparatus. The test is performed to determine the leaktightness of the breathing circuit; i.e., how well the apparatus isolates the user from the assumed-toxic environment. Passing the test is not a requirement of the 

regulations. The test was required by CSE to be performed by the user after field refurbishment of the 

AU-9A1; however, field service is no longer authorized. 

MSHA selected the participating mines with regard to 

type of mining operation, coalbed height, and SCSR deployment mode to obtain a representative cross section of 

U.S. mines. 

The BMS test consisted of the average metabolic work 

rate exhibited by the 50th-percentile miner weighing 87 kg 

while performing the 1-h man test 4 from 30 CFR 11. 

The metabolic workload (volumes at standard pressure 

and temperature, dry (STPD)) is given in table 2. In 

the treadmill testing, the subjects walked at whatever 

speed and grade resulted in an 0, consumption rate of 

1.35 L/min (STPD). The other parameters of the 
workload cannot be controlled in human test subjects, but 

are listed in table 3, all volumes at STPD. 

Table 2.4MS metabolic workload 

0, consumption rate .................... L/min .. 1.35 

CO, production rate ..................... L/min .. 1.10 

Ventilation rate ......................... L/min .. 30.0 

Tidal volume ..................... L per breath .. 1.68 

Respiratory frequency ............ breaths per min .. 17.9 

Peak respiratory flow rate: 

Inhalation .......................... Llmin.. 89 

Exhalation .......................... Llmin.. 71 

Table 3.--Human subject workloads In treadmill tests 

Subject Qco,, Ge, RF, 

L/min L/min breaths per min 

A ............. 1.20 35 25 

B ............. 1.25 26 25 

C ............. 1.35 25 10 

RF Respiratory frequency. 

CCO, CO, production rate. 

Ce Ventilation rate. 

The parameters monitored were inhaled levels of CO, 

and 0, inhalation wet- and dry-bulb temperatures, and 

inhalation and exhalation breathing pressures in both the 

BMS and treadmill testing. In the BMS testing, however, 

average inhaled levels of gas concentration were measured 

as opposed to minimum values of CO, and maximum 

values of 0, in the treadmill testing. Average inhaled gas 

levels include the effect of apparatus dead space, whereas 

minimum values of CO, for example, are only the lowest 

level of gas concentration during inhalation. The BMS 

measures average inhaled values by electronically summing 

all the CO, and 0, of each inhalation cycle, weighted by 

the instantaneous flow rate. The BMS also measures minimum inhaled CO, levels. End-of-breath, dry- and wetbulb temperatures, and peak inhalation and exhalation 

breathing pressures were measured. 

Tests on the BMS were terminated upon exhaustion of 

the 0, supply as indicated by large negative pressures 

coinciding with an empty breathing bag. Treadmill tests 

were terminated in the same manner or if inhaled minimum CO, levels reached 4 pct, maximum 0, levels fell 

below 15 pct, at which points negative physiological symptoms begin to occur, or if the test subject stopped because 

of subjectively high breathing pressures or temperatures. 

RESULTS AND DISCUSSION 

Experience with each brand of apparatus is discussed 

separately. The values of the monitored parameters were 

averaged over the entire test duration and are presented 

graphically (figs. 1-4) for each apparatus by parameter. 

The values for deployed units tested on the BMS can be 

compared with the values for new units tested on the 

BMS, and to some extent, with deployed units tested on 

human subjects on a treadmill, which are plotted afterward. Because human subjects may diffgr from each other. 

and from the BMS in terms of VCO, V,, and respiratory 

frequency, all of which wiU affect apparatus duration as 

well as all of the monitored parameters, these tests cannot 

be considered necessarily equivalent to the BMS tests even 

though the 0, consumption rate is the same. Missing data 

points are indicative of equipment malfunction or other 

anomaly that invalidated the data. 

The Wilcoxon rank-sum test was performed for each 

monitored parameter to determine whether or not the 

deployed units behaved differently from new units. It tests 

the hypothesis that the two samples are from populations 

with the same mean. The values from both samples are 

ranked in ascending order of magnitude. If the sum of the 

ranks of the smaller sample (T) (in this case, new units) 

falls within the acceptable range for the given sample sizes, 

then there is not sufficient evidence at the specified 

probability level (P=0.05, two-sided) to say that the means 

of the two samples &Her. The rank-sum test does not rely 

upon the assumptions that either the new- or deployedunit data are normal distributions or that they have identical variances, as does the t-test for two populations of 

independent samples. One limitation of the Wilcoxon 

rank-sum test is that it does not distinguish between large 

and small differences in values. The results of the twosided, P=O.OS, Wilcoxon rank-sum tests are presented in 

table 4. The probability of T, the rank sum of the new 

units, falling outside the given range is 0.05 if the populations have the same mean. 

Table 4.-Wllcoxon rank-sum test result. 

Duration Av Av Wet-bulb Dry-bulb Inhalation Exhalation 

Apparatus Range T inhaled CO, inhaled 0, temp temp pressure pressure 

Range T Range T Range T Range T Range T Range T 

CSE ...... 22-66 40 22-66 43 13-50 46 13-50 53 13-50 52 20-60 44 20-60 42 

Draeger ... 16-68 43 16-68 66 16-68 34 15-63 43 16-68 23 16-68 43 16-68 39 

MSA. ..... 16-44 34 16-44 26 16-44 34 1541 45 16-44 41 16-44 19 16-44 41 

Ocenco ... 1560 22 14-58 32 15-60 40 14-58 16 14-58 34 14-58 37 14-58 36 

T Sum of the ranks of the smaller sample (new units). 
110 

105 

C 100 

95 

i 90 

0 85 

G a 80; 

a 75-0 

n 

70 

85 

60 

E 3- 

8" 2- 

0 

W 

d 

I 1- B 

KEY 

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Wet bulb 

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. 1.1. . , . , . , . - 

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Figure l.-CSE units. 

0 Wovedunit 0 ~ew unit A Treadmill 

KEY 0 Average 

8 Minimum 

0 Avenge. new unit 

Minimum, newunit 

A Minimum, treadmill 

loor.I.,.,.,.,.l.,.I.,.l.,. 

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INDIVIDUAL UNITS 

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INDIVIDUAL UNITS 

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Figure 2.-Draeger units. 
KEY q Deployed unit 

0 New unit 

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too I I , 1 I , , , I , , I , , , , 

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z 3- 

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Figure 3.-MSA units. 

8 

V) 

w 

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= m -150- 

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0 1 2 3 4 5 6 7 8 9 1011121314151617 

INDIVIDUAL UNITS 

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INDIVIDUAL UNITS 

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Figure 4.4cenco units. 

- 

- A - OA. 

0 o • o A An 0 gB q q - o o"ooo o 0 

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CSE 

Five of the twenty apparatus sampled were found to 

have their original, unmodified 0, regulators. Because the 

original regulators have the potential to burst apart with 

great force upon opening of the cylinder valve, making the 

unit unusable and possibly injuring the user or persons 

nearby, the apparatus were recalled in 1986 to have their 

regulators modified. The regulator of one unit did burst 

upon opening prior to starting a BMS test. Normally, the 

damaged regulator would be replaced with a new one and 

then the unit tested. This was not done, however, since 

other components were damaged by the burst. The cylinder on the unit had been opened once before to check 

its constant flow rate with no problem, illustrating the 

random nature of the occurrence. The problem of endusers not complying with the manufacturer's request for 

recall was reported to MSHA. 

The modified regulators of two other units malfunctioned without bursting, but vented large quantities of 

stored 0, before being turned off. They functioned properly after reopening and were tested without further incident. Other than being frightening, the only negative 

impact is a loss of stored 0, and consequently, some 

apparatus duration. 

Eight of the apparatus failed the leak-tightness test. 

One apparatus had an empty 0, cylinder. This unit was 

refilled and tested. Several units had loose or disconnected CO, canisters and 0, cylinder straps. One unit had 

its relief valve disconnected from the breathing bag. The 

red seal was broken on the 0, cylinder of one unit indicating that the valve had been opened and closed, although 

still registering full. The belt strap of one unit was caught 

in the case seal. All these occurrences imply that the 

units were either not refurbished properly or developed 

the problems over the time that they were deployed 

underground. 

The Wilcoxon rank-sum tests for the wet- and dry-bulb 

temperatures showed higher values for new than deployed 

units. As can be seen from figure 1, however, the newunit values are only slightly higher than the deployed 

values; if deployment causes the apparatus to run cooler, 

that is no cause for alarm. It has been found that the 

temperature of the laboratory and the use of the exhaust 

fan significantly affect the inhalation temperature of the 

apparatus being tested. The higher new-unit temperatures 

may be attributed to coincidentally high laboratory temperatures. Real or coincidental, the finding is of little 

concern for this study. 

The higher breathing pressures in the human subject 

versus the BMS testing are directly related to higher ventilation rates by the human test subjects, possibly due to 

human reaction to super-ambient, average inhaled CO, 

levels. The BMS does not react to high CO, by increasing 

ventilation. 

Six deployed units tested on the BMS and one unit 

tested on a human subject reached 4 pct CO, @teakthrough) before the 0, supply was expended. The BMS 

tests were permitted to continue until the 0, supply was 

expended whiie the treadmill test was terminated at that 

time. One new unit tested on the BMS also experienced 

CO, breakthrough. Table 5 illustrates the situation. 

Table S.-CSE C4 breakthrough times, minutes 

Type of unit and test' coz Final 

method breakthrough termination 

EMS: 

Deployed . . . . . . . 87 90 

74 80 

70 90 

80 85 

73 75 

68 91 

New . . . . . . . . . . 75 81 

Human on treadmill: 

Deployed . . . . . . . 86 86 

BMS Breathing and metabolic simulator. 

The second treadmill-tested unit was removed at 81 min 

after the subject complained of high breathing pressures, 

which reached +I50 and -150 mm H,O. The minimum 

inhaled CO, level at that tie was 3.4 pct. Human reaction to high CO, is to increase ventilation rate. This 

results in higher breathing pressures that eventually limit 

ventilation rate, and, finally, 0, consumption rate, which 

limits work rate. 

DRAEGER 

One unit, SN 282, in BMS testing, exhibited high average inhaled CO, levels with low levels of minimum 

inhaled CO, A large spread between average and minimum inhaled CO, is usually indicative of large dead 

space-breathiig circuit volume containing exhaled air, 

uncleansed of CO, which will be rebreathed. Since this 

unit had a much higher spread than other units of this 

same model-a difference between average and minimum 

inhaled CO, of approximately 2.0 pct versus the usual 

0.6 pct--the unit was inspected after testing. It was found 

that the exhalation check valve was stiff and brittle, preventing it from shutting during inhalation, thus, increasing 

the volume of dead space. This appears to be caused by 

aging of the check valve material, natural rubber. The inhalation check valves, made of silicon, were in good condition. A review of past test data revealed that another 

unit (SN 585) experienced this same wide spread between 

average and minimum inhaled CO, but had already been 
disposed of before it could be inspected to confi a 

brittle check valve. 

This condition would affect a wearer increasingly as 

work rate and breath volume decrease making the dead 

space a larger fraction of breath volume. As this happened, average inhaled CO, would increase, causing most 

users to increase their breath volume in an attempt to 

dilute the CO, Some users are not as sensitive to CO, 

and would not increase their breath volume; they would 

experience higher CO, levels. This problem was reported 

to NIOSH and MSHA. Draeger was already replacing 

this check valve as part of a red replacing the breathiing 

hose so no further action was necessary. The breathing 

hose has been found in recent years to be taking a set in 

its folded position making it increasingly diff~culto open 

for use. 

Six of 25 units failed the leak-tightness test. One unit 

had a broken nose-clip clamp; it had not been sent back 

to the manufacturer in the red program of 1985 for 

replacement of the clamps. 

Two deployed units tested on the BMS and one unit 

tested on a human subject reached 4 pct CO, before the 

0, supply was expended. One of the two deployed BMS 

units, however, was tested in two sessions separated by 

40 days, due to equipment problems. This delay may have 

resulted in degradation of the bed. One new unit tested 

on the BMS also experienced CO, breakthrough (see table 6). 

Table 6.4raeger CO, breakthrough times, 

minutes 

Type of unit and test co2 Final 

method breakthrouah - termination 

BMS: 

Deployed . . . . . . . 55 65 

61 70 

New . . . . . . . . . . 54 72 

Human on treadmill: 

Deployed . . . . . . . 69 69 

EMS Breathing and metabolic simulator. 

MSA 

All the apparatus tested were carried by MSHA mine 

inspectors. Two of the 12 units sampled had dislocated 

shock mounts, presumably due to severe impact. These 

two were built in 1980 and were part of a group of apparatus sold to MSHA before the, apparatus was produced 

commercially. The commercially available apparatus built 

later incorporated design changes intended to remedy this 

tendency. Two of the apparatus failed the leak test. 

One of the apparatus with the dislocated shock mounts 

also experienced a sodium chlorate candle misfire. When 

it was started manually with multiple exhalations, a fine, 

white mist was visible coming back out through the 

mouthpiece. It is presumed that the mist was KO, since 

breathing it was extremely irritating. The unit was then 

run on the BMS without incident. A user would have 

needed to further wet down the breathing circuit with 

more breaths before it could have been worn. Since the 

defective filter that likely caused this incident is not found 

in commercially available units, and since MSHA has no 

more of this type of apparatus, no action was taken. 

Wet-bulb temperatures for new units were simcantIy 

higher than deployed units, but dry-bulb temperatures 

were in line with each other (fig. 3). This means that the 

humidity was higher in the new units than the deployed 

units. The reason for this is unknown. A review of the 

data revealed no relation between the wet-bulb temperature and test date or serial number. There may be some 

physical cause for this phenomenon related to the KO, 

bed condition, but no similar phenomenon was observed 

in previous phases of this study. In any case, decreased 

humidity in the breathing air is no great impediment to 

escape. 

Figure 3 shows also that the wet-bulb temperatures 

in the treadmill tests were slightly lower than in the BMS 

tests. The dry-bulb temperatures, however, were much 

lower, a phenomenon also seen in the Draeger tests 

(fig. 2). Both of these are chemical-0, units. In the 

compressed-0, units, the wet- and dry-bulb temperatures 

are similar for the treadmill and BMS tests. The reason 

for the difference is, at present, unknown; the BMS closely 

matches wet- and dry-bulb exhalation temperatures of 

human subjects breathiing similar wet- and dry-bulb gas 

mixtures. This will be further explored by the USBM. 

Five deployed units tested on the BMS reached 4 pct 

CO, before the 0, supply was expended. Three new units 

tested on the BMS also experienced CO, breakthrough 

(see table 7). 

Table 7.--MSA CO, breakthrough times, minutes 

Type of unit and test coz Final 

method breakthrough termination 

BMS: 

Deployed . 

New . . . . 

BMS Breathing and metabolic simulator. 
OCENCO 

One apparatus, SN 63886, had a low 0, constant-flow 

rate (0.67 L/min ATPD instead of the NIOSH-required 

1.5 L/min ATPD), and in the BMS test, exhibited low 0, 

levels. After testing, closer inspection of the unit revealed 

a cracked demand valve regulator housing. This permitted 

some of the gas flow to leak out of the circuit to ambient, 

and since the 0, supply rate was now lower than the consumption rate, the demand valve was activated. However, 

instead of drawing gas from the 0, cylinder, ambient air 

was drawn into the circuit through the cracks, thus, 

lowering the 0, level. In emergency use, the in-leakage of 

ambient air would have negatively affected the user. Even 

if the ambient air were not toxic or hypoxic, the in-leakage 

would have made the air in the breathing circuit go 

hypoxic, the extent depending upon the in-leakage rate of 

79 pct N, ambient air. It is presumed that the demand 

valve regulator housing was damaged from impact to the 

outer case. The gas supply hose from the cylinder attaches 

to the housing in such a manner that it acts as a lever arm, 

extending outwards and nearly touching the inside of the 

case. It can crack the housing at its point of attachment 

if it is deflected by an impact of the case. This problem 

has been reported to NIOSH and MSHA. 

None of the deployed apparatus passed the leak test, 

although new apparatus don't pass, either. In a short experiment, five of six units checked did pass this noncertification test when their relief valves were capped, implying 

backflow through the valves. The average leak rate exhibited by the apparatus at a moderate work rate is not 

believed to present a danger to the user, however. 

Four units were found to have damage that was sufficient to require them to be removed from service. One 

had a crack in the clear, polywbonate we; a second had 

its orange, U-channel, case seal pinched, a piece of loose 

orange rubber in the case, and a dented canister; a third 

had its U-channel case seal blown out of the case bottom; 

and the fourth had a small crack in its case and a visible, 

rusty canister rim. After opening, this unit was found to 

also have a dented canister and a broken cylinder neck 

clamp. All the units were able to be tested, however, and 

performed normally. 

The high inhalation pressures exhibited by some of the 

apparatus on the BMS (fig. 4) were caused by activation 

of the demand valve, which is relatively stiff. When the 

demand valve is not required, the inhalation pressures are 

low, reflecting low system resistance. 

Two deployed units tested on the BMS and one on a 

human subject reached 4 pct CO, before or at the time the 

0, supply was expended (see table 8). 

Table 8.--0cenco C02 breakthrough 

times, minutes 

Type of unit and test co2 Final 

method breakthrough termination 

EMS: 

Deployed . . . . . . . 93 99 

96 100 

Human on treadmill: 

Deployed . . . . . . . 92 92 

BMS Breathing and metabolic simulator. 

CONCLUSIONS 

The results of this study suggest that the large majority 

of SCSR's that pass their inspection criteria can be relied 

upon to provide a safe level of life support capability for 

mine escape purposes. Few problems have arisen involving subtle performance degradation due to the mining 

environment: the cracked demand valve-regulator housing 

on the Ocenco EBA 6.5 and possible loosening of internal 

component connections on the CSE AU-9A1. Some 

minor problems with materials have been noted due to 

age: the exhalation check valve and the breathing hose on 

the Draeger OXY-SR 60B. 

Some SCSR's collected during the study were damaged 

by daily, in-mine use and should have been removed from 

service. The damage was generally apparent and visible 

and should have been detected if the SCSR's had been 

properly inspected. Improved training is recommended. 

Problems were found with users not responding to manufacturer recalls. This may result in apparatus not functioning properly in an emergency as in the case of the 

bursting regulators on the CSE AU-9A1. Improved 

enforcement of manufacturer recalls is recommended. 

The results of this continuing program provided the 

groundwork and justification for the recently implemented 

service life plans for SCSR's deployed in underground coal 

mines. These plans will improve the reliability of SCSR's.