&uuu of klises Report of Investigations/l980 

1 

Face Ventilation ~easurkment 

With Sulfur Hexafluoride (SF6) 

By Robert P. Vinson, Fred N. Kissell, John C. LaScola, 

and Edward D. Thimons 

--. @ UNITED STATES DEPARTMENT OF THE INTERIOR 
Report of Investigations 8473 

Face Ventilation Measurement 

With Sulfur Hexafluoride (SF6) 

By Robert P. Vinson, Fred N. Kissell, John C. LaScola, 

and Edward D. Thimons 

UNITED STATES DEPARTMENT OF THE INTERIOR 

Cecil D. Andrus, Secretary 

BUREAU OF MINES 

Lindsay D. Norman, Acting Director 
CONTENTS 

Page 

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

Introduction ............................................................ 1 

Laboratory tests .................................................... 3 

Evaluating the spray fan ................................................. 7 

Evaluating scrubbers .................................................... 10 

Conclusions .............................................................. 16 

ILLUSTRATIONS 

SF6 concentration with respect to time .............................. 2 

Percent SF6 removed at 6. 000 cfm with 10-ft curtain setback ......... 3 

Laboratory test setup for SF6 studies ............................... 3 

Percent SF6 removed at different curtain distances .................. 4 

Percent SF6 removed in 1 min with.respect to curtain distance ....... 5 

Percent SF6 removed at different box depths ......................... 6 

SF6 detected at miner operator's position ........................... 7 

SF6 spray fan comparison at beginning of a box cut .................. 8 

SF6 comparison of the spray fan with 20-ft curtain setback and 

conventional ventilation with 10-ft curtain setback ............... 8 

SF6 spray fan comparison in a slab cut configuration ................ 9 

Percent SF6 removed in 1 min versus curtain distance ................ 10 

Test configuration for evaluating dual-scrubber system .............. 11 

SF6 scrubber comparison at 3. 000 cfm with 15-ft curtain setback ..... 12 

SF6 scrubber comparison at 3. 000 cfm with 20-ft curtain setback ..... 12 

SF6 scrubber comparison at 6, 000 cfm with 5-ft curtain setback ...... 13 

SF6 scrubber comparison at 6. 000 cfm with 10-ft curtain setback ..... 13 

SF6 scrubber comparison at 6. 000 cfm with 15-ft curtain setback ..... 14 

SF6 scrubber comparison at 6, 000 cfm with 20-ft curtain setback ..... 15 

SF6 scrubber comparison at 9, 000 cfm with 10-ft curtain setback ..... 15 

SF6 scrubber comparison at 9. 000 cfm with 15-ft curtain setback ..... 15 

SF6 scrubber comparison at 9, 000 cfm with 20-ft curtain setback ..... 16 
FACE VENTILATION MEASUREMENT WITH SULFUR HEXAFLUORIDE (SF6) 

by 

Robert P. Vinson, Fred N. KissellI2 John C. LaScola,3 and Edward D. Thimons4 

AB S TRACT 

The face ventilation measurement method developed by the Bureau of Mines 

involves releasing a small volume of tracer gas (SF6) on the off-curtain side 

of the working face at the start of the mining cycle. At the same time, gas 

bottle samples are taken in the immediate return airway. The gas samples are 

analyzed, and a curve is drawn of SF6 concentration versus time. From this 

curve, the percentage of gas removed per time is calculated. A curve showing 

a high percentage of the tracer gas removed in a short period would represent 

a well-ventilated face. 

The face ventilation measurement method was tested in a full-scale mine 

entry model. Subsequently it was used underground to evaluate the spray-fan 

ventilation system and in an MSHA test facility to test machine-mounted 

scrubbers. The method was shown to be a simple and effective way of evaluating face ventilation systems. 

INTRODUCTION 

Mine ventilation has always played a vital role in the health and safety 

of underground miners. The main objectives of mine ventilation are to provide 

the miners with a clean air supply and to remove hazardous dust and gas from 

the mine atmosphere. Dust and gas are greatest at the working face where coal 

is being extracted. It follows that proper ventilation of the working face, 

especially during mining, is essential for the health and safety of the miners. 

A method is needed to assess the many variables that affect ventilation in the 

face area, such as face configuration, curtain-to-face distance, air volume 

available to the section, and line curtain leakage. When the effect of these 

variables is understood, intelligent modifications can be made to optimize 

face ventilation systems with a minimum of effort. Such a method could also 

be used to evaluate machine-mounted air movers such as diffuserfans,scrubbers, 

and spray fans. 

1Physicist. 

2~esearch supervisor. 

3~hysical scientist. 

4~upervisory physicist. 

All authors are with the Pittsburgh Research Center, Bureau of Mines, 

Pittsburgh, Pa. 
Until now, the only way of measuring face ventilation was to measure 

methane at the face and in the return airway. If no methane was present, face 

ventilation could not be measured. 

The Bureau of Hnes has now developed a simple and quick method for measuring ventilation at the working face that eliminates the need of methane; it 

is called the face ventilation measurement (FVM) method. A small volume of 

SF6 tracer gas is released directly behind the cutters on the off-curtain side 

of the entry at the start of the mining cycle. At the same time, gas samples 

are taken periodically in the immediate return airway. These samples are 

analyzed for SF6 content. A curve is then plotted of SF6 concentration versus 

time (fig. 1). The area under this curve represents the volume of SF6 that 

passed through the return airway during the test period. The area within each 

time increment is divided by the total area under the curve to give the fraction of SF6 removed with each progressive time period. With this information, 

another curve is plotted showing the percentage of SF6 removed with respect to 

time (fig. 2). This curve gives a graphic picture of how well the face is 

being ventilated. A well-ventilated face will show a high percentage of SF6 

removal in a short time period. 

TIME, min. 

FIGURE 1. - SF6 concentration with respect to time (6,000 cfm, 10-ft curtain setback). 
LABORATORY TESTS 

- The FVM method was 

first examined by running a 

series of tests in a fullC 

machine (fig. 3). The mine 

entry had an adjustable face 

- to simulate box cuts to 

20 ft, and a movable line 

curtain for different curtain setback distances. The 

KEY 

- 

return airway was connected 

SF6releare - 

to an exhaust fan, the flow 

of which could be varied S SF6 sample point - from 3,000 to 9,000 cfm. 

10 

O- The mining machine had rotatScda, f t ing cutter drums and a water 

TIME, min spray system. To test the 

FVM method, a section of 

FIGURE 2. - Percent SF6 removed at 6,000 cfm with 10-ft 114-in-diameter plastic tubcurtain setback. ing was run along the right 

side (off-curtain side) of 

the miner fromthe operator's 

position to a location directly behind the right-hand cutter. A tee fitting 

was connected to the tubing at the operator's position. A portable air pump 

and a syringe containing SF6 were then connected to the tee fitting. Prior 

to each test the face configuration was set up, the air volume set, the sprays 

turned on, and the cutters rotated. The test was initiated by turning on the 

pump and injecting 50 cu cm of SF6 into the tubing. The pump pushed the SF6 

out of the tubing behind the right cutter drum. At the same time, air samples 

-Adjustable face to 

simulate box cuts 

FIGURE 3. - Laboratory test setup for SF6 studies. 
were taken with 10-cu-cm vacutainers5 in the immediate return airway and at 

the miner operator's position, at various preset time increments for 5 minutes. 

The Vacutainer samples were analyzed for SF6 content with a gas chromatograph. 

Graphs were then drawn showing percentage of SF6 removed per time. 

SF6 concentrations are not listed because the absolute accuracy of the 

chromatograph calibration curve was poor and gave SF6 concentrations that were 

higher than would be expected from the amounts released. However, because the 

FVM method is used to compare relative differences in the face ventilation, 

absolute errors do not affect the final results. 

The main objective of the laboratory tests was to determine if the FVM 

method was giving an accurate indication of how the face was being ventilated. 

This was determined by comparing curves from tests having the same face configuration and airflow, but with different curtain-to-face distances (curtain 

setback). Studies have shown that face ventilation declines as the curtainto-face distance is increased. The Mine Safety and Health Administration 

(%HA) requires that the curtain-to-face distance be kept within 10 ft. 

The FVM curves in figure 4 clearly show the effect of curtain aetback. 

TIME, min 

FIGURE 4. - Percent SF6 removed at different curtain distances. 

5Reference to specific equipment does not imply endorsement by the Bureau of 

Mines. 

6~uxner, J. V. Face Ventilation in Underground Bituminous Coal Mines. 

BuMines RI 7223, 1969, 16 pp. 

7~. S Code of Federal Regulations. Title 30, Mineral Resources; Chapter 1-- 

Mine Safety and Health Administration, Department of Labor; Subchapter O-- 

Coal Mine Health and Safety;Part75, Mandatory Safety Standards--Underground 

Coal Mines. Subpart D--Ventilation. Revised annually. 
For example, at 1 min about 90 pct of the SF6 is removed when the curtain setback is 5 ft, whereas only 40 pct of the SF6 is removed when the setback is 

20 ft. Figure 5 shows that as curtain setback is increased, the percentage of 

SF6 removed in 1 min decreases. This is a clear indication that the FVM gives 

an accurate indication of how well the face is being ventilated. 

The data from the laboratory tests were also used to see if box depth had 

any major effect on face ventilation. Curves of three FVM tests are shown in 

figure 6. Each test used about the same air volume and curtain setback; only 

the box depth was changed significantly, which had little effect on face 

ventilation. 

During the laboratory studies of the FVM method, air samples were also 

collected at the miner operator's position. Any SF6 detection at this location would indicate that air from the working face was recirculating back over 

the mining machine. In an actual mining situation, this would mean that dust 

and methane produced at the face were reaching the miner operator. The average SF6 concentrations at the operator's position are shown in figure 7. In 

all of the tests except one, SF6 was detected at the operator's position, with 

the average SF6 concentrations always being higher at the lower air volumes 

(3,000 cfm). These results indicate that higher air volumes reduce the probability of recirculation of contaminated face air. 

FIGURE 5. - Percent SF6 removed in 1 min with respect to curtain distance. 

100 - 

80 

C 

0 

a 60 

d 

W 

B 

40 

LL! 

V) 

20 

O5 

CURTAIN DISTANCE, ft 

I I I I 1 1 I I I I I I I I 1 

Lb a - 

0 

- A o - 

- - 

- - 

- - 

- - KEY il 

8 - 

A 6,000 cfm 

- - 

0 3,000 cfm 

- - 

- - 

I I I I I I 1 I 1 I I I I I I 

7 9 I I 13 15 17 19 2 1 

KEY EVALUATING THE SPRAY FAN 

FIGURE 7. - SF6 detected at miner 

tor's position. 

3,000 - cfm 

- 

- 

- 

- 

- 

- 

- 

- 

- 6,000 

cfm 

NO SF6 

detected - 

operaThe FVM method was first used 

underground to compare the spray fan 

ventilation system with a conventional 

ventilation system. * For this purpose, 

the laboratory procedure was modified 

somewhat to fit into the working environment of a coal mine. As in the laboratory tests, a 114-in plastic tube 

was connected to the continuous miner, 

so that SF6 could be injected into the 

tubing at the operator's position and 

released directly behind the cutterhead on the off-curtain side of the 

entry. Only 25 cu cm of SF6 was used 

for each test. A hand-operated tire 

pump was used to push the SF6 through 

the tubing. Return air samples were 

taken behind the line curtain airway 

with 10-cu-cm evacuated tubes. Prior 

to an FVM test the air volume entering 

the line curtain, the line curtain setback, and the face configuration were 

recorded. When the continuous miner 

began mining coal, the SF6 tracer gas 

was ejected directly behind the cutterhead. At the same time, air sampling 

of the return air started and continued in increments of 15 sec. Samples 

were taken as long as the miner operated, which was usually from 1.5 to 

2 min. The air samples were analyzed 

on a gas chromatograph for SF6 content. 

The resulting SF6 concentrations were 

used to construct graphs showing percentage of SF6 removed versus time. 

A series of FVM tests were conducted with the spray fan in use at 

different face configurations and line curtain setbacks. Comparisons were 

made with other FVM tests at similar face configurations and curtain setbacks 

using conventional ventilation (figs. 8-10). 

*wallhagin, R. E. (Foster-Miller Associates, Inc.). Development of Optimized 

Diffuser and Spray Fan Systems forcoal Mine Face Ventilation. BuMines Open 

File Rept. 14-78, November 1977, 256 pp.; available for reference at Bureau 

of Mines facilities in Denver, Colo.; Twin Cities, Minn., Bruceton and 

Pittsburgh, Pa., and Spokane, Wash.; at the Department of Energy facilities 

in Carbondale, Ill., and Morgantown, W. Va.; at the NationalMineHealth and 

Safety Academy, Beckley, W. Va.; and at the National Library of Natural 

Resources, U.S. Department of the Interior, Washington, D.C.; and from the 

National Technical Information Service, Springfield, Va., PB 277 987lAS. 
100 I 1 I 

Curtain 9ft , 

KEY 

R SF6 release point 

/ S SF6 sample point 

C 

0 0 10 

60 Scale, ft 

0" 

W 

P 

40 

LLW 

V) 

20 Curtain 85ft 

0 

0 

0 

-4' o* I 1 I I I 

0.25 0.50 0.75 1.00 1.25 1.50 1.75 

TIME, min. 

FIGURE 8. - SF6 spray fan comparison at beginning of a box cut. 

TIME, min 

FIGURE 9. - SF6 comparison of the spray fan with 20-ft curtain setback and conventional 

ventilation with 10-ft curtain setback. 
FIGURE 10. - SF6 spray fan comparison in a slab cut configuration 

80 

C 

0 

60- 

0" 

W 

B 

5 

40- 

L! 

m 

20- 

Figure 8 shows that, as the continuous miner began a box cut, the spray 

fan removed 60 pct of the SF6 in 0.5 min, whereas conventional ventilation 

removed only 10 pct of the SF6 in 0.5 min. An even more dramatic example of 

the ability of the spray fan is seen in figure 9, where the spray fan with a 

20-ft curtain setback removes the SF faster than conventional ventilation 

with only a 10-ft curtain setback. The curves show that within 1 min, the 

spray fan has removed 90 pct of the SF6 and the conventional system has 

removed only 50 pct. 

loof@ ,/- 

- 

Scale, ft 

When making a slab cut, the spray fan proved to be a vast improvement 

over conventional ventilation (fig. 10). In 0.75 min the spray fan had 

removed over 80 pct of the SF6, and the conventional ventilation had not 

removed even 5 pct. 

o* - 

1.25 

TIME, min 

Figure 11 gives the percent of SF6 removed in 1 rnin as a function of 

curtain setback and clearly shows the superiority of the spray fan, especially 

at the longer curtain setback distances. 
FIGURE 11. - Percent S F6 removed in 1 min versus curtain distance. 

- 

Spray fan ventilation - 

- 

z 

z - - 

- 

z 

- 40- n 

W Conventional ventilation 

> 

0 - 

EVALUATING SCRUBBERS 

r 

E 20- 

IP 

V) 

0 

The FVM method was next used to evaluate a dual-scrubber system consisting of two flooded fibrous-bed scrubbers mounted on the right and left side 

of the cutterhead of a continuous miner. MSHA was conducting a series of 

studies in the MSHA face ventilation appraisal and testing facility (FVATF) to 

evaluate different inlet and outlet locations of the scrubber system. The FVM 

method was used during one phase of the studies, when the inlet and outlet 

locations of the scrubbers were as in figure 12. The entry was 3-112 ft high 

and 20 ft wide. The width of the entry was narrowed to 16 ft for a box cut 

configuration. Also shown are the position of the full-scale miner and the 

inlet and outlet locations of the scrubbers along with the approximate release 

and sampling locations of the tracer gas. FVM tests were run with each 

scrubber operating at 2,400 cfm. At each air volume, curtain setbacks of 5, 

10, 15, and 20 ft were tested. Identical series of FVM tests were run with 

the scrubbers turned off for comparison. 

- 

- - 

I I I I I I I I I I I I 1 

8 10 12 14 16 18 20 22 

CURTAIN DISTANCE, ft 
KEY 

R Release point 

S Sample point 

FIGURE 12. - Test configuration for evaluating dual-scrubber system. 

The FVM comparison tests run with the air intake at 3,000 cfm and with 

15- and 20-ft curtain setbacks are in figures 13 and 14. Although the FVM 

tests at 3,000 cfm showed the scrubbers improved ventilation, personnel conducting the scrubber studies do not believe this particular scrubber exhaust 

configuration (fig. 12) will work under actual mining conditions. The FVM 

tests at 3,000 cfm showed the scrubbers improved ventilation because the line 

curtain in the FVATF was tightly secured to the roof and floor and was thus 

able to contain the return air in spite of a high-pressure zone, produced by 

the scrubbers' exhaust, at the entrance of the line curtain. Line curtains 

constructed in mines could not withstand the high-pressure zone but would leak 

and contaminate the intake air. Also, the high-pressure zone could block 

intake air. 

All of the F'VM tests conducted when the intake air was 6,000 cfm showed 

the influence the scrubbers had on face ventilation. When the curtain setback 

was 5 ft (fig. 15) the scrubbers actually reduced face ventilation; the 

scrubbers' exhaust was about 8 ft from the face, and with a 5-ft curtain setback the air exhausting from the scrubbers struck the line curtain rather than 

entering the return airway. The scrubbers improved face ventilation once the 

line curtain was set outby the scrubbers' exhaust at 10, 15, and 20 ft 

(figs. 16-18). 

In figures 19-21, the FVM curves show that the scrubbers had little or no 

effect on face ventilation when the incoming air was 9,000 cfm. 
- 

KEY 

With scrubber 

-- - Without scrubber 

TIME, min 

FIGURE 13. - SF6 scrubber comparison at 3,000 cfm with 15-ft curtain setback, 

- 

K EY 

With scrubber 

----Without scrubber 

TIME, min 

FIGURE 14. - SF6 scrubber comparison at 3,000 cfm with 20-ft curtain setback. 
FIGURE 15. - SF6 scrubber comparison at 

6,000 cfm with 5-ft curtain setback. 

TIME, rnin 

TIME, min 

FIGURE 16. - SF6 scrubber comparison at 6,000 cfm with 10-ft curtain setback. 

FIGURE 18. - SF6 scrubber comparison at 6,000 cfm with 20-ft curtain setback. 

TIME, min TIME, min 

FIGURE 19. - SF6 scrubber comparison at FIGURE 20. - SF6 scrubber comparison at 

9,000 cfm with 10-ft curtain setback. 9,000 cfm with 15-ft curtain setback. 
- 

KEY 

- - With scrubber 

----Without scrubber 

- 

- 

0 0.25 0.50 0.75 1.00 1.25 1.50 1.75 

TIME, min 

FIGURE 21. - SF6 scrubber comparison at 9,000 cfm with 20-ft curtain setback. 

CONCLUSIONS 

The face ventilation measurement (FVM) method developed by the Bureau of 

Mines is a quick and simple means of measuring face ventilation. It requires 

easy-to-use equipment, several tests can be run in a short time, and most 

important it does not interrupt the mining cycle. The only complicated equipment is a gas chromatograph for analyzing the air samples for SF6. 

The FVM method has been used successfully underground to evaluate the 

spray fan, and to evaluate a machine-mounted scrubber system in MSHA's face 

ventilation appraisal and testing facility.