I I I 

Bureau of Mines Report of lnvestigations/l982 

Sulfur Hexafluoride as a Mine 

Ventilation Research ToolRecent Field Applications 

By Robert J. Timko and Edward D. Thimons 

UNITED STATES DEPARTMENT OF THE INTERIOR 
Report of Investigations 8735 

Sulfur Hexafluoride as a Mine 

Ventilation Research ToolRecent Field Applications 

By Robert J. Timko and Edward D. Thimons 

UNITED STATES DEPARTMENT OF THE INTERIOR 

James G. Watt, Secretary 

BUREAU OF MINES 

Robert C. Horton, Director 
This publication has been cataloged as follows: 

Timko, Robert J 

Sulfur hexafluoride as ;I mine vcntilat ion resc.arch tool-rcc-vnt fic~lcl 

appl icat ion s. 

(K~'~ort of il~vc'sti~atiorl s ,' [[llited Stat cs llc-pnrt~nr~~t of tl~c, Interior, I%ureau of Mincs ; 87 15) 

Rib1 iography: p. 15. 

Si~pt. of I)OC.S. no.: 1 28.23:8735. 

1. Minc vc.~ltilation. 2. Sulplil~r hcxafluoridc. 3. 7'racc.r.; ((:hcrnistry). I. Tt~imc,ns, 1-dward I). 11. l'itlt.. 111. Svries: Keport of invrst ig;tt ion s (('nit ed State\. f3urenu of 3jinc.s) ; 8- 35. 

TN23,[]:13 [I1N:!O1] 22 2 82-600287 
CONTENTS 

Page 

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

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

Background ..................................................................... 2 

SFs in ventilation research .................................................... 5 

Limestone mine ventilation ................................................ 5 

Coal mine face ventilation ................................................ 5 

Jet fan effectiveness ..................................................... 7 

Air leakage across stoppings .............................................. 8 

Bagging-machine hood enclosure ............................................ 10 

Coal mine boreholes ....................................................... 10 

Other SF6 work ................................................................. 13 

Oil shale mine ............................................................ 13 

Lead-zinc-silver mine ..................................................... 13 

Coal mine fire ............................................................ 14 

Summary ........................................................................ 14 

References ..................................................................... 15 

ILLUSTRATIONS 

1 . Releasing SF6 for ventilation analysis .................................... 3 

2 . Taking samples of mine atmosphere to determine SF6 content ................ 4 

3 . Limestone mine . A. plan view; B. ventilation plan and SF6 experiments .... 6 

4 . Ventilation effects of various curtain distances from the face ............ 7 

5 . Fan comparison in a dead heading .......................................... 8 

6 . Stopping air leakage test setup ........................................... 8 

7 . Calculating stopping leak rates ........................................... 9 

8 . Bagging hood enclosure .................................................... 9 

9 . First borehole examination ................................................ 11 

10 . Second borehole examination ............................................... 11 

11 . Third borehole examination ............................................... 13 

12 . Lead-zinc-silver mine ventilation schematic ............................... 14 
SULFUR HEXAFLUORIDE AS A MINE VENTILATION RESEARCH 

TOOL-RECENT FIELD APPLICATIONS 

By Robert J. Timko and Edward 3. Thimons 

ABSTRACT 

Sulfur hexafluoride (SF6) is an odorless, colorless, nontoxic gas that 

has found acceptance as a tracer gas in research on ventilation patterns, measurement of air leak rates, respirable dust reductions due to 

bagging hood modifications, and the study of airflows relating to gob 

boreholes. Following a short review of the SF6 sampling technique, this 

report describes recent Bureau of Mines projects in which SF6 was used 

successfully as a tracer gas, enabling researchers to acquire representative data quickly and inexpensively. 

INTRODUCTION 

Analyzing mine air ventilation patterns can be tedious, time-consuming 

work. Smoke tubes can give only rough approximations of airflow direction and velocity. Anemometers are capable of accurately measuring air 

velocities, but large-scale mine airflows can only be derived through 

approximations. On the other hand, with tracer gas, not only can the 

airflow patterns throughout the mine be determined, but average air 

velocities can be accurately measured over substantial distances. 

Iphysical scientist, Pittsburgh Research Center, Bureau of Mines, Pittsburgh, Pa. 

*supervisory physical scientist, Pittsburgh Research Center, Bureau of Mines, 

Pittsburgh, Pa. 
BACKGROUND 

The Bureau of Mines has been using sulfur hexafluoride (SF6) tracer gas in ventilat ion measurement work for several 

years. SF6 is colorless, odorless, 

chemically and thermally stable, and can 

easily be dispensed i n a i r (1).3 In 

testing by the Bureau, SF6 was contained 

in metal, high-pressure bottles that hold 

approximately 42.5 L (1-1/2 ft3) of gas. 

It is released simply by opening a valve 

on the bottle (fig. 1). The mass of SF6 

released is equal to the weight loss of 

the bottle. 

The volume of gas released is determined by the equation: 

where V = volume of SF6 released, 

SF6 is sampled by inserting a 90% air 

evacuated, 10-1 ~acutainer4 test-tube 

into a plastic plunger, similar to a 

device used to extract blood for clinical 

testing. Inside the plunger is a hypodermic needle, which punctures a rubber 

bladder at one end of the test tube. As 

the bladder is punctured (fig. 2), ambient air enters the test tube and the Sample is complete. Withdrawing the test 

tube from the plunger reseals the rubber 

bladder, preventing the sample from escaping. Samples are taken at predetermined intervals, and the test tubes can 

be marked with any information pertinent 

to the sampling procedure. Samples are 

brought back to the laboratory, where 

0.1 ml of the sample is withdrawn with a 

syringe and i n j e c t e d into a gas chromatograph for SF6 analysis. 

n = moles of SF6 released, Data reduction is done in two separate 

steps. First , SF6 concent rat ion is 

and R = volume per mole (22.4 L). plotted with respect to time for each 

sampling position. The maximum SF6 conThis is a simplified version of the for- centration and dispersion rate immemula used initially (4): PV = nRT. - diately become evident. Second, the 

total quantity of tracer gas recovered is 

Since n = AM/M determined as (1) - 

where AM = weight loss of bottle, in 

grams , and M = molecular weight of SF6, 

equation (1) becomes 

where QSF6 = SF6 volume recovered, 

Qa = Volumetric airflow rate, 

and 

And since 

R = 22.4 m mole 

c = Instantaneous SF6 concentration at time t. 

the equation is reduced to 

Knowing V, the volume of SF6 released, 

the percent tracer gas recovered can be 

calculated: 

Determining the volume of SF6 released where Q'SF6 = percent SF6 recovered. 

becomes important when comparing the 

quantity released to that recovered. 

3~nderlined numbers in parentheses re- 4~eference to specific trade names is 

fer to items in the list of references at made for identification only and does not 

the end of this report. imply endorsement by the Bureau of Mines. 
FIGURE 1. - Releasing SF6 for ventilation analysis. 
FIGURE 23 - Taking samples of mine atmosphere to determine SF6 content. 
SF6 tracer gas is being increas- research using SF6 tracer gas. Several 

ngly accepted by the mining industry as ventilation research proj ects recently 

viable mine ventilation analysis completed by the Bureau illustrate the 

tool. S-Cubed (formerly Systems Science many diversified applications of SF6 that 

and Software) of La Jolla, Calif., are possible. 

now commercially performs ventilation 

SF6 IN VENTILATION RESEARCH 

Limes tone Mine Ventilation 

SF6 was used to study existing ventilation patterns (fig. 3A ) in a gassy underg round limes tone mine where venti.lation 

is provided by a positive-pressure fan 

blowing air down a shaft on the western 

side of the mine (fig. 3~). According to 

the mine ventilation plan, the air splits 

at the 600 level with air heading eastward and westward at the 600 level and 

vertically to the 960 level, the only 

active working level in the mine. Air 

moving westward at the 600 level travels 

vertically downward through the stopes. 

The air ventilating the 600 east level 

flows through a booster fan, vertically 

down through the old east side workings 

to the 960 east level, then westward to 

the main shaft. The ventilation air 

reaching the 960 west level is boosted to 

several openings from the 960 level to 

the 600 level were found and sealed. 

In two later tests (Test Group 2), ventilation patterns were examined in more 

detail. SF6 was again released at the 

960 main drift west advancing face for 

the first test and at the closest working 

stope for the second. Sampling points 

were on the 600 level as well as on the 

960 level. 

Results showed that no SF6 was found on 

the 600 level west of the conveyor belt. 

However, SF6 was being carried up the 

beltway, meaning that exhaust air was 

recirculating up the conveyor and into 

the 600 level. To alleviate this recirculation problem, airflow changes around 

the beltway were needed. 

the face with an auxiliary fan, then Coal Mine Face Ventilation 

exhausted eastward through the 960 main 

drift to the main shaft. 

In the initial test series (Test Group 

I), SF6 was released at the 960 west advancing face for the first test and the 

closest active stope for the second. As 

a check, oil of wintergreen was released 

with the SF6. If ventilation patterns 

were as predicted, all odor associated 

with the oil of wintergreen would exhaust 

through the 960 west main drift to the 

main shaft. However, miners told of 

smelling the odor throughout the day on 

the 600 level. 

Further evidence that the ventilation 

patterns were not as predicted was the 

small amount of SF6 recovered at three 

sampling positions on the 960 level. The 

amount of SF6 released was known. When 

the results from each position were 

graphed, the total amount recovered 

was less than 20% of the SF6 jeleased. 

These irregularities were reported to 

mine personnel. They replied that 

Adequate face ventilation to remove 

hazardous dust and gases is important in 

mining. A simple method was needed to 

measure face ventilation without exposing 

mine personnel to more hazardous types of 

tracer gases. The Bureau of Mines developed an easy, rapid SF6 technique for 

making face measurements. With this 

method, called the face ventilation 

measurement method (FVM) (8), a small 

quantity of SF^ is released at the 

start of the mining cycle just behind the 

continuous miner drum on the operator side, opposite the line curtain. 

SF6 samples are then taken at specific 

time intervals from behind the line curtain in the return. After data reduction in the laboratory, two graphs 

are generated: (1) depletion of SF6 

with respect to time, and from this 

(2) a cumulative percentage of SF6 

depleted with respect to time. The basic 

premise of this technique is that the 

faster the depletion, the better the 

ventilation. 
PLAN VIEW 

West East 

Intake 

shaft 

Nearest active stope 

to pump station 

Main 

shaft 

VENTILATION AND TESTING 

West 

- 

East 

LEGEND 

R - SF6 release points 

SI- Sampling points (test group I) 

S2- Sampl~ng points (test group 2) 

---, Planned ventilation, intake 

--+ Planned ventilation, exhaust 

---+ Actual ventilation (test group I) 

----.-b Actual ventilation (test group 2) 

FIGURE 3. - Limestone mine. A, plan view; B, ventilation plan and SF6 experiments. 
Using the FVM method it is graphically 

hown that keeping curtain-to-f ace disances within 10 ft is essential to good 

face ventilation (fig. 4). This supports 

the Mine Safety and Health Administration 

(MSIW) requirement that the inby side of 

the line curtain be within 10 ft of the 

working face (7). - 

In another project the FVM method was 

used to demonstrate the effectiveness of 

equipping a continuous miner with a spray 

fan ventilation system, consisting of a 

series of water sprays strategically 

located so as to sweep mine ventilation 

air over the entire face and direct it to 

the return. 

The FVM method was also used to evaluate the efficiency of a dual-scrubber 

system on a continuous miner and compare 

its effectiveness with that of conventional ventilation. SF6 testing enabled 

a quick determination of optimal curtainto-face distances and face ventilation 

velocities for machines equipped with the 

dual scrubber configuration. 

Jet Fan Effectiveness 

Underground mines circulate large quantities of ventilation air to dilute and 

remove hazardous gases. For certain 

areas, such as dead headings, where distribution of fresh air is inadequate, the 

Bureau examined the use of auxiliary ventilation provided by placing different 

fans in airways or work areas, without 

bulkheads or tubing on the fans. This 

type of ventilation is called impulse or 

jet ventilation (3). - 

SF6 was used to evaluate the effectiveness of various jet fans and their positions in dead headings. Position L2 

(fig. 5) was selected because Krause (2) 

suggests that better ventilation can Te 

expected if a jet expands in fresh air. 

However, underground experiments with SF6 

and smoke tubes proved position L2 to be 

greatly inferior to position L1. 

The superiority of SF6 over smoke tubes 

became obvious when attempting to examine 

the effectiveness of the jet fan in dead 

headings. It was found that air from a 

jet fan can purge beyond the penetration 

distance measured with a smoke tube. In 

fact, effective ventilation occurred at 

twice the distance that the jet was detected with smoke tubes. 

2 3 

TIME, min 

FIGURE 4. - Ventilation effects of various curtain distances from the face. 
4 I' 

FIGURE 5. - Fan comparison in a dead heading. 

gg

air through any imperfections in the 

stopping , 

A quantity of SF6 tracer gas is released into a known volume on the return, 

or low-pressure, side of the stopping. 

EXAMINING AIR LEAKAGE THROUGH STOPPINGS 

Parachute Test 

stopping stopping Curtain 

FIGURE 6. - Stopping air leakage test setup. 
TIME, min 

FIGURE 7. - Calculating stopping leak rates. FIGURE 8. - Bagging hood enclosure. 
rates through and around permanent concrete block stoppings. 

Bagging-Machine Hood Enclosure 

Machines that bag sand, flour, and 

other granular bulk products generate 

considerable quantities of dust. A 

hooded enclosure, developed by the Bureau, reduces the amount of dust escaping 

from the bagger (fig. 8) (6). SF6 tracer 

gas was used to quantitatively determine 

how effective this method of dust reduction is at three facilities where hoods 

had been installed (9). For this purpose 

SF6 was released wiFhin a hood during 

bagging and nonbagging cycles. Samples 

were taken periodically at various points 

around the outside of the hoods. If the 

enclosures operated as designed, no SF6 

would be detected in the samples. 

At the first facility the bagging hoods 

were enclosed in a plywood room, ventilated through a network of grills in the 

roof. SF6 was detected at various points 

around the hood during bagging and nonbagging cycles. Upon reviewing the data, 

it became apparent that SF6 release into 

the room was due to improper ventilation. 

Air jets, used for makeup air, were directed at the hoods, causing turbulent 

air and permitting gas to escape, 

At the second facility, the hooded baggers were again located in a room with 

exhaust and makeup ventilation systems. 

However, only a small amount of SF6 was 

detected here, probably because of a lack 

of air jets forcing air from the hoods. 

Any SF6 detected escaped through holes 

in the hood provided for the bagger 

nozzles. 

At the third facility, the bagging 

hoods were not enclosed in a room. An 

exhaust ventilation system was used to 

remove air from the bagging hoods. No 

SF6 was detected at any sampling point. 

Smoke-tube tests visually confirmed these 

results. 

At all three facilities SF6 tests on 

bagging hood enclosures enabled research 

personnel to determine the effectiveness 

of the enclosures. After analyzing the 

results, recommendations to vary airflows 

or modify the apparatus could be made. 

Coal Mine Boreholes 

SF6 was used in three borehole experiments at two different coal mines to 

determine the tightness of the gob and if 

ventilation air was diluting methane liberated in the gob. In each case, a longwall panel had advanced beyond the gob 

borehole location. If a gob was tightly 

caved, SF6 would be detected in the return air but not at the gob borehole. In 

essence, the ventilation air would sweep 

the gob but not penetrate it to any extent. Conversely, if the gob was loosely 

caved SF6 would be detected not only in 

the returns underground but also on the 

surface at the gob boreholes. 

At the first mine, SF6 was injected 

into an exhausting mine entry borehole 

(R), where a negative pressure fan pulled 

air from the mine (fig. 9). The fan was 

stopped, the borehole was capped, and an 

SF6 bottle was connected to a tapped fitting on the mine side of the shutoff 

valve. Approximately 42.5 L (1-1/2 ft3) 

of SF6 was then released into the entry 

borehole. Sampling was begun at a gob 

borehole approximately 1 km (0-62 mi) 

from the release point and underground in 

the return nearly 1.65 km (1 mi) away. 

Sampling at the surface lasted for 6 hr; 

underground for 5 hr. No SF6 was ever 

detected on the surface at the gob borehole. SF6 concentration in the return 

peaked less than 3-1/2 hr after tracer 

gas release. Unfortunately , sampling 

underground did not last long enough to 

determine the total amount of gas passing 

the sampling point. 

A second coal mine requested an SF6 

tracer gas study for a borehole (fig. 10) 

recently drilled above a longwall gob. 

The seam depth was approximately 275 m 

(900 ft). At about 180 m (600 ft) a void 

was encountered and drilling stopped. 

Methane began exhausting from the borehole and pressure increased, indicating 

some type of outgassing. It was not 

known at this time if the void extended 
FIGURE 10. - Second borehole examination. 
into the gob. At first researchers 

wanted to release SF6 underground and 

sample at several locations underground 

and on the surf ace at the borehole, but 

because the gas could not be released 

near the borehole underground, SF6 was 

again released on the s u r f a c e and forced 

down the borehole. 

Prior to capping the borehole, a 1803 

(600-f t) length of 6.4- (114-in) plastic tubing was extended down the hole to 

sample the void from the surface. A 

personal sampling pump operating at a 

flowrate of 2 ~/min was used to pull air 

from the void through the tubing. 

Next, 69.4 L (2.45 ft3) of SF^ was released through a tap into the borehole. 

This was followed by more than 11,300 L 

(400 ft3) of nitrogen, forcing the SF^ 

down the borehole. Actual sampling was 

begun j ust before release of SF6, so that 

a good baseline could be obtained. 

Sampling lasted 24 hr at the surface, 

72 hr underground. 

SF6 was detected only in the void at 

the bottom of the borehole. No tracer 

gas was ever detected underground. After 

sampling for 3 days and finding no SF6, 

it was apparent that the borehole was not 

connected to the mine. A complete hydrocarbon analysis at the borehole showed 

more than 95% methane being emitted. 

Additionally, borehole pressure continually increased to 27.3 cm (10.75 in) wg 

after only 24 hr. 

The void size was estimated by determining the volume of SF6 released into 

the borehole and assuming that this volume contained a 100% concentration of 

SF6. The average SF6 concentration for 

the 24-hr period appears to be near 1.5%. 

The volume of the void can be calculated 

approximately: 

Mass of SF6 released = 452.6 g molecular weight of SF6 = 146.1 glmole 

Moles of SF6 released = 452*6g =3.10moles 

146.1 glmole 

3.10 moles x 22.4 Llmole = 69.44 L = volume of SF6 released 

Approximate SF6 concentration for sampling period = 1.5% 

Approximate void volume = x 100 = 4,629.33 L (163.47 ft3) 1.5 

In tests on another borehole (fig. ll), 

SF6 was released underground near the 

longwall face but not in the face ventilation airstream. It was hoped that the 

SF6 would sweep the gob as well as penetrate the gob, with SF6 being detected on 

the surface at the borehole as well as in 

the returns. Sampling took place at five 

positions underground and one position on 

the surface at the borehole. Each underground location was sampled for 17 hr and 

the surface for 24 hr. 

SF6 was released behind brattice curtains that separated main ventilation air 

from gob bleeder air. The top of the 

borehole was approximately 460 m 

(1,500 ft) from the release point. In 

slightly more than 2 hr the SF6 concentration peaked at the borehole. No SF6 

was detected in the immediate longwall 

face return, but it was detected at various times in different bleeder evaluation 

points, depending upon distance from the 

release point. 

In all cases SF6 proved to be an excellent tool to measure underground ventilation. The sampling tubes can also be 

examined in a gas chromatograph for total 
hydrocarbons. This was done for the the sampling points from the SFs release 

third borehole experiment and showed con- point increased. Detection of SF6 in the 

elusively that the hydrocarbons in the borehole showed that ventilation air was 

return air increased as the distance of entering the gob. 

OTHER SF6 WORK 

Oil Shale Mine 

S-Cubed of LaJolla, Calif., performed 

several SF6 experiments at an oil shale 

mine in Colorado that uses a modified insitu method of burning to extract oil 

from shale. The material is rubblized 

and dumped into large underground voids 

that become retorts when burnis is 

begun. During burning, the retort has a 

negative pressure imposed on it by exhaust fans. If a fan fails, burning can 

cause the retort to become positively 

pressurized before one-way ventilation 

valves can prevent outgassing into the 

mine. A primary concern during outgassing is the amount of hydrogen sulfide 

(H2S) released into the mine workings. 

To quantitatively determine H2 S concentrations in the mine, enough SF6 was 

released into the underground retorts to 

produce a known concentration at a known 

pressure. Samples were taken at various 

positions throughout the mine. The 

quantity of ventilation air in the mine 

was known. If SF6 was detected in the 

mine, a lead rate from the retort, and 

thus the concentration of SF6 in the mine 

at that particular sampling point, could 

be determined. 

Samples taken from over 100 positions 

throughout the mine showed that SF6 concentrations, simulating H2S, were well 

within MSHA requirements. 

Lead-Zinc-Silver Mine 

Tracer gas tests were completed in 

a lead-zinc-silver mine (fig. 12) to 
Exhaust fan shaft. None of the intake air samples contained SF6; at the fan SF6 was detected for approximately 20 minutes. The 

data clearly showed that no ventilation 

air is short-circuiting between exhaust 

and intake shafts. 

Coal Mine Fire 

@ Release point 

@ Sample points 

Exhaust 

shaft 

FIGURE 12. - Lead-z inc-si lver mine ventilation 

schematic. 

determine if ventilation air was shortcircuiting from the exhaust back into intake air. The intake and exhaust are two 

separate shafts with workings at various 

levels between the shafts. It was feared 

that air was passing through old workings 

on upper levels and entering the intake 

shaft, rather than exhausting to the atI-------$ $-I 

leaking through the gob seals, it was 

suspected that some seals were not airtight. In an attempt to determine 

approximate airflow into the gob and ventilation patterns, SF6 was released 

behind a seal considered not airtight, 

Intake 

A fire occurred in a coal mine gob, requiring that the gob be sealed. Although 

shaft it was not known whether air was still 

and samples were taken at a seal on 

the opposite side of the gob. Both seals 

had sampling probes, so that release and 

sampling of SF6 in the gob presented 

no problem. The dispersal time for the 

SF6 was determined by taking samples 

behind the seal at which the SF6 was released. If there was little or no leakage, SF6 would disperse very slowly. 

Additionally, che gas should not 

arrive at the other seal for several 

hours. 

In fact, SF6 concentrations at the release point dropped rapidly. Within 

mosphere. If this was the case, the 45 min the gas was detected at the second 

integrity of the intake shaft as an es- seal. This gave a rough estimate of aircape route would be lost. flow patterns and qualitatively showed 

that air was leaking through seals, makSF6 was released about one-third of the ing it possible for management to take 

way up the exhaust shaft. Sampling took appropriate action to further reduce or 

place at the exhaust fan and about eliminate leakage through the seals to 

two-thirds of the way down the intake the burning gob. 

SUMMARY 

The uses for sulfur hexafluoride (SF6) 

as a tracer gas are becoming more numerous as researchers more fully understand 

its potential. This colorless, odorless, 

nontoxic gas is easily dispensed in air. 

Sampling is done by inserting 10-1, 90% 

evacuated Vacutainer test tubes into a 

plastic plunger containing a hypodermic 

needle. The needle punctures a rubber 

bladder on one end of the evacuated tube, 

permitting an ambient air sample to enter 

the tube. When the needle is withdrawn, 

the bladder reseals itself and can be 

returned to the lab, where 0.1 ml of the 

sample is withdrawn and injected into a 

gas chromatograph. After determining the 

amount of SF6 in the sample, the only 

other task is to reduce the data to tabular or graphic form. 
The tremendous benefit of SF6 is the Jolla, Calif., has seen the potential of 

ability to use it in ventilation problems SF6 and is commercially performing ventithat are difficult to accomplish with lation research using SF6. The future 

typical airflow instruments. The uses will see many more diversified uses for 

described in this report are only samples SF6 in studying unique mine ventilation 

of what can be done. S-Cubed of La problems. 

REFERENCES 

1. Drivas, P. J., P. G. Simmonds, and 

F . H. Shair. Experimental Characterization of Ventilation Systems in Buildings. 

Environ. Sci. Tech., v. 6, No. 7, 1972, 

pp. 609-6 14. 

2. Krause, D. Freistrahlen bei der 

Sonder bewetterung (Free Jets in Auxiliary Ventilation). Neve Berg bzutechnik, v. 2, No. 1, Jan. 1972, 

pp. 44-52. 

3. Matta, J. E., E. D. Thimons, and 

F. N. Kissell. Jet Fan ELfectiveaess as 

Measured With SF6 Tracer Gas. BuMines 

RI 8310, 1978, 14 pp. 

4. Thimons, E. D., R. J. Bielicki, and 

F. N. Kissell. Using Sulfur Hexafluoride 

as a Gaseous Tracer To Study Ventilation 

Systems in Mines. BuMines RI 7916, 1974, 

22 PP* 

5. Turk, A., S. M. Edmonds, H. L. 

Mark, and G. G. Collins. Sulfur 

Hexafluoride as a Gas-Air Tracer. 

Environ. Sci. Tech., v. 2, No. 1, 1968, 

pp. 44-48. 

6. U.S. Bureau of Mines. Dust Control Rox for Bag-Filling Machines. Tech. 

News, No. 54, Aug. 1978, 2. pp. 

7. U.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; Part 75, 

Mandatory Safety Standards--Underground 

Coal Mines. Subpart D--Ventilation. 

Revised annually. 

8. Vinson, R. P., F. N. Kissell, J. C. 

LaScola, and E. D. Thimons. Face Ventilation Measurement With Sulfur Hexafluoride (SF6). BuMines RI 8473, 1980, 

16 PP* 

9. Vinson, R. P., J. C. Volkwein, and 

E. D, Thimons. SF6 Tracer Gas Tests of 

Bagging-Machine Hood Enclosures. BuMines 

RI 8527, 1981, 10 pp. 

*U.S GOVERNMENT PRINTING OFFICE: 1982 - 605 - 015/104