Sulfur Hexafluoride As a Mine Ventilation Research Tool- Recent Field Applications

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Bureau of Mines Report of lnvestigations/l982

Sulfur Hexafluoride as a Mine Ventilation Research Tool- Recent 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 Tool- Recent 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~'~ortof il~vc'sti~atiorls ,' [[llited Stat cs llc-pnrt~nr~~tof tl~c, Inte- rior, I%ureauof Mincs ; 8715) Rib1 iography: p. 15. Si~pt.of I)OC.S. no.: 1 28.23:8735. 1. Minc vc.~ltilation. 2. Sulplil~rhcxafluoridc. 3. 7'racc.r.; ((:hcrn- istry). I. Tt~imc,ns, 1-dward I). 11. l'itlt.. 111. Svries: Keport of in- vrst ig;tt ion s (('nit ed State\. f3urenu of 3jinc.s) ; 8- 35.

TN23,[]:13 [I1N:!O1] 222 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 repre- sentative 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 direc- tion 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 sul- SF6 is sampled by inserting a 90% air fur hexafluoride (SF6) tracer gas in ven- evacuated, 10-1 ~acutainer4 test-tube tilation measurement work for several into a plastic plunger, similar to a years. SF6 is colorless, odorless, device used to extract blood for clinical chemically and thermally stable, and can testing. Inside the plunger is a hypo- easily be dispensed in air (1).3 In dermic needle, which punctures a rubber testing by the Bureau, SF6 was contained bladder at one end of the test tube. As in metal, high-pressure bottles that hold the bladder is punctured (fig. 2), ambi- approximately 42.5 L (1-1/2 ft3) of gas. ent air enters the test tube and the Sam- It is released simply by opening a valve ple is complete. Withdrawing the test on the bottle (fig. 1). The mass of SF6 tube from the plunger reseals the rubber released is equal to the weight loss of bladder, preventing the sample from es- the bottle. caping. Samples are taken at predetermined intervals, and the test tubes can The volume of gas released is deter- be marked with any information pertinent mined by the equation: to the sampling procedure. Samples are brought back to the laboratory, where 0.1 ml of the sample is withdrawn with a syringe and inj ected into a gas chromato- where V = volume of SF6 released, graph 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 con- This is a simplified version of the for- centration and dispersion rate imme- mula 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, where QSF6 = SF6 volume recovered, equation (1) becomes Qa = Volumetric airflow rate,

and c = Instantaneous SF6 concen- And since tration at time t. R = 22.4 m mole Knowing V, the volume of SF6 released, the percent tracer gas recovered can be calculated: the equation is reduced to

Determining the volume of SF6 released where Q'SF6 = percent SF6 recovered. becomes important when comparing the quantity released to that recovered.

3~nderlinednumbers 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 several openings from the 960 level to the 600 level were found and sealed. SF6 was used to study existing ventilation patterns (fig. 3A ) in a gassy under- In two later tests (Test Group 2), ven- g round limes tone mine where venti.lation tilation patterns were examined in more is provided by a positive-pressure fan detail. SF6 was again released at the blowing air down a shaft on the western 960 main drift west advancing face for side of the mine (fig. 3~). According to the first test and at the closest working the mine ventilation plan, the air splits stope for the second. Sampling points at the 600 level with air heading east- were on the 600 level as well as on the ward and westward at the 600 level and 960 level. vertically to the 960 level, the only active working level in the mine. Air Results showed that no SF6 was found on moving westward at the 600 level travels the 600 level west of the conveyor belt. vertically downward through the stopes. However, SF6 was being carried up the The air ventilating the 600 east level beltway, meaning that exhaust air was flows through a booster fan, vertically recirculating up the conveyor and into down through the old east side workings the 600 level. To alleviate this recir- to the 960 east level, then westward to culation problem, airflow changes around the main shaft. The ventilation air the beltway were needed. reaching the 960 west level is boosted to the face with an auxiliary fan, then Coal Mine Face Ventilation exhausted eastward through the 960 main drift to the main shaft. Adequate face ventilation to remove hazardous dust and gases is important in In the initial test series (Test Group mining. A simple method was needed to I), SF6 was released at the 960 west ad- measure face ventilation without exposing vancing face for the first test and the mine personnel to more hazardous types of closest active stope for the second. As tracer gases. The Bureau of Mines devel- a check, oil of wintergreen was released oped an easy, rapid SF6 technique for with the SF6. If ventilation patterns making face measurements. With this were as predicted, all odor associated method, called the face ventilation with the oil of wintergreen would exhaust measurement method (FVM) (8), a small through the 960 west main drift to the quantity of SF^ is released at the main shaft. However, miners told of start of the mining cycle just behind the smelling the odor throughout the day on continuous miner drum on the oper- the 600 level. ator side, opposite the line curtain. SF6 samples are then taken at specific Further evidence that the ventilation time intervals from behind the line cur- patterns were not as predicted was the tain in the return. After data reduc- small amount of SF6 recovered at three tion in the laboratory, two graphs sampling positions on the 960 level. The are generated: (1) depletion of SF6 amount of SF6 released was known. When with respect to time, and from this the results from each position were (2) a cumulative percentage of SF6 graphed, the total amount recovered depleted with respect to time. The basic was less than 20% of the SF6 jeleased. premise of this technique is that the These irregularities were reported to faster the depletion, the better the mine personnel. They replied that ventilation. PLAN VIEW West East

Intake Main shaft shaft Nearest active stope to pump station

VENTILATION AND TESTING West East-

LEGEND R - SF6 release points SI- Sampling points (test group I) S2- Sampl~ngpoints (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 remove hazardous gases. For certain hown that keeping curtain-to-f ace dis- areas, such as dead headings, where dis- ances within 10 ft is essential to good tribution of fresh air is inadequate, the face ventilation (fig. 4). This supports Bureau examined the use of auxiliary ven- the Mine Safety and Health Administration tilation provided by placing different (MSIW) requirement that the inby side of fans in airways or work areas, without the line curtain be within 10 ft of the bulkheads or tubing on the fans. This working face (7).- type of ventilation is called impulse or jet ventilation (3).- In another project the FVM method was used to demonstrate the effectiveness of SF6 was used to evaluate the effective- equipping a continuous miner with a spray ness of various jet fans and their posi- fan ventilation system, consisting of a tions in dead headings. Position L2 series of water sprays strategically (fig. 5) was selected because Krause (2) located so as to sweep mine ventilation suggests that better ventilation can Te air over the entire face and direct it to expected if a jet expands in fresh air. the return. However, underground experiments with SF6 and smoke tubes proved position L2 to be The FVM method was also used to evalu- greatly inferior to position L1. ate the efficiency of a dual-scrubber system on a continuous miner and compare The superiority of SF6 over smoke tubes its effectiveness with that of conven- became obvious when attempting to examine tional ventilation. SF6 testing enabled the effectiveness of the jet fan in dead a quick determination of optimal curtain- headings. It was found that air from a to-face distances and face ventilation jet fan can purge beyond the penetration velocities for machines equipped with the distance measured with a smoke tube. In dual scrubber configuration. fact, effective ventilation occurred at twice the distance that the jet was de- Jet Fan Effectiveness tected with smoke tubes. Underground mines circulate large quantities of ventilation air to dilute and

2 3 TIME, min FIGURE 4. - Ventilation effects of various curtain distances from the face. 0 2 5 50 Air Leakaee Across Sto~~ines -Scale, f t SF6 is used to measure air leakage through and around permanent concrete block stoppings in coal mines. Two different methods are used, depending upon the location of the stopping with respect to the ventilation fans,

For the SF6 technique to work, a pressure differential is created across the penetration of any fan stopping. For stoppings with less than as determined by 1-in-wg pressure differential, (1) a par- Drager smoke tube achute is anchored by fastening its lines to roof bolts on the intake side of the C rC stopping, and (2) a fan forces air behind In the parachute, inflates it against the -(D Sampling point 60 ft from crosscut floor, roof, and ribs of the crosscut and I creates a positive pressure on the stopping (fig. 6). The pressure differential forces air through any imperfections in the stopping and depletes the SF6 in the known volume.

When pressure differentials of greater than 1 in wg exist across the stopping, - the parachute and fan are not needed. I 57,000 cfm The natural driving force of the ventilation air is great enough to send air through any imperfections in the stopping ,

4 I' A quantity of SF6 tracer gas is released into a known volume on the return, FIGURE 5. - Fan comparison in a dead heading. or low-pressure, side of the stopping.

EXAMINING AIR LEAKAGE THROUGH STOPPINGS

Parachute Test stopping stopping Curtain FIGURE 6. - Stopping air leakage test setup. The volume is predetermined by hang- curve is drawn and stopping leak rates ing brattice curtain completely across obtained (fig. 7). The leak rate is the crosscut, some distance from the given by stopping, and multiplying this distance by the width and height of the crosscut.

One end of a rubber sampling tube is where Q = air leak rate (CFM) draped over the brattice into the volume, with the other end connected to a person- C1 = SF6 concentration (PPB) at al sampling pump. At predetermined in- time T1 tervals, the pump is removed from the sampling line and an SF6 sample is taken. C2 = SF6 concentration (PPB) at When reducing the data, an SF6 depletion time T2

= 1,000 I I I V stopping to brattice curtain DETERMINING STOPPING - volume (ft3). LEAK RATES n ' In both cases, low air leak rates on various types of stoppings could be measured. SF6 analysis provided an accurate Q=Air leak rate (cfm) and repeatable means of determining leak C,=SF~conc (ppb) at timeT &=SF6conc (ppb) at timeT2 s- 100 n CA 0- = 137 cfm

TIME, min FIGURE 7. - Calculating stopping leak rates. FIGURE 8. - Bagging hood enclosure. rates through and around permanent con- of the enclosures. After analyzing the crete block stoppings. results, recommendations to vary airflows or modify the apparatus could be made. Bagging-Machine Hood Enclosure Coal Mine Boreholes Machines that bag sand, flour, and other granular bulk products generate SF6 was used in three borehole experi- considerable quantities of dust. A ments at two different coal mines to hooded enclosure, developed by the Bu- determine the tightness of the gob and if reau, reduces the amount of dust escaping ventilation air was diluting methane lib- from the bagger (fig. 8) (6). SF6 tracer erated in the gob. In each case, a long- gas was used to quantitatively determine wall panel had advanced beyond the gob how effective this method of dust reduc- borehole location. If a gob was tightly tion is at three facilities where hoods caved, SF6 would be detected in the re- had been installed (9). For this purpose turn air but not at the gob borehole. In SF6 was released wiFhin a hood during essence, the ventilation air would sweep bagging and nonbagging cycles. Samples the gob but not penetrate it to any ex- were taken periodically at various points tent. Conversely, if the gob was loosely around the outside of the hoods. If the caved SF6 would be detected not only in enclosures operated as designed, no SF6 the returns underground but also on the would be detected in the samples. surface at the gob boreholes.

At the first facility the bagging hoods At the first mine, SF6 was injected were enclosed in a plywood room, venti- into an exhausting mine entry borehole lated through a network of grills in the (R), where a negative pressure fan pulled roof. SF6 was detected at various points air from the mine (fig. 9). The fan was around the hood during bagging and non- stopped, the borehole was capped, and an bagging cycles. Upon reviewing the data, SF6 bottle was connected to a tapped fit- it became apparent that SF6 release into ting on the mine side of the shutoff the room was due to improper ventilation. valve. Approximately 42.5 L (1-1/2 ft3) Air jets, used for makeup air, were di- of SF6 was then released into the entry rected at the hoods, causing turbulent borehole. Sampling was begun at a gob air and permitting gas to escape, borehole approximately 1 km (0-62 mi) from the release point and underground in At the second facility, the hooded bag- the return nearly 1.65 km (1 mi) away. gers were again located in a room with Sampling at the surface lasted for 6 hr; exhaust and makeup ventilation systems. underground for 5 hr. No SF6 was ever However, only a small amount of SF6 was detected on the surface at the gob bore- detected here, probably because of a lack hole. SF6 concentration in the return of air jets forcing air from the hoods. peaked less than 3-1/2 hr after tracer Any SF6 detected escaped through holes gas release. Unfortunately , sampling in the hood provided for the bagger underground did not last long enough to nozzles. determine the total amount of gas passing the sampling point. At the third facility, the bagging hoods were not enclosed in a room. An A second coal mine requested an SF6 exhaust ventilation system was used to tracer gas study for a borehole (fig. 10) remove air from the bagging hoods. No recently drilled above a longwall gob. SF6 was detected at any sampling point. The seam depth was approximately 275 m Smoke-tube tests visually confirmed these (900 ft). At about 180 m (600 ft) a void results. was encountered and drilling stopped. Methane began exhausting from the bore- At all three facilities SF6 tests on hole and pressure increased, indicating bagging hood enclosures enabled research some type of outgassing. It was not personnel to determine the effectiveness known at this time if the void extended @ SF. release point @ SF. sampling point

FIGURE 9. - First borehole examination.

FIGURE 10. - Second borehole examination. into the gob. At first researchers Sampling lasted 24 hr at the surface, wanted to release SF6 underground and 72 hr underground. sample at several locations underground and on the surf ace at the borehole, but SF6 was detected only in the void at because the gas could not be released the bottom of the borehole. No tracer near the borehole underground, SF6 was gas was ever detected underground. After again released on the surf ace and forced sampling for 3 days and finding no SF6, down the borehole. it was apparent that the borehole was not connected to the mine. A complete hydro- Prior to capping the borehole, a 1803 carbon analysis at the borehole showed (600-f t) length of 6.4- (114-in) plas- more than 95% methane being emitted. tic tubing was extended down the hole to Additionally, borehole pressure continu- sample the void from the surface. A ally increased to 27.3 cm (10.75 in) wg personal sampling pump operating at a after only 24 hr. flowrate of 2 ~/minwas used to pull air from the void through the tubing. The void size was estimated by determining the volume of SF6 released into Next, 69.4 L (2.45 ft3) of SF^ was re- the borehole and assuming that this vol- leased through a tap into the borehole. ume contained a 100% concentration of This was followed by more than 11,300 L SF6. The average SF6 concentration for (400 ft3) of nitrogen, forcing the SF^ the 24-hr period appears to be near 1.5%. down the borehole. Actual sampling was The volume of the void can be calculated begun j ust before release of SF6, so that approximately: a good baseline could be obtained.

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), from gob bleeder air. The top of the SF6 was released underground near the borehole was approximately 460 m longwall face but not in the face venti- (1,500 ft) from the release point. In lation airstream. It was hoped that the slightly more than 2 hr the SF6 concen- SF6 would sweep the gob as well as penetration peaked at the borehole. No SF6 trate the gob, with SF6 being detected on was detected in the immediate longwall the surface at the borehole as well as in face return, but it was detected at vari- the returns. Sampling took place at five ous times in different bleeder evaluation positions underground and one position on points, depending upon distance from the the surface at the borehole. Each under- release point. ground location was sampled for 17 hr and the surface for 24 hr. In all cases SF6 proved to be an excel- lent tool to measure underground ventila- SF6 was released behind brattice cur- tion. The sampling tubes can also be tains that separated main ventilation air examined in a gas chromatograph for total I. Borehole KEY @ SFs release point

\ ~eturns' 11 Longwall panel FIGURE 11. - Third borehole examination. 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 released into the underground retorts to produce a known concentration at a known S-Cubed of LaJolla, Calif., performed pressure. Samples were taken at various several SF6 experiments at an oil shale positions throughout the mine. The mine in Colorado that uses a modified in- quantity of ventilation air in the mine situ method of burning to extract oil was known. If SF6 was detected in the from shale. The material is rubblized mine, a lead rate from the retort, and and dumped into large underground voids thus the concentration of SF6 in the mine that become retorts when burnis is at that particular sampling point, could begun. During burning, the retort has a be determined. negative pressure imposed on it by exhaust fans. If a fan fails, burning can Samples taken from over 100 positions cause the retort to become positively throughout the mine showed that SF6 con- pressurized before one-way ventilation centrations, simulating H2S, were well valves can prevent outgassing into the within MSHA requirements. mine. A primary concern during outgassing is the amount of hydrogen sulfide Lead-Zinc-Silver Mine (H2S) released into the mine workings. To quantitatively determine H2 S concen- Tracer gas tests were completed in trations in the mine, enough SF6 was 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

A fire occurred in a coal mine gob, re- Exhaust Intake quiring that the gob be sealed. Although shaft I------$ $-I shaft it was not known whether air was still 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, and samples were taken at a seal on @ Release point the opposite side of the gob. Both seals @ Sample points had sampling probes, so that release and sampling of SF6 in the gob presented FIGURE 12. - Lead-z inc-si lver mine ventilation no problem. The dispersal time for the schematic. SF6 was determined by taking samples behind the seal at which the SF6 was re- determine if ventilation air was short- leased. If there was little or no leak- circuiting from the exhaust back into in- age, SF6 would disperse very slowly. take air. The intake and exhaust are two Additionally, che gas should not separate shafts with workings at various arrive at the other seal for several levels between the shafts. It was feared hours. that air was passing through old workings on upper levels and entering the intake In fact, SF6 concentrations at the re- shaft, rather than exhausting to the at- lease 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 air- cape route would be lost. flow patterns and qualitatively showed that air was leaking through seals, mak- SF6 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) permitting an ambient air sample to enter as a tracer gas are becoming more numer- the tube. When the needle is withdrawn, ous as researchers more fully understand the bladder reseals itself and can be its potential. This colorless, odorless, returned to the lab, where 0.1 ml of the nontoxic gas is easily dispensed in air. sample is withdrawn and injected into a Sampling is done by inserting 10-1, 90% gas chromatograph. After determining the evacuated Vacutainer test tubes into a amount of SF6 in the sample, the only plastic plunger containing a hypodermic other task is to reduce the data to tabu- needle. The needle punctures a rubber lar or graphic form. bladder on one end of the evacuated tube, 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 venti- that 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 Environ. Sci. Tech., v. 2, No. 1, 1968, F . H. Shair. Experimental Characteriza- pp. 44-48. tion of Ventilation Systems in Buildings. Environ. Sci. Tech., v. 6, No. 7, 1972, 6. U.S. Bureau of Mines. Dust Con- pp. 609-6 14. trol Rox for Bag-Filling Machines. Tech. News, No. 54, Aug. 1978, 2. pp. 2. Krause, D. Freistrahlen bei der Sonder bewetterung (Free Jets in Aux- 7. U.S. Code of Federal Regulations. iliary Ventilation). Neve Berg bzu- Title 30, Mineral Resources; Chapter 1-- technik, v. 2, No. 1, Jan. 1972, Mine Safety and Health Administration, pp. 44-52. Department of Labor; Subchapter O-- Coal Mine Health and Safety; Part 75, 3. Matta, J. E., E. D. Thimons, and Mandatory Safety Standards--Underground F. N. Kissell. Jet Fan ELfectiveaess as Coal Mines. Subpart D--Ventilation. Measured With SF6 Tracer Gas. BuMines Revised annually. RI 8310, 1978, 14 pp. 8. Vinson, R. P., F. N. Kissell, J. C. 4. Thimons, E. D., R. J. Bielicki, and LaScola, and E. D. Thimons. Face Venti- F. N. Kissell. Using Sulfur Hexafluoride lation Measurement With Sulfur Hexa- as a Gaseous Tracer To Study Ventilation fluoride (SF6). BuMines RI 8473, 1980, Systems in Mines. BuMines RI 7916, 1974, 16 PP* 22 PP* 9. Vinson, R. P., J. C. Volkwein, and 5. Turk, A., S. M. Edmonds, H. L. E. D, Thimons. SF6 Tracer Gas Tests of Mark, and G. G. Collins. Sulfur Bagging-Machine Hood Enclosures. BuMines Hexafluoride as a Gas-Air Tracer. RI 8527, 1981, 10 pp.

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