y , , 

and Fred N. Kissell 

@ &GNT ?.. ~i ,. -., UNITED STATES DEPARTMENT OF THE INTERIOR r c, *' '%' ,"w*$Cr,C 

"4U OF 
UNITED STATES DEPARTMENT OF THE INTERIOR 

Cecil D. Andrus, Secretary 

BUREAU OF MINES 

Lindsay D. Norman, Acting Director 
This publication has been cataloged as follows: 

- 

Thimons, Edward D 

Forecasting methane hazards in metal and nonmetal mines. 

(Report of investigations ; 8392) 

Bibliography: p. 9. 

1. Mine gases, 2, Methane. 3. Mine safety. I. Vinson, Robert 

P,, joint author. 11. Kissell, Fred N., joint author, 111. Title. IV. 

Series: United States, Bureau of Mines, Report of investigations ; 

8392. 

TN23.U43 no. 8392 [T~305] 622'.08s [622'.42'028] 79-15652 
PREFACE 

Shortly before this report was to be printed, five men were killed in a 

methane gas mine explosion that tragically underscored the need for reliable 

methods of forecasting methane hazards in mines. 

The explosion occurred on June 9, 1979, in a Louisiana salt mine. As a 

result of the explosion, this mine and three other salt mines have now been 

reclassified as gassy by the Mine Safety and Health Administration. The mine 

where the explosion 0ccurred.i~ shown in table 1 of this report as mine number 48. Also reclassified as a result of this explosion was mine number 50, 

shown in the same table. 

The return air methane concentration for mine number 48 was 90 ppm. Use 

of the 100-ppm guideline as an indication of a methane hazard, as suggested in 

this paper, would have indicated that a potential methane hazard might exist 

in this mine. Mine number 50, with a return air methane concentration of 

165 ppm, was the only mine in the study that was not previously classified as 

gassy having concentration above 100 ppm. 

The new information and reclassifications that resulted from this explosion have led the authors to suggest that a guideline of about 70 ppm might be 

more appropriate, since every mine in this study having a return air methane 

concentration of more than 70 ppm is now classified as gassy. New analyses 

are now needed to establish the most appropriate concentration for use as a 

guideline. In the meantime, this paper shows that methane concentration is 

potentially valuable as an indicator of methane hazards in mines. 
iii 

CONTENTS 

Page 

Preface .... ............................................................ i 

Abstract. .......................................................O....... 1 

Introduction ......................O...............O.............O....... 1 

Sampling and analysis ...............................o..............o... 2 

Discussion .............................................................. 5 

The 100-ppm guideline . .................................................. 6 

Commodity mined and depth as gllidelines ............................... 6 

Conclusions .... ........................................................ 8 

Bibliography. ....o...O.................................................. 9 

ILLUSTRATIONS 

1 . Semi-logarithmic chart of methane concentrations found in returns of 

mines sampled ..................................................... 4 

2 . Methane concentration versus depth of mine .... ...................... 8 

TABLES 

1 . Methane concentrations found in mines ............................... 3 

2 . Average return air methane concentrations for various types of mines 

sampled .o.....................................................O... 7 
FORECASTING METHANE HAZARDS IN METAL AND NONMETAL MINES 

by 

Edward D. Thirnons, ' Robert P. vinsonI2 and Fred N. Kissell 3 

ABSTRACT 

Because of the high number of accidental methane gas ignitions in metal 

and nonmetal mines, the Bureau of Mines searched for a simple guideline that 

would allow mine personnel to evaluate the methane hazard in a given mine. 

Air samples were collected by the Bureau in 53 metal and nonmetal mines and 

analyzed for trace evidence of methane gas. Samples were collected in the 

returns and at the working faces. 

Those mines classified as gassy by the Mine Safety and Health Administration had a significantly higher average methane concentration than those 

classified as nongassy. Of the 9 gassy mines sampled, 7 had methane concentrations above 100 ppm, whereas only 1 of the 44 nongassy mines had a concentration above 100 ppm. The 100-ppm concentration may be used as a simple and 

convenient guideline for forecasting the methane hazard in a mine, whether or 

not the mine is classified as gassy. 

There was no consistent correlation between commodity mined and methane 

concentration, nor was there a correlation between mine depth and methane concentration. Neither of these factors can be considered a guideline for predicting methane hazards. 

INTRODU 'CTION 

Methane, although usually associated with underground coal mines, also 

occurs in significant concentrations in some metal and nonmetal mines. It is 

found in mines that penetrate carbonaceous shales or in mines that are located 

near rock formations containing carbonaceous materials (L, - 3).* Hundreds of 

miners' lives have been lost as a result of unexpected methane gas explosions. 

Supervisory physicist. 2 Phys icis t . 3 Research supervisor. 

All authors are with the Pittsburgh Mining and Safety Research Center, Bureau 

of Mines, Pittsburgh, Pa. 

4~nderlined numbers in parentheses refer to items in the bibliography at the 

end of this report. 
Furthermore, the occurrence of methane in metal and nonmetal mines is not confined to the United States. Methane ignitions and explosions have also 

occurred in European and South African mines, In Poland, almost all salt 

mines are classified as gassy (z), and in some Polish mines, large quantities 

of methane are released in conjunction with rock salt outbursts, Also, numerous ore mines in Canada and the U.S.S.R. experience methane gas problems (6). - 

The Mine Safety and Health Administration (MSHA) of the U.S. Department 

of Labor classifies U,S. metal and nonmetal mines as either gassy or nongassy. 

A mine that meets any one of the following four criteria is classified as 

gassy and so must comply with certain safety standards. These criteria, as 

set forth in the Code of Federal Regulations, 30 CFR 57.21-1 (5), - are-- 

a. The State in which the mine is located classifies the mineas gassy; or 

b. Flammable gas emanating from the orebody or the strata surrounding 

the orebody has been ignited in the mine; or 

c. A concentration of 0.25 pct or more, by air analysis, of flammable 

gas, emanating only from the orebody or the strata surrounding the orebody, 

has been detected not less than 12 inches from the back, face, or ribs in any 

open workings; or 

d. The mine is connected to a gassy mine. 

Approximately 10 U.S. mines are classified as gassy because they fit one 

or more of these criteria. However, an ignition occasion all^ occurs in a mine 

not previously classified as gassy, and where no gas hazard was suspected. 

For this reason, the Bureau of Mines undertook an in-mine study to determine 

if trace methane gas measurements made in the working areas or air returns of 

metal and nonmetal mines could be used by mine operators to predict potential 

methane hazards. An attempt was made to establish a correlation between the 

methane concentrations found in noncoal mines classified as gassy and those 

in mines listed as nongassy. Correlations were also sought between the 

methane concentration measured in a mine and the depth of the mine, or 

between the methane concentration and the commodity mined. 

SAMPLING AND ANALYSIS 

Gas samples were collected by the Bureau of Mines in 53 metal and nonmetal mines selected to represent a wide variety of commodities mined, mining 

methods, age, size, and depth of operation. Nine of these mines were classif ied as gassy by MsHA.' At each mine, samples were taken in the return airways, and in most of the mines, samples were also taken from the working areas. 

Surface samples were taken at most of the mine sites for use as base readings 

to compare underground samples against. Samples were collected in 10-ml evacuated bottles and analyzed on a chromatograph in the ~ureau's analytical laboratory at Bruceton, Pa. Methane concentrations were determined in parts per 

million (table 1). 

5Two of the 53 mines used for this study have been reclassified by MSHA as 

gassy, following a Louisiana salt mine explosion which occurred after this 

report was written. As a result, two more of the mines tested are now 

classified as gassy than are shown in this report. See "Preface." 
TABLE 1. - Methane concentrations found in mines 

. - 

the adit, a room is mined out and long horizontal holes are drilled into the oil-bearing 

Mine No. 

1. .......... Z........... 

3.0......... 

4.. .............. 5....... 

6. .......... 7........... 

8. ............... 9..........0 

lo........... 

ll.........O. 

12. ............... 13. ............... 14........... 

15.......... . 16........0.. 

17... ........ 18........... 

19..........0 

ZO.......... . 21. .......... 22 ........... 23........... 

24.......... 

25......0.... 

26.... ............ 27. ............... 28.. ......... Zg........... 

30........... 

31.. .............. 32... ............. 33.......... 

34. ............... 35. ............... 36........... 

37......... 

38........... 

39......... .. 40 ........... 41....... .... 42........... 

43... ............. 44........... 

45. .......... 46.... ............ 47..... ........... 48. ............. 49; ............... 50" .............. 51........ 

52........... 

53........... 

G Gassy. N 

''This oil mine 

strata. Oil flows from the holes into a scmp. 

"AS a result of an explosion June 9, 1979, at the mine shown here as number 48, the mines numbered in this table as 48 and 50 have been reclassified as gassy by MSHA. The explosion 

occurred after this research was completed. See "Preface .If 

Commodity mined 

Lead and zinc...... 

..... do. ........... ..... do..... ....... do ............ ......... do....... ..... Gold and silver.... 

..... do ............ do............ 

..... do.. .......... Copper ............. ..... do. ........... do. ........... do.. .......... Tungsten. .......... Molybdenum ......... ..... do...... ...... Iron............... 

Gypsum ............. ..... do.... ........ Silicates... ....... ~arble ............. Uranium.. .......... ..... do.,. ......... ...... do.. .......... ..... do...... ...... do. ........... do. ........... Limestone.. ........ ..... do.. .......... ..... do ............ do ............ do. ........... ...... do..... ....... do ............ do....... ..... ..... do.. .......... ....... do............ 

..... do............ 

Oil shale .......... Oil1 ............... Trona.............. 

..... do. ........... do. ........... ..... do. ........... Salt... ............ do ............ do ............ .do. ........... do........... . .do. ........... ........ d~...........~ 

..... do............ 

...... do............ 

Nongassy. NA Not 

consists of a 1,000-foot-long 

Mine 

classification 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

G 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

G 

N 

N 

N 

G 

N 

N 

N 

N 

N 

N 

N 

N 

N 

N 

G 

G 

G 

G 

G 

N 

N 

N 

N 

N 

N 

G 

N 

N 

At the bottom of 

Methane 

Return air 

10 

6 

7 

6 

4 

4 

10 

7 

10 

4 

5 

10 

9 

2 

1 

3 

30 

2 

9 

6 

9 

4 

3 

3 

110 

5 

9 

3 

7 83 

41 

7 

1 

5 4 

10 

10 

10 

5 

31 

10 

115 

1,000 

61 

340 

2,000 

7 0 

30 

4 

90 

19 

165 

200 

2 

2 

analyzed. 

adit 

concentration, 

Working area 

8 

N A 

9 

7 

3 

9 

10 

7 

9 

N A 

N A 

7 

9 

2 

0 

3 

2 7 

2 

3 

8 

4 

3 

3 

2 

35 

5 

9 

2 

N A 

43 

11 

N A 

64 

8 

6 

8 

5 

49 

40 

85 

N A 

N A 

700 

N A 

7 0 

N A 

N A 

N A 

N A 

19 

130 

2 

2 b 

sloping 15' from 

ppm 

Surface air 

2 

4 

3 

3 

1 

4 

2 

1 

2 

2 

1 

2 

4 

4 

0 

2 

2 

3 

1 

1 

3 

2 

2 

2 

NA 

N A 

2 

2 

13 

N A 

2 

1 

18 

2 

N A 

2 

N A 

N A 

N A 

2 

N A 

2 

2 

N A 

2 

N A 

N A 

N A 

N A 

2 

3 

3 

3 

horizontal. 
FIGURE 1. - Semi-logarithmic chart of methane concentrations found in 

returns of mines sampled. With only three exceptions, the 

broken line separates concentrations found in gassy mines 

from those found in nongassy mines. This line is at 100 

ppm, the simple guideline determined by this i nvestigation 

for identification of a methane hazard. 
Table 1 shows that for those mines where working area samples were taken 

there is usually a close correlation between methane concentrations in the 

returns and at the working areas. If the concentration in the returns is high, 

the working area concentration is also high. For almost every mine, the surface air samples had very low methane concentrations, indicating that no significant amounts of methane were entering the mines with the intake air. 

A semi-logarithmic chart (fig. 1) of the methane concentrations found in 

the returns of both the gassy and nongassy mines shows a very obvious trend, 

Of the 44 nongassy mines, 43 have return methane concentrations below 100 ppm; 

But for the gassy mines, 7 out of 9 have return methane concentrations above 

100 ppm. 

The average methane concentration in return airways of the 44 nongassy 

mines was about 17 ppm, and the average for the 9 gassy mines was about 

512 ppm. 

DISCUSSION 

An analysis of the data obtained from this study shows that certain general trends exist. Before discussing these trends, the following point 

should be made. It can be logically argued that the methane concentration in 

any mine is a function of the mine's ventilation. When more fresh air reaches 

the working areas, lower methane concentration can be expected in these areas 

and in the returns. It might therefore be assumed that mines having high 

methane concentrations are poorly ventilated. But in fact, it is generally 

true that the mines with high methane concentrations are better ventilated 

than those with lower concentrations. This is because the mines having the 

highest concentrations are classified as gassy, and therefore must meet the 

more rigid MSHA ventilation standards for gassy mines (5). - 

In this study, mine airflows were not taken into account for three 

reasons : 

1. MSHA classification standards for gassy mines are based solely on 

methane concentration and do not take airflow rates into account, 

2. Concentration data can both reveal a high methane release rate and 

also indicate whether or not current ventilation is adequate for that rate of 

methane release. Therefore, the concentration figure may be considered a 

reasonable indicator of the true hazard at the time of measurement without 

allowance for airflow. 

3. Airflow measurements in many metal/nonmetal mines are sometimes 

difficult to measure accurately because of large aimay sizes and changes 

in the airflow rate. 
THE 100-PPM GUIDELINE 

As noted earlier, 43 of the 44 nongassy mines had return air methane concentrations less than 100 ppm, and 7 of the 9 gassy mines had return air concentrations greater than 100 ppm. One mine, a copper mine classified as gassy 

by MSHA, had a return air methane concentration of only 5 ppm. A discussion 

with MSHA inspectors from that district revealed that a gas ignition occurred 

in this mine over 20 years ago, but no significant methane concentrations have 

been measured since. The inspectors feel that the mine should not be classified as gassy. Therefore, it is more realistic to state that seven out of 

eight mines had concentrations above 100 ppm. The only gassy mine below this 

level was a trona mine with a return air methane concentration of 61 ppm, 

which is still substantially above the average for the nongassy mines. These 

findings suggest that 100 pprn may be used as a simple guideline for determining if potential methane hazards exist in metal and nonmetal mines. 6 

COMMODITY MINED AND DEPTH AS GUIDELINES 

The first 17 mines in table 1 produce materials chemically classified as 

the transition elements and their neighbors and commonly referred to as metals. 

All 17 of these mines have low methane concentrations, averaging about 8 ppm. 

Limestone and salt mines tend to have higher methane concentrations, although 

only a few are classified as gassy. The 11 limestone mines sampled had an 

average return air concentration of 87 ppm. However, if the one mine classified as gassy is excepted, the average concentration drops to about 17 ppm. 

The nine salt mines had an average concentration of 67 ppm. The oil mine and 

four trona mines all had high methane concentrations, and all are classified 

as gassy. Five of the uranium mines sampled had low methane concentrations. 

The sixth mine, which is classified as gassy, had more than 100 ppm. 

Table 2 presents the average methane concentrations in returns for the 

various types of mines. While some general trends do exist between commodity 

mined and methane concentration, this study indicated that no reliable guideline could be established on the basis of commodity. 

GAS a result of a mine explosion and subsequent reclassification of several 

mines by MSHA, which occurred af ter this report was written, the authors 

suggest that the guideline be set at a lower concentration. A more appro- 

~riate concentration might be 70 ppm, the authors suggest, in light of this I- - 

new information. See refac ace." 
TABLE 2. - Average return air methane concentrations for 

various types of mines sampled 

Type of mine 

Transition elements and 

neighbors. ............. Urani~m~~.....~~~.~..... 

Limestone..,............ 

Salt..O.Q......O..O....O 

Oil.OO.O.OO....o.O.O.O.. 

Tr~na.~..~~..~~....~.... 

other1 ....O......O...... 

G Gassy mines, 

1 Gypsum, silicates, marble, and oil shale. 

Number 

of mines 

sampled 

17 

6 

11 

9 

1 

4 

5 

It is a commonly known fact that deeper coal mines generally have more 

methane gas problems than those of lesser depth, and one objective of this 

study was to determine if this is also true for metal and nonmetal mines. 

Depth information was obtained for 35 of the mines sampled in this study. For 

the remaining mines, depth varied from location to location so much that a 

meaningful value could not be obtained, A graph of methane concentration 

versus mine depth (fig. 2) shows no obvious relationship between methane concentration and depth. Many mines having high methane concentrations are quite 

shallow, while several deep mines have low concentrations. Thus, depth alone 

cannot serve as an indicator of the gas hazard. 

Number 

of gassy 

mines 

1 

1 

1 

1 

1 

4 

0 

Averagemethane concentration, ppm 

Gassy and 

nongassy 

mines 

8 

22 

87 

67 

115 

850 

7 

Nongassy 

mines only 

8 

5 

17 

50 

G 

G 

7 

Gassy 

mines only 

5 

110 

783 

200 

115 

850 

0 
CONCLUSIONS 

lo3 

E 10'- 

Q 

Q 

m5 

- a 

a 

z 

a 

c 

a 

Z 

I* 

0 

I 

0 

Since only 1 of 44 

nongassy mines and 7 of 9 

gassy mines had methane concentrations greater than 

100 ppm, this level of concentration may be considered 

a simple guideline for metal 

and nonmetal mine personnel 

to use in evaluating the 

potential methane hazard in 

a mine. 7 

Although some general 

trends do exist, this study 

indicates that no reliable 

guideline for predicting 

methane hazards can be based 

upon the correlation between 

commodity mined and me thane 

concentration. Furthermore, 

no correlation whatsoever 

was found between mine depth 

and methane concentration. 

DEPTH OF MINE, lo3 ft 

FIGURE 2. - Methane concentration versus depth of mine. 

1 1 I 1 1 1 - 0 - - - - - - - d 

- - 

- 0 - 0 

- 

- - - - - - 

- 0 - 

IO 

- 

- 

- 0 0 - 

- - o 

10'- 00 0 0 - - - - - 0 0 - - 000 - 3 - - 00 0 0 1 

- 0 0 - 

- 0 - 

Id 1 I I 11 

I 2 3 4 5 6!8 

In general, metal and 

nonmetal mines classified as 

gassy by MSHA have significantly higher methane concentrations at their workings 

areas and in their returns 

than do nongassy mines. The 

average return air methane 

concentration was 512 ppm 

for the 9 gassy mines 

sampled, and only 17 ppm for 

the 44 nongassy mines. 

> 

'see footnote 6, 
1. Cash, F, E, (rev. by), Fires, Gases, and Ventilation in Metal and 

Nonmetallic Mines. Metal and Nonmetallic Mine Accident Prevention 

Course, Section 5. BuMines Miners' Circ. 55, 1957, pp. 66-73, 

2. Cybulski, W., C. Gorol, T. Gotkowski, and J. Sobala. Charakterystyka 

Zagrozenia Metanowego w Polskich Kopalniach Soli (Characteristic Features of Methane Hazard in Polish Salt Mines.) SMRE Transl. No, 6344, 

Prace Glownego Inst. ~drmictwa, Komun. 567, 1972, p. 1. (Safety in 

Mines Research Establishment Transl. No. 6344.) 

3. Forbes, J. J., and Go W. Grove. Mine Gases and Methods for Detecting Them, 

BuMines ~iners' Circ. 33, rev. 1954, pp. 6-7. 

4. Harrington, D., and E, W. Denny. Gases That Occur in Metal Mines. 

BuMines Bull 347, 1931, pp. 2-4, 

5. U,S. Code of Federal Regulations. Title 30--Mineral Resources; Chapter I-- 

Mining Enforcement and Safety Administration; Subchapter N--Metal and 

Nonmetallic Mine Safety; Part 57--Health and Safety Standards, Metal and 

Nonmetallic Underground Mines, 1974, pp. 292-293. 

6. Voitov, G. I. (Gas Emanation in Ore Mines,) Sec. in Air Pollution in 

Mines, Theory, Hazards, and Control, Academy of Sciences of the U.S,S,R,, 

Mining Institute, Moscow, 1962, Israel Program of Sci. Transl., 

Jerusalem, 1966, pp. 142-161. 

8Titles enclosed in parentheses are translations from the language in which 

the item was published. INT.-BU.OF MINES,PGH.,PA. 24128