FACTORS AFFECTING THE LOCATION OF METHANOMETERS ON MINING 

EQUIPMENT 

C.D. Taylor 

NIOSH, Pittsburgh Research Lab 

E.D. Thimons 

J.A. Zimmer 

Pittsburgh, PA, USA NIOSH/Pittsburgh Research Lab 

Pittsburgh, PA USA 

ABSTRACT 

The U.S. Code of Federal Regulations (Title 30) requires that a methane monitor be placed on every mining machine to 

continuously observe and record methane levels at the face. The monitor must provide a warning whenever methane 

levels are 1.0 percent or higher. An effective monitoring system will indicate a methane concentration of 1.0 percent on 

the mining machine before methane levels at the mining face reach 5.0 percent. Where the methane monitor is located on 

the mining machine is one of the most important factors that determines how effectively face methane levels can be 

predicted. Any change in the sampling location will result in a change in measured methane concentration. To protect the 

methanometer, it is usually located on the cutting boom at least 1 to 1.8 m (3 to 6 ft) outby the front cutting bits. 

A face ventilation system using blowing tubing was simulated in a full-scale test facility. Methane released from the face 

area was monitored at multiple locations on a model mining machine as well as locations near the face. Based on the 

relationship between concentrations measured on the machine and at the face, criteria were developed for selecting the 

best machine locations for monitoring methane. Recommendations are given for revising methane action levels for 

alternative sampling locations.

KEYWORDS 

Methane sampling, underground coal mining, monitoring, ventilation 

BACKGROUND 

Federal regulations require that, during mining, 

methane levels must be continuously monitored near the 

mining face. The law requires that methane levels at this 

sampling location be maintained below 1.0 pct. 

Ignitions can occur at the face when methane 

concentrations exceed 5.0 pct. Since it is not possible to 

measure concentrations at the face, safety depends on 

the machine-mounted monitor reading 1.0 pct before the 

concentration at the face reaches 5.0 pct. Past 

experience has shown that when methane concentrations 

on the mining machine are kept below 1.0 pct it is 

unlikely that any ignition will occur near the face. 

The location where the methanometer is placed on the 

mining machine is one of the most important factors 

determining how effectively methane monitoring 

provides safety for the workers. Federal Regulations 

require only that „...the sensing device must be installed 

as close to the working face as practical (30 CFR 

§ 75.342).” The mining company, with the approval of 

MSHA, usually specifies the location for mounting the 

methanometer on the mining machine. The sensor head 

for the methane monitor is normally placed 1.8 to 2.4 m 

(6 to 8 ft) from the face. Placing the instrument closer to 

the face can subject it to physical damage. 

Research has been conducted at the National Institute 

for Occupational Safety and Health’s (NIOSH) 

Pittsburgh Research Laboratory (PRL) to develop more 

effective techniques for monitoring methane levels at 

the mining face (Taylor, 1997). Special emphasis has 

been placed on methane sampling strategies used during 

extended cut mining. The objective of the current study 

is to develop guidelines for selecting methane-sampling 

locations on the mining machine. At these locations the 

methane measurements will provide good predictions of 

the highest methane concentrations at the face. A 

technique is given for revising methane action levels 

(maximum allowable concentration) when alternative 

sampling locations are chosen. 

TEST FACILITY AND MINING MACHINE 

The NIOSH Methane Test Gallery at PRL is an „L” 

shaped building (Figure 1). One side was designed to 
model an underground mining face entry with 

dimensions, 4.3 m (14 ft) wide by 2.1 m (7 ft) high by 

37 m (120 ft) long. 

For these tests, an exhaust fan drew approximately 5.9 

m3

/sec (12,500 cfm) of air into the gallery. The return 

air was directed behind a brattice-covered wood wall 

constructed along the right side of the entry to the 

outside. Two auxiliary fans, operating in parallel, 

provided and airflow of either 1.9 or 3.3 m3

/s (4,000 or 

7,000 cfm) through 0.5 m (18 in.) diameter blowing 

tubing. The tubing was extended to either 0.6 or 3 m 

(2 or 10 ft) from the rear of the mining machine. A 3.7 

m by 2.3 m (12 ft by 7.5 ft) box was placed behind the 

miner to represent the inby section of a continuous 

haulage system. The inby end of the blowing tubing, 

which was supported by the simulated haulage system, 

was approximately 1.5 m (5 ft) from the left wall and 1 

m (3 ft) from the floor. 

Figure 1. Methane test gallery 

 A full-scale-model mining machine was located at the 

center of the mining entry. The machine was equipped 

with a 4.3 m (14 ft) wide drum that was positioned 1 m 

(3 ft) from the floor, a water spray system, and a 

simulated dust scrubber. The water spray system 

consisted of 11 hollow-cone (BD-3) sprays, which were 

mounted on top of the boom and directed straight 

toward the face. With the sprays operating, the pressure 

was 965 kPa (140 psi) with a flow of 53 l/min (14 gpm). 

The water sprays were operated only when the scrubber 

was on. 

The scrubber system (Figure 2) consisted of: 

− inlets on each side of the mining machine 

approximately 2.7 m (9 ft) from the bit tips, 

− two fans with attached ducts to move the air from the 

inlets to the exhaust, and 

− an exhaust opening at the right rear of the machine 

chassis. 

Tests were conducted with the scrubber off or flows 

of either 1.9 or 3.3 m 3

/s (4,000 or 7,000 cfm). 

 METHANE RELEASE AND INSTRUMENTATION 

During the continuous mining of coal, most 

methane liberated in the face area comes from either 

the newly exposed face, or pieces of broken coal as 

they are crushed by the rotating miner head. To 

model face emissions, methane was released through 

four, 3.7 m (12 ft) long copper pipes that were 

equally spaced horizontally, and located 0.1 m (4 in.) 

away from the face. Holes 2 mm (1/16 in.) in 

diameter, were drilled 5 cm (2 in.) apart on top and 

bottom of each pipe to provide a relatively uniform 

discharge of gas. The gas flow rate for each test was 

3.3 l/sec (7 cfm). 

Figure 2. Scrubber system and machine methane 

sampling locations 

METHANE SAMPLING LOCATIONS 

Methane gas concentrations were monitored 

concurrently at nine locations using catalytic heat of 

combustion methanometers. The locations were grouped 

into „face” and „machine” areas as shown in Figure 2, 

and described below. 

Face areas: 

 #1 - 0.3 m (1 ft) from roof and manifold and 0.5 m (1.5 

ft) from right wall, 

 #2 - 0.3 m from roof and manifold at the center of 

entry, and 

 #3 - 0.3 m from roof and manifold and 0.5 m from left 

wall. 

Machine areas: 

 #4 - Right side of machine, 1.5 m (5 ft) from face, 

 #5 - Left side of machine, 1.5 m from face, 

 #6 - Right side of machine, 2 m (6.5 ft) from face, 

 #7 - Left side of machine, 2 m from face, 

 #8 - Right rear of machine, 7.9 m (26 ft) from face, 

 #9 - Left rear of machine, 7.9 m from face. 
 

Table 1. Test Operating Conditions 

Test Condition 

Blowing Tubing 

Distance from Rear of 

Machine, (m) 

Intake Air Flow Quantity, 

(m3

/s) 

Scrubber Flow, 

(m3/s) Sprays, On/Off 

1 0.6 1.9 Off Off 

2 3.0 1.9 Off Off 

3 0.6 3.3 Off Off 

4 3.0 3.3 Off Off 

5 0.6 1.9 1.9 On 

6 3.0 1.9 1.9 On 

7 0.6 3.3 3.3 On 

8 3.0 3.3 3.3 On 

Table 2. Results for „Best Straight Lines” 

Highest Face Concentration 

Face Loc. Y-Intercept (b0) Slope (b1) T-test 95% confidence 

(significance) R2

 (%) P-Value 

4 0.33 1.12 Yes 61.5 0 

5 0.82 -0.01 No 0 0.98 

6 0.17 1.34 Yes 65.4 0 

7 0.81 -0.002 No 0 0.99 

8 0.12 3.47 Yes 72.6 0 

9 0.87 -0.92 No 0.91 0.72 

OPERATING CONDITIONS 

Blowing tubing location, intake air flow, scrubber flow, 

and spray operation were varied to simulate different 

operating conditions that could be encountered during 

mining. The variables for each test are given in Table 1. 

DATA COLLECTION 

Prior to the start of each test the desired operating 

conditions were set. Next, methane gas was introduced 

into the gallery for 5 min to allow the gas and air to mix. 

After the mixture reached a relatively steady state 

concentration, data was collected at each location for 5 

minutes. 

Data from each methanometer was downloaded every 

two seconds to a personal computer via an analog to 

digital conversion board. For each of the locations 

sampled, the average methane concentration for each 

five minute sampling period was calculated using an 

electronic spreadsheet file. 

RESULTS 

The highest of the three concentrations measured at 

the face was compared to each of the six concentrations 

measured at the sampling locations on the machine. 

Scatter diagrams, (Figure 3) drawn for each of these 

locations, include data for all 8 test conditions. Each test 

was repeated one time. The „best straight line” was 

drawn through each of the scatter diagrams using the 

method of least squares. Estimators of each line’s slope 

(b1) and y-intercept (b0) are given in Table 2. 

Figure 3. Comparison of highest face methane 

concentrations and concentration on mining machine 
 

The student t distribution was used to determine, for 

each straight line, if there is a statistically significant 

difference (95% confidence) between the slope of the 

line and zero. Relationships between the variables 

(concentration on the machine and at the face) are 

significant only if the slope is significantly greater than 

zero. „P values” are also given in Table 2 for each 

straight line. A „P value” less than 0.05 indicates there 

is a statistically significant relationship between the 

highest concentrations at the face and sampling 

locations on the machine at the 95% confidence level. 

Based on the T-test, there is a significant relationship 

between the highest face concentration and the 

concentrations measured at locations 4, 6, and 8. The 

relationships between the highest face concentration and 

machine locations 5, 7, and 9 were not significant. Pvalues were less than 0.05 for locations 4, 6, and 8 and 

greater than 0.05 for locations 5, 7, and 9. 

Airflow patterns drawn with the aid of smoke tubes 

were also used to evaluate the location of 

methanometers on the mining machine. Figure 4 

illustrates a typical airflow pattern drawn for the 

ventilation systems tested. In general, air from the 

tubing moved up the left side of the entry, across the 

face, where the methane was released, and back the 

right side of the entry to the return. Based on these flow 

patterns it would be expected that: 

− Methane concentrations would be higher at the 

sampling locations closer to the face where the 

methane was released. 

Figure 4. Face airflow patterns 

− Methane concentrations would be higher at sampling 

locations on the right side of the face where the air 

passes as it moves toward the return. In addition, because 

the air from the face passes directly over the right side, 

but not the left side sampling locations, it is more likely 

there would be some direct relationship between the 

concentrations at the face and locations 4, 6, and 8. 

These expectations were confirmed by the sampling 

results. 

DISCUSSION AND CONCLUSIONS 

Prevention of face ignitions depends on maintaining face 

methane levels below 5 pct. The peak or highest methane 

concentration measured at the face is the best indicator of 

the potential for a face ignition. During normal mining it is 

not possible to measure methane concentrations at the face, 

but, for these tests conducted in a simulated mine 

environment, methane concentrations were measured at the 

face. The highest of the three face concentrations was used 

to represent the peak face concentration. Concentrations 

measured on the mining machine were compared to the 

highest methane concentrations measured at the face. 

To compare concentrations on the machine to the highest 

face concentration, the „best straight line” was drawn 

through each of the plots. The straight-line model is the 

simplest one for comparing the data and there was no reason 

to believe a more complex model would fit the data better. 

The t-test, used to evaluate the slope of each straight line, 

showed that there was a statistically significant relationship 

between machine and highest face concentrations for 

locations 4, 6 and 8. The t-test alone should not be used as 

the only criteria to determine if a location should or should 

not be used as a machine sampling location. For example, 

when selecting a sampling location, the law requires that the 

sampling location be as close to the face as practical. 

Although, based on the t-test, location 8 is a possible 

sampling location; it is unlikely that it would be selected 

because it is so far 7.9 m (26 ft) from the face. 

When comparing concentrations measured on the 

machine and at the face, the scatter of the data points around 

the best straight lines should also be considered. Based on 

the R2

 values, which are a measure of the clustering of the 

data around the best straight line (see Table 2), there is 

similar scatter of the data for each of the possible sampling 

locations on the right side of the face. Part of the variation 

was due to changes in operating conditions between tests. 

Further studies are needed to determine the effects of these 

factors on sampling precision. 

The study results show that location 4 is one possible 

sampling location for the machine-mounted methanometer, 

although placing it that close to the face (approximately 1.5 

m) could result in physical damage. Using the best straight 

line model for data collected at the face and location 4 

(Figure 5), it is possible to predict the highest face 

concentrations corresponding to concentrations measured 

at location 4. For example, if the concentration at location 

4 is 1.0 pct, the highest predicted face concentration would 

be approximately 1.5 pct. The dashed lines in Figure 5 are 

the prediction limits (95% confidence) for the best straight 

line. Using the prediction limits it can be seen that 95 pct of 

the time the highest face methane concentration will not 

exceed 2.3 pct as long as the concentration at location 4 
 

does not exceed 1 pct. As long as methane levels at 

location 4 do not exceed 1 pct, methane levels at the face 

will remain below 5 pct. 

Although the level of safety provided by sampling at a 

specific machine location is never known exactly, 

changing the sampling location will usually affect the level 

of safety. Before moving the sampling location it should be 

shown that the level of safety would not be reduced by 

moving the methanometer. 

Figure 5. Comparison of highest face and location 4 

concentrations with prediction limits 

Maintaining the same level of safety may require that the 

action level (maximum allowable concentration) be 

reduced for the new sampling location. One technique for 

determining the action level for an new sampling location 

can be illustrated by using methane measurements made at 

locations 4, 6, and 8. 

Let location 4 be the designated machine sampling 

location, and locations 6 and 8 the possible alternative 

sampling locations on the mining machine. The methane 

concentration at location 4 can not exceed 1 pct. In order to 

maintain an equivalent level of safety for the worker, what 

should be the maximum allowable methane concentrations 

if methanometers are located at either locations 6 and 8. 

The scatter plots in Figure 6 compare concentrations 

measured at location 4 with concentrations at locations 6 

and 8 for the test conditions described earlier. The best 

straight line, drawn for each plot, is used to predict what 

the concentration at locations 6 and 8 would be when the 

concentration at location 4 is 1.0 pct. When the 

concentration at location 4 is 1.0 pct, the predicted 

concentrations at locations 6 and 8 are 0.96 and 0.38 pct 

respectively. If the sampling location was moved to either 

location 6 or 8, the maximum allowable concentrations 

would have to be reduced to these levels to maintain the 

equivalent level of safety. 

Equivalent safety is provided to the worker as long as the 

highest face concentration does not increase. During these 

tests the highest face concentration was measured and the 

parameters for the best straight lines were calculated (Table 

2). The equations for relating the highest face 

concentration (y) to the concentration measured on the 

machine (x) are: 

Location 4: y = 1.12(x) + 0.33 

When x = 1.0 pct, y = 1.5 pct 

Location 6: y = 1.34(x) + 0.17 

When x = 0.96 pct, y = 1.5 pct 

Location 8: y = 3.47(x) + 0.12 

When x = 0.38 pct, y = 1.5 pct 

Figure 6. Comparing methane concentrations at location 4 

with concentrations at locations 6 and 8 

Substituting the maximum allowable methane 

concentration of 1.0 pct for location 4, 0.96 for location 6 

and 0.38 for location 8, the predicted highest face 

concentration is the same (1.5 pct). Again this 

demonstrates how the action level for methane 

concentrations can be revised for new sampling locations 

in order to provide an equivalent level of safety. 

It is the methane reading taken at the designated location 

on the mining machine (and not the face concentration) 

that determines compliance with the 1 pct standard and it is 

the reading at this location that establishes the level of 

protection provided to the worker. Alternative locations 

should be used only if it can be demonstrated that these 

locations provide equivalent protection for the workers. 

This study provides guidelines for selecting sampling 

locations on the mining machine obtained during tests that 

simulated a range of operating conditions typical of one 

type of extended cut mining. The guidelines will vary 

depending on the type of mining operation. 

REFERENCES 

Taylor C.D., and Goodman G.V.R., 1997, „Use of 

Methane Monitors for Estimating Face Gas Conditions," 

Applied Occupational & Environment Hygiene 

(AOEA), 12(12), December, pp. 947-951