EVALUATION OF THE WET HEAD CONTINUOUS MINER TO REDUCE 

RESPIRABLE DUST 

Jeffrey M. Listak, National Institute for Occupational Safety and Health, Pittsburgh, PA 

Gerrit V.R. Goodman, National Institute for Occupational Safety and Health, Pittsburgh, PA 

Timothy W. Beck, National Institute for Occupational Safety and Health, Pittsburgh, PA

Abstract 

 The National Institute for Occupational Safety and 

Health (NIOSH) conducted field tests to evaluate the 

effectiveness of a wet head continuous mining machine 

for reducing dust exposure for continuous miner 

operators. Wet head technology delivers water via sprays 

to the continuous miner's cutter head as opposed to 

traditional standard sprays located on the boom and body 

of the mining machine. The sprays, positioned directly 

behind each bit on the cutter head, deliver water at the 

point of attack, serving to cool the bits during mining to 

reduce the potential for frictional ignitions. The sprays 

also flood the coal with water to potentially suppress dust 

generation. Dust surveys were conducted at several 

mines to evaluate the wet head's effectiveness to control 

respirable dust exposure at the continuous miner operator 

location and in the immediate return. Results show that 

the wet head miner improved air quality at both locations 

to varying degrees in some cases and not in others when 

compared to a continuous miner with a standard spray 

system. 

Introduction 

 Under NIOSH’s Coal Workers’ X-Ray Surveillance 

Program, over 90,000 chest x-rays have been performed 

on underground coal workers from 1980 to 2008 to track 

and document the incidence of pneumoconiosis. Trends 

are evident from these x-rays and it can be shown that, 

after years of decline, pneumoconiosis has been 

increasing among underground coal miners since the year 

2000. There is also evidence in these x-rays to suggest 

that the recent increase in pneumoconiosis cases is 

associated with coal workers exposure to excessive 

amounts of respirable crystalline silica (A. Scott Laney, et 

al., 2009). Many operations cut rock along with coal to 

create a more favorable working height for machinery and 

personnel. However, this rock is typically the source of 

the silica that often requires mines to be placed on a 

reduced dust standard lower than the current 2.0 mg/m3

regulatory standard. Mine operations are placed on a 

reduced standard when the amount of silica on the dust 

filters exceeds 5% by weight. The dust standard is 

reduced using the expression, 10 divided by % silica. 

MSHA dust samples collected by inspectors from 2004 to 

2008 show that 7.3 % of the samples from the continuous 

miner operator exceeds the permissible exposure limit 

(PEL) of 2.0 mg/m3

. However, when mines are placed on 

a reduced dust standard for silica content in respirable 

dust samples, nearly 20 % of the inspector samples are 

exceeded. (US Department of Labor, 2009). 

 Typically, respirable dust is controlled by water 

sprays mounted on the continuous miner (CM). This 

method has been an effective means of controlling 

respirable dust for CM operators for many years, but the 

increase in the incidence of overexposure suggests that 

the use of water sprays is no longer consistently providing 

protection to operators. As new methods of controlling 

face hazards are developed and adopted by the mining 

industry, their potential for controlling respirable dust will 

continue to be evaluated. 

Typical mining machines place water sprays on the 

cutting boom approximately 30-40 cm away from cutting 

bits to protect the spray manifolds. The wet head 

continuous miner introduces water via sprays located 

directly behind each cutting bit on the cutting drum 

(Figure 1a; Figure 1b). The spray angle of the nozzles 

over the bits keeps the bits cool during the cutting process 

increasing bit longevity and lessening the potential for 

frictional ignitions. In addition, these water sprays wet 

coal surfaces and have the potential to prevent airborne 

respirable dust generation by placing the water sprays as 

close as possible to the coal surfaces. It has been shown 

that the closer the water sprays are to the surface being 

1 
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cut, the more effective they become (Foster-Miller, Inc, 

1986). The wet head introduces water in close proximity 

to the point of attack of each bit and therefore has the 

potential for limiting dust generation while mining. 

However, several studies of wet head sprays versus 

standard machine mounted sprays have either not shown 

or could not prove a significant difference in dust 

reduction from one system to the other (Chugh, et al, 

2006, Goodman, et al., 2006, Fields, et al., 2005). In an 

attempt to clarify the effectiveness of the wet head miner 

to limit coal and silica dust exposure of the CM operator 

and downwind personnel, NIOSH conducted five in-mine 

dust studies to measure respirable dust levels at the CM 

operator location and in the immediate return. 

Figure 1a. Wet head bit block showing water spray 

behind the bit. 

Figure 1b. Wet head sprays on continuous miner cutter 

head. 

Mine Site Investigations 

These studies took place in five mines that are 

located in four states: Virginia, West Virginia, Kentucky, 

and Illinois. The five mines will be identified by letters A 

through E to ensure anonymity of the mines that 

cooperated for this study. In three of the mines, sampling 

took place on the same continuous miner configured with 

either a wet head spray system or a regular system of 

boom sprays. When running the wet head, for example, 

most of the boom sprays were plugged and a valve thrown 

to send water to the wet head sprays. Two studies took 

place on a super section that utilized two machines, one 

with standard boom sprays and one with a wet head. Dust 

samples were taken concurrently; as each miner unit was 

ventilated with its own air split. Of the five mines, three 

used blowing ventilation schemes and two were 

exhausting. All but one mine took extended cuts and all 

but one used a scrubber. The mine that did not take 

extended cuts used exhausting ventilation with a system 

of directional sprays called a sprayfan. No scrubber was 

used at this operation. 

When possible, the ventilation and dust control plans 

were reviewed. Air velocity readings were taken before 

each cut and production was recorded at the end of the 

shift. Spray pressure, spray type, and number of sprays 

were noted on both standard and wet head spray systems. 

Test Design 

The sampling strategy for these studies consists of 

both area and personal sampling to evaluate the different 

spray system’s affect on respirable dust levels at the 

miner operator location and in the immediate return of 

each cut (Figure 2). These samples were not collected for 

full shift and therefore the results cannot be correlated to 

compliance sampling. 

Figure 2. Sampling package locations for a typical cut on 

an exhausting ventilation scheme. 
 For area sampling, dust sampling packages were 

hung in the immediate intake and return of the individual 

continuous miner cuts. Dust generated in the cut and in 

the return can be directly related to the mining of that 

particular cut by subtracting the intake dust measurement 

from that at the operator and return. The sampling 

packages were repositioned at the start of each new cut 

(place change). 

For personal sampling of dust exposure at the 

operator location, the CM operator wore a Personal Dust 

Monitor (PDM). The PDM provides data that allows for 

time periods to be extracted during the shift to calculate 

dust concentrations for individual cuts during the shift. 

The PDM data is downloaded at the end of the shift then 

reset for the next sampling day. 

Area sampling packages for the sections consisted of 

two gravimetric samplers and a Personal Data RAM 

(pDR) (Thermo-Fisher) hung in the immediate intake and 

return entries. Gravimetric samplers use a cyclone, filter, 

and vacuum pump to collect dust particles. The 

permissible sampling pumps were calibrated at 2 

liters/minute before the study. These pumps draw dustladen air through 10-mm nylon cyclones to deposit the 

respirable dust fraction onto pre-weighed 37-mm PVC 

filters. All filters were pre- and post-weighed at the 

Pittsburgh Research Laboratory and respirable dust 

concentrations calculated for the total shift dust 

concentration. The filters were then sent to a third party 

to determine silica content of the dust. The MSHA P-7 

method was used to measure the silica content in the 

samples. 

The pDRs measure respirable dust particles by light 

scattering techniques and provide a relative dust 

concentration. The pDRs sample every 10 seconds and 

give a real-time reading of the relative dust concentrations 

over the entire shift. The pDR’s are used in conjunction 

with the gravimetric samplers to monitor dust levels 

instantaneously. The instantaneous readings can account 

for variations in dust levels during mining that the 

gravimetric samplers cannot provide. NIOSH researchers 

conducted time-studies during the mining operations in 

order to relate gravimetric and pDR data to the operations 

at that particular time. The calculated concentrations 

from the gravimetric samplers are compared to the 

associated total shift pDR concentration. The pDR total 

shift dust concentration is a relative measurement (based 

on a calibration dust) and will vary from the true 

measured dust concentration given by the gravimetric 

samplers. To correct for this difference, the total pDR 

dust concentration measurements are adjusted based on 

the total gravimetric concentration. The adjustment factor 

is determined by dividing the concentrations from the 

gravimetric samplers by the pDR total average 

concentration. After the adjustments are made, the 

adjustment factors can then be applied to the 

instantaneous readings from the pDRs to determine the 

true concentrations during individual time periods (e.g. 

time in cut). Figures 3a and 3b show the samplers used 

for the dust surveys. 

Figure 3a. Gravimetric/pDR samplers 

Figure 3b. Personal Dust Monitor 

Dust Survey Data 

Dust measurements from each of the mines were 

analyzed at the machine operator and in the immediate 

return to determine dust levels of each spray system at 

each location. Ultimately, the miner operator location is 

the where the protection is most important. However, 

dust levels at this location can be affected by many 

variables therefore, measurements in the return were 

necessary to determine whether one system was more 

effective than the other. All of the intake air and dust 

generated during mining must go into the return and 

therefore the return measurements were used to compare 

the two spray systems over all the mines surveyed. The 

other variable that directly affects dust generation is 

production. For all of the surveys, the dust levels were 

normalized for production. 

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4

Table 1 shows the specific parameters for each 

machine at operation A through E. Although mining 

heights were fairly consistent between operations, rock 

thicknesses varied from negligible to nearly 1 m. NIOSH 

researchers noted little variation in scrubber capacities 

between studies. 

Table 1. Operating parameters for study mines. 

Mine designation A B C D E 

Average mining ht. (m) 1.8 2.0 2.1 1.7 1.8 

Average rock thickness 

cut (m) 

0.4 <1.01 0 0.2 0.3

Scrubber capacity (m3

/s) 3.1 3.4 3.2 3.2 2See 

note 

Wet head 

operation 

No. of wet 

head sprays 

63 73 73 73 76 

Ave. wet 

head pressure 

(kPa) 

621 550 620 660 620 

Ave. tonnage 

(t) 

610 620 1590 1347 930 

Standard 

spray 

operation 

No. of boom 

sprays 

25 27 36 36 15 

Ave. boom 

spray 

pressure 

(kPa) 

1030 1160 620 690 760 

Ave. tonnage 

(t) 

680 500 1400 1239 930 

Notes: 1

Rock thickness ranged from .1 to nearly1 m during sampling 

2

Continuous miner at Mine E did not use scrubber; but used 15 

directional sprayfan sprays on cutting boom. 

Thirty two shifts were sampled over the course of the 

study accounting for a total of 156 production cuts. The 

individual cuts were compared within each mine to 

determine consistency of collected data. The many 

confounding variables within a single mine setting are 

difficult to limit and therefore comparing individual cuts 

from mine to mine was not deemed significant and will 

not be presented. Dust concentrations measured during 

standard boom spray system operation were compared to 

those obtained during wet head spray operation at the 

miner operator and return airway sampling locations. 

Table 2 shows the combined shifts for all mines 

surveyed. The table is segregated by mine designation 

and shows the shifts surveyed at each according to the 

type of spray system and the operator and return 

locations. The table shows the range of dust levels 

measured at each location for each spray system. Withinmine concentrations are consistent for both spray systems 

at each location. However, Mine E shows much higher 

return concentrations due to the lack of a scrubber on the 

continuous miner. Mines A through D utilized scrubbers. 

As seen in the table, on most of the shifts, there are 

reduced concentrations on both operator and return 

locations using the wet head. However, most 

improvements are small and some shifts show the wet

head concentrations higher. Mine C shows poor 

performance at the operator location when using the wet 

head system. This super section operation used a standard 

spray miner on one side and a wet head miner on the 

other. Blowing ventilation was used on both sides of the 

section. However, the miner operator on the wet head 

machine maintained a large curtain setback distance 

claiming that dust conditions were improved by this 

action. This practice kept him out of the mouth of the 

curtain and, as can be seen by the dust concentrations, 

exposed to higher levels of dust than the operator on the 

standard spray section. 

Table 2. Gravimetric and PDM dust concentrations from 

all mines participating in the study. 

 Operator Return

Wet Wet 

 Shifts Standard head Standard head 

 Mine A 1 0.79 0.31 2.89 1.69 

Scrubber, 2 n/s n/s 4.66 1.14

blowing vent., 3 0.79 0.39 3.96 2.22 

 super section 4 0.65 0.89 2.88 2.37 

 Mine B 1 3.17 2.03 2.47 6.86 

Scrubber, 2 2.68 1.76 4.84 1.57

exhausting vent., 3 2.21 1.47 2.40 1.89 

 same continuous 

miner 4 3.12 2.31 3.96 3.66

 5 2.72 5.92 2.90 4.28 

 Mine C 1 0.33 1.31 1.00 1.02 

Scrubber, blowing 

vent., 2 0.74 2.42 1.80 1.37

 super section 3 0.39 1.83 1.04 1.20 

Mine D 1 1.24 0.45 1.92 1.32 

 Scrubber, blowing 

vent., same 

continuous miner 2 1.40 0.91 1.06 0.95 

Mine E 

No scrubber, 

exhausting vent, 1 0.95 0.83 12.62 7.22 

same continuous 

miner 2 1.55 1.51 11.74 10.53 

Note: n/s = not sampled 

 

 

 To further illustrate the results, dust concentrations 

were averaged from each shift for each of the mines 

surveyed. Figure 4 shows the dust levels of each spray 

system in the return. The chart shows that of the five 

mines sampled, Mines A and E show reductions of 33% 

and 27%, respectively in the return when the wet head 

sprays are used but little or no improvement at the other 

mines. 
Figure 5 shows the dust levels at the operator 

5

location. It is obvious that Mine C shows elevated dust 

levels at the operator but as noted, this was due to the 

curtain setback during sampling. Mine D showed an 

improvement of 48% at the operator when the wet head 

was used. 

Return Dust Levels

0

2

4

6

8

10

12

14

ABCDE

Mine

Dust levels, mg/m3

Stnd

WH

Figure 4. Dust measurements in the return for all mines 

surveyed. 

Continuous Miner Operator Dust Levels

0.00

0.50

1.00

1.50

2.00

2.50

3.00

AB CDE

Mine

Dust levels, mg/m3

Stnd

WH

Figure 5. Dust measurements at the CM operator for all 

mines surveyed. 

 Respirabl

dust, varied betw

e silica levels, in the form of quartz 

een the wet head and standard spray 

machines at Mine A (Table 3). On the wet head, 

measurable levels were not detected on the operator 

sample and only low quartz levels were present on the 

return samples. With the standard spray system, quarts 

levels were higher at the operator and return sampling 

locations. At Mine B, much higher quartz levels were 

present in the operator and return samples. This was 

likely due to the significant amount of rock being cut 

during operation of the wet head and standard sprays. 

Again, higher respirable quartz levels were measured on 

the standard spray machine. This trend continued to be 

seen, to a lesser degree, in Mines C and D. At Mine E, 

the higher quartz measurement occurred on the wet head 

sprays. 

Table 3. Average respirable quartz levels, μg/m3 

Mine Wet head sprays Standard sprays 

ID operating operating 

Operator Return Operator Return 

A ND 27 70 143 

B 311 359 356 413 

C n/s 0 n/s 29 

D 35 21 34 29 

E n/s 742 n/s 694 

Notes: 

ND = not detected 

n/s = not sampled 

Summary 

There are mixed results from the study as to the 

effectiveness of the wet head spray system to reduce 

respirable dust. The dust data reveals that some mines 

show improvements, some do not. Respirable silica 

levels were less on the wet head miners in all but Mine E. 

Over the course of surveying the mine, some 

observations were made that may have affected the 

results. At the onset of the study, super sections were 

preferred because both spray systems could be monitored 

during the same shift in the same section with the 

assumption that variables such as production and air 

quantities would be similar between each CM unit on the 

section. These assumptions were correct for these 

operations. However, it became apparent that other 

factors influenced dust measurements between the two 

sections. For example, the CM’s scrubber flow and 

efficiency were not the same, the mine conditions from 

one side to the other were different, and the CM operators 

mining habits were different, as was evident by the 

curtain setbacks at Mine C. The data can be normalized 

for some but not all variables. In addition, the scrubbers 

are very efficient dust eliminators and could influence the 

dust concentration in the return. Four of the five mines 

(A, B, C, and, D) used scrubbers. In addition, three of 

these mines used blowing ventilation. On a properly 

maintained blowing ventilation system, an argument can 

be made that the operator should be in fresh air all the 

time and therefore would not be subjected to dust 

exposure no matter what control technology is being used 

for dust control. 

Mine E did not use a scrubber, was not a super 

section, and used exhausting ventilation. The same CM 

unit was used for each spray system. Other than Mine A, 

this was the only mine the showed reduction of respirable 

dust in the return entry. However, silica levels were 

higher. 

From visual observations and interviews with mine 

personnel, there were very favorable responses to the wet 
6

head use at the face. All operators found that the wet 

head system greatly increased visibility while mining. 

Also, the dust cloud created at the miner’s boom while 

loading shuttle cars was eliminated when the wet head 

system was used. This cloud often infiltrated the cab area 

of the shuttle car operators during loading. The increased 

visibility may be attributed to the close proximity of the 

sprays to the face, thus decreasing misting or the wet head 

sprays may be eliminating some of the non-respirable dust 

fraction. 

References 

1. Chugh, Y. P., Patwardhan, A., Gurley, H., Moharana, 

A., and Saha, R. (2006). A Field Demonstration of 

the Joy Wet-Head Miner Technology. Ed. 

Mutmansky J. M. and Ramani, R. V. Proc. 11th

U.S./North American Mine Ventilation Symposium, 

The Pennsylvania State University, University Park, 

PA. pp. 233-240. 

2. Fields, K. G., Schultz, M. J., Rude, R. L., Tomko, D. 

M., Atchison, D. J., and Gerbec, E. J. (2005). 

Respirable Dust Survey Conducted at the Big Ridge 

Inc., Willow Lake Portal (Mine ID No. 11-03054), 

Saline County, Illinois. US Dept of Labor, Mine 

Safety and Health Administration. Pittsburgh Safety 

and Health Technology Center. Dust Division. 

Obtained from Mark Schultz. 

3. Foster-Miller, Inc. (1986). Development of Optimal 

Water Spray Systems for Ventilation of Coal Mine 

Working Faces. Contract Report No. J0113010, U.S. 

Bureau of Mines, 292 pp. 

4. Goodman, G.V.R., Beck T.W., Pollock, D.E., 

Colinet, J.F., and Organiscak, J.A. (2006). 

Emerging Technologies Control Respirable Dust 

Exposures for Continuous Mining and Roof Bolting 

Personnel. Ed. Mutmansky J. M. and Ramani, R. V. 

Proc. 11th U.S./North American Mine Ventilation 

Symposium, The Pennsylvania State University, 

University Park, PA. pp. 211-216. 

5. Laney, A. Scott, Petsonk, Edward L., and Michael D 

Attfield. (2009) “Pneumoconiosis among 

underground bituminous coal miners in the United 

States: is silicosis becoming more frequent?” Occup. 

Environ. Med. published online. 

6. US Department of Labor (2009). Mine Safety and 

Health Administration, Program Evaluation and 

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Information System, Arlington Virginia.