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No. 430, March 1994

Translucent Face Partition Reduces
Longwall Workers’ Dust Exposure

Objective

Create two air splits along the longwall face 1o isolate
the shcarer-generated dust to the immediate face area,
maintaining a cleaner split of air in the workers’ walkway.

Approach

Previous U.S. Bureau of Mines (USBM) studies have
shown that an extended facc-conveyor spillplate barrier
can create two air splits effectively, but it proved to be
impractical because the workers could not sce the face
area and a reliable radio remote control was not yet
available for the shearing machines. The USBM’s current
approach to air splitting consists of using a polyester mesh
partition to overcame the visibilily problems of a solid
barricr, A permeable mesh partition is expected to pro-
vide adequate air-splitting capabilities as long as the prcs-
sure differential between the face and worker walkway is
minimal. New, reliable, radio remote shearer-control tech-
nology supplemented the development of this air-splitting
technology.

Laboratory Test Results

Experiments at the USBM’s Lake Lynn Laboratory
near Fairchance, PA, were conducted to determine the
i intaining two parallel splits of air with
several different sizes of a permeable polyester mesh
and to selec an optimum mesh size for underground

application. The meshes tested had 6.35-mm (1/4-in),
3.18-mm (1/8-in), and 1.59-mm (1/16-in) opening sizes,
exhibiting open areas of 83.7, $2.5, and 30.0 pet, re-
spectively. Each mesh size was evaluated to separate a
152.4-m-Iong (500-ft-long) entry into two parallel splits of
airflow, Both baseline (no mesh) and mesh tests were
conducted over a range of typical air velocities (1.02-
4,06 m/s [200-800 ft/min]) used at longwalls. Dust was
released on one side of the entry, and dust sampling was
conducted along 30.5-m (100-ft) intervals on both sides of
the entry.

Results showed that effective air splitting can be
achieved with the 3.18-mm (1/8-in) and 1.59-mm (1/16-in)
mesh opening sizes. Notable dust reductions were meas-
ured on the one side of the entry opposite the dust feed
source with the mesh partition. Average dust reductions
at 30.5 m (100 ft) and 71.0 m (200 fi) downstream of the
source for the various air velocities were 58 and 36 pct,
respectively, for the 318mm (1/8-in) mesh, and 79
and 55 pet, respectively, for the 1.59-mm (1/16-in) mesh.
At the higher air velocities (3.05 m/s and 4.06 m/s
[600 ft/min and 800 fi/min]), marginal differences were
observed between the 3.18-mm (1/S-in) and 1.59-mm
(1/16-in) mesh sizes,

Underground Test Results

Underground testing of the mesh partition was con-
ducted at a longwall operation to verify its effectiveness as
a control technique. A cooperative effort was conducted
with the mine to incorporate the mesh into its operation.

‘This document was prepared by the Bureau of Mines. Neither the United States Government nor any person acting on behalf of the United States
Government assume any liability resulting from the use of the information contained in this document, or warrants that such use be free from privately

owned rights



The mine extracted a highly volatile group B bituminous
coal from a seam with a historically low rate of methane
emission, notably reducing any potential methanc buildup
arcas while testing the mesh partition. The 3.18-mm
(1/8-in) mesh was selected for this study because the
experimental results showed that this size material pro-
vided nearly the same air-splitting effectiveness with the
mine’s higher face air velocity as the 1.59-mm (1/16-in)
mesh, while providing 75 pet more open area for improved
worker visibility. The mesh partition was hung contin-
uously from rods sccured to the light fixture bolts on the
underside of each shield canopy. Between cach shield,
amber latex tubing was attached to the end of each bar to
provide the flexibility for continuously hanging the mesh,
Additional mesh material was folded between the shields
to allow for support movement.

During this study, fire-retardant polyester mesh material
was used that was tested and classified as a low-risk fire
hazard, "Class A," as defined by the ASTM E-162 test,
"Standard Method Test for Surface Flammabi of
Materials Using a Radiant Heat Source.” Cap lamps were
mounted temporarily and focused at the shearer drums to
provide some face-side backlighting to improve operator
visibility through the mesh.

Underground dust sampling of this operation verified
that the mesh partition can be an effective air splitting
method by reducing the dust concentrations downstream
of the shearer. Mobile dust sampling was conducted
15.2 m (50 ft) upstream, 30.5 m (100 (1) downstream, and
71.0 m (200 ft) downstrcam of the shearer with and with-
out the mesh. During the head-to-tail cul pass, dust levels
were reduced with the mesh by 52 and 43 pet at 30.5 m
{100 ft} and 71.0 m (200 ft) downstream of the shearer,
respectively. These results were very similar to the Lake
Lynn Laboratory tests. However, during the tail-ta-head
cleanup pass, negligible dust reductions were achieved
downstream of the shearer. Part of the mesh surface
during this pass was not always parallel to the airflow since
supports were advanced between the shearer and down-
wind sampling locations. The mesh was perpendicular
to the airflow where the supports were being advanced,
which probably caused dusty air to pass through the mesh,
Thus, the mesh material must be parallel to the airflow to
be effective. Airflow measurements taken over the face
conveyor and in the workcr walkway indicated that the
mesh curtain had minimal effect on the face ventilation
characteristics of this operation,

Longwall Application Challenges

For the mesh partition to work effectively, several
operational issues must be addressed. The mesh partition
concept was found to separate effectively one split of
ventilation into two separate splits provided the mesh was
parallel to the airflow. Improved application methods
must be developed to reduce the significant bends in the
mesh (perpendicular to the airflow) created by support
movement during the USBM’s underground study. One
possible technique to curtail these significant mesh devia-
tions is to hang the mesh from cable supported by heavy-
duty, self-adjusting, “pogo-stick-type” poles secured to
the face conveyor. This system would climinate the mesh
orientation dependence on shicld movement and would
subject the mesh to milder orientation deviations of less
than 5 degrees.

Poor visibility of the face area through the mesh also
was encountered underground by the shearer operators.
The cap lamps mounted to the shearer did not provide
adequate backlighting necessary for suitable worker visi-
bility, This lack of visibilily through the mesh can prob-
ably be resolved by providing higher intensity lights
powercd by the shearer and/or additional shield-mounted
lights on the face side of the mesh.

Since the mesh restricts the intermixing of the face and
walkway airflows, dust and/or methane produced at the
face or workway area will be subjected to less dilution and
diffusion, Application of this concept at gassy longwalls
could possibly lead to higher than normal methane levels
at the face or in the walkway depending on its origin {such
as the face, floor, or gob). Thus, more methane monitor-
ing and caution must be used when applying this concept
in gassy mines,

For More Information

Further details or additional information about this de-
velopment may be obtained by contacting the principal
investigator for this project:

John A. Organiscak
Pittsburgh Research Center
U. S. Bureau of Mines
P.O. Box 18070

Cochrans Mill Road
Pittsburgh, PA 15236-0070
(412) 892-6675

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