Technology News

From the Bureau of Mines, United States Department of the [Interior

Tachnology news describes testad developments from Bureau af Mines programs. It is published to encourage the
‘tanster of this information to the minerals industry and its application in commercial practice. Mention af company

‘or product names is for documentation only and does not imply endorsement of specific firm or product.

Bureau of Mines ressarch is performed and reported under mandate of the United Statas Congress, For a free
subscription to Tochnology News, write to Office of Technology Transfer, Bureau of Mines, MS 6201,

810 7th St, NW., Washington, DC 20281-0001.

No. 447, March 1995

Dust Collector Discharge Shroud Reduces Dust Exposure
to Drill Operators at Surface Coal Mines

Objective

To reduce airborne respirable dust generated from
emptying dry dust collectors on small truck-mounted drills
used at surface coal mines.

Background

Exposure to crystalline silica dust during rock drilling
can cause respiratory disease. The U.S. National Institute
for Occupational Safety and Health (NIOSH) recently
issued a NIOSH Alert, “Request for Assistance in Pre-
venting Silicosis and Deaths in Rock Drillers’ (DHHS
(NIOSH) 92-107). In this report, NIOSH documents
numerous cases of acute, accelerated, and chronic silicosis
in surface mine drill operators. The workers affected are
as young as 25 years old, and many arc only in their 30's.
NIOSH concluded that the disease stems from inadequate
dust controls on many small mobile rock drills.

Tn response to this NIOSH Alert, the U.S. Bureau of
Mines (USBM) conducted dust surveys at small surface
mine drilling operations. Most of the drills were truck-
mounted and used dry dust collection systems. In the
immediate drill vicinity, respirable dust concentra-
tions ranged from 0.1 to 133.8 mg/m? and averaged
21.3 mg/m?. The crystalline quartz content in the re-
spirable dust samples analyzed was found to be significant,
usually higher than 10%. A contributing factor to these
hazardous dust levels is the cleaning of dry dust collectors
after drilling every few holes. The most common dust
collection system used on small truck-mounted drills is a

Rotoclone! dust collector, Hoppers are used to retain the
dust removed by the Rotoclone and must periodically be
cleaned by manual cmptying. A trap door is opened on
the bottom of each hopper, allowing the matcrial to falt to
the ground a distance of 0.9 to 12 m G to 4 fi) (sce fig-
ure 1). The impact of the material and subsequent disper-
sion by wind creates significant airborne dust exposure.
The drill operator often stands in the dust cloud to bang
the side of the hopper with a hammer to loosen the
packed cuttings stuck inside the hopper.

Approach

A control measure developed by the USBM to address
this dust generation problem is a barrier or shroud placed
around the hopper discharge doors extending to the
ground, This shroud confines the dust collector fines
during dumping to an enclosed space, thus reducing air-
borne dust entrainment into the surrounding worker envi-
ronment. Although this dust control technique was devel-
oped by the USBM for surface mine rock drills, it can be
universally applied to many mobile rock drills operating in
the construction industry as well.

Results

Figure 2 shows the temporary installation of a shroud
around the hopper doors to measure respirable dust re-
duction. The shroud consisted of brattice material and
was mounted by large magnets for easy installation and
removal during testing, Two flaps were cut in the shroud

4Reference to specific products does not imply endorsement by the
US. Bureau of Mines.

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

privately owned rights.



to allow the operator access to the hopper doors for open-
ing and closing. Average airborne respirable dust concen-
trations during the dump cycle were lowered around the
hopper discharge point from 25.4 mg/m? to 4.9 mg/m?
when using the shroud, reflecting @ dust reduction of 81%.
Any dust present while using the shroud was attributed
primarily to leakage at the open vertical seam in the
sbroud during testing. A more permanent installation
would have a sealed seam and would be expected to pro-
vide even better respirable dust control.

For More Information

Further details about these USBM research results may
be obtained by contacting the principal investigators,
John A. Organiscak (phone: 412/892-6675) or Steven J.
Page (phone: 412/892-6669), at the U.S. Bureau of Mines,

Sr a NO?
eS

ae 2

Figure 1.—Dust generated from emptying a dry dust col-

lector on a surface drill.

Pittsburgh Research Center, Cochrans Mill Rd., P.O. Box
18070, Pittsburgh, PA 15236-0070 (fax: 412/892-4259).
Technology News Nos. 286, 308, 338, and 440 provide
additional information on techniques to control respirable
dust emissions from highwall drills. Single copies may be
obtained free of charge from the principal investigators.

‘WIIAT IAS TIE U.S. BUREAU OF MINES
PUBLISHED LATELY?

“New Publications of the Bureau of Mines" lists all of our recent
publications and includes abstracts for many of them. To receive
this free bimonthly listing, send your name and address to

“New Publications" Mailing List
U.S. Bureau of Mines, MS 9800
810 Seventh Street, NW
Washington, DC 20241

Figure 2.—Shrouding the dust collector to reduce respir-
able dust exposure to drill operators.