U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health TRAPED

MENT OF HEALTH & HUMAN SERVICES . USA

Using In-Place Stone Stoppings To Direct Air 

in Underground Stone Mines

Objective

To improve the ventilation of large-opening underground stone mines by using stoppings made from stone

left in place.

Background

Underground stone mines typically use large roomand-pillar openings with little ventilation control. Stone

miners may be exposed to contaminants that include

silica dust, diesel particulate matter (DPM), exhaust

gases, nuisance dust, and face shot (blasting) fume gases.

The health risks from breathing these fine particles and

toxic organic materials are well documented. Although

contaminants such as dust or diesel exhaust can be somewhat controlled at the source, the escaping contaminants

are often diluted and removed from work areas using

ventilation with minimal controls. In many cases, current

mine ventilation practices use trial-and-error techniques

to improve ventilation. The growing realization of the

importance of a healthy work environment along with

increased regulations will require many stone mines to

implement new ways to improve ventilation. In-place

stone stoppings are one option.

Mine air flows from one point to another because of a

pressure differential between those points. This pressure

differential is established using a mechanical fan in

conjunction with separations (stoppings) between highpressure (intake) and low-pressure (return) airways. The

separation of intakes and returns is an important concept

that is used in most other types of mines. Normally, air

moves through underground stone mines with minimal

control technology. Fans are placed in locations where

they are thought to be most beneficial, and intakes are not

separated from returns. In a few smaller underground

stone mines, proper ventilation can be achieved with a

few strategically placed fans. However, as these mines increase in size, moving adequate quantities of air throughout the mine becomes harder, and separation of intakes

and returns becomes a problem. Building traditional mine

stoppings to separate the intake and return airways in

entries with a cross-section area often exceeding 800 ft2

 is

difficult. The stoppings must be able to withstand both

the dynamic pressure from face shots and the static pressures created by the fans. Construction and maintenance

difficulties, as well as high costs, are the main factors

preventing these traditional mine stoppings from gaining

wide acceptance by the stone mining industry.

In-Place Stone Stopping Concept

In-place stone stoppings eliminate many of the drawbacks associated with traditional constructed mine stoppings. Stone stoppings that connect pillars create a large

air wall that is strategically orientated to direct the air to

the working face. The stone stoppings are created by

eliminating the last face shot that would normally break

through two adjoining pillars. To direct the air, the stone

stoppings are oriented parallel to the ventilation airflow.

Several types of in-place stone stoppings are shown in

figure 1.

Technology News

Milestones in Mining Safety and Health Technology

SAFER HEALTHIER PEOPLE

No. 500 December 2002
Figure 1.—Various types of in-place stone stoppings. A, Solid

stopping; B, notched stopping; C, notched stopping with opening wide

enough for truck travel.

Depending on the layout of the underground mine,

in-place stone stoppings can be temporary or permanent.

Three mine ventilation methods have been previously

described by NIOSH researchers: perimeter, split-mine,

and unit-ventilation. The perimeter ventilation system is

designed to keep the active faces, or the outside perimeter

of the mine, always under intake air using air walls.

Under this method, the in-place walls are created perpendicular to the development direction and are used

until a second air wall is developed several crosscuts

ahead of the original wall. Mine development can be adversely affected because of the decrease in the number of

working faces when developing around the in-place

stoppings. Alternate faces must be used to reduce adverse stone production associated with creating the

in-place stone stoppings. Upon completion of the second

air wall, the original stone stoppings can be mined

through for optimum stone recovery, and bench mining

may take place if desired.

Split-mine ventilation is designed to split the mine into

two parcels, intake and return, separated by an air wall.

Under the split-ventilation method, the in-place walls are

created parallel to the development direction and are

permanent. The unit-ventilation method is used when a

series of units or sections are created that are the active

mining areas. In the latter method, in-place pillars help

in building the mining units. Mining can be both parallel

and perpendicular to the working face. In both split ventilation and unit ventilation, development is not adversely

affected because face availability is constant. However,

the stone must be left in place until the end of the

mine's life.

As part of this research, two cooperating mines are

using in-place stone stoppings in their mine design for

further evaluation of this technique to control and

separate stone mine ventilation.

For More Information

For more information on in-place stone stoppings,

contact Roy H. Grau III or Robert B. Krog, NIOSH

Pittsburgh Research Laboratory, Cochrans Mill Rd., P.O.

Box 18070, Pittsburgh, PA 15236-0070, phone: (412)

386-6562 or (412) 386-6729, respectively; e-mail:

RGrau@cdc.gov or RKrog@cdc.gov, respectively.

To receive additional information about occupational safety and health problems, call 1-800-35-

NIOSH (1-800-356-4674), or visit the NIOSH

Web site at www.cdc.gov/niosh

Mention of any company name or product does not

constitute endorsement by the National Institute for

Occupational Safety and Health.