TECHNOLOGY FOR REMOTE MINE SEAL CONSTRUCTION

Michael A. Trevits John E. Urosek

 NIOSH MSHA

 Pittsburgh, PA Pittsburgh, PA

ABSTRACT

Mine fires can be especially perilous because toxic

products can quickly spread well beyond the fire zone thereby

exposing all underground miners to dangerous and deadly

conditions. Since November 1998, there have been six major

underground coal mine fires or explosions in the United States

(Willow Creek (twice), Sanborn Creek, Loveridge No. 22, West

Elk and the Jim Walter Resources No. 5 Mine). In each case, the

entire mine or specific areas of the mine had to be sealed due to

the build-up of dangerous gases and the fear of uncontrolled

spread of the fire. Effective placement of mine seals can deprive

a mine fire of oxygen and is often followed by water flooding or

injection of inert gas into the affected area. When access to the

fire zone is impossible because of safety reasons, airtight mine

seals can be constructed, in the area of the fire, remotely from the

surface through vertical boreholes. Remotely constructed mine

seals are commonly made from cementitious material. Since

these mine seals are typically erected blindly, it is difficult to

determine if mine roof-to-floor and rib-to-rib closure has been

obtained. This paper provides a review of the available materials

and technology used to remotely construct mine seals through

vertical boreholes. 

INTRODUCTION

Mine fires constitute one of the greatest threats to the

health and safety of those working in the underground mine

environment. Since November 1998, there have been six major

underground coal mine fires or explosions in the United States.

Table 1 shows a summary of these events. As can be observed

in the table, mine fires occur with an alarming frequency and each

event has the potential for disastrous consequences. A mine fire

can be especially perilous because the toxic products of the fire

can spread well beyond the fire zone in a very short period of

time.

The technology employed to control and extinguish a mine

fire is usually focused on removal of one leg of the fire triangle

(oxygen, heat, and fuel). The most direct approach involves the

application of water, foam, chemicals, rock dust or sand. This

method is very effective, because the extinguishing material is

placed directly on the fire. Unfortunately, this approach also

places firefighters in close proximity to the fire and can expose

them to deadly hazards. Furthermore, this approach is limited to

the very early stages of mine fire development. 

An indirect approach is used when the fire cannot be fought

directly because of safety reasons (build-up of gases, bad mine

roof conditions, etc.), the supply of available firefighting materials

is limited, the fire zone is too large for available underground

firefighters, or underground access is blocked or limited. The

indirect approach involves the construction of mine seals to limit

the inflow of oxygen and enclose the fire zone. Mine seals can be

constructed from within the mine or remotely through vertical

boreholes. The process can be followed by flooding the affected

area or the entire mine with water, inert gases, silt or other

material to control and extinguish the fire. 

Besides addressing the immediate need to isolate mine

fires, mine seals (in-mine construction) are also used extensively

to isolate mined-out areas, to control the air exchange between

the sealed and open mine areas, to prevent toxic and/or

flammable gases from entering the active workings, and to closeoff those mine areas susceptible to spontaneous combustion. A

seal must also be capable of preventing an explosion from

propagating into or out of the sealed area (Weiss et al., 1993). It

is estimated that more than 20,000 seals have been erected in

underground coal mines in the United States for these purposes

(Sapko and Weiss, 2001). 

Table 1. Summary of the Most Recent Coal Mine Fires or Explosions.

Date of Fire Mine Name Nearest City, State Fatalities

36123 Willow Creek Mine Price, UT 0

36185 Sanborn Creek Somerset, CO 0

36332 Loveridge No. 22 Mine Fairview, WV 0

36552 West Elk Mine1 Somerset, CO 0

36737 Willow Creek Mine Price, UT 2

37156 Jim Walter Resources No. 5 Mine Brookwood, AL 13

1Considered a thermal event by MSHA
When underground access is impossible or too dangerous,

remote mine seal construction can be attempted through vertical

boreholes. In theory, this method has great merit because

boreholes can be drilled to specific areas of the mine and seals

can be positioned close to a fire zone. In this manner, oxygen

inflow can be controlled and the spread of a fire can be limited

without exposing miners to the hazards. The technology

currently employed (injection of cementitious material) however,

can be largely ineffective when the seals leak and do not provide

effective barriers to air flow or cannot be used to impound water

and other inerting materials. Unfortunately, no other viable

alternatives exist other than to seal the entire mine at the ground

surface.

IN-MINE SEAL CONSTRUCTION

Since the early 1990's, the former US Bureau of Mines, the

National Institute for Occupational Safety and Health (NIOSH),

and the Mine Safety and Health Administration (MSHA) have

been cooperatively investigating various existing and new in-mine

seal designs. The focus of this work is to evaluate whether or not

these seal designs meet or exceed the requirements of Title 30,

Part 75.335 of a Code of Federal Regulations (Code of Federal

Regulations, 2001).

According to the Code of Federal Regulations, (CFR), a

seal constructed in the mine after November 15, 1992, shall be–

• Constructed of solid concrete blocks at least 15.2 x 20.3 x

40.6 cm (6 x 8 x 16 in), laid in a transverse pattern with

mortar between all joints; 

• Hitched into solid ribs to a depth of at least 10.2 cm (4 in)

and hitched at least 10.2 cm (4 in) into the floor;

• At least 40.6 cm (16 in) thick. When the thickness of the

seal is less than 61.0 cm (24 in) and the width is greater

than 4.9 m (16 ft) or the height is greater than 3.0 (10 ft),

a pilaster shall be interlocked near the center of the seal.

The pilaster shall be at least 40.6 cm (16 in) by 81.3 cm

(32 in); and 

• Coated on all accessible surfaces with flame-retardant

material that will minimize leakage and that has a flamespread index of 25 or less, as tested under ASTM E162-

87, “Standard Test Method for Surface Flammability of

Materials Using A Radiant Heat Energy Source.”

Alternative methods or materials may be used to create a

seal if they can withstand a static horizontal pressure of 1.38x102

kPa (20 psi) provided the method of installation and the material

used are approved in the ventilation plan. If the alternative

methods or materials include the use of timbers, the timbers shall

be coated on all accessiblesurfaces with flame-retardant material

having a flame-spread index of 25 or less, as tested under ASTM

E162-87, “Standard Test Method for Surface Flammability of

Materials Using A Radiant Heat Energy Source” (CFR, 2001). 

Before any new in-mine seal design type can be deemed

suitable by MSHA for use in underground coal mines, the seal is

generally required to undergo full-scale performance testing at

NIOSH’s Lake Lynn Laboratory (LLL) located near Fairchance,

Pennsylvania (Triebsch and Sapko, 1990; Sapko and Weiss,

2001).

REMOTELY CONSTRUCTED MINE SEALS

Remotely constructed mine seals have been used in both

abandoned and active mines. In the abandoned mine

application, the technology is used to stabilize the mine opening

(in the case of actively collapsing mine workings or subsiding

overburden, the technology is often called grouting), to serve as

a barrier for water, air, and gas migration, and to block the

advancement of a mine fire. The types of material used in the

construction of seals in an abandoned mine case includes a wide

range of materials with cementitious properties (including

combustion by-products from power plants).

In an active mine, the materials used have been generally

restricted to the cementitious-based materials because of

problems associated with the impact of extreme heat or fire.

Resin-based materials have not been recommended for

application in proximity to an active mine fire because of the

possibility that the material may be combustible and as such

rendered useless. The combustion of the non-cementitious seal

material could also produce toxic products of combustion. Some

manufacturers however, claim that certain additives are available

that can retard the combustion of resin-based materials (Zekas,

2001). 

Underground conditions in the area of a borehole can

dictate whether or not an entry can be effectively closed when

using remote mine seal technology. If the entry is free of debris,

then remote sealing is indeed possible. However, if the mine

opening is obstructed with roof fall material, timber, cribbing,

pipes or pipelines, equipment or conveyor structures, etc., then

construction of effective air-tight seals, using the current

technology, becomes somewhatproblematic. Conditions become

even more difficult if the mine opening is partially flooded because

the effects of additional water may significantly change the

properties of the seal material if it is not specifically designed for

application in a wet mine environment.

Because this technology of seal construction occurs blindly,

it is impossible to know if the material being pumped underground

is flowing around obstructions and filling the void spaces.

Typically, pumping of seal material continues until refusal, until a

specified pressure has been achieved, or a specific volume of

material has been injected into the borehole. Unfortunately, one

does not know if an air-tight seal has been constructed until the

pumping process is completed. At this point, it is impossible to

reenter the borehole and backfill any remaining voids. If the seal

is not effective, then another borehole must be drilled and the

extent of the sealing operation can be evaluated using a television

camera. If the prior pumping process is deemed inadequate, then

the process must be repeated in a new borehole or the one used

for the television scan. In some cases, several boreholes can be

used along an entry. Bulkheads are constructed through the

outside boreholes and grout or seal material is injected under

pressure through the interior boreholes (Gray, 1992).

MSHA and NIOSH-Pittsburgh Laboratory have recently

initiated a cooperative research project to evaluate single

borehole remote mine seal construction technology. Work under

this project includes a review of the available material, in-mine

construction and testing of seals at NIOSH’s LLL, and a field

demonstration.

REMOTE MINE SEALING TECHNOLOGY

Several companies that construct mine seals were

contacted to determine the kind of material and technology that

is either being used or could be used to remotely construct mine

seals. Table 2 shows the reported properties and characteristics

of remote mine seal material. Although this list of companies may

not be all inclusive, it provides a good sampling of the types and

kinds of material available. Table 3 shows remote mine seal

surface site and borehole considerations. It should be reported

that the information shown in table Nos. 2 and 3 were provided by

the individual companies. The reported material properties or

capabilities were not verified by the government as part of this

study. The following provides a discussion of each table.

Table 2 - Material Properties and Characteristics

Material Type - Cement and non-cement based materials

were selected as the broad category headings primarily because

they represent two differing types of in-mine applications. Resinbased (non-cement) materials may be very useful as a sealant or

bonding material in some mining applications, but cement-based

materials appear to be the most appropriate choice for mine seal

construction near a fire zone. It was reported earlier however, 
Table 2. Properties and Characteristics of Remote Mine Seal Material.

Companya

MATERIAL PROPERTIES AND CHARACTERISTICS

Material Type

Compressive Strength of

Material, kPa (psi)

Will Material Flow in

a Mine Opening

Application in

Flooded Mine

Conditions Cement d

Basedb

Non-Cement

Basedc

Fosroc

(Amick, 2002) Y N

1.38x102

 - 2.76x104

(20- 4000) Y Y

Heintzmann-Heitech

(Breedlove, 2002) Y N

1.38x103 -8.28x103 

(200 - 1200) Y N

Halliburton

(Bour, 2002) Y N

2.07x104

(3000) Y Y

Micon Services, Inc.

(Zekas, 2002) Y Y

12.1-1.38X105

(1.75 - 20,000) Y Y/Ne

Howard Concrete Pumping Co.

(Crayne, 2001) Y Y

3.45x103

(500) Y Y

R.G. Johnson

(Adasiak, 2002) Y Y

1.38x103-1.38x104

(200-2000) Y Y

a

 Mention of a specific company name does not imply endorsement by NIOSH or MSHA.

b

 Also includes fly-ash and other power plant by-products.

c

 Includes chemical resin-based materials.

d

 Includes partially flooded workings.

e

 Depends on the material used for the mine seal.

Table 3. Remote Mine Seal Site and Borehole Considerations.

Company1

SITE AND BOREHOLE REQUIREMENTS

Bulk Mixing Requirements Minimum Diameter Borehole

Needed, cm (in)

Material Mixing Requirements

In Transit On Site Surface2 Downhole

Fosroc

(Amick, 2002) Y

3 Y 12.7 (5.0) Y Y

Heintzmann-Heitech

(Breedlove, 2002) N Y 10.2 (4.0) N Y

Halliburton

(Bour, 2002) N Y 5.1 (2.0) Y Y

Micon Services, Inc.

(Zekas, 2002) N Y 15.2 (6.0) Y Y

Howard Concrete Pumping Co.

(Crayne, 2001) Y

3 Y3

15.2 (6.0) Y N

R.G. Johnson

(Adasiak, 2002) Y

3 Y

3 10.2 (4.0) Y

Y

4

1

 Mention of a specific company name does not imply endorsement by NIOSH or MSHA.

2

 Includes mixing tanks and in-line applications.

3

 Depends on the material used.

4

 Depends on downhole conditions.

that additives are available to retard the combustion of the resinbased materials (Zekas, 2001). 

Compressive Strength - This category was included to give

insight to the range of strength of the materials that are available.

An examination of the reported values shows that the strength of

the material available varies from 12.1 kPa to 1.38X105kPa

(2.0 psi to 20,000 psi). 

Generally speaking, the higher compressive strength

materials are most desirable. This assumes that the material can

be used to remotely construct a mine seal of an appropriate

geometry for the mine opening and that the seal extends from the

mine roof-to-floor and from rib-to-rib.

Will Material Flow in a Mine Opening - Since the floor area

of a mine opening could contain debris from a roof fall or

otherwise be obstructed as discussed earlier, it is important to

know if the material being used will flow into and fill openings

without separating into solid and liquid portions. If the material is

designed to set up quickly in the mine opening, it may not flow

laterally very far and may simply build up and form a mound

below the borehole.

Application in Flooded Mine Conditions - This category was

included because it is common to find partially or fully flooded

mine workings underground. It is therefore important to know if

a particular mine seal material will break down, not cure, or
become otherwise unusable in a wet mine environment. Table

No. 2 shows that some materials cannot be used in a flooded

mine environment. Typically, seal material must be specifically

designed for application in partially to fully flooded mine workings.

 If dry mine materials are used in a wet mine environment and if

mine water is added through mixing in the mine opening before

the material can set-up, the resulting seal material may not have

the desired properties.

Table 3 - Site and Borehole Requirements

Bulk Mixing Requirements - This category was included

because it is important to know, in advance, the required

geometry of the surface location around an injection borehole. If

the material can be mixed while in transit to the site, then a

smaller surface excavation may be required. If the materials are

brought in and mixed on-site, then a bulk mixing plant may be

required and a larger surface site must be prepared. In some

cases, the surface site conditions are dictated by costs and the

volume of material to be injected into a borehole or series of

boreholes. One way to avoid a large surface excavation at each

borehole is to mix the material at a central plant positioned near

one of the injection boreholes. The material can then be

transported via temporary pipelines to the other injection hole

sites. 

Minimum Borehole Diameter Needed - This category

represents a key factor for correctly sizing the drill rig required,

the diameter of borehole to be drilled, and casing needs. This

factor may also dictate if the drill rig must stay on location

because of material or pipe handling considerations or if a smaller

workover rig can be used during mine seal construction

operations.

Material Mixing Requirements - At first glance, this may

seem to be a repeat of the Bulk Mixing Requirements category,

rather, this category focuses on how the material is mixed and

whether mine seal material mixing occurs on the surface (in-line

or in a mixing tank) or at the bottom of the borehole. This has

implications on the required size of the borehole to be drilled and

cased. This factor is especially important if the lower part of the

borehole is to be used as a mixing chamber for the various

components of the seal mix.

As can be observed in table Nos. 2 and 3, a wide range of

products are available to the mine operator. In the case of a mine

fire, the availability of suitable materials to meet the underground

conditions, the capability for a swift response, level of experience,

and the financial aspects will dictate which company or product

will be utilized.

Each mine operator should evaluate their specific

conditions, the characteristics of the proposed material, the local

availability of materials and equipment, and the ability to deliver

the materials within the prescribed schedule. It is strongly

recommended that a test pour be made into a framework, form or

surface excavation that simulates a mine opening before any

material is pumped into the mine opening. In this manner, the

mine operator can make an on-site evaluation of the material mix,

the delivery technology, and if necessary make adjustments.

This procedure may not necessarily be required in each

application, if the mine operator is familiar with both the material

to be used and the experience of the company constructing the

mine seal. 

SUMMARY

Mine fires constitute one of the greatest threats to the

health and safety of those working in the underground mine

environment. A mine fire can be especially perilous because the

toxic products of the fire can easily spread well beyond the fire

zone, via the ventilation system, in a very short period of time.

When direct underground access to a fire zone cannot be

obtained, mine seals are constructed to limit the inflow of oxygen

and enclose the fire zone. Mine seals can be constructed either

from within the mine or remotely through boreholes. The

requirements for in-mine construction are included in Title 30,

Part 75.335 of the Code of Federal Regulations.

A wide range of materials is available for use in remote

mine seal construction. Not all of the products discussed in this

study can be deemed appropriate for application near an active

mine fire zone. The mine operator should evaluate their specific

conditions at the time of need, the mine area to be addressed, the

characteristics of the proposed material, the local availability of

materials and equipment, a company’s level of experience, the

ability to deliver the materials within the prescribed schedule, and

the underground environment. If the conditions warrant, a survey

of the mine opening with a permis sible downhole television

camera will provide useful data for designing the material mix for

the mine seal. It is also strongly recommended that a test pour

be made into a framework, form or surface excavation that

simulates a mine opening before any material is pumped into the

mine opening. In this manner, the mine operator can make a

direct, on-site evaluation of the material mix and the delivery

technology. 

REFERENCES

Adasiak, R., 2002, Personal communication, January 21.

Amick, M., 2002, Personal communication, February 5.

Bour, D., 2002, Personal communication, February 6.

Breedlove, J., 2002, Personal communication, February 7.

Code of Federal Regulations, 2001, Title 30–Mineral Resources,

Chapter I–Mine Safety and Health Administration

Department of Labor, Part 75–Mandatory Safety

Standards–Underground Coal Mines, Subpart

D–Ventilation Sec. 75.335 Construction of Seals. July 1, p.

477.

Crayne, L. M., 2001, Personal communication, December 17.

Gray, T. A., Gray, R. E., 1992, “Mine Closure, Sealing, and

Abandonment”, Mining Engineering Handbook, Second

Edition, Society of Mining Metallurgy and Exploration, Inc.,

Chapter 8.7, pp. 659-674. 

Sapko, M. J., Weiss, E. S., 2001, “Evaluation of New Test

Methods and Facilities to Test Explosion Resistant Seals”,

Proceedings of the 29th International Conference of Safety

in Mines Research Institute, October 8 -11, Katowice,

Poland, pp. 157-166.

Triebsch, G. F., Sapko, M. .J., 1990, “Lake Lynn Laboratory: a

State-of-the-Art Mining Research Laboratory”, in

Proceedings of the International Symposium on Unique

Underground Structures, June12-15, Denver, CO, Chapter

75, pp. 75-1 to 75-21.

Weiss, E. S., Perry, J. W., Stephan, C.R., 1993, “Strength and

Leakage Evaluations for Coal Mine Seals”, Proceedings of

the 25

th International Conference of Safety in Mines

Research Institutes, September 13-17, Pretoria, South

Africa, pp. 149-161.

Zekas, M., 2001, Personal communication, February 5.