Use of Rocsil® foam to remotely 

construct mine seals

M.A. Trevits

Senior research scientist, Pittsburgh Research Laboratory, National Institute for 

Occupational Safety and Health (NIOSH), Pittsburgh, Pennsylvania

C. McCartney

President, Strata Mine Services, Richlands, Virginia

Abstract

The National Institute for Occupational Safety and Health (NIOSH) is conducting a program of research 

to evaluate and improve remote mine seal construction technology for mine fire control and suppression. 

The main focus of this work is to develop reliable technology that will remotely seal a mine opening from 

floor-to-roof and rib-to-rib. NIOSH, in partnership with Strata Mine Services Inc.,1

1Mention of a specific product or company name does not imply 

endorsement by NIOSH.

is evaluating the 

capability of a two-component phenolic foam-based product, called Rocsil®, that is intended for cavity 

filling, air and gas sealing, and consolidation of highly fractured strata. Rocsil® can be rapidly applied, 

has a quick cure time, a high expansion rate, good compressive resistance and excellent anti-static properties. When the resin and catalyst are mixed, an immediate foaming reaction occurs followed by rapid 

expansion up to 30 times the original volume. By virtue of its fire-resistance properties, Rocsil® foam 

has application for sealing underground mine areas undergoing heating from spontaneous combustion, 

and it could be useful for remote mine seal construction to aid in mine fire control and suppression. 

This paper presents an overview of remote mine sealing technology, introduces the use of Rocsil® foam 

for remote mine seal installations, offers a case study of the use of this rigid foam material to remotely 

construct a temporary in-mine seal and discusses technology improvements.

Introduction

Previously, federal mining laws required mine operators in 

the United States to report to the U.S. Mine Safety and Health 

Administration (MSHA) any unplanned mine fire event that 

was not extinguished within 30 minutes of discovery (Code 

of Federal Regulations, 2007). Subsequent to the accidents 

at the Sago and Aracoma Alma Mines in January 2006, this 

regulation was modified to include all unplanned mine fire 

events that are not extinguished within 10 minutes of discovery. According to MSHA, in an underground environment, if 

miners attempt to fight a fire for 30 minutes and are unsuccessful, the fire will probably become uncontrollable. The 

revised reporting requirement is expected to result in earlier 

activation of fire-fighting plans as miners will notify supervisors more quickly who, in turn, can call in firefighting crews 

and allow miners to safely escape (Federal Register, Rules 

and Regulations, 2006.

During the time period from 1990-2007, there were 1,601 

reportable fires that occurred in the U.S. mining industry (an 

average of 89 fires per year), and 138 of these fires occurred 

in underground coal mines (an average of eight fires per year) 

(DeRosa, 2008) (Fig. 1). The leading causes of mine fires include 

flame cutting and welding operations, frictional heating and 

ignitions, electrical shorts, mobile equipment malfunctions and 

spontaneous combustion (National Institute for Occupational 

Safety and Health, 2008). The fact that mine fires occur with 

an alarming regularity reinforces the importance of recognizing 

and eliminating the potential hazards and the overall need for 

improved fire control and suppression technology to ensure 

the best possible outcome during a mine fire.

The technology used to control and extinguish a mine fire 

is usually focused on removal of one or more sides of the fire 

tetrahedron (oxygen, heat, fuel and the chemical reaction). If a 

mine fire is discovered early in its development, extinguishing 

agents are directly applied to the fire. This approach can be 

very effective, but it also places miners in close proximity to 

the fire and can expose them to the deadly hazards of the fire. 

-
Mine fires are fought indirectly when access to the fire zone 

is impossible because of safety reasons, blocked underground 

access, a limited supply of available firefighting materials and 

a fire zone that is too large for available underground personnel. This approach involves sealing the mine or construction 

of in-mine temporary seals (ventilation-control structures, 

hereinafter referred to as mine seals) to isolate the fire area. 

These in-mine seals can be constructed from within the mine 

or remotely through boreholes. Sealing the mine (or isolating 

the fire area) is designed to control or extinguish the fire by 

reducing the oxygen concentration in the mine atmosphere 

to a level that will not support combustion. The benefit of 

remote mine sealing technology is that the size of the fire zone 

enclosed by the seals can be reduced without exposing miners 

to the fire dangers. Once the fire zone is sealed, the affected 

area can be flooded with water, inert gases or gas-enhanced 

foam to control or extinguish the fire. This paper presents an 

overview of remote mine sealing technology, introduces the use of Rocsil® foam 

for remote mine seal installations, offers 

a case study of the use of this rigid foam 

material to remotely construct a temporary 

in-mine seal and discusses technology 

improvements.

Background

Cement-based remote mine seal construction. Commercially available remote 

mine seal placement technology places cement-based mine seal material (commonly 

without the use of downhole cameras) to 

the mine level in the following manner. A 

tubing string is placed into a borehole that 

has been drilled and cased to the mine void. 

Attached to the lower end of the tubing is 

a mixing tool, and accelerator material is 

pumped into the borehole via the tubing 

string (Fig. 2). Cement is concurrently 

pumped into the annular space between 

the tubing and the borehole casing. The 

cement and accelerator then mix in the 

lower portion of the borehole. The mixed 

material then flows into the mine opening and away from the 

borehole. The material is designed to set up quickly as it exits 

the borehole resulting in an accumulation of cement at the bottom of the borehole that flows outward towards the mine ribs 

and upward towards the mine roof. When sufficient pressure 

builds (indicating a significant build-up of material directly 

below the bottom of the borehole) in the borehole, pumping 

is stopped and the pressure is monitored. If the pressure falls 

(indicating that the material build-up has slumped), pumping 

is resumed until another pressure build-up is observed. The 

cycle of pumping and observing pressure decline continues 

until the pressure does not fall. If the pressure does not decline, 

pumping is terminated.

Figure 1 — Reported mine fires in the United States 1990-2007 (DeRosa, 

2008).

Figure 2 — Downhole depiction of a conventional remote 

mine seal installation.

By design, the seal material is supposed to flow and fill the 

mine roof-rib interface areas. However, this technology is not 

always successful, as underground observations of remotely 

installed mine seals show that the material often does not fully 

close the mine opening (Figs. 3 and 4). If a mine seal does not 

completely close the opening, then oxygen inflow cannot be 

stopped, which can lead to growth or further expansion of the 

fire. Mine seals that do not completely close the mine opening 

may be used to restrict or control the amount of air or inert 

gas that passes in or out of a fire area (depending on the size 

of the remaining open area in the seal).

In an effort to improve the technology, NIOSH contracted 

Howard Concrete Pumping Company and GAI Consultants 

Inc.to develop an alternative method for remotely constructing 

cement-based mine seals. After much testing at the NIOSH 

Lake Lynn Experimental Mine, an improved new grout-based 

material was developed along with a novel material placement 

technology (Gray et al., 2006). The system developed creates 

a mine seal in two stages. The first stage uses a string of pipe 

and a directional elbow that is positioned at the bottom of the 

injection borehole. The pipe string and elbow are designed to 

place bulk material into the mine void in a series of lifts to fill 

most of the mine opening. The second stage uses two strings 

of pipe (one inside of the other) in the injection borehole to 

convey two components of a specially designed grout material 

to a spray nozzle. The spray nozzle blends a two-part grout 

and accelerator mix while allowing sufficient air velocity to 
transport the grout to the mine roof-and-rib areas (Fig. 5). 

Figure 3 — Cement-based remotely installed mine seal. 

Note the open void areas.

Figure 4 — Cement-based remotely installed mine seal 

(Urosek, 2005). Note the open void areas.

Figure 5 — Spray nozzle directing material towards mine 

rib (Gray et al., 2006).

Once the spray nozzle is positioned in the mine opening 

above the bulk fill, the spray nozzle is rotated in a back-and-forth 

motion towards the mine rib areas to fill in the gaps between the 

bulk fill and the mine roof-rib interface. As the mine roof-rib 

intersections areas are filled, the grout builds up and migrates 

back towards the spray nozzle and the injection borehole. Filling of the remaining area near the borehole is accomplished 

by lowering the spray nozzle into the accumulated wet grout 

material below the nozzle and then rotating the spray nozzle 

through a 360-degree arc. Eventually, the material builds-up 

around the nozzle and closes the mine opening. In practice, the 

spray nozzle could be used to construct the entire mine seal; 

however, this would increase the cost of constructing the mine 

seal. This system can construct a 60 m3 (80 cu yd)mine seal in 

about 12 hours. It should be noted that for effective mine seal 

construction, this technology requires a second nearby borehole 

that is outfitted with a downhole camera to observe and direct 

seal material placement. This new technology offers a viable 

alternative to the commercially available system and should 

improve cement-based remote mine seal construction. 

Rigid foam remote mine seal construction. The final area of 

remote mine seal testing under the NIOSH research program 

involves investigating the use of rigid foam (polyurethane 

and phenolic foam). Rigid foam offers a unique capability, 

such that when the components of this material are mixed, it 

expands up to 30 times the original volume. This property is 

important and can be useful when trying to fill a mine void 

because the cement-based materials do not expand and often 

leave open areas along the intersection of the mine-roof and 

rib (as discussed earlier). However, because rigid foam material can be negatively affected by the heat of a mine fire, it is 

thought that mine seals constructed of this material would be 

placed farther away from the mine fire zone. 

Rocsil® foam is a unique two-component phenolic foam 

(phenol-formaldehyde) distributed by Strata Mine Services in 

the United States. The product is typically used for cavity filling, air and gas sealing and consolidation of highly fractured 

strata in underground mines (Fig. 6). When the components 

of Rocsil® foam are mixed in a 4:1 volume ratio, the resin 

and catalyst produces an immediate foaming reaction that is 

followed by a rapid expansion to as much as 20 to 30 times 

its original volume. Once the mixed material has polymerized, Rocsil® foam sets up in 5 minutes at 15°C (59oF) and 

2 minutes at 25°C (77oF) (Fig. 7). Rocsil® foam has a high 

compressive strength for rigid foam, i.e., the compressive 

strength at 10% deformation is 100 to 200 kPa (14 to 29 psi); 

an excellent antistatic properties and is reported to be fire 

resistant (Strata Mine Services, 2008). Because of its unique 

properties, NIOSH in partnership with Strata Mine Services, 

decided to test the application of Rocsil® foam for remotely 

constructing mine seals. 

Case study of remote sealing using Rocsil®

foam

An underground mine operator was interested in remotely 

constructing temporary seals in a slope area of a coal mine 

that contained a beltline conveyor structure. This is typically a difficult opening to remotely fill because conventional 

cement-based seal material does not always flow around and 

through the structure and can easily result in open voids in 

the seal. Strata Mine Services’ engineers determined that this 

would be an ideal mine application for Rocsil® foam because 

the material would flow laterally for a short distance below 

the conveyor and would then grow upwards through the conveyor structure as the chemical reaction between the resin 

and catalyst occurred. The mine area of interest was accessed 

using multiple boreholes; two boreholes were used for placing the Rocsil® product into the mine and another was used 

for observing the sealing operation by means of a downhole 

camera. The approximate dimensions of the arched-shaped 

mine opening were 4.6 m (15 ft) wide by 4.6 m (15 ft) high. 

The injection and monitoring boreholes were located about 6 

to 9 m (20 to 30 ft) apart.
Figure 6 — Use of Rocsil® foam to fill a cavity (Strata Mine 

Services, 2008).

Figure 7 — Rocsil® foam.

Due to the shallow overburden conditions at this mine site, 

the downhole mixing head was lowered into the mine void 

using the material delivery hoses instead of using a string 

of pipe. The downhole mixing head contains a static in-line 

mixing element that ensures that the Rocsil® resin and catalyst 

products are properly mixed before they are pumped into the 

mine void. Injection of Rocsil® began with the mixing head 

positioned near the lower portions of the conveyor. The mixing 

head was then moved upward towards the roof as the foam 

product polymerized and expanded (Figs. 8 and 9). 

Figure 8 — Screen capture from video showing early backfilling operations. Note numbers in the upper right hand 

corner of the image indicate to borehole depth.

Figure 9 — Screen capture from video showing backfilling 

operations progressing. Note that the numbers in the upper 

right hand corner of the image indicate borehole depth.

The position of the mixing head was adjusted and the extent 

of mine void filling was constantly monitored, from an adjacent 

borehole, using the downhole camera. The second injection 

borehole was used when it was observed that the foam had not 

completely closed the area below a walkway on the conveyor 

system that had not been previously identified to Strata Mine 

Services. Injection of Rocsil® was completed when it was 

observed by the downhole camera that the mine void had been 

filled (Fig. 10). In all, a total of 240 m3 (314 cu yd) of Rocsil®

foam were used to seal the mine opening.

Technology modifications and improvements

Although the mine seal discussed in this case study was 

not constructed for the purposes of fighting a mine fire, the 

successful remote installation of this seal has important 

implications on the use of this technology in a mine fire 

situation. It was demonstrated that a difficult mine opening 

could be effectively closed using Rocsil® foam, albeit that 

multiple boreholes were used. As a means of improving the 

technology for placing and monitoring the extent of mine 

seal construction, a new delivery system was designed and 

constructed to combine the downhole mixing head and the 

camera system. This design eliminates the need for a second 

observation borehole and could facilitate directed placement of the foam material. The mixing head is mounted to 

a rigid frame and an explosion proof housing (containing a 

low-lux camera, two high-intensity LED lights and batteries 

for power) is positioned immediately above the mixing head 

(Fig. 11). A coaxial cable connects the camera to a compact 

digital video recorder on the ground surface for viewing and 

recording mine seal construction operations. The system’s 
rigid frame is connected to a string of pipe that extends to 

the surface to enable engineers to raise, lower and pan the 

system during seal construction. The entire system (mixing 

head and camera equipment) is designed to fit in a 152-mm 

(6-in.) cased borehole, ensuring application at most mine 

sites. The camera and lights are designed to illuminate and 

observe mine seal construction activities at distances up to 

6 m (20 ft) from the mixing head. This entire system will be 

fully evaluated during remote mine seal construction work 

using Rocsil® foam at the NIOSH Lake Lynn Experimental 

mine is the spring of 2008.

Figure 10 — Screen capture from video showing completed 

seal. Note that the numbers in the upper right hand corner 

of the image indicate borehole depth.

Figure 11 — Improved foam delivery system that combines 

the downhole mixing head and the camera system.

Results and conclusions

Mine fires occur with an alarming regularity in the United 

States, which reinforces the importance of recognizing and 

eliminating the potential hazards and the overall need for improved fire control and suppression technology to ensure the 

best possible outcome during a mine fire. NIOSH is conducting 

a program of research to evaluate and improve remote mine 

seal construction technology for mine fire control and suppression. One part of the work is focused on the development of 

reliable technology that will remotely seal the mine opening 

from floor-to-roof and rib-to-rib. Underground observations 

indicate that conventional cement-based remote mine sealing 

technology often does not close the mine opening which can 

lead to growth or further expansion of a mine fire. NIOSHresearch has led to the development of novel downhole spray 

nozzle technology and improved grout mixtures.

Rocsil® is two-component phenolic foam that is typically 

used for cavity filling, air and gas sealing and consolidation 

of highly fractured strata in underground mines. Rocsil® foam 

expands to as much as 20 to 30 times its original volume 

and is fire resistant. Rocsil® foam has application for sealing 

underground mine areas undergoing heating from spontaneous combustion and it was thought that it would be useful for 

remote mine seal construction to aid in mine fire control and 

suppression.

Rocsil® foam was successfully used to close a sloping 

mine opening that was obstructed with a conveyor structure 

using multiple boreholes. A new foam delivery system was 

designed and constructed to combine the downhole mixing 

head and the camera system. This design eliminates the need 

for an observation borehole, will allow for directed placement 

of foam material and should be a significant improvement in 

the technology. The new system will be fully evaluated during 

remote mine seal construction work at the NIOSH Lake Lynn 

Experimental mine in the spring of 2008. 

Disclaimer

The findings and conclusions in this report are those of the authors and do not necessarily represent the views of NIOSH.

Acknowledgments

The authors recognize Danny McGlothlin and Michael Fabio, 

Strata Mine Services, for their assistance in the conduct of the 

fieldwork and collection of information needed to complete 

this study. The authors also recognize Thomas A. Gray, Tetra 

Tech; Charles D. Campbell, MSHA; and Michael Fabio, Strata 

Mine Services, for their expertise in providing the technical 

review of this paper.

References

Code of Federal Regulations, 2007, Part 30, Subsection 50.2 (6), July 1, http://

www.msha.gov/30cfr/50.2.htm.

Federal Register, Rules and Regulations, 2006, Vol. 71, No. 236, Dec. 8, pp. 

71429-71455.

DeRosa, M.I, 2008, Industrial Hygienist, Pittsburgh Research Laboratory, NIOSH, 

Personal Communication, February 7.

National Institute for Occupational Safety and Health, 2008, Mining Webpage, 

http://www.cdc.gov/niosh/mining/topics/topicpage19.htm, February 6.

Urosek, J.E., 2005, Chief, Ventilation Division, Pittsburgh Safety and Health 

Technology Center, MSHA, Personal Communication, March 22.

Gray, T.A., Trevits, M.A., Crayne, L.M., and Glogowski, P., 2006, “Demonstration 

of remote mine seal construction,” Transactions of the Society for Mining 

Metallurgy and Exploration, Inc, Vol. 320, pp. 31-37.

Strata Mine Services, 2008, http://stratamineservices.com/rocsilSMS.html, 

February 6.