Novel stopping designs for large-opening metal/nonmetal mines 

R.H. Grau III 

U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National 

Institute for Occupational Safety and Health, Pittsburgh Research Laboratory, Pittsburgh, PA, USA 

G.M. Meighen 

Wabash Holding Co, Foundation Coal Co, Keensburg, IL, USA 

ABSTRACT: Improving the air quality in metal/nonmetal mines is important in protecting the health of miners. Air quality can be improved in metal/nonmetal mines by developing proper ventilation techniques. Mine 

ventilation systems require stoppings to direct the airflow and establish pressure differentials throughout the 

mine. Due to their large size, stoppings in large-opening mines are cumbersome and costly to construct and 

maintain. As part of its mining health and safety program, the National Institute for Occupational Safety and 

Health (NIOSH) designed and tested two novel stoppings (Super Stopping and the EZ-Up Curtain Stopping) 

at its Lake Lynn Laboratory (LLL). The Super Stopping is designed as a long-term permanent stopping for 

use in the main entries of the mine, while the EZ-Up Curtain Stopping, although very durable, is designed 

more for portability and ease of installation. This paper describes the design, materials, and construction 

methods used for these stoppings as well as their performance and durability when subjected to tests simulating actual production face blast pressures. 

1 INTRODUCTION 

Stoppings play a significant role in underground 

mines by coursing and separating ventilation airflows. The utilization of stoppings, combined with 

proper mine designs, are essential components of a 

reliable ventilation system (Grau 2002, 2004a, b, 

Head 2001a, Krog 2004). In addition, supplying sufficient fresh air quantities to work areas to remove 

airborne contaminants will significantly improve air 

quality (Head 2001b, Robertson 2004, Haney 1998) 

thereby improving miners health. The design, construction, and maintenance of effective stoppings in 

large-opening mines are often challenging for mine 

operators. The choices for the design, materials, and 

construction techniques depend on a number of sitespecific utilization factors, such as the intended life 

and required effectiveness of the stopping. 

Stoppings have not always been widely used in 

large-opening stone mines. Capital expense, construction, and maintenance problems have impeded 

this segment of the mining industry from fully utilizing stoppings. Their use is particularly problematic 

in the larger, more established mines where stoppings have not previously been incorporated into the 

mining plan. In those mines, retrofitting the operation to include the use of stoppings to course the air 

requires building large numbers of stoppings requiring a significant investment in time and expense. 

The Super Stopping and EZ-Up Curtain Stopping 

are designed for use as a practical and cost effective 

means to control and direct ventilation airflows 

throughout the mine. A reduction in worker exposure to diesel particulate matter (DPM), gases from 

production blasts and diesel equipment, and silica 

dust (Chekan 2002, 2004) can be accomplished by 

using an enhanced ventilation system that includes 

these stoppings. 

2 SUPER STOPPING 

The Super Stopping (Fig. 1) was constructed by 

NIOSH at the LLL in cooperation with several 

manufacturers. The stopping is designed for use as a 

permanent, long-term ventilation control, and is constructed from oversized Omega Blocks, which are 

low density, composite cement and fly ash blocks 

manufactured by Burrell Mining Products, Inc. The 

individual blocks are 1.22 m (48 in) long by 1.22 m 

(48 in) high by 0.81 m (32 in) wide and weigh approximately 544 kg (1200 lb) each. The Super Stopping constructed at LLL is 17.4 m (57 ft) wide by 

9.1 m (30 ft) high. Construction of the Super Stopping is conducted in three phases: Phase I - Site 

Preparation and Foundation Building; Phase II -

Block Stacking; and Phase III - Capping and Sealing. 
Figure 1. Schematic of Super Stopping. 

2.1	 Phase I - Site Preparation and Foundation 

Building 

For a stable installation, the stopping should be built 

on a level surface which is best achieved using a 

concrete footing. The approximate footing dimensions are the distance across the mine opening width 

by 1.12 m (44 in) in depth, with a minimum 0.15-m 

(6-in) concrete thickness. A footing width of 1.12 m 

(44 in) provides an extra 0.15 m (6 in) on each side 

of the 0.97-m (32-in) wide stopping block. The footing should consist of 20,680-kPa (3,000-psi) standard mix concrete, embedded with standard 0.15-m 

(6-in) by 0.15-m (6-in) wire mesh reinforcement material, which is sufficient to withstand the weight of 

the wall. 

2.2	 Phase II – Block Stacking 

An extended reach forklift is used to lift and position 

the blocks (Fig. 2-3) during the stacking phase. 

 

 

Figure 2. Setting blocks for construction of a Super Stopping 

using extended reach fork lift and precast lifting holes. 

Figure 3. Placing Supper Stopping block in place after applying 

adhesive. 

The 

blocks have two factory cast holes on one side to receive the forklift tines. Articulation of the blocks is 

necessary for their proper alignment in the structure 

to maintain stability and vertical trueness. It is critical to establish a stable structure as the stopping 

height increases. The first course of blocks is aligned 

along a chalk line struck on the concrete footing. 

Each block is secured in place with a high grade 

polyurethane construction adhesive. The adhesive 

used on the Super Stopping at LLL was the Touch 

‘N Seal Mine Mortar Adhesive manufactured by 

Convenience Products. The adhesive is applied in a 

zigzag pattern with each line spaced approximately 

5.08 cm (2 in) apart and distributed on all contacting 

sides of each block (Fig. 3). The blocks must be positioned tightly to ensure proper adhesive distribution between blocks. The standard masonry technique of staggering blocks on successive layers is 

recommended to maximize the strength of the stopping (Fig. 1). The fly ash blocks can be scribed and 

readily cut to fit with a simple hand saw or axe. Successive layers of blocks are laid until the remaining 

gap between the top of the blocks on the highest row 

and the roof is less than the 1.22-m (48-in) height of 

a full block. 

2.3	 Phase III – Capping and Sealing 

To complete the structure, smaller fly ash blocks, 

0.61 m (24 in) by 0.41 m (16 in) by 20.32 cm (8 in) 

or 15.24 cm (6 in), are used to cap the top of the 

stopping. As with Phase II construction methods, the 

smaller cap blocks are staggered and cut to conform 

to the roof as well as the ribs, and secured in place 

with an adhesive. The final row of cap blocks should 

be placed within approximately 7.62 cm (3 in) of the 

roof and walls of the mine opening. 

The remaining gaps at the top and sides of the 

stopping are sealed using an expansion foam product. Since the foam is applied using a handheld apparatus, access to areas beyond reach is achieved using a man-basket. The stopping constructed at the 

LLL was sealed using Touch ‘N Seal Mine Foam 

manufactured by Convenience Products. The foam is 

applied to approximately half the depth of the 

blocks, or until expansion of the foam completely 

fills the voids. The expansion foam acts to conform 

to the shape of both the cut blocks and surfaces of 
the mine opening, thus increasing structure stability. 

Since the fork lift holes do not pass through the entire block, they do not require sealing. 

3 THE EZ-UP CURTAIN STOPPING 

The EZ-Up Curtain Stopping (Fig. 4) was also constructed by NIOSH at the LLL in cooperation with 

several manufacturers. This stopping is designed 

primarily for use as a temporary or portable stopping, although test results indicate it may remain 

useable for an extended time. The EZ-Up Curtain 

Stopping can be constructed from a variety of fabrics including mine brattice. Evaluations were performed on EZ-Up Curtain Stoppings composed of 

two separate curtain materials: (1) NOVA-Shield 

RU88XFR-6, a high density polyethylene woven 

fabric, manufactured by Intertape Polymer Group, 

Inc. and (2) Dura-Skrim D15CFB, which is composed of two layers of film laminated with polyethylene that sandwiches a scrim reinforcement, manufactured by Raven Industries, Inc. The EZ-Up 

Curtain Stopping is manufactured with a sewn-in 

loop so it can easily be laced onto tubing while laid 

out on the ground. It is then hoisted to the mine roof 

with a strap and ratchet mechanism system. Since 

the EZ-Up Curtain Stopping is constructed primarily 

on the ground, workers’ exposure to accidents related to the typical 6.10-m (20-ft) to 12.20-m (40-ft) 

working heights associated with large-opening 

mines is reduced. 

The EZ-Up Curtain Stopping is constructed in 

four phases: Phase I - Preparation and Ratchet Assembly Installation; Phase II - Curtain Preparation; 

Phase III - Curtain Hoisting; and Phase IV - Securing the Perimeter and Floor. 

3.1	 Phase I - Preparation and Ratchet Assembly 

Installation 

The walls and roof of the stopping installation area 

should be fully scaled to prevent injuries from falling rock during construction, and to provide a solid 

foundation to secure the stopping to these surfaces. 

The stopping is attached to the mine roof with four 

ratchet assemblies anchored by roof bolts (Figs. 4-

5).

 

Figure 4. Schematic of EZ-Up Curtain Stopping that is constructed using fabric strips. 

Figure 5. Ratchet assembly for hoisting EZ-Up Curtain Stopping. 

 For the LLL stopping, a 30.0-cm (12-in) long by 

2.5-cm (1-in) diameter roof bolt that was anchored 

in competent roof material provided substantial support to suspend the curtain. 

The ratchet assembly (Fig. 5) was constructed by 

welding the ratchets to U-angle steel stock, drilling 

two holes into the stock for the roof bolts, and welding a nut on the ratchet for easier winching. The 

ratchets used for these assemblies are standard offthe-shelf ratchets used for equipment tie-downs on 

trucks. The four ratchet assemblies are positioned in 

a straight line across the roof of the entry. One 

ratchet assembly should be mounted near each entry 

wall, with the two additional assemblies spaced 

evenly across the entry. After mounting, the ratchet 

mechanisms are ready to accept the straps for lifting 

the curtain. 

3.2	 Phase II - Curtain Preparation 

The fabric size used for the EZ-Up Curtain Stopping 

should be full entry width and height, plus several 

feet excess in both dimensions to allow for attachment to the rib and for sealing on the mine floor. A 

stopping composed of material strips that can also be 

used as a drive through stopping can be constructed 

by hanging strips of fabric as shown in figure 4. A 

similar designed, but one-piece fabric stopping, can 

be made by having the fabric distributor sew the 

strips together or, if available, ordering from the 

manufacturer a custom designed one piece fabric to 

fit the entry. Both a hanging strip stopping and a one 
piece stopping were constructed and tested for blast 

pressures at LLL. In either case, the fabric along the 

top edge of the fabric material is folded over and 

sewn at the factory to form a loop, through which 5-

cm (2-in) diameter tubing or conduit is threaded 

(Fig. 4). The individual lengths of tubing can be 

joined together with either threaded or tapered connections to span the entire length of the entry. For 

the hanging strip curtain stopping, to limit air leakage, each curtain panel is overlapped horizontally 

approximately 0.6 m (2 ft) onto the adjoining panel. 

The loop at the top of each panel must be cut away 

on one side to allow for the 0.6-m (2-ft) overlap. 

3.3 Phase III - Curtain Hoisting 

The lift straps are suspended from the ratchet 

mechanisms and attached to the tubing through a 

narrow slot cut with a small handheld electrical 

grinder (Fig. 4). The flat plate hook is fitted into the 

slot, and bolted if necessary, to secure attachment to 

the tubing. After attaching all lift straps, the EZ-Up 

Curtain Stopping is lifted using the ratcheting

mechanism. 

Lifts should be made approximately 1.5 m (5 ft) 

at a time by alternately ratcheting each mechanism. 

This will ensure the curtain tubing is kept as level as 

practical (Fig. 6). 

Figure 6. Raising the EZ-Up Curtain Stopping into position. 

The curtain is hoisted until the tubing is flush with the pulley, which will place the top 

of the curtain near the roof of the mine entry. 

3.4 Phase IV- Securing the Perimeter and Floor 

The final step in the installation process is to secure 

the EZ-Up Curtain Stopping to the walls using vertical boards with dimensions of 3.8 cm (1.5 in) by 8.9 

cm (3.5 in) by 3 m (10 ft) (Fig. 4). The first set of 

boards should be bolted to the walls from the roof to 

the floor in line with the edge of the curtain. Excess 

fabric on the sides of the curtain is then wrapped 

onto a second set of vertical boards. This wrapping 

prepares the curtain for attachment to the existing 

wall mounted boards to create a sandwich effect. 

Care should be taken to avoid wrapping the curtain 

too tight, or stretching the fabric, since the curtain 

should be able to yield slightly when subjected to 

variable pressures. The wrapped curtain boards on 

the prototype stopping at LLL were attached to the 

wall boards using 0.6-cm (0.25-in) diameter by 10-

cm (4-in) long lag screws. Test results, described below, revealed that larger or different anchors would 

be better. When the curtain is anchored to the rib, 

excess curtain material along the bottom is trimmed 

to the desired length to complete the perimeter. 

The curtain stopping can be further secured by 

laying sand bags on the excess curtain material 

draped on the floor. The bags serve two purposes: 

they seal the stopping from excessive leakage, and 

they provide for pressure relief to help reduce stopping damage in the case of a face blast that produces 

excessive pressures against the stopping. In an overpressure scenario, the curtain will be blown free 

from the sand bags preventing damage, but the 

sandbags will need to be replaced to reestablish the 

seal. 

4 RESULTS OF BLAST TESTING 

Stoppings in an underground metal/nonmetal mine 

must withstand air blasts associated with development and production blasting. Evaluation of the 

structural integrity of such stoppings can be investigated by subjecting them to unconfined blasts. Performance testing using consecutive charges of 1.4 kg 

(3 lb), 2.3 kg, (5 lb), 3.2 kg, (7 lb), and 4.5 kg (10 lb) 

of 50/50 Pentolite (50% TNT/50% PETN) unconfined explosive charges were conducted at LLL on 

the Super Stopping and the EZ-Up Stopping. The 

explosive charges were positioned at about 1.83 (6 

ft) above the floor in the entry, approximately 18.29 

m (60 ft) from the stoppings. 

The unconfined blast tests confirmed the integrity 

the stopping construction and the materials used. 

The Super Stopping evaluation included observing 

how well the stopping held up to the blasts, i.e. the 

strength of the adhesive between the blocks, the effectiveness of the perimeter foam, and the overall 

stability of the stopping. Similarly, the integrity of 

the EZ-Up Curtain Stopping was tested for material 

strength, especially at the critical high-tension perimeter areas. From the multitude of blasts test performed, the stoppings were subjected to an incident 

maximum peak pressure of up to 17.2 kPa (2.5 psig) 

and up to an incident maximum pulse pressure of 

0.14 kPa/s (0.02 psig-s). The incident maximum 

peak pressure for each test was: 1.4 kg (3 lb), 9.0 

kPa (1.3 psig); 2.3 kg (5 lb), 11.7 kPa (1.7 psig); 3.2 

kg (7 lb), 14.5 kPa (2.1 psig); and 4.5 kg (10 lb), 

17.2 kPa (2.5 psig). Although the exact relationship 

between the pressures created and acting on stop-
pings from free standing blast charges and actual 

face production blasts is unknown, actual pressures 

from production blasts in operating stone mines have 

been measured at approximately 6.9 kPa (1 psig) 

(Mucho et al. (2001)). The Super Stopping showed 

no structural damage from the tests, although small 

amounts of superficial foam sealant was dislodged 

during the 2.3-kg (5-lb), 3.2-kg (7-lb), and 4.5-kg 

(10-lb) explosive charge blast tests. The EZ-Up Curtain Stopping had no rips or tears in either material 

tested due to blast pressures. However, during the 

3.2-kg (7-lb) blast, several lag screws pulled out that 

were sandwiching the curtain material to the wood 

plank that was secured to the rib but damage was not 

increased during the blast using the 4.5-kg (10-lb) 

charge and the overall integrity of the stopping remained intact. 

5 CONCLUSION 

The Super Stopping and EZ-Up Curtain Stopping 

developed by NIOSH, in cooperation with several 

manufacturers, provide a practical and effective 

means to direct ventilation airflows within largeopening mines. The stoppings are durable and withstood test pressures that may be well above normal 

mine production blast pressures. The stoppings are 

constructed using economical, readily available materials. The stoppings are a practical and effective 

means to improve ventilation systems in largeopening mines, and thus reduce worker exposure to 

airborne contaminants 

6 DISCLAIMERS 

The findings and conclusions in this report are those 

of the authors and do not necessarily represent the 

views of the National Institute for Occupational 

Safety and Health. Mention of any product or company does not constitute endorsement by NIOSH. 

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