FIGURE 3. Inflatable stopping strapped in position during inflation.

inflation. Once the stoppings established contact with the airway perimeter and developed some internal pressure, they remained in place without help from the straps.

The inflatable production stoppings were designed to be inflated by mine air lines. Generally, the pressure in a mine air line system is between 80 and 100 psig. For this reason, it was necessary to be careful not to overinflate the stoppings.

Since most of the stoppings still showed some leakage even after patching, and since it was expected that minor leaks would develop in the stoppings from daily usage, the shutoff ball valves connecting the stoppings to the mine air lines had 0.010-inch holes drilled through the balls. In this way, when a ball valve was closed, a small steady flow of air was constantly being supplied to the stopping to compensate for any air leakage that might occur. This helped guarantee against collapse of a stopping owing to small leaks.

To prevent over inflation of the stoppings during inflation or from leakage through the drilled ball valves, stoppings 1 through 5 were each supplied with a pressure relief safety valve located near the inflation port. These valves had an adjustable cracking pressure of 8, 12, and 16 inches water gage, and were capable of passing at least 10 cfm of air when the stopping pressure was 14 inches water gage above the cracking pressure. Stoppings 6 through 9 did not have pressure relief valves and care had to be taken not to overinflate them.

Since it was intended that the stoppings be deflated before blasting occurred in the area, it was important that the deflation time be as short as possible. Stoppings 8 and 9 proved difficult to deflate within a reasonable time because they only had 1-inch inflation ports and deflated very slowly under their own weight. On the other hand, stoppings 1 through 5 were designed with 2-inch inflation ports. In addition, stoppings 1 through 5 were equipped with specially developed deflation aspirators (fig. 4). tion aspirator makes use of the venturi effect, in which high-velocity air from a mine's compressed air line is used to entrain the air in a stopping and

The defla

remove it at a fast rate. When the aspirator has been attached to the stopping's inflation port, the mine air line is connected through a ball valve to the 1/2-inch female fitting at the bottom of the aspirator. During inflation, the knurled cap on the aspirator is screwed on and the air from the mine air line is forced into the stopping. To deflate the stopping the knurled cap is removed from the aspirator and the mine air is turned on by opening the ball valve. With the aspirator, a stopping that would normally take at least 1 hour to deflate can be completely deflated in less than 10 minutes. This was true for all of the stoppings tested.

UNDERGROUND TESTS

The inflatable production stoppings were tested in two western noncoal

mines under different test conditions.

In the first mine, a Colorado molybdenum mine, they were deployed at loca tions very near to the working areas of the mine. The results in this mine proved the stoppings to be unacceptable as reliable mine air barriers because they did not form airtight seals and because they were constantly damaged by

nearby blasting. Table 2 lists the airway descriptions where stoppings were tested in this first mine, the air-sealing efficiencies of the stoppings, and the differential pressures across the stoppings. In general, the air leakage past the stoppings was too great to render them acceptable. Most of the air leakage past the stoppings was occurring at the corners of the airway and at locations of pronounced surface irregularity on the walls, roof, and floor such as piping, tracks, or rock projections. Attempts to seal these locations met with only limited success. Leaks at the floor could be sealed fairly well with waste dirt, stone, or sandbags, but the packing materials used to plug leaks around the walls and roof usually blew through the gaps or formed ineffectual air seals. Only the very small 2-foot-diameter stoppings (stoppings 6 and 7) proved to be good air barriers. The larger stoppings never reduced the airflow more than 85 percent. A second problem was that stoppings were damaged or destroyed when mine work crews failed to deflate them before blasting nearby. Of the seven stoppings tested in this mine, five were damaged beyond repair as a result of blast forces within a matter of weeks after they were installed. These stoppings were positioned at distances ranging from 35 feet to 200 feet from the secondary blasting that damaged them. ure 5 shows an example of the blast damage to these stoppings; one stopping was torn almost in two by a nearby blast. The remaining two stoppings were located at considerable distances from working areas and were not destroyed, although one was damaged and required repairs.

Fig

In the second mine, a New Mexico uranium mine, the stoppings proved very successful. Here, the stoppings were located far enough away from blasting areas to avoid damage. Also, some leakage past the stoppings did not cause any problems and, in some distances, was desirable. Table 3 presents some test findings with these stoppings. Stopping 3 was deployed in a stope at a > location far from any blasting. It was used to seal off an unworked area of the stope. It reduced the airflow into the unworked area about 87 percent. The 13-percent leakage that did occur was desirable because some airflow is needed in the unworked area to prevent excessive radiation levels from developing. Although this stopping did develop some small internal leaks, it was still possible to maintain it in place due to constant leakage of air into the stopping through the hole in a ball valve and by adding additional air about once each week.

Stopping 5 was first set up in a subdrift off of a main haulageway at a substantial distance from any blasting. Its purpose was to cut off airflow into the drift, which was not being mined at the time, and direct the airflow to other locations. Its air-sealing efficiency was about 93 percent. This stopping remained in place about 2 months. During this time, small amounts of air from the mine air lines had to be added about once every 2 weeks to reestablish the rigidity of the stoppings. Stopping 5 was then moved to a new location. In this location, it was used to seal off the flow of high-radiation air from a contaminated drift into a working drift. The stopping reduced the leakage about 92 percent and resulted in a decrease in the radiation in the working drift from 2.5 working levels to 0.5 working levels. The stopping has been in this location for about 3 months without developing any major leaks. Some air has to be added to the stopping about every 2 weeks to reestablish an effective air seal. A larger hole in the ball valve might have eliminated the need to add air in this way, but the mine air line was not always connected to the stopping.

Air-sealing capabilities of inflatable stoppings tested in a Colorado molybdenum mine

Description of
airway

...... Concrete haulageway

with pipes along

walls and track,
11 ft high, 10 ft
wide at roof, 12

TABLE 3.

nearby blast.

Air-sealing capabilities of inflatable stoppings tested in a New Mexico uranium mine

It is important to note that the increased air-sealing efficiency of the stoppings in this uranium mine no doubt resulted from the fact that the stoppings were oversized for the airways where they were installed. For example, stopping 3, which was a 13-foot-diameter sphere with a perimeter of almost 41 feet, was installed in an airway where the perimeter was about 32 feet. The air-sealing efficiency of the stoppings was further improved because of the low differential pressures that existed across the stoppings--always less than 0.15 inch water gage.

Because of the lower velocities and differential pressures encountered in this mine, it was not necessary to secure either of the stoppings with straps during inflation.

CONCLUSIONS

The inflatable stoppings tested by the Bureau of Mines for use in producing noncoal mines were found to be acceptable for some day-to-day mine applications, but only under limited circumstances. They can only be deployed in production if they are located at safe distances from blasting areas and if