N. N. Goncharova, D. I. Medvedovskaya, and Ya. Ya. Shkarban

Effectiveness of Dust-Control Measures in Underground Work in the Krivoy Rog Basin

From the Ukrainian Central Institute of Occupational Hygiene and Occupational Diseases and the Krivoy Rog Industrial Sanitation Station

The investigations were conducted at the Gigant mine of the Dzerzhinsky mining administration and at the Lenin mine of the Ordzhonikidze mining administration. The Gigant and Lenin mines are the largest in the Krivoy Rog basin. The thickness of the main ore bodies reaches 250 m. The $\mathrm{SiO}_2$ content of the rocks ranges from 3 to 80% (according to analyses of rock samples by Professor L. I. Karyakin). The Gigant mine is 190 m deep, and the Lenin mine is 367 m deep. At the Gigant mine, extraction is carried out at 170 working faces, 68 of which have been converted to wet drilling; at the Lenin mine, extraction is carried out at 140 faces, 100 of which have been converted to wet drilling.

At the working faces of mines in the Krivoy Rog basin, hand-held percussive drills are used, and in 1946 deep-hole drilling with an electric drill began to be introduced. Rock removal is 45–50% mechanized through the use of scraper winches

and PML machines (pneumatic-mechanical shovels). Ore is brought to the surface by cage and skip hoists.

The ore deposits are worked by three methods: 1) sublevel caving over intervals of 3 to 10 m; 2) sublevel drift stoping over intervals of 10 to 16 m; and 3) sublevel and level caving using deep boreholes up to 55–60 m in length.

I. Dust Levels during Dry and Wet Drilling

To determine dust levels in mine workings, the workplaces of drillers, scraper operators, shovelers, and chute operators were surveyed. Dust levels in the mines were studied by the konimetric method using an Owens I counter and by the gravimetric method. At the Gigant Mine, 137 samples were collected for dust-particle counts and 105 for gravimetric analysis; at the Lenin Mine, the corresponding figures were 46 and 36. The results of dust-particle counts during dry and wet drilling are presented in Table 1.

Table 1. Mean number of dust particles per 1 cm³ of air during dry and wet drilling

At the Gigant Mine, investigations were conducted at ore and quartzite faces, as well as at faces containing jaspilite and roofing slate. At the Lenin Mine, no investigations of dry drilling were conducted because there were very few such faces.

As Table 1 shows, dust levels at the faces of mine workings are considerable. The dust-particle counts showed that flushing during drilling reduces the concentration of dust particles by 63% in ore and by 51% in quartzite.

The wide range between maximum and minimum dust levels can be explained by the fact that samples were taken during drilling in rocks of different types and strengths and with different iron and quartz contents. Similarly high dust levels are observed at the auxiliary workplaces of shovelers, scraper operators, and chute operators. Data on the number of dust particles at auxiliary workplaces are presented in Table 2.

Gravimetric determinations of dust levels also yielded very high figures. The results of these investigations are presented in Table 3.

The wide range between maximum and minimum dust levels is explained by the same factors as in the counting methods. The effectiveness of wet drilling as measured gravimetrically

Table 2. Number of dust particles per 1 cm³ of air at auxiliary workplaces

Table 3. Average dust content by weight in 1 mg/m³ of air

…is higher by the gravimetric method than by the counting method. During drilling in ore, dust concentration decreases by 85.5%, and during drilling in quartzite, by 86%. This is readily understandable, since water wets the largest dust particles, thereby reducing the mass concentration of dust.

The average dust concentration data obtained in studies conducted in 1947 and 1948 are presented in Table 4.

The substantial reduction in dust concentration at the Gigant Mine during dry and wet drilling in quartzite in 1948 compared with 1947 is explained by improved sanitary and hygienic conditions in the mines: a large number of working faces were converted to drilling with flushing (40% of faces at the Gigant Mine and 70% at the Lenin Mine); the number of ventilation installations at the working faces increased; and sanitary and technical supervision improved.

As regards the size of dust particles during dry and wet drilling, no difference could be detected. The data obtained are presented in Table 5.

During drilling with flushing, as during dry drilling, 98.7% of the dust particles are up to \(2\ \mu\) in size. This is explained by the fact that the Owens I counter cannot be used to study all dust fractions (only those up to \(3\ \mu\)) and that water is not a sufficiently effective means of combating highly dispersed dust.

Table 4. Comparative average data on airborne dust concentrations in 1947 and 1948

Table 5. Average dust-particle size distribution during dry and wet drilling (percent)

II. Dust concentrations during drilling with water flushing and the use of additives (mylonaft)

The investigations were carried out using mylonaft at various concentrations (0.085, 0.125, 0.2, and 0.3%). The results are presented in Table 6.

The data obtained using the particle-counting method indicate that the optimum mylonaft concentration is 0.2%, which reduces dust concentrations by 44.5 to 54.2% compared with water flushing.

The gravimetric method does not reveal an effect of adding mylonaft to the water, apparently because mylonaft particles increase the measured weight. This was clearly evident from the discoloration of the cotton wool in the sampling tube. It is also possible that, during drilling with water flushing and added mylonaft, larger dust particles entered the sampling tube as a result of flocculation. The gravimetric method must therefore be considered unsuitable for evaluating the effectiveness of mylonaft.

Table 6. Airborne dust during drilling with flushing

III. Airborne Dust during Deep-Hole Drilling

Deep-hole drilling is carried out using an electric drill rig converted by engineer Minyailo from a rotary exploration drill. Drilling proceeds by extending the drill rod with its bit every \(1\frac{1}{2}\)–\(2\) m. The boreholes are 30–50 m long. Drilling is performed with water flushing. The investigations were conducted in four ore blocks. Air samples were collected in the worker’s breathing zone throughout the drilling of each borehole at various depths.

Preliminary investigations showed very high airborne dust concentrations. A total of 36 observations were made. The number of particles per cm³ of air was 9,926 on average, 30,470 at maximum, and 1,733 at minimum. This sharp increase in dust concentration during deep-hole drilling led us to suspect the presence of additional sources of dust.

Samples taken before the start of the shift showed an average airborne dust concentration of up to 18,345 dust particles per cm³ of air. To eliminate additional sources of dust, we isolated the block from the other workings. We first ventilated the block as thoroughly as possible with compressed air and then covered its entrance with a tarpaulin. Under these conditions, we obtained the particle-count data per cm³ of air presented in Table 7.

As Table 7 shows, in the isolated block the number of dust particles during deep-hole drilling is the same as during percussion drilling in ore with water flushing.

Comparative data on dust concentration by weight are presented in Table 8.

Such a sharp difference in the amount of dust by weight between deep-hole and percussion drilling, despite equal particle counts, is possible only if the dust produced by deep-hole drilling is finer. We cannot confirm this, however, because we measured dust particle sizes only down to \(2\,\mu\) (Table 9).

As Table 9 shows, during deep-hole drilling and percussion drilling in ore with flushing, 98.5% of the dust particles have a size...

…with water and the addition of mylonaft at different concentrations

Table 7. Airborne dust levels during deep-hole drilling in an isolated block and during rock-drill operations

Table 8

…up to \(2\,\mu\) in size. This can be explained by the fact that fine dust particles are not wetted by water even during deep-hole drilling.

Thus, as a first approximation, it can be said that deep-hole drilling does not differ from rock drilling with water flushing in terms of dust generation. However, when drilling deep…

Table 9. Dust particle size distribution for different drilling methods, in percent

…deep-hole drilling offers every prospect of sharply reducing dust formation through better contact between the drill dust and water, owing to the length of the drill hole and the large supply of water without air.

Although we took measures to isolate the block in which the observations were made from the other workings, in order to exclude the influence of the general dustiness of the air in the underground workings, we cannot be certain that it did not affect our results. The observations should be repeated with more thorough isolation from the other workings, or with other measures that exclude the influence of the general dustiness of the air in the workings on dust formation during deep-hole drilling. This is all the more necessary because deep-hole drilling is a progressive method from both an economic and an occupational hygiene standpoint: it eliminates vibration, noise, and the static component of the work, and reduces the amount of drilling required.

Conclusions

1. The studies lead to the conclusion that none of the methods used to control dust during drilling yet produces an entirely satisfactory occupational hygiene outcome.
2. Work should continue to find new wetting or foaming agents for more effective dust control during drilling.
3. Until new dust-control agents are found, however, water should be widely used, since it considerably reduces airborne dust, especially with the addition of 0.2% mylonaft.