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Mine Health and Safety Act, 1996 (Act No. 29 of 1996)

Notices

Guideline for the Compilation of a Mandatory Code of Practice for the Prevention of Flammable Gas and Coal Dust Explosions in Collieries

Annexures

Annexure 3 : Stone dust inertisation standard, compliance sampling and analysis of samples

1. Stone Dust Sampling Programs

 

A sampling program that will ensure compliance with the requirements of incombustible matter content and the taking of samples must be set out as follows:

 

1.1. Inertisation of coal dust

 

1.1.1. Degree of Inertisation

In order to ensure adequate inertisation of coal dust, the COP must cover at least the following:

1.1.1.1. Inbye of the face area, intake airways must be maintained at a minimum percentage by mass of incombustible matter content of 80%;
1.1.1.2. Outbye the face area, intake airways must be maintained at a minimum of 65% incombustible matter content. Workshops, sub-stations, battery charging stations and other similar places where work is done or equipment is maintained, situated in intake air must nevertheless be maintained at a minimum of 80% incombustible matter content;
1.1.1.3. In return airways, a minimum percentage by mass of incombustible matter content of 80% must be maintained up to a minimum distance of 1000 m from the face. Beyond this distance, a minimum percentage by mass of incombustible matter content of 65% must be maintained. Where barriers are installed, the incombustible matter content by mass, outbye the face area and outbye of the barriers must be maintained at not less than 65%;
1.1.1.4. All accessible roads within a 250m radius from areas in the process of being sealed off, must contain a minimum percentage by mass of incombustible matter content of 80%;
1.1.1.5. In conveyor roads, a minimum percentage by mass of incombustible matter content of 80% must be maintained up to a minimum distance of 180m from the face. Beyond this distance, a minimum percentage by mass of incombustible content of 65%. The installation of stone dust/water barriers is mandatory; and
1.1.1.6. Before any area is sealed off, the roof, sides and floor, as far as reasonably practicable, must be stone dusted to ensure a minimum percentage by mass of incombustible matter content of 80%.
1.1.2. Inertisation of coal dust by using water

To ensure the inertisation of coal dust of using water the COP must cover at least the following:

1.1.2.1. The areas of the mine to be treated by this method;
1.1.2.2. The method of applying water;
1.1.2.3. The frequency of application;
1.1.2.4. Methods for the determination that sufficient water has been applied; and
1.1.2.5. Responsible persons to ensure that these requirements are adhered to.
1.1.3. Inertisation of coal dust by the application of stone dust

To ensure the inertisation of coal dust by the application of stone dust the COP must cover at least these measures to ensure that the suppliers of stone dust comply with the following minimum quality requirements:

1.1.3.1. Stone dust must preferably be pulverized limestone or dolomite and light in colour;
1.1.3.2. It contains not less than 95% by mass of incombustible matter, and with a density similar or equal to pulverised limestone;
1.1.3.3. It contains not more than 5% by mass of free silica, or any other toxic substance in concentrations detrimental to health;
1.1.3.4. It is of such fineness that, when dry, all will pass through a sieve of 600 micrometres aperture and at least 50% by mass through a sieve of 75 micrometres aperture;
1.1.3.5. Unless directly wetted by water, it does not cake and will readily disperse into the air;
1.1.3.6. Test each batch delivered and issue a certificate showing the results of these; and
1.1.3.7. Should any other incombustible dust be used, compliance with the ability to stop flame propagation of a coal dust explosion must be tested and approved for use at a SANAS accredited institution.
1.1.4. Extent of stone dust application

To ensure the correct extent of stone dust application the COP must cover at least the measures below to ensure that the underground workings of a bituminous coal mine are protected by the application of stone dust within 12m from all the working faces, unless such workings:

1.1.4.1. Are inaccessible, unsafe to enter; or
1.1.4.2. Extend to the face from and including the last through road, in which the coal dust is too wet to propagate an explosion during the cutting process.
1.1.5. Frequency for the application of stone dust

To ensure the correct frequency for the application of stone dust is adhered to, the COP must cover at least the following:

1.1.5.1. Face area

Stone dust must be applied, and re-applied, as often as is necessary, to maintain the incombustible matter content by mass at a minimum of 80%. The frequency rate of application must not be less than once in every four production shifts, unless a risk assessment, which includes rates of deposition of float coal, or other sampling indicates otherwise. This also applies to roads within the face area including roads carrying return air.

1.1.5.2. Pillar extraction operations

In pillar extraction operations, stone dust must be applied on a retreat basis at the same frequency rate as in paragraph 1.1.5.1 above.

1.1.5.3. Total extraction operations

In total extraction operations, stone dust must be injected regularly into the mined areas before the occurrence of the initial goaf, so as to render inert the dust cloud that will be raised when it occurs.

1.1.5.4. Return Airways

In both longwall and shortwall mining, stone dust must be introduced, during coal winning, into the return airways.

 

1.2. Compliance sampling

 

1.2.1. Samples must be systematically collected from the roads of all accessible workings of a colliery;
1.2.2. The workings of a colliery must be divided into the face areas and zoned back areas and these areas must be clearly demarcated on a plan;
1.2.3. The sample of the dust on the roof and sides must be taken separately from the sample of dust on the floor;
1.2.4. In the case of dust on the roof and sides the sample must be taken to a depth not exceeding 6 mm and in the case of dust on the floor to a depth not exceeding 25 mm;
1.2.5. Every sample taken must be representative of the whole surface of the roof and sides as well as the floor of the length of road being sampled and must be collected by a method of strip sampling by which the dust is collected from a succession of transverse strips, 100 mm wide and equally spaced not more than 5 m apart. Intersections must be sampled diagonally across to include a sample from at least two pillar corners;
1.2.6. Where it appears that the roof and sides or the floor, as the case may be, are wet, the sample must nevertheless be collected. Excess water must be drained off by placing the sample on a 2 mm aperture sieve, for at least one minute; and
1.2.7. Areas where water has collected in pools on the floor, need not be sampled but must be recorded as such.

 

1.3. Sampling of face and back area

 

1.3.1. Face area
1.3.1.1. Samples from face areas must be taken at intervals not exceeding 14 working days, or at lesser intervals, if so determined by risk assessment;
1.3.1.2. In the face area, a composite sample must consist of the combined material, collected from 5 equally spaced transverse strips (except where measurements are affected by diagonal sampling at intersections), over a measured distance of 20 m. The dust on the roof and sides must be taken separately from the samples of dust on the floor and the two sets of results reported separately;
1.3.1.3. A series of three composite samples must be collected from all return airways, the belt road, and at least one intake airway, over a distance not less than 60m length of roadway, commencing at a location approximately 15m from the face. Similarly, a series of composite samples must be collected over the full length of the last through road; and
1.3.1.4. In the case of either longwall or shortwall mining, a series of 5 composite samples must be collected from all gate roads over not less than 100m length of roadway, commencing at the face.
1.3.2. Back area requirements
1.3.2.1. The workings of a colliery outbye of the face area must be divided into zones not exceeding 1 200m in length. These zones must further be divided into sub-zones, not exceeding 100m in length, from which representative samples must be taken at intervals not exceeding 30 days;
1.3.2.2. In the back area, a composite sample must consist of the combined material collected from 11 equally spaced transverse strips (except where measurements are affected by diagonal sampling at intersections) over a measured distance of 100m. Samples from the roof and sides should be treated separately from those obtained from the floor;
1.3.2.3. Samples from sub-zones must comprise of composite samples taken from at least one return airway, the belt road and one other intake airway; and
1.3.2.4. Sampling of zones must be scheduled so that each sub-zone is sampled at least once per year.

 

1.4. Analysis samples

 

1.4.1. Samples must be analysed by either the colourimetric method or by a laboratory determination of mass of incombustible matter, or by both methods. Samples may also be analysed using a portable stone dust analyser. Only laboratories accredited by SANAS and analysers approved by a certification body accredited by SANAS may be used for laboratory determination.
1.4.2. Dust collected at a mine must without delay be processed and the incombustible matter content of the samples determined. Descriptions of the two methods are set out in 1.4.2.1 and 1.4.2.4. below.
1.4.2.1. Colourimetric method
1.4.2.1.1. Analysing of samples by using the colourimetric method can be done on surface or underground. In both cases the method described remains the same. For the underground option drying facilities and adequate lighting must be provided. This option evaluates the degree of inertisation in the shortest possible time, permitting immediate remedial action. (Moisture correction is not considered in this option);
1.4.2.1.2. The colour of a sample of dust must be compared with that of a scientifically prepared standard colour sample, known to contain eighty percent, or sixty five percent of incombustible matter content. When on such comparison, the colour of the sample is found to be the same colour or lighter than that of the standard sample, the incombustible matter content in the dust must be taken to comply with the prescribed percentage of the total incombustible matter content;
1.4.2.1.3. Any sample that appears to be below the prescribed ten percent of incombustible matter content must be analysed using the laboratory method described below; and
1.4.2.1.4. In addition to (c) above, at least 10 percent of the remaining samples must be analysed using the laboratory method.
1.4.2.2. A separate standard colour sample must be prepared for each geographical/working area of a mine in the following manner:
1.4.2.2.1. Grind some dry coal dust from the seam in each area for which the standard colour sample is being prepared so that it passes through a 250 micrometres sieve;
1.4.2.2.2. Determine the ash content of the sieved coal dust. The ash content must not exceed 20 percent by mass on a dry basis;
1.4.2.2.3. Pass through 250 micrometres sieve some dry-stone dust of the type used in the mine;
1.4.2.2.4. Weigh quantities of the sieved coal dust and sieved stone dust in proportions that will give the desired incombustible matter content i.e. 65% and 80%;
1.4.2.2.5. Mix the dust thoroughly by stirring, shaking or rolling but do not grind the mixture;
1.4.2.2.6. Using the approved laboratory method, determine the incombustible matter content of the mixture and verify that it is not less than the required;
1.4.2.2.7. Whenever there is change in the colour/reflectivity of the stone dust supplied to the mine, and whenever the colour of the coal seam changes distinctly, new standard samples must be prepared; and
1.4.2.2.8. At intervals of not more than three months, re-test the standard and keep a record of the results of these tests. If the standard has an incombustible matter content which is less than that required, replace the standard with a new one.
1.4.2.3. The procedure for the preparation and evaluation of collected dust samples is as follows:
1.4.2.3.1. Split the sample and retain one half of the sample, if required, for laboratory analysis. Air-dry the portion to be compared if necessary. Sieve the sample through a 250 micrometres sieve and mix the sample thoroughly but do not grind it;
1.4.2.3.2. Compare the colour of the mixed sieved sample with that of the standard colour sample. The comparison must be made under good and even illumination. When conditions permit, and if by choice, this comparison is done underground, it must take place at a designated site. The comparison must be done in a suitably designed light box. The person performing this duty must be trained to prepare the samples and to conduct the colourimetric test. Furthermore, his ability to distinguish between the colour ranges, must have been determined; and
1.4.2.3.3. If any sample fails the comparison test, this must be reported without delay to the employer who must ensure that the area concerned is properly inertised timeously.
1.4.2.4. Laboratory method

Analysis of samples in a laboratory must be carried out by the following method or by other methods approved by the laboratory concerned.

1.4.2.4.1. The residue of a weighed quantity of dust, after that quantity has been dried at a temperature not exceeding 140°C, and the loss of mass attributable to moisture ascertained, must be heated in an open vessel to a temperature not less than 480°C, and not more than 520°C, until the coal is completely burnt away. The incinerated residue must be weighed; and
1.4.2.4.2. The sum of the masses of moisture and incinerated residue must be recorded as incombustible matter and be expressed as a percentage of the total mass of the dust; and 1.4.2.3 where samples were air dried before analysis by the laboratory method, a correction may be made to the incombustible matter content of the dust sample analysed by laboratory method. The corrected total incombustible content is equal to M+I (100 - M/100) where M is the percentage loss of mass during air-drying and I is the percentage of total incombustible matter in the dust as determined by the method described in the preceding paragraph.

 

1.5. Keeping of records

 

1.5.1. The certificates showing the quality of stone dust supplied to the mine must be retained for two years; and
1.5.2. A record of the stone dust sampling analysis must be kept for two years of the date, places sampled and results of the analysis of the mine dust sampling program. Failure of more than 20% of the number of samples of a given area is unacceptable and requires immediate remedial action. Resampling of the sub-standard area must be done after corrective action was taken and the records must be retained for two years.