54
2 Environmental Conditions in the Mine
This is a simple and economical method in which the quartz collected in the
same filter can also be analysed. However, it does not offer adjusted results at low
concentrations (<0.6 mg m
−3 ) and is not selective, since carbonaceous or sulphurous
mineral powders, oil mists and cigarettes can interfere with the measurement (Ayers
2017).
(b) Thermal–Optical Analysis (TOA) (NIOSH 5040):
This method uses Organic Carbon (OC) and Elemental Carbon (EC) as a proxy for
determining DPM. The procedure involves the following previous steps:
• The thickest particles (>1 µm) are separated from the airstream by means of
cycloning.
• The undersized material (<1 µm) passes through a quartz fibre filter.
• Particles <0.9 µm are retained in the filter.
• A portion of the filter is separated and placed in a special oven.
• Finally, OC and EC are measured from the evolved gas by means of TOA.
Mineral Dust
Samples are obtained with devices that are similar to those described in the previous
section. These are mainly of relevance to the monitoring of respirable dust, for
which standard Dorr-Oliver cyclones are generally used. The procedure is as follows
(Verpaele and Jouret 2012):
• The air is aspirated at a speed of 1.0 l s
−1 .
• The weight of the powder mass is obtained through weighing by difference.
• The concentration of dust in the air (mg m
−3 ) is obtained from the ratio between
1000 times the weight gains in the filter (mg) and the product of the airflow (l
min
−1 ) times the monitoring time (min).
• Silica dust can be studied via X-Ray Diffraction (XRD) (NIOSH 7500). A
sufficient amount of sample must be collected to do so (Stacey et al. 2014).
2.6 Heat Inside Mines
2.6.1 Geothermal Gradient
Geothermal gradient is the main reason why the temperature increases as one goes
deeper into a mine. This increase is approximately 1 °C every 70–110 m in the
case of deep metal mines, and 1 °C every 20–50 m in the case of European coal
mines (Houberechts 1962). The heat that is present is usually the residual heat from
planetary accretion from Earth’s earlier eras and the decay of radioactive isotopes.
Both of these things cause the terrestrial nucleus to be around 5700 °C and its heat
flow outwards to be an average of 0.07 W m
−2 . This heat penetrates the mine. The
thermal conductivity of local materials influences the entry of heat into the mine.
2 Environmental Conditions in the Mine
This is a simple and economical method in which the quartz collected in the
same filter can also be analysed. However, it does not offer adjusted results at low
concentrations (<0.6 mg m
−3 ) and is not selective, since carbonaceous or sulphurous
mineral powders, oil mists and cigarettes can interfere with the measurement (Ayers
2017).
(b) Thermal–Optical Analysis (TOA) (NIOSH 5040):
This method uses Organic Carbon (OC) and Elemental Carbon (EC) as a proxy for
determining DPM. The procedure involves the following previous steps:
• The thickest particles (>1 µm) are separated from the airstream by means of
cycloning.
• The undersized material (<1 µm) passes through a quartz fibre filter.
• Particles <0.9 µm are retained in the filter.
• A portion of the filter is separated and placed in a special oven.
• Finally, OC and EC are measured from the evolved gas by means of TOA.
Mineral Dust
Samples are obtained with devices that are similar to those described in the previous
section. These are mainly of relevance to the monitoring of respirable dust, for
which standard Dorr-Oliver cyclones are generally used. The procedure is as follows
(Verpaele and Jouret 2012):
• The air is aspirated at a speed of 1.0 l s
−1 .
• The weight of the powder mass is obtained through weighing by difference.
• The concentration of dust in the air (mg m
−3 ) is obtained from the ratio between
1000 times the weight gains in the filter (mg) and the product of the airflow (l
min
−1 ) times the monitoring time (min).
• Silica dust can be studied via X-Ray Diffraction (XRD) (NIOSH 7500). A
sufficient amount of sample must be collected to do so (Stacey et al. 2014).
2.6 Heat Inside Mines
2.6.1 Geothermal Gradient
Geothermal gradient is the main reason why the temperature increases as one goes
deeper into a mine. This increase is approximately 1 °C every 70–110 m in the
case of deep metal mines, and 1 °C every 20–50 m in the case of European coal
mines (Houberechts 1962). The heat that is present is usually the residual heat from
planetary accretion from Earth’s earlier eras and the decay of radioactive isotopes.
Both of these things cause the terrestrial nucleus to be around 5700 °C and its heat
flow outwards to be an average of 0.07 W m
−2 . This heat penetrates the mine. The
thermal conductivity of local materials influences the entry of heat into the mine.