# Assessment of the Dust in Underground Coal Mine
## 1 Introduction  
High concentrations of coal dust produced in surface or underground coal mines can lead to death or serious damage to the health of miners. It can also lead to coal dust explosions or even gas explosions, which can result in serious personal injury, environmental and economic losses. An explosion in a mine is usually caused by a sudden ignition and explosion of flammable gases (methane) or coal dust. Methane and air form an explosive mixture which is described by the lower explosive limit (LEL), about 5% by volume of methane, and the upper explosive limit (UEL), about 13% by volume. Preventive measures for mines against explosions consist of a good supply of fresh air, which reduces the methane concentration below 5% by volume. More dangerous is the mixture of agitated coal dust with air. Coal dust explosions are prevented by humidification or pulverisation with stone dust. Dust can be defined in different ways. [PERSON] states that \"dust is defined as a collection of fine particulate matter of arbitrary size and composition that is generally dispersed in the air\" [1]. In contrast is the statement of [PERSON], who argues that \"we consider dust to be a particulate matter of inorganic or organic origin that is dispersed in a gaseous environment and does not include smoke\" [2]. Different definitions for the term dust can be found in different literature and professional sources and, in particular, different values for its maximum particle size. While according to STN 83 4501:1997-07 [3] dust particles do not exceed 75 \(\upmu\)m in diameter, according to the World Health Organization (WHO) dust can be considered as particles with a maximum diameter of 100 \(\upmu\)m. For the purpose of this research, however, the most relevant definitions of dust are those that consider dust particles to be between 1 \(\upmu\)m and 500 \(\upmu\)m in size, such as according to [3, 4]. Combustible dust is dust containing particles of arbitrary structure and shape, with a maximum size of 500 \(\upmu\)m, which at normal temperature and atmospheric pressure can be stirred up into the surrounding air and form explosive atmosphere. Due to gravity, they may settle to form a layer at least 1 mm high, which is then capable of explosion [5, 6]. We deduce that dust can be considered as particles dispersed in a gaseous environment, most often air, which have a certain size and for their specificity we have to take into account their origin. The size of dust particles ranges from 1 \(\upmu\)m to 100 \(\upmu\)m. The size of dust particles larger than 30 \(\upmu\)m is referred to as coarse dustand sediment very quickly in the environment [1]. According to its origin, dust is divided into organic (animal or plant) and inorganic dust (metallic, non-metallic and mixed). For mining purposes, the Slovak Mining Authority Decree No. 21/1989 Coll. defines dust as solid particles found in the mining air [6]. According to its origin, mining dust can be divided into [2]: dust originating in the mining massif--the action of natural forces, for example, rock crushing during the movement of rock blocks and massifs; technological dust--the originators of dust are technological operations, for example, cutting, boring, drilling, blasting, and extraction of rubble; surface dust--intruded into the mining environment by the main ventilation stream directly from the surface. Dust particles of various sizes are present in mining operations. According to the size of dust particles and the way they behave in the mining environment, dust can be divided into four basic groups [7]: respiratory dust--particle size ranges from 0.5 um to 10 um.