# Coal Dust and Methane as a Hazard in Coal Preparation Plants
## 1 Introduction  
Coal dust and methane represent two of the most critical hazards in coal preparation plants, significantly impacting both worker safety and operational efficiency. Coal dust, a by-product of mechanical processes such as coal extraction, transportation, and beneficiation, poses severe risks due to its potential to cause catastrophic explosions under specific conditions [1; 2]. Similarly, mine dust frequently encountered in these environments presents hazards ranging from injuries and fatalities to long-term occupational illnesses [3]. The generation of mine dust in coal preparation plants occurs during the mechanical extraction and transport of coal, as well as during the processing of coal and waste rock. Key factors influencing dust generation include:  
* geological characteristics of the coal seam and the properties of the coal mined (location, mineral composition, hardness, degree of coalification, etc. ),
* mining method, run-of-mine haulage method to the coal preparation plant (type of machinery and equipment for mining and loading, modes and means of transport),
* technology adopted for the preparation of coal in the preparation plant (beneficiation methods, type of machinery and equipment),
* Physical properties of the dust, such as particle size and dispersibility. Suspended coal dust is transported by air currents, with some particles depositing on structures and machinery. Resuspension of this deposited dust can elevate atmospheric concentrations, posing persistent hazards to workers [4; 5]. Coal dust recognized as a hazardous factor in a coal preparation plant originates from a coal seam and has a volatile content of more than 10% (particle size <1 mm). All currently mined hard coal seams in Poland contain more than 10% volatile matter in dry ash-freeconditions. Such dust mixed with air in quantities of 50 to 1000 g/m\({}^{3}\) constitutes a mixture that, under the right conditions and as a result of initiation, can lead to an explosion. Explosive dust atmospheres are divided into three zones based on the International standard IEC 60079-10-2 [6], which in the case of coal dust are classified as follows:  
* zone 20--a place in which an explosive dust atmosphere, in the form of a cloud of dust in air, is present continuously, or for long periods or frequently,
* zone 21--a place in which an explosive dust atmosphere, in the form of a cloud of dust in air, is likely to occur in normal operation occasionally,
* zone 22--area in which an explosive dust atmosphere, in the form of a cloud of combustible dust in air, is not likely to occur in normal operation but, if it does occur, will persist for a short period only. Prolonged exposure to coal dust at high concentrations poses significant health risks to workers. This is addressed in the Regulation of the Minister of Labour and Social Policy [7,8], which establishes the Maximum Allowable Concentration (MAC) for workplace dust exposure. The MAC represents the concentration level that, over an 8-h workday and a typical workweek, should not cause adverse health effects during a worker's lifetime or affect the health of future generations. This regulation underscores the importance of maintaining strict control over workplace dust concentrations to safeguard worker health. The regulation specifies permissible dust concentrations based on the silica content in the dust. The Maximum Allowable Concentration (MAC) values cited in Table 1 are derived from [7], rather than [8], as the comparison focuses on results prior to 2018. Adverse effects of coal dust mine on human health have been widely investigated [9, 10, 11, 12] contributing to obstructive lung disease, pulmonary fibrosis, and lung cancer, in addition to the Coal Workers' Pneumoconiosis (CWP) and silicosis that receive greater attention. Therefore, fighting coal dust not only contributes to the safety in terms of explosion hazard but also contributes to the overall health of workers. The second important hazard in coal preparation plant is methane.