Assessment of the Costs of Preventive Works Concerning Fire Hazard on the Example of Selected Longwalls of Two Mining Companies

Aim: The article aims to present and evaluate the costs of preventive works carried out in 16 selected longwall panels in the mines of two coal mining com- panies. The article is based on the analysis of data made available by the companies, which the author has properly prepared to enable their comparison. Introduction: Fires occurring in coal mines are one of the more frequent technical hazards. Consequently, the mine’s ventilation departments are re-sponsible for carrying out preventive measures to limit and minimise the fire risk. The danger of a fire in mine workings is connected not only with the possibility of exogenic fire, which is influenced by external factors such as machine and equipment failures, short-circuits in electrical installations or the possibility of a fire on transport routes, but also with endogenic fire, which the low-temperature oxidation of coal may cause with the remains left in long wall caving. The costs of prevention depend on the method of ventilation of the longwall faces and the coal’s susceptibility to spontaneous combustion. Methodology: The costs of coal mining are very high. They are related to the increasingly difficult mining conditions, which are influenced mainly by the increasing depth of exploitation and the increase in natural and technical hazards during mining work. The costs of mining within a longwall area are usually divided into the costs of starting up the longwall, its exploitation and liquidation. Within this division, more detailed cost analyses are rarely conducted. As part of the research conducted since 2015, ways of cost assessment were developed on the basis of appropriately prepared cost tables for various natural and technical hazards occurring within the ventilation hazards presented in the example discussed in the article. Based on the analyses of unit costs of fire hazard prevention elements obtained in coal companies and the developed cost tables, the costs of prevention works were compiled. The costs of prevention works were evaluated and compared for 16 longwall faces using the elaborated indices. Conclusions: Correctly applied fire hazard prevention in hard coal mines is one of the main elements of maintaining functional safety. Costs of hazard prevention in mines were usually compared together with the costs of exploitation, longwall equipment, media and crew working days. Cost tables were developed as part of the research to allow for cost assessment and determination of fire prevention cost indices.

Fires occurring in mine workings can be divided into technical fires, which are called exogenic fires due to the external nature of the applied source causing ignition, and endogenic fires, associated with the natural low-temperature oxidation of coal and the possibility of its self-ignition during the accumulation of thermal energy in the place of self-ignition.
Both exogenous and endogenous fires have occurred in coal mining in the last five years, and their number is shown in Table 1 Table 2.
The range of fire risk prevention works used in longwall 1, together with their unit costs, is summarised in   (1)
As it results from the statement (see Table 3), the costs of fire hazard prevention for one longwall are not low. The biggest cost is represented by the use of inert gases and man-days connected with the prevention works, especially for the mine rescuers who conduct fire prevention works in hard coal mines.
In the further part of the article, an analysis of the costs of prophylactic works for fire hazard for selected longwalls of two coalmining companies will be presented on the basis of the developed cost indices.

Prevention costs and cost indicators for longwalls
The following cost indicators [11][12][13][14] have been developed to assess the cost of fire prevention: The percentage share of the prevention measure costs U P was calculated using the formula: (1) where: K P -prevention cost, PLN, P c -total revenue from coal sold, PLN.
The cost of prevention per 1 Mg of mined coal K PMg was calculated based on the formula:

PLN
(2) where: K P -prevention cost, PLN, W c -total output from the longwall face, Mg.
The cost of prevention calculated per 1 m of longwall face progress K Pmb was calculated according to the formula: where: K P -prevention cost, PLN, W śc -total run of the longwall face, m.
SFT VOL. 59 ISSUE 1, 2022, PP. 182-197 The cost of prevention calculated per 1 day of the longwall face run K Pd was calculated using the formula: where: K P -prevention cost, PLN, l d -number of working days of the longwall run, day.
Quite interesting results were obtained for the last two indices; fire prevention cost per 1m of the longwall progress (see Figure 6) and fire prevention cost per 1 day of the longwall run (see Figure 7).     However, it must be said that fire prevention offers the most choice among the available methods of combating the hazard.
When comparing the costs of fire prevention to other natural and technical hazard prevention, it can be said that the costs of fire prevention are the lowest. However, there are situations where it is necessary to seal the longwall area together with precious valuable assets such as powered roof supports, shearers and other longwall equipment. However, it is not always possible to recover the lost equipment, and its cost often exceeds PLN 100 million. Therefore, a fire hazard prevention is the primary determinant of safety in the longwall area during coal seam mining.
The necessity of applying goaf inertisation takes the highest share of the cost of fire prevention. On the other hand, the highest share of the fire prevention cost is taken by the necessity to use caving inertia and working day's pay spent on fire hazard control, especially working day's spent by the rescuers on fire prevention.
It should also be noted that the overriding condition for conducting mining works is the safety of the crew, and therefore the size of the costs of the preventive works is of little importance.