Proceedings of the International conference "Health and Safety at Work - SESAM 2003", INSEMEX Petrosani, Petrosani, September 2003, Romania. ------

Zygmunt KAJDASZ, Ph.D., Eng. Piotr BUCHWALD, Ph.D., Eng. Stanisław SUCHOCKI, M.Sc., Eng.

DECISION PROCESS, WHEN TO APPLY NITROGEN IN PREVENTING AND FIGHTING MINE FIRES

1. INTRODUCTION

1.1. Application of nitrogen in the world deep mining

Nitrogen is widely used in combating underground fires, first of all in France, Germany, Bulgaria, Ukraine, and India. In other countries with developed underground mining the application of nitrogen is deemed as a supplement to other methods of preventing underground fires (e.g. in Great Britain, USA, Poland, Russia, Slovakia, Turkey). In France nitrogen has been used in mining since 1971. This gas is applied in particular in the Lorraine coal basin. Since 1986 a central distribution system for gaseous nitrogen was used there that had been connected to a local chemical plant based in the 40-kilometre distant Riche-mont. In the framework of the system there were maintained on-ground pipelines that were connected to an underground pipeline network. In need, an on-ground pipeline was used to continuously supply gaseous nitrogen at a volume flow rate of 12,000 cubic metres per hour. German experiences in this field cover, first of all, preventive inerting gobs by means of transportable high-capacity evaporators and equipment for generating nitrogen from the atmospheric air. For the purposes of underground mining a nitrogen plant was built close to the BOBINO mine in the BOBOV DOL lignite basin in Bulgaria in the early 80’s. The high-capacity nitrogen plant with its production based on the cryogenic method was capable of supplying gaseous nitrogen at a capacity of 4,500 cubic metres per hour without an interruption to the BOBINO mine for preventive purposes. In case of a need a volume flow of 550 cubic metres of gaseous nitrogen per minute was secured for a 19-hour period of time. Because of the inerting properties of nitrogen it was used throughout the world mining history for the following purposes:

- Elimination of explosion hazard, - Reduction of fire range and fire intensity, 2

- Chilling fired workings.

Inerting by means of nitrogen was applied among others in the following cases:

- Longwall mining both advancing and retreating, - Fire outbreak in workings with circulating ventilation, - Fighting fires in workings with the auxiliary ventilation, - Reducing the fire range and eliminating the seat of a fire.

So far in the framework of inerting operations for fighting underground fires in mines all over the world nitrogen was supplied:

- from steel cylinders or special containers, - from transportable or special stationary modular evaporators, - from special units, - from special furnaces.

1.2. Application of nitrogen in the Polish mining

In the Polish mining nitrogen for inerting the mine atmosphere was applied in the gaseous and liquid forms. Liquid nitrogen was poured (pumped) directly to the workings on fire. Whereas gaseous nitrogen was forced through pipelines into spaces embraced by fire. Nitrogen used in the gaseous form was produced either based on gasifying liquid nitrogen or directly by processing the atmospheric air. In the first case liquid nitrogen was brought to a mine from a manufacturer by means of a tank truck or tank wagon. In the latter case a special transportable device for generating nitrogen of the atmospheric air was used. Liquid nitrogen was applied in the Polish mining, among others, in the following ways :

1) direct forcing of liquid nitrogen into a fire area through boreholes drilled from the surface, 2) pouring liquid nitrogen from a tanker to special cisterns adapted for underground haulage, transport of the cisterns with liquid nitrogen to a fire area, and then forcing liquid nitrogen behind the fire seals and sprinkling the gas in the space embraced by the fire, 3) gasifying in special evaporators and forcing in the gaseous state through pipelines from the surface into the fire area.

Nitrogen in the gaseous state in the Polish mining was supplied:

4) from steel cylinders, which were transported underground to the place, from where nitrogen was to be supplied. 5-Nm3 cylinders under a pressure of 100 atm. The gas was simultaneously delivered from three cylinders and the volume flow of the nitrogen delivered in the gaseous state amounted to 100 cubic metres per hour. 3

5) from special devices designed for generating nitrogen directly from the atmospheric air (apparatus HPLC). The possibility to use such a device for fighting a fire and bringing explosion hazard under control has often been perceived during fire-fighting operations performed in the last years and during many, as well in many preventive activities.

2. DEFINING PRINCIPLES OF APPLYING NITROGEN IN PREVENTING AND FIGHTING FIRES

In 2002 the Central Mine Rescue Station in Poland worked out „Principles of Conducting Rescue Operations and Preventive Activities with the Use of Inert Gases”. The principles constitute a set of framework guidelines concerning application of inert gases for preventing and fighting fires. They standardise the proceedings covering decision making about the use of inert gases, that in particular determine:

1) basic technical and technological requirements for the application of inert gases, 2) a methodology of defining efficient procedures of the use of inert gases aimed at bringing fire and gassy hazards under control, 3) a methodology of performing running analysis of effects resulting from the influence of inert gases on the state of fire hazard, the spontaneous combustion process of coal, the behaviour of an existing fire.

The decision of application of inert gases as a measure for fighting an underground fire or bringing gas explosion hazard under control, during a rescue operation is made by the rescue operation manager after consulting it with the management of the Central Mine Rescue Station. Whereas decisions about the necessity to take preventive measures with the use of inert gases are made by the chief manager of a mine in consultation with the management of the Central Mine Rescue Station.

The application of nitrogen as an inert gas requires:

4) performing detailed analysis of ventilation conditions, 5) defining of the place where nitrogen should be delivered, 6) performing tests for the air migration in gobs by means of a marking gas and appropriate processing of the data gained during the test, 7) determining the place and quantity of nitrogen that is allowed to leak to active workings from the workings or gobs assigned to be filled with the inert gas, 8) defining the way of air circulation to minimise the air quantity flowing through the workings to be filled with nitrogen, 9) defining the technology of delivery of the inert gas, 10) defining measures needed to make active workings a safe workplace, 4

11) defining methods of inspection during the process of supplying nitrogen.

Application of inert gases in mines during rescue operations or preventive activities should be done based on an approved technical documentation that defines, among others, the scope of the applied method, the way of use and inspection of applied equipment, the kind of safety and protection means as well as forecast of consequences of the action.

The documentation is: 12)worked out by the managing staff of the operation and approved by the manager of the operation, in case a rescue operation is in progress, 13)worked out by the chief ventilation manager and approved by the chief manager of the mine, in case preventive activities are in progress.

In both the cases the documentation should be opinionated-on by the Central Mine Rescue Station. Application of inert gases in the course of a rescue operation or in the framework of preventive activities should be done, depending on conditions, together with other proved measures like the ventilation ones (regulation of the air circulation, equalisation of aerodynamic potentials), increasing the longwall face advance, additional gob and rock mass sealing by means of chemical or mineral substances. The isolating stopping behind which inert gases are to be supplied should be tight so that no gases leak into active workings. Pipelines and other equipment installed in the isolating stopping should be sealed with particular care. The difference between the pressures before and behind the isolating stopping, behind which inert gases are to be forced, should be negative. After starting supplying inert gases the functioning of the forcing equipment should be recorded and in defined places test samples of the mine air should be taken with the object of performing chemical analyses of the air as well difference pressures at the isolating and fire stoppings should be affirmed. Changes in the chemical composition of the air and fire gases in the fire- endangered workings or gobs and difference pressures at the stoppings closing mine areas being filled with inert gases should be analysed as they come in respect to: 14) the explosibility of a gas mixture, 15) the content of oxygen as well as flammable and poisonous gases, 16) tightness of stoppings and rock mass in their vicinity, 17) maintaining the volume flow rate of the applied inert gas on the level that prevents increasing content of oxygen and inflammable or poisonous gases, and that neutralises influence of atmospheric pressure changes, 18) the assessment of the aerodynamic potential distribution around the endangered area.

Supplying inert gases may be stopped after the assumed goal of inerting the endangered area has been reached or in case there are no prospects for reaching the goal. Then some other methods and measures of bringing the hazard under control should be considered. 5

Devices designed for applying nitrogen in preventive activities or controlling fire and gas hazards may be installed both on the surface and in the underground workings. The existing pipeline networks (e.g. designed for hydraulic filling, water or compressed air supply) may be used to deliver nitrogen in the gaseous state to the place of application. If not, new pipelines should be installed.

3. DETERMINING ORGANISATIONAL AND SAFETY REQUIREMENTS OF NITROGEN USE IN PREVENTING AND FIGHTING FIRES

Each use of nitrogen as an inert gas should proceed according to a detailed documentation specially drawn up for each individual case. Forcing inert gases into the underground workings must be performed in the presence of a supervisory staff member assigned by the rescue operation manager in case of a rescue operation and the chief manager of a mine in case of preventive activities. During inerting activities the main fan have to be working all the time. During the time it is also forbidden to change working parameters of the fan. If the main fan (or main fans) cease to function during while forcing inert gases into the endangered area is in progress the forcing should be stopped. Forcing inert gases should also be ceased in case of failure of the auxiliary ventilation if nitrogen pipelines are installed in these workings. There should be determined the places in underground workings where air composition is to be tested during forcing inert gases into the area endangered by fire or gas explosion. Before the appliances for supplying inert gases are started, they should be carefully checked in respect to appropriateness of their assembly, their serviceability and appropriateness of indications of measuring instruments. The pipeline supplying inert gases from the devices that generate the gases to their destination have to be tested for tightness before each forcing cycle if an over 24-hour long working break of the installation took place. The pipeline supplying inert gases have to be tested for tightness by forcing compressed air at a pressure of 0,25 – 0,3 MPa. It is deemed tight if the fall of pressure in it during an hour does not exceed 10 per cent of the primary pressure. During inerting operations the whole installation have to be inspected by working teams consisting of at least two men. The workers have to be appropriately trained and equipped with self-contained self-rescuers (i.e. contained breathing apparatuses) and devices for monitoring oxygen content in the mine air. The inspection-and-measuring work in the endangered zone may be carried out exclusively by mine rescue workers. During inerting work manning movements in the workings in which the pipelines supplying inert gases to their destination have to be inspected in accordance with regulations by the chief manager of a mine. Also operational telephone communication between the operator’s workplace and the inert gas destination has to be assured. 6

Workers operating devices for gasifying liquid nitrogen have to take precautions to prevent any direct contact with the liquid nitrogen as well as with any non-insulated elements of the equipment supplying liquid nitrogen. Hard coal mines extracting seams prone to spontaneous combustion should define in their rescue work plans the was of use of existing pipelines for the purposes of a possible application of inert gases. The time needed for preparation of pipelines to supply inert gases should not exceed 12 hours.

In order to apply inert gases in a mine the following preparation actions should be performed:

19) determination and adaptation of a place to install devices and equipment, 20) securing power supply, heating media, etc., 21) assuring the service for pipelines or haulage equipment, necessary devices and equipment to be transported to underground workings.

Devices and equipment for supplying inert gases, specialists trained in applying inert gases and operating the devices and equipment are provided by the Central Mine Rescue Station that maintains a specialised emergency service for inerting the mine atmosphere. The Central Mine Rescue Station is also in charge of maintaining the devices and equipment in working order, preparing them for supplying inert gases, and delivery of liquid nitrogen. In the scope of an inert gas application the Central Mine Rescue Station assures:

22) delivery of the devices for supplying inert gases to the premises of a mine, 23) assembly of the devices and equipment, 24) service of the devices and equipment, 25) technical consulting in the scope of preventive activities and / or rescue operations.

4. CONCLUSIONS

1) Nitrogen is known in the Polish and world mining as a basic or supplementary technical means of: 2) controlling gas explosion hazard, 3) reducing the range and intensity of a fire, 4) chilling inflamed workings.

5) In Poland nitrogen is used based on the „Principles of Conducting Rescue Operations and Preventive Activities with the Use of Inert Gases”. The principles define the decision process about when to apply nitrogen inerting in preventing and fighting a fire. 7

6) Application of inert gases in mines during rescue operations or preventive work shall be conducted in accordance with an approved operational documentation.

7) In Poland organisational principles, responsibilities and activities of mines and rescue organisations connected with the implementation, production, transport and forcing inert gases are defined.

BIBLIOGRAPHY

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2. Both W., Mueller R.: Application of Nitrogen for Fighting Underground Fires. Glückauf, 197, t: 115

3. Both W.: Fighting Mine Fires by Means of Nitrogen in the German Mining Industry. Mining Engineering 1981, t: 440.

4. Brook D.L., Hunneyball S., Fee B, R 11 District,: A Successful Stopping of a Fire and Reactivation of a District by Opening the Fire Area with the Use of Nitrogen. Mining Engineering 1993.

6. Budryk W.: Fires and Explosions in Mines. Underground Fires. Part 1, Superior Mining Office, Katowice 1956.

7. Fighting a Fire by Means of Nitrogen Inerting in a Mine in the Lorraine Basin. Ind. Miner. Tech. 1982.

8. Froger C.E.: Experiences in Fire Fighting in the French Underground Mines. Ind. Miner. Tech. 1986.

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10.Ondrejniska E., Scarnicky F.: Application of Liquid Nitrogen for Fighting Underground Fires. Uhli, 1984.

11.Group work by the Central Mine Rescue Station and the Academy of Mining and Matallurgy in Cracow – unpublished: Methodology of Controlling Aerologic Hazards by Means of Nitrogen as an Inert Gas in Preventive Work and Rescue Operations. Bytom 2002.

12. A Collection of Operational Regulations Governing the Mine Rescue Work. Katowice 2002.