Some 280 to 300 million years ago, what we call as Jharkhand in eastern India used to be a lush green dense forest. So dense was the forest that it was pitch-dark even during day time. Fortunately we were not around to hack those strong sentinels of the nature. Alas, nature does not spare any one. The turmoil within the earth ensured an on site burial of those forests. So quick was the burial that those trees could not even gasp and were not decomposed as in a normal burial. The heat inside the earth was so much that those trees got converted in to coal.
Today, Jharia in Jharkhand is a town sitting right over the coal seams. Coal, a source of energy for us; runs not only our hearths but our industries too. It is a different issue that the smoke from the same coal used by us is enriching the carbon dioxide content of the atmosphere and abetting global warming. The story is not about global warming; instead it pertains to sub-surface coal fires that have threatened the very existence of human habitation on the surface.
Jharia with a population of plus 85000 is sitting over red hot ambers. The fire was first noticed in 1916 and since 1972 more than 70 fires have been detected says the Wikipedia. The coal seam fires could be due to natural or anthropogenic causes. Lightening, forest fires etc are amongst the former and accidents, negligent mining, domestic fires and lighting fires in underground mines for illegal brewing of alcohol are some of the later causes. Not only in India such fires are known from all over the world. Unfortunately Jharia is perhaps the only densely populated place with a fire in the sub-surface.
In Jharia the situation is really grim. As per a news paper report published in Deccan Herald (10th March, 09) 71000 families are living in the danger zone. There are 75 pockets of sub-surface fire, consequently the vegetation on the surface has become thin ads the report. One can see blue flames leaping out of no where at night as one walks along the fields.
Ground subsidence, accidental roasting of miners inside a mine, pollution of water bodies through the sulphur content of coal ash and air pollution are some of the hazards. The burnt coal is a valuable loss of the precious fuel.
In case of forest or bush fires it is easy to locate it from a distance or even from air. Once identified, steps are taken to control it and if required to shift the affected or likely to be affected population to a safer area. However, in case of an underground fire such measures don't work. It becomes more hazardous when the area over-ground, as in Jharia is populated.
Since locating and mapping the fire from surface or through normal means of observing from air do not work in case of a sub-surface fire, satellites have come to the rescue. Arindam Guha, K.V. Kumar and M.V.K. Kamaraju of National Remote Sensing Centre, ISRO, Hyderabad have come out with a solution to at least map the hidden fire.
In order to map the sub-surface fire satellite mounted special thermal sensors are used. These sensors are able to detect any changes in the temperatures on the surface or sub-surface precisely. These sensors measure thermal infrared radiation of any object. The biggest advantage of this technique is that one can measure all the parameters from the safe distance of a satellite. Earlier if a coal seam fire had to be evaluated, boreholes were either drilled or the temperatures were measured in the existing boreholes. Now the advancement in science has brought this technique to give a comprehensive picture of the sub-surface temperatures.
The residents of Jhariya and Raniganj await the monsoon rains eagerly-not because they need water to irrigate their crops, but in the hope that the rains would douse the burning earth. Lot of studies based on remote sensing have been carried out in Jharia coalfields. However, recently Raniganj coalfield has also caught the attention of the researchers. This is because in Raniganj coalfields high grade coal is being mined and precious coal being lost in fire hits the coal mining industry below the belt. This apart since Raniganj has more of open cast mines, coal fires cause serious air pollution. It is elementary science that oxygen is required to burn anything. Coal being mined from open cast mines exposed to atmosphere burns more quickly. The main coal seam does not burn that easily, but the coal dust and fragments of coal left during mining operations catch fire easily. Once there is a fire it tends to spread and keeps smoldering for years together. In under ground mines coal seam fires are due to natural reason, but unfortunately in the open cast mines the fires are frequently due to human errors/accidents/sparks from the machinery being used.
Guha and his co-workers attempted to delineate the distribution of coal fires till December 2006 in Raniganj and also tried to find out if there was any relationship between coal fires and mining practices. Moreover at present there is a dire need of developing a satellite based mapping technique, so that managing sub-surface fires as in Jharia becomes easier.
Their study in Raniganj revealed two broad zones of fire in Raniganj coalfield. One zone extends from Ramnagar open cast pit (OCP) to Banjimari OCP. This zone is in the western and northwestern part of the coalfield and it is spread over a large area. The other zone is restricted to North Jambad-South Jambad OCP, say Guha and his co-workers. In addition to these there are many small patches of fire and smoke coming out of cracks and crevices of rocks. Since they are too small they can not be picked up by the satellite sensors.
A fire, whether in the sub-surface or on the surface in an open cast mine leads to a rise in temperatures. A satellite born sensor, can however, only sense if the temperature is above a threshold value on the ground. Thus, as a first step in this type of studies is to fix a threshold value of land surface features at night time. The fires can be visually recorded by the satellite cameras only at night. The night temperatures of the objects on the ground like the crops, roads etc in the month of December 2006 ranged from 15-25 degrees Celsius (C). Therefore the threshold value of temperature was fixed at 25 degrees C to delineate fire from the background say Guha and colleagues.
On the basis of data obtained from the sensors, using complex mathematical formulae temperatures higher than the threshold were plotted by Guha et al. Finally a coal fire map of Raniganj emerged. The map was physically checked by the researchers by measuring actual ground temperatures. For example in Ramnagar OCP actual temperature of burning ambers was found to be above 336 degrees Celsius. Even the temperature of the ground surrounding the burning ambers was found to be above 80 degrees Celsius.
Life on such ambers is really tough. Apart from the risk of getting roasted alive, the sulphur fumes released due to burning of coal pervade the atmosphere in the area say Guha et al. Their observation is filed further confirmed the deduction based on satellite data that the open cast quarries are the most vulnerable places in Raniganj where coal is burning constantly. Mining activities produce lot of coal dust-which remains heaped up with fragment of coal and other carbonaceous matter. These are highly inflammable. At places the burning coal seam is covered with a layer of sandstone. Red hot patches on the sandstone can be seen from a distance. At places the in the open cast pits smoke emanating form the walls of the pits indicates the inferno in the near sub-surface.
Controlling and containing the fire is imminent to save the hazard to the humanity exposed to the risk and also to save the precious fuel. Satellites have helped in delineating the fire bound areas. May be the day is not far when they will assist in controlling the fire too! However, educating the labors working there against the hazard and also making settlements away from the fire prone areas should be a priority.