The worst mine disaster in the history of Turkey occurred in Soma more than a year ago. Investigations of causes that led to the catastrophe took time. Ayhan Yüksel, Director of the Chamber of Mining Engineers (Turkey) disclosed investigation results during XIII International Forum on Industrial Safety annually organized by GCE Group. TechNADZOR was an information partner of the event.
Soma coal basin is one of the oldest one in Turkey. Totally, the basin has been developed for one hundred and fifty years and Turkish Coal Enterprises have been operating it since 1939. Proven lignite reserves in Soma amount to app. 800 million tons. 704 tons were extracted under the permits issued by Turkish Coal Enterprises and Lignite Mining Enterprises of Aegean Region. In 2013, 25 million tons were extracted from sectors developed by Lignite Mining Enterprises of Aegean Region: 5 million tons were extracted from open pit mines, the rest 10 million tons – from sub-level mines. Coal extracted in the mine ensure operation of thermal power plants (1 034 MW). The Soma coal basin contains three lignite seams. Km-2, the area where the accident occurred, is the deepest one. One of the main features of this lignite seam is multiple cracks between layers.
Three shifts conducted works in the emergency area. Each shift contained 90-95 miners, in total – approximately 3000 miners. The accident occurred on 13 May, 2014 and 787 miners were blocked underground. Ignition that led to the tragedy started 1 350 meters from the inlet of the mine ventilation gallery. Coal seam ignition is a typical and one of the most serious problems of coal basins development. Over the last years, deep mining was started and a problem of methane releases occurred.
Кm-2 coal seam has a thickness of 20–30 meters and inclination of 10–20°. A longwall caving-retreat mining method was applied. When the first floor is 2–2.5 meter height.
On 13 May 2014, an explosion at a coal mine in Soma, Manisa, Turkey, caused an underground mine fire that led to rock fall. According to preliminary data, short circuit was the main reason of explosion and smoke spread. 787 miners were underground when the accident occurred. More than 360 of them were rescued. 80 persons were taken to hospitals due to injuries and carbon monoxide poisoning. Turkey declared three-day national mourning.
A longwall caving-retreat method is applied. When the first floor is developed by 25-30 meters, development of the second floor is started 6-8 meters deeper. While developing one coal face, the upper 6-8-meter layer is caved and retreated. If there is the third floor, after developing 25-30 meters of the upper floor, all operations that were applied to the second floor shall be repeated.
This mine with mechanical ventilation systems has several particularities: air flows from East to West via two air ducts and one ventilation shaft. Capacity of the suction air duct is 2 400 m³/s. Having two inlets, air ducts constitute a single line, if the length doesn’t exceed 1000 meters, and are separated into the Northern and the Southern lines, if the length is up to 400 meters. One air duct goes to sections A and H, the other – to section S. The mine was equipped with two separate air inlets for air supply that merged into one outlet. Such ventilation plan has deficiencies. Air distribution in the mine was provided by additional fans and gates.
In coal faces, chain coal conveyors deliver coal to main transportation line. Delivered coal then goes to inclined discharging shafts via belt conveyors and after that belt conveyors lift it to the surface. Area where the accident occurred was located near conveyor No.4. The fire started and reached this area via conveyors. Turkey presented two official reports on the topic: the first one was developed by inspectors of the Ministry of Trade and Social Protection, the second one is the report issued by an expert community designated to conduct preliminary investigation for the prosecutor office. In parallel, the Parliament of Turkey formed an investigation commission that also presented investigation results. Turkish Coal Enterprises, Turkish Association of Coal Industry and the Ministry for Emergency Situations provided data to this commission. Though, all issued reports are similar, there are important differences. The most crucial difference is assumptions on the place where the accident occurred.
Hypothesis No. 1: Causes of accident presented by Ministry of trade and social protection Experts concluded that fire in the mine occurred because of air that concentrated in the lignite left in the goaf area. Air was in the mine and additional air entered due to soil shrinkage on the surface. The fire started as a result of coal oxidation and spread over the goaf area creating high temperatures and pressure due to mixing with methane. The fire, moving through fractures and cracks, reached discharging shaft of conveyor No. 4. Fire engulfed lower part of the conveyor and wooden details of metal constructions.
Hypothesis No. 2: Causes of accident presented by the expert community. Autopsy reports showed that most of deaths occurred due to carboxyhaemoglobin poisoning. Carbon monoxide concentration couldn’t be that high and lead to poisoning even if the conveyor belt, wooden details and polyvinylchloride pipes were on fire. Main reason of lethal cases was asphyxiate gas – carbon monoxide that appeared after self-ignition of coal piles left without control near the transformer U-3 and reached fresh air inlet.
Fig. 1. Mechanized longwall caving-retreat method
Fig. 2. Transportation scheme
Smoldering coal mixed with fresh air and the fire started. The fire spread via conveyor No.4, engulfed conveyor No. 3, wooden details, PVC pipes and electrical cables. Finally, after watering, carbon monoxide and hydrogen chloride formed.
Hypothesis No. 3 Causes of accident presented by the Grand National Assembly of Turkey According to the investigation report issued by the commission under the Grand National Assembly of Turkey, a cavity formed due to coal extraction in the area “C” was filled with methane and carbon monoxide. Gases spread over the mine due to slow and then faster contraction of rock. This time, methane released and spread in the area “A”. Highly-concentrated methane started to spread from the unprotected conveyor belts and motors that resulted in smoldering fire.
There are other hypotheses about the accident.
Technical causes of the accident
The most crucial problem of Soma coal field is self-ignition of coal. Works on proven coal reserves enhancement were conducted in 2010 and resulted in increasing of methane release at 300-meter depth. I would like to focus on several safety options that ought to be undertaken to prevent the accident. Belt conveyors, electrical cables, constructions and other equipment ought to be noncombustible. There was no drainage for methane, no protection for electrical equipment and no safety and oxygen masks for personnel that could protect them from carbon monoxide poisoning. Central gas control system was insufficient to monitor the situation. Ventilation system didn’t correspond to the needs of this particular mine. There was no monitoring system that identifies location of miners, and miners themselves were not properly skilled and instructed in terms of occupational safety that led to high death toll, despite the fact that there was enough time to stop the production process and escape.
Main social aspect of the tragedy is promotion of subcontracting. By subcontracting I mean the system when key contractor involve other professional organizations for conducting particular works and delivering services. Very often subcontractors are involved to avoid economic and trade union restrictions. Table 1 presents mine accident statistics from 1983 to 2014. The last column indicates the death toll.
One of main causes that led to Soma disaster is intensive production process. Turkish Coal Enterprises extracted 3.5 million tons of coal instead of agreed 1.5 million tons by labor intensification and providing minor investments instead of mechanization at complex sites. All these led to high death toll.
The Ministry of Energy and Natural Resources and the Ministry of Trade and Social Protection control occupational health and safety issues in our country. However, legislative documents have contradictory statements due to existing problems and irregularities in the process of mining sector control. Soma disaster showed that legislative documents regulating safety in the mining sector are not sufficient to prevent lethal cases and work-related diseases. The accident proved inadequacy of legislation that determines actions to be undertaken in case of emergency. The entire system and legislation that regulates occupational health and safety shall be reconstructed, as the most important scientific and technical aspects are not considered in the mining sector.
Internal control shall be provided by a technical inspector, having the specialization of a mining engineer, who shall be designated in accordance with Paragraph No. 31 of the Mining law No. 3213, and the second person – an occupational health expert acting in accordance with the Law No. 6331. Works on the site where the disaster happened were regulated by subcontractual agreement and the Control Dept. of Turkish Coal Enterprises bearing responsibility in accordance with the legislation and design documents.
The Ministry of Energy and Natural Resources and the Ministry of Trade and Social Protection regulate safety and occupational health. Internal control was insufficient due to such subcontracting practices when occupational health experts received salary from the employer. External control failed due to deficiencies in legislation. Besides, targets of trade unions shall not be limited by following the corporate labor agreement signed at a work place. Trade unions shall also control meeting the requirements of the whole scope of labor laws. Our country has never faced any strikes targeted to labor conditions improvement. Fundamental human rights include a right for human living conditions and safe labor conditions that don’t affect health negatively. These are fundamental and democratic rights for people. If a country doesn’t ensure a right for safe labor conditions and faces constant problems with work-related diseases and accidents, we cannot talk about democracy and human rights in this country. Consequently, labor safety and health protection are issues that shall be resolved by democracy. Soma disaster has become a starting point in the mining sector history. Proposals developed by the Chamber of Mining Engineers and supported by the whole mining sector shall obtain the legal basis. Taking into account specific conditions of the coal basin, it is necessary to implement preventive measures to ensure occupational health and safety. It is required to prevent excessive intensification of the production process. Occupational health and safety legislation in the mining sector shall correspond to legislation of advanced economies. Educational programs for mining engineers require improvement. Educational institutions that provide insufficient qualification and are dealing with personnel problems shall be closed. It is necessary to sign an agreement with World Trade Organization and to implement it. Occupational health and safety shall be under proper control of independent experts to avoid situations when employers pay salary to technical and occupational safety experts. It is necessary to change the mining sector policy to introduce innovative technologies and knowledge. Professional chambers, trade unions and universities shall improve “Mining law” and “Occupational safety and health protection of employees” to solve arising issues in the mining sector and ensure meeting with the requirements.
Fig. 3. Plan developed by Turkish Coal Enterprises
Table 1. Accident statistics