Disaster analysis

EXPERTS from the Mine Ventilation Laboratory of Strata Mechanics Research Institute in Cracow, Poland have followed the series of events leading up to, and including, the disastrous methane explosion that killed 23 miners in Poland last month.
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The Halemba mine's new ventilation system prior to the explosion.

Angie Tomlinson

Jerzy Krawczyk from the Polish Academy of Sciences recently released a document that detailed the accident. The document was compiled from information from Institute head Waclaw Dziurzynski and from the State Mining Authority.

Whilst an official investigation by the prosecutor, NIK Supreme Chamber of Control and Commission of the WUG State Mining Authority, is still ongoing, Krawczyk concluded a methane and probably a coal dust explosion killed the 23 miners.

The incident occurred on November 22 at the state-owned Halemba mine. At the time, a longwall that was 1030m below the surface was in the process of being abandoned. The seam the longwall had been extracting from had been subjected to interconnected hazards of methane bumps, water, coal dust explosion and spontaneous combustion.

A continuous methane monitoring network, capable of immediately switching the power supply off, was in operation at the time. Following the method of an early detection of spontaneous combustion, developed by the Central Mining Institute, gas samples were being taken for chromatography analysis.

The longwall extracted a 340m panel at a height of 1.7m operated with caving. A bump in February had limited coal flow and due to a risk of increased spontaneous combustion, the Local Mining Authority ordered the site to be sealed in August.

The mine was later allowed to reopen under strict supervision and frequent gas sampling.

After reopening, the ventilation system was changed (see diagram). A ventilation bridge was made to separate return from intake air. Forced auxiliary ventilation was installed to dilute methane in the last 50m of the longwall. Two methane sensors were installed in this section and another one was inbye of the auxiliary fan.

On the day of accident, the shearer and conveyers had been removed but 340m of power supports were left. A group of workers from a company contracted by the mine were removing power supports under the supervision of the mine’s personnel. Twenty of the total 220 sections had been removed.

At 4:30pm that day, a strong explosion occurred, damaging the sensors. Thirty one people were present in the hazard zone. Acting immediately, rescuers from the mine and from the Rescue Station managed to evacuate eight of them.

When rescuers approached the site, they realised that the ventilation bridge was damaged. They managed to walk through the ventilation bridge and reach the last few meters of the longwall. They also managed to install tubes taking gas samples inbye the longwall and in the return.

Between 7pm and 10pm, the bodies of six miners were found. At 12pm, rescuers were told to withdraw from the mine due to the rise of methane content to explosive range. This change was caused by the bridge, which had restricted ventilation.

It took several hours to rebuild the bridge and restore ventilation. Meantime, water from a pipeline broken by the explosion caused additional obstruction to the flow.

The rescuers re-entered the site as soon as restored ventilation decreased the temperature and concentration of methane. They found the bodies of the remaining 17 miners. Gas samples taken in the meantime indicated no traces of spontaneous combustion. Fortunately the explosion did not cause a fire.

Opinions expressed by the rescuers indicate that in the short blind end of the longwall, there was an explosion of methane that might have triggered the coal dust explosion, which was capable of damaging the ventilation bridge and killing the first six miners. Toxic gases killed the remaining miners.

As a part of the investigation, Krzysztof Cybulski of the Experimental Mine Barbara will examine samples of the coal dust and Stan Wasilewski of EMAG will examine the records of monitoring system.