Two ignitions of firedamp occurred separated by six hours, behind the part completed tailgate stopping of a salvaged longwall retreat district. No persons were injured but 141 persons were evacuated from the mine and 69 self rescuers were worn. The second explosion was violent enough to destroy air doors and an overcast, to disrupt the stopping, to damage air doors some 275m away and to open air doors at a booster fan site 890m away. The district 'was known to contain a spon. com. heating and this is concluded to be the source of ignition. The district was in a high risk seam and had ceased production some 21 weeks previously, with a fault on the face.
1. The initial ignition was caused by spontaneous combustion activity in the waste of 124s salvage district, possibly igniting paper or timber and hence an explosive mixture of fıredamp.
2. The second ignition was also initiated behind the stoppings of 124s, possibly by a hanging flame remaining from the initial ignition. This explosion was much more violent.
3. Although the level of activity was indicated by air sample analysis to be low, there was - nevertheless sufficient activity to initiate at least one ignition.
4. The spontaneous combustion was allowed to develop by the manager not ensuring that the district was salvaged and sealed within 13 weeks, in compliance with known industry good practice and the company's own Policy Instruction 3/97. After 12 weeks of salvage, the work was 10 weeks behind program.
5. The district was at particular risk, having faulting present at the time of production cessation. This was ignored.
6. By ineffective management of the colliery manager, the Director of Mining failed to detect that the salvage program was grossly behind schedule, and accordingly no steps were taken to redress the situation. It appeared that the managers performance was judged on production only.
7. The extension to the salvage program was asked for too late; stopping materials required to be on site were not on site, and the extension was granted without proper consideration for the consequences.
- 8. The resulting heating was of relatively low activity, but the activity increased as the stoppings were erected. The failure to alter alarm level settings on the tube bundle system after the lines were changed may have prevented this increased activity being detected.
9. This is the second time a heating has been allowed to develop by the failure to seal a district with a fault on it in recent months. On this occasion a coal dust explosion was not propagated, but had it been the results would have been catastrophic.
10. After the incident, accounting for, and evacuation of, personnel was completed efficiently and without further incident.
11. The introduction of the multigas analyser near to the problem area eliminated 3 hours delay in obtaining air analysis results, and gave much higher confıdence.
Recommendations
RECOMMENDATIONS
1. That an Improvement notice be served on RJB Mining to require a safe system of work be in place and followed for the salvage and sealing of all coal face districts.
2. That consideration be given to including a 13 week time limit for sealing, in forthcoming Mines Environmental or Ventilation legislative packages.
3. That when tube bundle lines are re-connected, alarm levels are altered to suit.
4. That consideration be given to developing a replacement for the few remaining and now old and unreliable, multigas analysers.