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Likelihood of High Overpressures on Seals

Underground » Ventilation, Gas Drainage and Monitoring

Published: November 12Project Number: C17015

Get ReportAuthor: R. L. Davis, J. W. Oberholzer, M. Gido, A. D. S. Gillies, H. W. Wu | Simtars and Gillies Wu Mining Technology

The US Sago mine disaster in 2006 caused mine seals to be destroyed by an atmospheric explosion. Investigations into the appropriateness of seal strength requirements to withstand a pressure event followed. New designs have been developed and various US changes implemented.  Australian reviews of coal mine safety in the mid 1990s after the Moura Number 2 explosion in a similar way directly resulted in changes to management of hazards.

 

The primary objective of this project was to examine the Australian industry's approach to the use of seals; also the new US approaches to sealing and their possible application to Australian conditions. The current situation has been evaluated through comprehensive surveys of a number of coal mines in Queensland and NSW, seal manufacturers and the Queensland and NSW Inspectorates.

 

A general conclusion was that seal design should start from the premise that it is impossible to build a perfect seal and that leakage is most likely through surrounding strata and along the rock/seal interface. Seals should be rated to "seal" and not on structural applied pressure loading. The aim should be to keep goaf gases out of ventilation air and oxygen out of goafs. Seals should, however, be competently engineered structures that normally meet a 140kPa pressure rating.

 

More understanding of goaf gases ignition potential is needed, with more information on the variability of gas concentration data across the extent of a goaf. There is no evidence of mine atmosphere explosion detonations; every mine explosion has remained within the limits of deflagrations. Monitoring of the goaf atmosphere and requirements for inert gases is critical.

 

In many ways Australia and the US are similar, however Australian approaches to the management of hazardous mine atmospheres differ significantly. Australian risk management approach to handling hazardous situations implies the adoption of international industry best practice. There has been a move for Australia to consider the new US standards for seal pressure rating codes. The Australian industry has debated how the US information on seal behaviour and new regulations should be incorporated, if at all, into Australian practice. The industry as a whole, including mines' management, state Inspectorates and mining unions have decided not to adopt the principal dictates of the 2008 US seal regulations.  

 

The project has undertaken a review of international literature on the topic. The Australian mining industry has a history of gas and dust monitoring and inerting practices particularly when goaf atmospheres "pass through the explosibility triangle". Simtars' Explosion Propagation Tube was used to undertake fundamental tests to further understand the nature of pressure generation. The principal aim of this section of the project was to study the theoretical basis for a detonation or significantly higher pressures occurring, and the conditions under which they would occur in Australia.

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