Inrush from ventilation shaftMines safety alert no. 368 | 21 August 2019 | Version 1
An inrush occurred when developing a roadway connecting a ventilation shaft to the underground workings. When the roadway broke through into the shaft, a quantity of mud and water still contained in the shaft flowed into the roadway. The face workers retreated from the area without injury.
The mine used small diameter holes, drilled from the roadway into the shaft to attempt to drain the shaft. When fluid ceased flowing through the drain holes, management gave permission to recommence mining. Water and mud was still contained in the shaft, above the level of the drain holes.
How did it happen?
The risk assessment conducted at the mine did not require measuring the volume of material drained from the inrush source. It relied on the absence of flow through the drain holes to determine the level of hazard.
When an inrush hazard is to be eliminated by removing the fluid, by draining or pumping, management should use reliable methods to confirm the hazard has been eliminated, to ensure the risk is as low as reasonably achievable.
1. When assessing inrush hazards, ensure all potential sources of inrush have been identified.
2. Quantify the volume of fluid expected to be contained in the inrush hazard.
3. Use suitable diameter drainage holes and regularly check they have not blocked.
4. Compare the fluid volume drained out against the volume of fluid calculated to be contained by the hazard, to verify that the hazard has been eliminated.
5. Have effective contingency plans for those circumstances where the volume of fluid released from the inrush hazard is different to the volume expected to be released.
Authorised by Shaun Dobson - Chief Inspector (Coal Mines)
Contact: Stephen Smith, Acting Deputy Chief Inspector (Coal Mines), +61 7 4936 0120 firstname.lastname@example.org
Issued by the Queensland Department of Natural Resources, Mines and Energy