Jumbo Incident – A Failed Permit to Work System

Introduction

This article discusses the contribution of an underground mining “Permit to Work” (ATE) process and a  jumbo drill rig, drilling into an adjacent bored and uncharged face in a development heading.

The Incident

The jumbo operator was drilling ground support holes in the walls and backs of an access drive.

During the drilling process, the jumbo operator lost water pressure on the drill string.

He suspected that the drill had encountered a void or an adjacent drill hole in an adjacent open area.

He stopped drilling immediately and investigated a nearby active development heading (chamber).

He found the drill had encountered a drill hole in the bored face of this chamber.

The bored face was meant to be, but had not been charged, with explosives at the time, as the charge up crew had been called away to assist with another matter in the mine.

It was pure luck that the development face was not charged up with explosives and detonators.

The chamber and access drive mining locations were relatively close to each other, which would have normally been picked up on the Authority to Excavate (ATE) Permit to Work, which specified activity (Drilling) and excavation hold points.

Incorrect hold points were specified on the Jumbo Operator’s “Authority to Excavate” (ATE) Permit to Work.

The short-term plan of intent (STPOI) for the Chamber and ATE for the access drive was inadequate. They failed to use the mining check list which highlighted the need to assess voids within 20 metres of the proposed mining activity.

The job safety analysis was inadequate for the assessment of the hazards due to the interaction of parallel mining activities occurring in the Chamber and the access drive.

The JSA scope only considered hazards when breaking though from the Chamber Heading to the Access drive.

It appeared that the paperwork (Permit), authorisation and communication processes were token efforts only – were either not supported, not followed and/or were defective.

Corrective actions

1. Conduct a “Gap Analysis” on the planning process, Short-Term Plant of Intent (STPOI) and Approval to Excavate (ATE) Permit to Work processes and procedures, and train personnel.
2. Review Company roles and responsibilities for the STPOI and ATE processes, ensuring underground mine production and technical services support personnel have a mutual understanding.
3. Review and reinforce the roles and responsibilities for the Mining Contractor shift boss and jumbo operators
4. To ensure they do not go beyond hold points specified on ATE plans.
5. Incidents of this nature are reported immediately to the site contractor manager.
6. Work does not proceed until permission given by the Client underground manager
7. The planning process accounts for all mining activities, incorporating schedules, design, and major hazards.
8. Conduct a review of the mining checklists used for the STPOI and the ATE and include trigger events to conduct a team-based risk assessment. One trigger event would be approaching another active mining area.
9. Include a final “Approved for Issue” signature on the STPOI and ATE
10. Include a mechanism on the STPOI and ATE procedures and working documents to ensure “Physical and Schedule Changes” are referred for signature approval to all parties
11. Include on the STPOI and ATE any critical safety information and related hold points
12. Issue a guideline on appropriate risk assessment tools used, and train superintendents, supervisors, and mining professionals.
13. Communicate actions arising out of JSA’s, and Risk assessments to all personnel who have responsibility completion of these actions.
14. Review the use of the mining contractor JSA format and ensure it complies with the Client JSEA procedure.
15. Business process and procedure documents are approved and managed through a document control system including changes to documents.
16. Review the process of issuing of ATE documents to the contractor and their document control, to ensure up to date plans are issued to the workforce and out of date plans are removed from circulation.