Alert no. 418 | 06 October 2022 | Version 1

Roof bolt nuts

What happened?

Routine testing of a 24mm roof bolt nut at an underground coal mine found a crack running through the face of the nut. Additional testing identified that the same issue had affected a small number of other roof bolt nuts, prompting the mine to replace current stocks of the items.

Roof bolt nuts are used to support roof materials in underground coal mines. Faults in roof bolt nuts could potentially compromise the integrity of roof support commonly used in underground mine roadways.

How did it happen?

• Routine testing of a roof bolt nut identified a crack running through the face of the nut. The damaged 24mm nut was found to have a crack running the length of the nut.
• Additional testing found similar faults in a small number of the samples suggesting that the problem may be more widespread.

Key issues

• The identified faults found in the additional sample set varied from minor defects in the surface of the nuts to full cracks along the length.
• The potentially defective nuts may have been distributed to more than one mine site in Queensland.
• Defective roof bolt nuts are likely to have been used on sites – more than one example was discovered during the initial investigation.
• The nuts have been manufactured in an overseas facility and distributed by a supplier.

Recommendations

Site Senior Executives should:

• Review their testing regime to ensure that a good sample size of items have been tested and conduct additional testing if defective items have been identified.
• Contact their suppliers of roof support materials as a matter of urgency to determine if their supplies have come from the same manufacturing source.
• Review preventative and mitigating controls to:
• Determine if any affected roof bolt nuts are installed in their workings.
• If items have been installed, develop a method of determining where these potentially affected roof bolt nuts have been installed.
• Conduct technical evaluations of the areas to understand the potential effects on strata support.
• Develop plans to mitigate any increase in risk to Coal Mine Workers and the underground environment.