Explosives safety alert no. 61 | 13 August 2012 | Version 1

Flyrock damage outside the blast-exclusion zone

What happened?

A crib hut, located at a distance of approximately 1230m, was damaged when a flyrock incident occurred at a coal mine in Central Queensland. (The image below, shows the damage.) The blast-exclusion zone was set at 1000m. Blast guards and other people were just outside the exclusion zone. The flyrock was linked to a face defect that was not noticed before firing the overburden blast that ejected rock from a face burst. (See the image below.)

Recommendations

1. Conduct blast survey for correct blasting parameters and design.
2. Review design and load plan when under burden, defects, ground abnormalities or excessive back break is identified.
3. Survey blast faces accurately before marking out blastholes and loading explosives.
4. Loading procedures are to be followed, including recording of explosives loaded per hole and slumping.
5. Be aware of the quantity of explosives used, particularly when voids and cracks might be filled.
6. Consider the use of shelters for blast guards for protection from flyrock.
7. Keep the blast design, drilling and loading within known parameters.
8. Prior to a blast, consider any variations encountered and adjust the blast-exclusion zone accordingly, or perform other mitigations such as using overburden or leaving holes free of explosives.
9. Review safety management systems to ensure that there are suitable controls and procedures to address recommendations 1 to 8 above.
10. All people involved in these activities ensure that the safety management system, controls and standard operating procedures are followed and that on-the-job risk assessments are made and acted on.

What factors contribute to flyrock?

Many factors contribute to flyrock, in particular front-row holes. Examples are:

• weak rock structure including ground geology, fault, back break etc.
• insufficient front-row blasthole burdens
• stemming depth
• initiation sequence
• blasthole diameter, angle and depth
• blast pattern
• stemming material, decking, solid and air
• charge weight per hole
• failure to inspect the free face for defects.

See also AS2187.2, page 70.

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Authorised by Geoff Downs - Chief Inspector of Explosives

Contact: Manager, Explosives Licensing , +61 7 3199 8057 explosives@dnrm.qld.gov.au

Issued by Queensland Department of Natural Resources and Mines

Safety: This information is a guide only and is issued to promote safety through experience. It is not to be taken as a statement of law and must not be construed to waive or modify any legal obligation.

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