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Definition
“Flyrock” means rock that is thrown through the air because of blasting. Flyrock is an integral part of blasting that needs to be properly controlled. If flyrock is uncontrolled the rocks, which can travel significant distances, pose a risk to persons involved with blasting as well as anyone else around the blast. There is also the potential for damage to nearby property or equipment (Education, 2006).
What are the causes of flyrock?
According to ([PDF] Prediction and Controlling of Flyrock Due to Blasting for Kyaukpahto Gold Mine | Semantic Scholar, n.d.), fly rocks are caused due to mis-match of ex-plosive energy with the geo-mechanical strength of the rock mass surrounding the explosive charge. Factors responsible for such mismatch are discussed below:
Burden
An insufficient burden is a primary cause of flyrock from a high wall face. Problems related to burden causing flyrock.
Blast Hole Loading
Blast hole over charging is one of the frequent causes of the fly rock occurrence. Such overloading generates excessive release of energy. It happens due to loss powder in fissure, joints voids and cracks. To prevent overloading, it is necessary to load holes as designed using the correct charge weight. Additionally, a blast stemming should be sufficiently high to eliminate the possibility of excessive charging and holes must be monitored to check the rise of the explosives.
Stemming
Stemming materials provide confinement and prevent the escape of high-pressure gases from blasting holes. This material must be free from rocks and properly tamped. Inadequate stemming results in stemming ejection from the holes resulting in fly rocks.
Detonator Fining Delay
Critical elements of any blast design are firing delays between adjacent holes in a row. Proper firing delay helps to achieve good fragmentation. Rock fragmented by previous hole must be given chance to move prior to firing the subsequent holes.
Blasthole Pattern
Inaccuracies in the design of blasting pattern, including large deviation from planned pattern results in flyrock occurrences.
How can you mitigate fly rocks?
In order to control fly rocks, several measures can be implemented. These include optimizing blast design, establishing clearance zones, complying with regulations, monitoring and controlling blasts, providing personnel training, raising public awareness, and enhancing overall communication (Understanding The Risks of Flyrock in Mine and Quarry Blasting, 2023).
Blast design
Good blast design is generally the primary method of avoiding flyrock (Queensland & Mines, 2020).
- Select the direction of blasting face to place any person or buildings at the rear of the face.
- Avoid shallow blasting that is generally less than 1 metre. It must be remembered that the surface provides a free face. Ensure a blast ratio (tonnes of rock per kilogram of explosives) sufficiently high to eliminate the possibility of excessive charging. Use smaller hole diameters where possible.
- Choose a burden of sufficient magnitude to reduce the possibility of blast through (generally, between one third to half the depth of holes).
- In general, keep the stemming length not less than 25 times the blast hole diameter or not less than the burden, whichever is the greater. Stemming material must be free from rocks and properly tamped.
- Where possible use sequential or delay firing so that all shots fire from the face backwards. The delay sequence should be carefully checked.
- Take special care when carrying out secondary blasting to avoid overcharging.
Drilling and loading
While the blast pattern generally determined by experience may be satisfactory, inaccuracies in drilling or incorrect blast hole angle can cause quite large deviations from the planned pattern with excessive noise, vibrations and/or flyrock resulting. The extra time spent on making sure that the blasthole is in the right position is especially warranted. Instruments should be used to set out the drilling pattern. There will be difficulty in estimating the burden in hilly terrain. The correct charge weight must be employed in the blast hole. When using ANFO or any other free running explosive, pour measured quantities of the explosives into the hole and monitor the build up of the explosive column by tape measure or wooden pole. This is to avoid overcharging which may result from fissures or chambers in the rock (Queensland & Mines, 2020).
Cover
Where any doubt exists, or where the blast situation demands added precautions eg: shallow blasting or proximity to protected works, sufficient cover must be placed on the blast to further minimise the possibility of resulting flyrock. Where backfilling is used to cover loaded holes, this should be sorted material without stones. The cover should be placed with care to avoid damage to connecting wires, shock tube or detonating cord trunklines and should be to a minimum depth, which would eliminate flyrock (Queensland & Mines, 2020).
Conclusion
Fly rocks hazard is common in blasting. They can have many effects on equipment and even personnel. If not well designed, blasting patterns can cause dangerous fly rocks. Several parameters such as stemming, burden, delays and loading have much influence on blasting results. To ensure proper blasting and avoid fly rocks, you must first of all optimize your blast design, train your blasting operators and maintain good communication with nearby communities and stakeholders.
Reference
Education, N. S. L. and A. (2006, May 5). Flyrock Incidents in the Province of Nova Scotia: NS Labour and Advanced Education, Hazard Alerts. https://novascotia.ca/lae/healthandsafety/flyrock.asp
[PDF] Prediction and Controlling of Flyrock due to Blasting for Kyaukpahto Gold Mine | Semantic Scholar. (n.d.). Retrieved March 14, 2025, from https://www.semanticscholar.org/paper/Prediction-and-Controlling-of-Flyrock-due-to-for-Lwin-Aung/487b573ac477c6f913b1fbd342cf2ae08353363b
Queensland, jurisdiction=Queensland; sector=government; corporateName=Resources S. and H., & Mines, Q. D. of N. R. and. (2020, August 26). Precautions against flyrock (Queensland) [Document]. Resources Safety and Health Queensland. https://www.rshq.qld.gov.au/safety-notices/explosives/precautions-against-flyrock
Understanding The Risks of Flyrock in Mine and Quarry Blasting. (2023, November 14). https://ergindustrial.com/understanding-and-minimizing-the-risks-of-flyrock-in-mine-and-quarry-blasting/
