Blasting is a widely used technique to break down rocks or hard soil into manageable fragments with the use of explosives. The blasting process generally involves drilling holes, installing detonators and charges, detonating the explosives, and then clearing the resulting debris. When carried out properly, blasting can be an effective and efficient method for excavation, mining, and construction projects. However, due to the inherent dangers involved with explosives, strict safety precautions must be followed to protect workers and the environment. This article focuses on how to safely conduct blasting operations in hard rock or soil.
Blasting Operation in Hard Rock
Blasting in hard rock involves carefully planned and controlled steps to ensure both efficiency and safety. The process starts with drilling boreholes in predetermined locations where explosives will be loaded. These holes are then charged with cartridges connected to detonators and safety fuses before being fired in a controlled sequence to fracture the rock. A typical blasting operation requires precise execution and adherence to safety protocols to avoid accidents.
Safety Precautions before Blasting
Safety begins well before the explosives are detonated. The entire operation should be supervised by an authorized blasting engineer responsible for overseeing every step. When using dynamite, borehole positions must be marked clearly with white paint to avoid any confusion during drilling.
Boreholes must be drilled to the correct size to allow the easy insertion of explosive cartridges. Once drilling is complete, the engineer inspects the holes to ensure that only the designated holes have been drilled, avoiding any extra or misplaced boreholes.
Each borehole’s charge is prepared separately and boreholes are cleaned thoroughly before inserting cartridges. For tamping—the process of packing the explosives inside the hole—only cylindrical wooden rods should be used. Metal rods, especially those with pointed ends, are strictly prohibited as they can damage the cartridges or create sparks.
Cartridges must be carefully placed into boreholes, pressed gently without ramming. Multiple cartridges can be added to achieve the necessary explosive charge. The topmost cartridge in each borehole is connected to a detonator, which is in turn connected to safety fuses of appropriate lengths.
Fuses should be cut without joints whenever possible. If joints are unavoidable, they must be made by cutting a semi-circular notch from one fuse end and fitting it into the notch of the other, then securely wrapping the joint with string and waterproof tape if exposed to dampness.
No more than eight boreholes should be loaded and fired at one time, and the charges must be detonated successively, not simultaneously. Before firing, a clear warning must be given, and all personnel should retreat to a safe location. Ignition of the safety fuses should only occur in the presence of the supervising engineer, who will set the countdown to the blast.
After detonation, the engineer inspects the site carefully to identify any anomalies or safety concerns.
Safety Precautions during Blasting
During blasting, safety remains paramount. The area around the blast site must be clearly marked with red flags to alert workers and bystanders. All workers must maintain a safe distance of at least 200 meters from the blast site.
An audible warning, such as a whistle, must be sounded prior to igniting the fuse to alert everyone nearby. The blasting should only be performed by trained personnel under close supervision.
Blasting should not be conducted within 200 meters of any existing structures unless explicit written permission is granted by the engineer. All blasting activities must comply with relevant regional and national safety regulations regarding the use, handling, and disposal of explosives.
Precautions against Misfire
Misfires are dangerous and require careful handling. If a blast fails to detonate, the safety fuse must be cut obliquely using a knife. The detonator’s interior should be cleared of sawdust by blowing or gently tapping—metal tools must never be used to avoid accidental ignition.
If water is present in the borehole or detonator, the fuse-to-detonator junction must be sealed with grease or another suitable waterproof material as specified by the engineer. The detonator should be inserted into the cartridge so that about one-third of the copper tube remains exposed, and the safety fuse above the detonator must be securely tied.
Waterproof fuses are essential when drilling in damp or wet conditions to ensure reliable ignition and prevent failures.
Conclusion
Blasting in hard rock is a complex but essential operation in many industries, from mining to construction. Ensuring safety at every stage—before, during, and after the blast—is critical to prevent accidents and ensure the operation runs smoothly. Following the guidelines for drilling, charging, tamping, and firing explosives under expert supervision, while respecting safety distances and regulations, makes blasting a safe and effective technique for rock excavation.