When is sequential firing used in blasting techniques?

Sequential firing is utilized in blasting techniques primarily during controlled blasting operations to enhance safety and minimize damage to surrounding structures. This method involves detonating charges in a predetermined sequence rather than all at once. By doing so, the energy release is more controlled, which helps to reduce the peak particle velocities and air blasts that can potentially harm nearby facilities or the environment.

In controlled blasting, sequential firing can also aid in achieving a more precise fragmentation of rock, which is crucial in operations where the control of noise and vibration is essential, such as near populated areas or sensitive structures. This technique allows for a more effective and measured approach to blasting, ensuring that the operation meets regulatory and safety standards.

The other options do not accurately represent the primary application of sequential firing. For instance, while deep rock blasting may require specific techniques, it doesn't inherently involve sequential firing. Urban areas can pose challenges, but sequential firing is chosen for safety in dense environments. Lastly, sequential firing is not limited to single charge methods; rather, it can be applied across various charge configurations to achieve controlled blasting results.