Why BlastClear

Drill and blast teams spend a great deal of time on clearance perimeters, from design through to distribution. Most stay with the circle. Here is what the circle gives you, what it cannot do, and what the ballistic dome changes.

What the circular perimeter gives you

Centred on the blast's centroid, it is the minimum any clearance plan must carry. It serves three purposes.

• Assess the reach of the throw, at maximum range, over the surroundings of the blast.
• Warn personnel and machine operators, and protect fixed or hard-to-move installations.
• Test the effect of the blast parameters, charge per delay and stemming height, on the reach of the throw.

Its two limits come from its shape

They do not come from how it is applied: a circle can do neither.

It ignores the ground. A single radius is applied to a topography that is anything but uniform. It is under-estimated towards low ground, where a fragment lands further out, and over-estimated towards high ground, where it lands closer in. The first is a risk; the second ties up ground for nothing.

It ignores the direction of the blast. Throw is not equal in every direction: the firing sequence gives it a dominant one. A fixed radius therefore treats the back of the blast like the front, and holds the maximum range everywhere.

Several blasts, one plan

It gets harder when several neighbouring blasts go in the same round. Each perimeter has to be computed, then merged into a single outline, and all of it from files produced by several different programs before the drawing exists.

Every manual step is an opportunity for error, on a figure that decides whether people are moved out of the way.

What the ballistic dome changes

It answers both limits at once, and brings four things.

• It is built on the real geometry of the blast. The outermost holes of the outline define it, not the centroid alone.
• It is intersected with the site topography. The resulting perimeter follows the ground, its benches and its breaks of slope, rather than a theoretical horizontal plane.
• It is graded by sector. Each sector takes its own radius according to the blast direction, instead of one radius applied everywhere.
• It makes the result repeatable. The same data and the same settings give the same perimeter, whoever computes it.

What BlastClear makes of it

BlastClear applies this approach to all three families of blast in a single environment: closed contours for production, polylines for pre-splitting, points for boulder blasting. Blasts of the same round merge into a single perimeter, and the result comes out as a PDF drawing, as DXF or as an image.

On one open-pit operation, the time recovered from this handling is estimated at around two hundred hours a year. Actual gains depend on site context.