Subdrill or subgrade is the length of blasthole drilled beneath bench floor level below the required floor of the excavation.

Subdrilling is carried out to ensure explosives are placed below the bench floor level to assist with floor grade control. The correct amount of subdrill is critical to the entire operation. Too little subdrill and digging becomes difficult, floor grades are poor and wear and tear on equipment increases. Too much subdrill and drilling is adversely affected due to excessive preconditioning of the next bench down.

Note where these is a weak or valuable horizon at grade (such as when blasting to coal) the blast holes will be drilled to finish above the grade line. This is the opposite of subdrill and is known as ‘Standoff’.

Optimum amount of subdrill depends on:

• Strength and density of the rock mass
• Diameter and inclination of blastholes
• Type of explosive and, more particularly, the energy generated per metre of blasthole
• Mean inclination of the face and the effective toe burden distance
• Location of primers in the charge.

The design properties of a blast hole are shown in the following diagram

Note that for vertical holes subdrill and subgrade are the same.

Access to Exploasives of SSAN by a worker occurs under the supervision of an authority holder or authorised person, or when working in a defined supervised area as detailed in the security plan.

Weatherford’s SureFire detonation system is a wireline-conveyed gun that detonates safely, efficiently, and reliably.

The proprietary system features a vented detonating block that eliminates damage that usually occurs with top-fire or quick-change detonators, and it has a shunt cap that enables operators to safely secure the detonator to the quick-change.

Surefire detonators have a pin that when not depressed shorts the live wire in the detonaotr to ground.

View of top of surefire detonator showing pin that is depressed on assembly.

A surface delay comprises a low energy detonator housed in a plastic block.

The block enables a number of shock tubes to be clipped in. Surface delays are the main means for sequencing non electric blasts for open cut operations.

A swimlane (or swimlane diagram) is used in process flow diagrams, or flowcharts, that visually distinguishes job sharing and responsibilities for sub-processes of a business process. Swimlanes may be arranged either horizontally or vertically.

The swim lane flowchart differs from other flowcharts in that processes and decisions are grouped visually by placing them in lanes. Parallel lines divide the chart into lanes, with one lane for each person, group or sub process. Lanes are labelled to show how the chart is organized.

In the accompanying example, the vertical direction represents the sequence of events in the overall process, while the horizontal divisions depict what sub-process is performing that step. Arrows between the lanes represent how information or material is passed between the sub processes.

Alternately, the flow can be rotated so that the sequence reads horizontally from left to right, with the roles involved being shown at the left edge. This can be easier to read and design, since computer screens are typically wider than they are tall, which gives an improved view of the flow.

Use of standard symbols enables clear linkage to be shown between related flow charts when charting flows with complex relationships.

The advantage of a swim lane is that users can quickly identify what their role and responsibility is in the process simply by looking down the column under their role descriptor.

The disadvantage of a swim lane is that it is possible to lose the sense of the bigger picture as the layout can be more complex and the level of detail of each of the steps is greater.

Detonation of an explosive charge caused by the shock wave from the explosion of an adjacent charge.