Blast site activity hazards

Premature initiation of signal tube ('snap, slap, shoot')

Incidents have occurred when vehicles driving over loaded shots have caught on the signal tube, stretching and snapping it. In some cases, the signal tube has initiated and a loaded hole has fired.

To prevent this hazard, there are several control measures that should be implemented:

• Follow the manufacturer's recommendation for the maximum weight loading for the tube.
• Ensure that excessive tension is not placed on the tube, such as pulling on the signal tube of a primer jammed in a blast hole.
• Avoid or limit vehicles operating on the blast site. When vehicles are on site, personnel should rigorously follow procedures when operating vehicles near signal tube.
• Use spotters to assist vehicle drivers manoeuvre on the shot during loading and stemming activities.

Dropping primers down blast holes

Poor practices have involved primers progressing down blast holes at higher speeds than those recommended by the manufacturer.

Problems that may occur include:

• Excessive impact when the primer reaches the bottom of the hole may cause the explosive to initiate prematurely.
• Misfires may also occur when cord is cut when passing over sharp irregularities in the sidewall of the hole.
• The detonator may be dislodged from the primer.

Suggested control measures include the following:

• Ensure that safe loading procedures are followed according to site procedures and the manufacturer/supplier technical data sheet.
• Don't allow sensitive initiating explosives, such as detonators, detonating cord and boosters, to be thrown or to freewheel down blast holes. They should always be lowered slowly according to applicable procedures.