Sensitiveness (Critical Diameter)

Sensitiveness is the characteristic of an explosive that defines its ability to propagate through the entire length of the column charge and controls the minimum diameter for practical use. It can be expressed as the maximum separation distance (in centimeters) between a primed donor cartridge and an unprimed receptor cartridge, where detonation transfer will occur. It is measured by determining the explosive’s critical diameter. The term “critical diameter” is commonly used in the industry to define the minimum diameter in which a particular explosive compound will detonate reliably.

All explosive compounds have a critical diameter. For some explosive compounds, the critical diameter may be as little as a millimeter. On the other hand, another compound may have a critical diameter of 4 in. The diameter of the proposed borehole on a particular job will determine the maximum diameter of explosive column. This explosive diameter must be greater than the critical diameter of the explosive to be used in that borehole or it may not detonate. Good planning for a site is to allow for a somewhat larger borehole, often around an inch larger, than the critical diameter for the particular compound(s) to be used. Table 3 lists the critical diameter of some commonly used explosives.