Dyno Nobel Asia Pacific Pty Ltd.

When NH4NO3 emulsions are used in blast holes containing pyrite, they can exothermally react with pyrite, causing the emulsion to intensively heat and detonate prematurely. Such premature detonations can inflict fatal and very costly damages. The mechanism of heating of the emulsions is not well understood though such an understanding is essential for designing safe blasting. In this study the heating of an emulsion in model blast holes was simulated by solving the heat equation. The physical factors contributing to the heating phenomenon were studied using microscopic and calorimetric methods. Microscopic studies revealed the continuous formation of a large number of gas bubbles as the reaction progressed at the emulsion-pyrite interface, which made the reacting emulsion porous. Calculations show that the increase in porosity causes the thermal conductivity of a reacting region of an emulsion column in a blast hole to decrease exponentially. This large reduction in the thermal conductivity retards heat dissipation from the reacting region causing its temperature to rise. The rise in temperature accelerates the exothermic reaction producing more heat. Simulations predict a migration of the hottest spot of the emulsion column, which could dangerously heat the primers and boosters located in the blast hole.

The underground mining and civil construction industry requires the design, drilling, blasting, and excavation of many tens of thousands of meters of tunnel development per yr.The majority of this tunnel driving is still carried out by using pneumatically loaded bulk ANFO, with the use of cartridge emulsion explosives in the bottom row of "lifter" holes being widespread.Occasionally however, the presence of running water or excessive quantities of mine water and humidity render the use of prilled AN based explosives impractical due to product loss through dissolution in water.Under these circumstances, the operator must use water-resistant products such as bulk or cartridge emulsions.The latter choice is to date more common due to ease of supply and the low tech. nature of the required handling.Many operators report, however, that when cartridge emulsion products are used exclusively in wet faces, the incidence of unbroken hole length (butts) increases.This tendency was observed independently of explosive manufacturer and product.Initially it was postulated that such a reduction in blast/explosive performance was due to dynamic desensitization (dead pressing) of the solid sensitized emulsion explosive, particularly in the burn cut region of the round where inter-hole distances may fall below 25 cm.However vibration monitoring studies and direct observation of blast results calls into question this hypothesis.In its place, it was suggested that inadequate coupling of the explosive cartridge with the borehole wall may reduce the explosive energy/rock transfer to such a degree that rock fragmentation is inhibited and inadequate round performance results.In the case that this were so, it was further postulated that any change in explosive characteristics/charging techniques which were to bring about an improvement in this coupling, should consequently cause an improvement in tunnel blast performance as measured by linear advance per drilled and charged meter.The following paper describes a series of exptl. measurements designed to quantify the impact of cartridge length and tamping practices on the degree of explosive/rock coupling.The resultant coupling factors are shown to have a marked effect on anticipated explosive performance in the development blasting application.

Alfred Nobel first invented a practical detonator in 1863 and then the blasting cap in 1865.At that time the detonator was used on the end of a length of safety fuse to initiate nitroglycerin-based explosives.Since then the detonator has gone through a number of changes.The instantaneous elec. detonator was the first to allow remote firing.The elec. delay detonator followed and allowed for timing between holes.In the mid 1970s the NONEL Tube was invented.This tube combined with NONEL detonators meant that many of the safety issues, such as stray current and radio frequency, associated with elec. delay detonators were eliminated.This system gave the mining industry a reliable and fairly accurate system with which to detonate shots of any size.Since the early 1980s a large amount of research and development work was done around the world to create a more accurate detonator for the mining and quarrying industry.After years of research, electronic detonators have emerged as the most accurate and precise initiation system available to the mining and quarry industry today.Electronics provide the user with millisecond timing accuracy.The improved level of timing control allows operations to improve fragmentation, throw and reduce vibration levels.There are now a number of different electronic detonator suppliers on the market today.In 2004 Dyno Nobel formed a joint venture called DetNet with AECI.DetNet has a suite of electronic detonators, DigiDet, HotShot, and QuickShot.This paper focuses on the HotShot system, the first of the three new initiation systems to be released to the market in Australia by Dyno Nobel.