ABSTRACT
Fumes are obviously related to the stoichiometry of the explosive composition. An explosive with a negative oxygen balance is expected to produce carbon monoxide while an explosive with positive oxygen balance is expected to produce oxides of nitrogen. The current problem is not how
1 INTRODUCTION
Commercial explosives are mixes of oxidizers and fuels. Typically their composition is of the CHNO type and often it is stoichiometrically balanced to avoid noxious fumes. Literature studies have provided evidence that nitrogen oxides can be present in the fumes of commercial explosives, with consequences to health and safety as well as energy output in blasting. The main toxic gases produced by blasting are carbon monoxide (CO) and oxides of Nitrogen (NOx). According to the commonly used Russian formula for fume toxicity, the relative fume toxicity (RFT) is expressed as RFT = {CO} + 6.5{NOx} reflecting the higher toxicity of NOx than the toxicity of CO. Other gases, such as NH3 are also toxic and have been used in amended formulas (Wieland, 2006). The toxicity and the impact of carbon monoxide on blasting operations are well known (Harris and Mainiero, 2007), and remedial measures have been recommended. To protect workers, many countries have established test procedures and requirements for the maximum permitted fume production per unit mass of explosive. However, research has shown that toxic fumes depend on the environment of use, which may not be considered by regulations. For example, explosives desensitized during blasting, may produce fumes having increased toxicity levels (Ruhe and Wieland, 1991). Recently, there
stoichiometry affects fumes but why explosives of proper stoichiometry produce objectionable products of detonation. Rowland and Mainiero (2000) have reported that in their experiments with ANFO, decreasing the thickness of the confining steel pipes resulted in increased NO2 production. They also associated fume production to non-ideal explosive behavior. They reported that remedial measures included the increase of fuel content; however increase beyond a point had a detrimental effect and ammonia seemed to be on the rise with such increases. Water contamination, even at minor concentration appeared to also increase NOx. Such effect is expected for ANFO, which is attacked by water, although the percentage of water contamination needed to produce NOx appears to be very small. According to subsequent work by Rowland et al. (2001) even emulsion explosives, which have not been associated to NOx fumes, and to a larger extent blends of emulsion and ANFO, produced significant amounts of fume after prolonged contact with water. The results of the investigation suggested that sleeping times are of importance. Traditionally, blasting engineers have looked into sleeping times for loss of performance of explosives. Apparently, prior to loss of performance, the fume spectrum is modified.
