Water resistance is the ability of an explosive to withstand exposure to water without it suffering detrimental effects in performance. Explosive products have two types of water resistance, internal and external. Internal water resistance is defined as water resistance provided by the explosive composition itself. As an example. some emulsions and water eels can be pumped directly into boreholes filled with water.
These explosives displace the water upward but are not penetrated by the water and show no detrimental effects if fired within a reasonable period of time. External water resistance is provided not by the explosive materials itself, but by the packaging or cartridging into which the material is placed.
As an example, ANFO has no internal water resistance yet, if it is placed in a sleeve or in a cartridge within a borehole, it can be kept dry and will perform satisfactorily. The sleeve on a cartridge provides the external water resistance for this particular product.
The effect which water has on explosives is that it can dissolve or leach some of the ingredients. or cool the reaction to such a deme that the ideal products of detonation will not form even though the product is oxygen-balanced. The emission of reddish-brown or yellow fumes from a blast often indicates inefficient detonation reactions frequently caused by water deterioration of the explosive. This condition can be remedied if a more water-resistant explosive or better external packaging is used.
Manufacturers can describe the water resistance of a product in two different ways. One way would be using terms such as excellent, good, fair, or poor. When water is encountered in blasting operations, the explosive with at least a fair water resistance rating should be selected and this explosive should be detonated as soon as possible after loading. If the explosive is to be in water for an appreciable amount of time, it is advisable to select an explosive with at least a good water resistance rating. If water conditions are severe and the exposure time is significant, the prudent blaster may select an explosive with an excellent water resistance rating. Explosives with a poor water resistance rating should not be used in wet blastholes.
Water resistance ratings have also been given numbers, such as a Class 1 water resistance would indicate 72 hours of exposure to water with no detrimental effects; Class 2 – 48 hours, Class 3 – 24 hours, and Class 4 – 12 hours. The descriptive method of rating water resistance is the one commonly seen on explosive data sheets. In general, product price is related to water resistance. The more water resistant the product, the higher the cost.
The ability to remain unaffected by high static pressures is defined as water pressure tolerance. Some explosive compounds are densified and desensitized by hydrostatic pressures which result in deep boreholes. Combinations of factors such as cold weather and small primers will contribute to failure. Under these conditions, energy release may be minimal. Problems with water pressure tolerance most often occur with slurry and heavy ANFO.
