Some oil companies (geophysicists) have very specific likes and dislikes relative to different types of explosives. In most cases the geophysicist has been favourably impressed by the characteristics of an explosive, usually the high velocity which produces a very nice, clearly-defined first break.

An example of a very desirable explosive, as mentioned above, is what is generically termed cast pentolite. All pentolite cartridges have a velocity of ± 26,000 feet per second (± 7,925 mps).

The characteristics of this product are:

  1. it is cap sensitive
  2. it has a high density of 1.6
  3. it is completely waterproof
  4. it will never decompose due to long sleep times.

Nitro-glycerine based explosives, by comparison have a considerably reduced velocity of ± 22,000 feet per second (± 6,700 mps).

The characteristics of this product are:

  1. it is cap sensitive
  2. it has a slightly lower density of 1.4
  3. it has good water resistance (2-3 months)
  4. it will only decompose over a long period of time.

A recent addition to the choice of seismic explosives is a cast product with neither of the foregoing compositions and a velocity of ± 22,000 feet per second (± 6,700 mps).

The characteristics of this product are:

  1. it is cap sensitive
  2. it has a high density of 1.78
  3. it has very good water resistance
  4. it will decompose after approximately 2 years.

Various emulsions are available and have velocities of ± 17,700 feet per second (± 5,400 mps).

The characteristics of some of them are:

  1. they are cap sensitive
  2. they have a density of 1.2
  3. they have very good water resistance
  4. they will decompose after more than 1-2 years.

Note: I have listed the above in order of decreasing velocities and for no other reason.

From a safety and environmental point of view, what is the best explosive to use and why?

Any explosive purchased for use in seismic is dependent on a good substantial cartridge to stand up to difficult loading conditions. This is pretty well under control by today's manufacturers. Our greatest concern as explosives users is that the quality control is excellent and that the explosive content is fully contained within the cartridge and does not leak out or protrude from that cartridge.

Poor or sloppy cartridging should be reported to the supplier and the Canadian Association of Geophysical Contractors (CAGC) and the product should be saved, not used.

I have personally observed pentolite cartridges that have been supplied with the pentolite open, exposed to damage from the outside packaging and handling.

The hazard here is that when pentolite flakes off due to abrasion or abuse, it can be contaminated with foreign material. If this happens, it can become extremely sensitive to detonation due to friction.

The coupling together of this type of cartridge, with the condition as above, can be a hazardous procedure.

I bring this example to the readers' attention because there are alternatives to using what I consider hazardous products, sometimes poorly packaged.

The other comparison of significance is the hazard created by misfired, stuck or otherwise unexploded charges which are essentially abandoned.

Any explosive that is wholly or in part composed of pentolite will nor deteriorate. This remains an explosive that could detonate if the conditions were right.

What conditions?

Surface mining operations can and have dug into such explosives.

Road building or other excavating construction also can and have dug into such explosives.

Various opinions exist as to the relative danger of such an event occurring. The important consideration here is this - are you prepared to accept the responsibility of a sensitive abandoned explosive being struck and detonated causing bodily harm or death?

I intend to pursue this topic further with consideration to both products and procedures.

Our industry relies on the results obtained in part from the detonation of many thousands of tonnes of explosives. We have an obligation to ourselves and the public at large to control the explosives we purchase and use. Hopefully this and up-coming articles will help to improve our control over this very essential energy source.

'Til next time, at work or play, Live Safely!



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