Safety Jack

As in all industries there has been a lot of people movement in ours. This includes all of the fashionable names for staff reduction including the ever encroaching word - retirement. Either I’m seeing less and less of my old acquaintances in the field or I’m starting to meet more and more new ones. Either way you look at it, we all have a spot in the passing parade and we probably all know where our seat is.

The purpose of this preamble is this; a few weeks ago the newly formed Canadian Rockies Chapter of the International Society of Explosives Engineers held their first conference at Nisku. For a first event it was classed a great success. Papers were presented from all types of explosives users including federal and provincial groups. AI Schroeder and yours truly were to have cosponsored a paper on Seismic Explosives over the years. Unfortunately, a commitment of greater importance took AI’s attention and a spot of bad health kept yours truly hospitalized during this time. Not wanting to disrupt a well scheduled program, we managed to conscript an old friend at the last moment by the name of Rupert Goodhart.

Safety Jack and Rupert (as well as many of you readers) have worked together on and off over a 20 year period. Rupert seemed the obvious choice to give a highlight of some of the things we have tried to do to enhance the signal from a shot of some type of seismic-grade explosive. On very short notice Rupert took our skimpy notes and slides and did a very good job of presenting Al & Jack’s paper.

In this column, I want to do a brief on that paper to give some of the newer geophysicists and operations types an idea of what they might have missed in the “early” years.

One theory (which still exists in a lot of minds) is hit it deep and hit it hard - 150 lbs. at depths to 200 ft. wasn’t too uncommon. This was usually wanted in tough drilling conditions and cold weather. Can you imagine at least three, 20 ft. strings of powder, lowered gently by at least three people and with a total of at least six detonators. I’m sure we shoot some of those same areas today with 2 kg at 18 m (5 lbs. at 60 ft.).

Naturally as well as heavy deep charges we also drilled some pretty fancy shallow patterns, as we do today. In many cases we used what was called a “greased cap”, more cap than powder, and there was also the old “seismic booster”. This was a copper sleeve approximately 4" long with a recess designed to hold the cap firmly and was used as the complete charge or frequently as the cap and booster for larger (up to 50 Ibs.) of special Nitro-Carbo-Nitrate (NCN) marine charges.

Pattern charges always have had and probably always will have an interest to the geophysicist so we won’t dwell on those better known configurations here.

We have imported a fair number of interesting ideas from the United States in the past. One of the more “exotic” were “bump” charges. These were 2" diameter metal cans designed to couple end to end to each other. They were in two general configurations:

1. The heavier charge was a primer can of a high velocity explosive, TNT or possibly a cast primer. In between these cans you would use several cans of lesser cost and lesser velocity explosive (NCN) and you would have several series of five one-pound cans of NCN, then a high velocity booster, and this would be repeated as often as desired.

2. There was another variety of this “bump” charge where the high velocity can was fitted at either end of an eight foot cardboard tube. These two charges were coupled by a “low velocity lead clad detonating card”. If my memory serves me, it was 2 grains per foot. These were also designed to couple together to attain whatever number of one-pound “bumps” the geophysicist wanted. It was not uncommon to have a break in that very frail 2 grain per foot lead cord.

It would be impossible to also cover shaped charges, vertical and horizontal lin? ear charges and maybe a couple of others in this article. In order to remind you that the explosives end of seismic was also as interesting and variable as the electronics end, these will be addressed in future issues.

’Til next time, at work or leisure, LIVE SAFELY!