During the first 15 years of my contracting career most trenches in rock were blasted, before good productive and dependable rock trenchers were developed.
We had one crew that their primary job was drilling and shooting (term we used for blasting) rock.
We were building a new subdivision right behind the Bannockburn Baptist Church, before it was built, on Brodie at McCarty Lane in southwest Austin.
All was going real good on that project. Don the crew foreman and our ace blaster was short handed, so he hired an old hippie that happened by.
The old hippie’s only job was to put the fertilizer in after Don would drop the dynamite and cap down the hole. To insure that you had the correct amount of fertilizer in hole, you had a wooden tamping pole that had a mark on it and as you poured in fertilizer you slowly tamped and felt with the stick until the mark arose in the hole and became visible. That would leave a certain amount of cover (the dirt) over the shot. The weight of the cover kept the explosives from blowing out and causing danger to life, limb and property. It is very important to have that predetermined amount overburden above the intended shot. You can tell how important that was by the amount of explaining I’m doing here, right?
Sometimes the crew may drill and load holes all day with the detonation coming at the end of the day.
I drove up just before the “fire in the hole” was called out. When Don pushed the detonator button, you could see the time delays at work, with the ground rising as the blasts below ignited. It happened in milliseconds, but it was fun to watch several hundred feet of trench line just raise up the ground right before your eyes.
Suddenly it was like a bomb had gone off. In fact a bomb had gone off. The Ammonia Nitrate Fertilizer mixed with diesel fuel is more explosive than the dynamite, pound per pound and is much cheaper to use. The dynamite is really just used to ignite the fertilizer.
Luckily there was only a little rock in the the bottom of the trench he was blasting and mostly dirt, black clay soil, on top. So most of what filled the air was dirt and big dirt clods.
I was driving a brand new Buick Rivera and was parked at what I thought was a safe distance away. One huge dirt clod came flying my way and hit the passenger door, caving it in.
Other than that, the only damage was a house that was adjacent to the project. The roof was completely covered with dirt and dirt clods. Luckily it was a renter that was kind enough to let us send a crew over and shovel off his roof. I’m sure if it had of been a homeowner, we would have been putting on a new roof.
When I asked what had happened this is what I was told. The Old Hippie had followed Don’s instructions, only filling up the hole to the certain mark on the tamping pole. But what no one knew was there was a small cavern below ground, and it took about 3 or 4 bags of fertilizer to fill the hole and get it to the correct marking on the stick. Generally 1/4 of a bag was doing the trick. Hence the problem.
I think the Old Hippie had to find employment elsewhere.
Things like this happened often. That was the nature of that business.
The last day we ever had to do blasting was a happy day for me.