Seamus I chuckled like mad when I read your story. I could see the whole episode in my mind, it reminded me of the time when I dabbled with experimental physics and caused an unexpected outcome.

My first job was in a hardware store in Dublin. It was 1965 I was 15. We sold weedkiller by the pound, it was if my memory is correct, potassium chloride????? Well whatever it was, I was informed that if it was mixed with sugar and then lit it would explode, I was also told that if it was packed into a copper pipe and the ends were sealed and a fuse placed in a small hole in the pipe that it would make a small bomb.
Now my father had given me the job to dig the back garden of a new house we had recently moved into. The rear gardens of these houses had been used as a road during the construction of the houses and consequently the ground was as hard as the hobs of hell. It was slow, tedious and backbreaking work.
You can see it unfolding can't you?
I dug a deep hole and into it I placed a 2" copper pipe about 12" long packed with 4lbs of this concoction. At first it wouldn't work, because the fuse would extinguish as soon as I shovelled loose clay into the hole. So I made a detonator by winding a piece of fuse wire into a spiral, then I soldered a long flex to the two ends. I inserted it deep within the pipe, sealed the ends, placed it at the bottom of the hole and packed the hole with clay. I took the two ends of the wire and stood behind a low wall. I then connected the flex to a battery.
For a couple of seconds nothing, but when the coil within the device got hot enough. BANG! the ground erupted, tons of clay and gravel shot high into the air, the blast was so loud that I was deafened, a massive swoosh of air, birds everywhere flying in panic, then clay and earth began to rain down from above, the entire neighbour hood was covered in clay and dust. People came running in panic, praying that nobody was injured or worse, dead. Even though I was deafened, dazed and covered from head to toe in fine clay particles I had the presence of mind to retrieve the length of wire and I concealed it and the battery behind the coal bunker.
Well when the smoke cleared you should have seen the crater, no exaggeration it was 5 foot deep and 8 feet in diameter. The police arrived to investigate, with my ears still ringing from the explosion I told them that I was digging the garden when the spade had struck something hard and then BANG.
The gas company was called, but no gas pipe was found. The electricity company was called, no cable was found. The army was called, the Officer in charge told the police that the crater was definitely caused by a bomb, so my family and the neighbours were evacuated and moved a safe distance away. After hours of fruitless searching with mine-detectors and metal-detectors they confessed that it was a mystery to them what had caused the explosion, they hypothesised that maybe it was the remains of an old IRA dump, unexploded ordinance from the World Wars or some mysterious and rare natural phenomenon.
Nobody ever suspected or ever found out what it was I that caused the bang, but it sure cured me of my interest in experimental physics. It must have also left an indelible mark on my psyche because forty years latter the sight of a garden spade still causes me to break out in a sweat and duck behind a wall, but nowadays I keep my ears well covered.
Fergus