A Little Knowledge

Propane bottle after 50 years

A Little Knowledge … or how I almost blew my mother’s socks off

Ashland Drive, Boise, Idaho, about 1964

I suppose everyone has had more close calls in their life than they know about, and that’s a good thing, otherwise we’d be a quivering mass of protoplasm, fearful of every next move. Usually these close calls come and go, and we move right along in the rapid pace of life with little to show for our narrow scrapes with destiny. But I have in my hand a tangible artifact, a 50 year-old remnant of my closest call, my nearest to a terminal experience.

I must have been about sixteen, a junior with short hair at Borah High School in Boise, Idaho. I enjoyed that year, and the next, the classes and the music, with a bare minimum of social life, spending far more time playing cello than chasing girls. (It was going to take me a long time to understand that gender, but that is another story.)

Chemistry was my favorite academic class. I was already set up to get a kick out of that subject: my dad always talked fondly about his high school chemistry teacher in Portland, Oregon, (who had also been Linus Pauling’s teacher) and the awesome experiments they did in the lab. He sparked my interest with valence diagrams and hands-on demonstrations in the kitchen. Like the Sunday after breakfast that he showed me – at the age of about five – how normal air pressure could crush an empty tin Log Cabin® syrup container. Or the time we separated water into its component elements using hydrolysis. We removed and cleaned the hotdog sized carbon rods from a couple of big, old fashioned, used-up dry cell batteries, attached wires, and positioned them under – and up into – a little wide-mouth Mason jar full of salty water that was inverted in a glass cake pan that had more salty water in it. Why didn’t the water in the jar just run out into the cake pan? Air pressure, I learned, was pushing down on the exposed water and up into the jar. When we applied voltage to the carbon rods, bubbles formed, oxygen from the positive rod, hydrogen from the negative. The bubbles floated up, burst and began replacing the water in the jar, appearing to push it slowly down and out, until the carbon rods were nearly high and dry. Then Dad asked me to stand back, lifted the jar straight up and lit the mouth of the jar.  Boom! A flash of light. The hydrogen and oxygen recombined instantly, reversing the separation process that the electricity had powered, releasing energy and a puff of hot steam. The choice of a small strong wide-mouth jar was critical: a big narrow-mouth jar would have turned into shards of glass flying through the kitchen.

So maybe it was inevitable that I would eventually get interested in calcium carbide – harmless-to-handle little gray stones that foam up with bubbles when you drip water on them – bubbles of highly flammable acetylene gas, which is made of carbon and hydrogen.  Hydrogen is the simplest, lightest element in the periodic table, with an atomic weight of only one. It and carbon are two of the key ingredients in all life forms as we know them, including people. The sun’s energy, which is the source of all our surface energy on earth, comes from the nuclear marriages of hydrogen atoms. The hydrogen bomb is a tiny short-lived man-made sun-burst. And of course water is H2O.  But I digress. (It won’t be the last time.)

Acetylene had many applications during the Industrial Revolution of the 19th and 20th centuries, but two of its enduring uses were as fuel for welding torches and for special-purpose lamps such as big ones in light-houses and little ones on miners’ and cave explorers’ head-bands.  Such lamps draw oxygen from the air to support the flame. Some cavers still prefer old-school calcium carbide headlamps over the modern LED types. But serious miners have switched to electric lamps to avoid the possibility of the lamp’s flame igniting pockets of naturally occurring under-ground methane gas (which is mostly hydrogen) and causing a catastrophic explosion.

I did some playing around with calcium carbide and the acetylene that it makes when wet, collecting it and making little flames. But I needed to know more about it, so off I went to the Boise Public Library to read up on my chemical interest du jour, little suspecting that a couple years later, after my first year in college, I would be back there (and doing a better job) researching sex with my first real girlfriend, soon to be wife. But off I go again; now focus, Tim! Oh well, I wasn’t very eyes-on-the-prize as a kid either, a bit of a dreamer. Luckily the road is a lot wider than the car, so to speak, and there’s some tolerance for those of us who tend to detour a bit. So I read and assimilated enough to grasp the general properties and the calculations for how much calcium carbide and water would be needed to produce a given amount of acetylene, which easily converts to pressure within a given volume. All I needed was a lab experiment in the subject to confirm and refine my understanding.

One afternoon I was loitering in the garage attached to our house up on the “second bench” in southwest Boise. We had some basic tools and materials to work with, including a standard steel propane canister that was nearly used up from years of little plumbing, silver soldering and other odd jobs around the house. It was about 10 inches long by about 2-1/2 inches in diameter; you can get them in any hardware store. I thought it would be interesting to refill it with acetylene and see how it works as a torch. After all, acetylene is a well-known welding torch fuel. I was already thinking about how to do it as I read the whole label on the canister for the first time and noted the strange warning that it was a violation of federal law to attempt to refill the canister. I remember thinking, that’s all well and good, but I’ll go ahead and investigate the possibility anyway. Maybe the injunction was for safety, or maybe there was some other purpose – maybe just financial, like the canister makers wanting to sell more propane canisters.

Confident that I knew what I was doing, just substituting C2H2 acetylene for C3H8 propane – same elements, different arrangement – I got the idea of mixing calcium carbide powder and water inside the canister.  But how to get the materials in there, and what if the pressure grew too high?

The canister had a threaded fitting on top where the torch head screwed on.  The little hole in the middle of the fitting looked a lot like the little hole in the middle of the valve stem on the inner tube of a bicycle or the tire of a car.  Once I had emptied all the propane from the canister, it was an easy matter to unscrew the little valve and gain access to the inside.  Another little hole, on the top shoulder of the canister, was more of a mystery. I figured it had to be an over-pressure release because it didn’t make sense for the manufacturer to design and sell a fuel canister for consumers that might explode if it were somehow warmed to the point of over-pressure, like being left in a tool box in the sun.

I crushed a measured amount of calcium carbide into powder and used a paper funnel to put it down into the canister.  It was easy. Next I tipped the canister nose down at a 45 degree angle and tapped lightly with a piece of wood to shake the powder off the bottom and down into the shoulder area near the nose without spilling out of the still-open hole. Then I tipped the canister nose up at a 30 degree angle and clamped it in the bench vise. A long narrow plastic tube came in handy for pouring a measured amount of water directly down into the bottom of the canister, where it pooled and remained separated from the calcium carbide powder that was poised on the sloping canister wall above it. I put my ear the little hole and heard a faint sizzling sound that faded out as the little bit of residual powder reacted with the water. Soon it was silent. I screwed in the valve to seal it, and attached the torch head assembly.

It must have been a weekend because Mom, Dad and Tom were all home. I went into the house and announced the big plan, inviting one and all to come and witness the experiment.

Tom is about four years younger than I am, so he must have been about twelve. The garage was big enough for a single car, which was rarely parked in it during the warm weather. There was a woodpile of neatly split and stacked logs at the end. We parked our bicycles leaning against the side wall opposite the workbench. We all traipsed out to the garage through the kitchen door, leaving it open. The rollup door was also open; that’s where Mom stood. The wooden door to the patio and back yard was closed. I can see the scene as if it were yesterday. I took the time to go into detail about how I had been studying up on calcium carbide and acetylene, and how I intended to charge the spent propane canister with it to a pressure of only a couple of atmospheres – about 30 pounds per square inch – and try it out as a torch. Dad asked some good technical and procedural questions, which I answered with aplomb, assuaging the safety concern with my reasoning that the second hole in the canister was an over-pressure safety valve, which would save the day if my calculations were off the mark.

The whole setup was primed and ready to go. The moment came. I gingerly released the canister from the bench vise, shook it hard a few times to mix up the calcium carbide powder and the water, and waited a moment, wondering when I should turn the brass knob and open the torch valve to test it. Suddenly I said, “It’s getting hot!” It was going to burn my hands. I put it down on the garage floor and stepped back about three feet to watch it. Three seconds later it exploded with stupefying force and a blinding flash.

I stood in shock, dazed, hearing only the noise inside my head like a hundred whistles screeching different incoherent pitches. The upper air was nearly opaque with smoke. The canister was gone. I turned and saw my father and brother standing stunned in the cloud, expressionless. Mom was still standing over near the garage door. I asked, “Are you OK?” and felt my lips moving but could not hear my own voice nor any response they may have spoken. Black powder of different particle sizes was slowly floating down all around us. I realized I was shaking, heart racing. I turned the other way and saw the canister body ripped open, with a big piece missing and no torch head on it.

Gradually we started to come out of it. There was so much black dust in the garage that we all started walking into the kitchen. But there was nearly as much in there: a fine carbon dust filtering down, making the air seem visible. Same in the living room. A minute had passed. I wiped my finger on a table and it came up black. It was snowing soot everywhere. But it was even stranger that when we tried to talk to each other I could barely hear the voices, as though at a great distance, and couldn’t make out their meaning without staring at their lips. I don’t remember the others saying they were nearly deaf, but my ears were not working properly and did not recover to anything like normal for at least two whole days.

After waiting a few more minutes for the dust to settle, we all went back into the garage to see what happened. Tom noticed a new ragged hole in the patio door. He also discovered a red mark on the end of one of the firewood logs at the back of the garage. I brought the still-warm canister body over, and it matched the color of the mark. Then Dad looked in the direction of the bicycles and found the missing piece of the canister.  To our amazement, it was severely dented in 13 places and punctured clear through in 4 places exactly matching the position of the 10-speed’s sprocket teeth on the back wheel hub. It had been hurled with such force that even after losing energy by ricocheting off the firewood at an acute reflection angle, it had impaled itself upon 17 steel teeth and bent itself around a frame member like tin foil. Yet the steel of the canister, about thirty thousandths of an inch thick, is so strong that I cannot bend it with my fingers. If it had hit one of us…

As I write this, 50 years after the event, with the punctured piece and the rest of the red canister body on my desk as vivid reminders, I can wipe my finger along an inside surface and come away with black dust and an appreciation for the good fortune that was with our family: none of us was visibly injured that day.

The heavy brass torch head had ripped through the patio door. Opening it, we found that a piece of brick was missing from a corner of the outside garage wall at a height and position that agreed with the trajectory of the hurtling metal. Tom aligned a sighting through the hole in the door and the missing brick piece to help us narrow the back yard search. Nothing showed up in the lawn. But eventually he found a newly ripped hole in the board fence at our property line, about 60 feet out from the patio door. The torch head was never found as far as we know.

Years later, when I began engineering music recordings, I wondered if I should take into account some residual damage to my ears that I might not be aware of. So I had my hearing tested. The result showed that while both ears have a normal roll-off as frequency (and age) increases, the right ear has a dramatic dip in sensitivity in a narrow range at about four kilohertz. That is about the fundamental frequency of the top note on a piano. The audiologist asked what loud insults my ears had been subjected to over the years. Tom and Frances would have left fly with a wisecrack following a juicy invitation like that. But not thinking fast, I just mentioned the recurring ear infections I had as a young child, that only stopped for good when my tonsils were removed; and working on the Air Force flight line back in the 1960’s, usually with ear protection but not always; and playing strongly amplified music in various bands; and standing three feet from a deafening explosion when I was in high school. “Bingo!” he said. “There is your textbook trauma notch.”

The result, albeit rare, has been that my stereo imaging for a recording mix can sometimes be off. Depending on the harmonic content and the key, my right ear may report a momentarily weaker signal to the brain than my left ear, and if I adjust the mix balance to make that sound seem centered, it will sound way off center to everyone with normal ears. There have even been a few sounds that seemed to jump around in the stereo image, like an acoustic guitar player leaping to different positions on stage. But it is simple to check if things like that are real or artifacts: I swap the sound in the speakers or earphones between right and left, and see if any off-center sounds fail to shift by the same amount with the switch-up of the left-right assignment.

The good news is that my hearing recovered just fine for music and conversation during these five decades. I was not killed or maimed; none of us was. No blood was spilled. But sometimes it has crossed my mind that if my eyesight had been lost I might have become a far more dedicated musician and sensitive listener. Oh, the wasted hours and years in the visual world. Crazy thoughts! But maybe everyone has a few of those crazies locked away in a closet of the brain, where they really ought to stay.

Even as a fringe Unitarian with no need for a creed, contented with the unknown and unexplainable, I still find “why questions” arising from time to time, most often regarding extraordinary good luck rather than the other way around. Is reality emergent from nearly infinite little pieces unfolding to reveal this moment and the next and the next? Like the brain’s emergent intelligence from the networking of 100 billion neurons? Is it productive – is it even interesting – to ask if there is a Guiding Hand? Or does the very question miss the point that the miracle of existence is independent of how it works or how it got started?

Back to the story. Someone looked at Mom’s legs and noticed that there were little holes in her stockings as though they had been blasted by tiny pieces of hot material, myriad micro versions of the way nylon rope reacts to the heat of a cigarette lighter when you fuse the ends to prevent unraveling. The flame of the explosion must have gone her way, opposite the way the canister and its associated pieces had been thrown.

The upshot of the whole thing was that I felt lucky to be alive, and even now I take each day as a gift. I might not have woken up this morning, but in fact I did, and I can take the opportunity to question some of yesterday’s assumptions, decide afresh what needs to be done to make this day count, willing to move beyond my comfort zone. My knee jerk superego chimes in, “Don’t do stupid things.” But the mistake in this story wasn’t stupid, as in a stupor. It may have been hubris, and it certainly exemplified the danger in over-confidence that can come from “a little knowledge.” Speaking of which, within a week, I was back down to the library again, reading a lot more about acetylene. Sure enough, if the molecules are free to move around in the container and the pressure rises to greater than one atmosphere, they can go into a very exothermic reorganization reaction, releasing enormous amounts of energy … and it does not require any oxygen. Rising temperature can get it started too. I gave the canister excess pressure and a rapid temperature spike, and oxygen was in the canister: I had never purged it. A triple threat. The explosion was inevitable. So how do welding and cutting torch cylinders manage acetylene pressures? By special designs that restrict the movement of the unstable molecules, such as fiber packing materials with huge surface areas, and acetone into which the acetylene can dissolve. Any knowledgeable welder could have told me this, but I didn’t ask. And of course there was no internet to Google back then.

But what about that little safety valve, why didn’t it work? I found the following excerpt recently from a Navy aviation document online …

The acetylene cylinder is equipped with a safety plug, which has a small hole through the center. This hole is filled with a metal alloy which melts at approximately 212°F or releases at 500 psi. When a cylinder is overheated, the plug will melt and permit the acetylene to escape before a dangerous pressure can build up. The plug hole is too small to permit a flame to burn back into the cylinder if the escaping acetylene should become ignited.

So the answers are…

  1. The temperature in the high-volume, low-mass (thin-walled), belly area of the canister rose too fast to melt the escape valve alloy in the low-volume, high-mass (thick-walled), shoulder area; and
  2. The pressure only needed to rise to about 30 psi to cause an acetylene explosion in that propane canister, nowhere near 500 psi.

Parting thoughts: Don’t violate the law by trying to refill that kind of propane canister. If the label says don’t, then don’t. But what about my dad’s attitude regarding authority? Even though he was very much a law-abiding citizen and apt to say, “If you don’t like the law then get it changed,” I remember him sometimes railing against “the tyranny of the majority,” quoting Thomas Jefferson. When I was a little kid he lectured me about the Oregon legislature having no business outlawing firecrackers, saying, “If I injure myself, that’s my own damn business.” He didn’t mention forest fires on that occasion, nor the danger to children. But come to think of it, his two thumbs were not the same: one was a lot wider and shorter than the other. I questioned him about it a few times over the years, and he always down-played it, saying they had always been that way, then changing the subject. But I connected it with the story he told about holding a lit firecracker too long as a kid, and it blowing up in his hand. In fact he always liked fire, starting and managing a campfire, or the fireplace in our house. His big log dream house at “The Point” above Lucky Peak Reservoir was mainly heated by wood, and he died with seven cords cut, hand-split, stacked in the wood room, ready for the flame, which turned into a lyric line in one of the songs I wrote “with” him, so to speak, posthumously. I remember as a little kid when he took me over to the Washington State side of the Columbia River where fireworks were still legal, and we set them off on the boulders.  Of course he was young then, in his early 30s and full of enthusiasm for the pioneering spirit. Still, although he never spoke of it, I always imagined that he kicked himself for not taking a more direct interest in my acetylene project, even a supervisory interest, even a cease-and-desist interest in it! An involvement like that might have avoided a maiming or death that day in the garage, which thankfully was avoided anyway – by chance. 

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