News story on Foxnews about an explosion near a San Francisco mall.

“All of a sudden there was a big, big, big boom and the lights flickered off,” said Ellen, who joined other workers in a smoky stairwell as she made her way to the street from the 28th floor above the Ralph Lauren store. She wouldn’t give her last name, but said she worked for Charles Schwab.

“I thought it was a bomb,” she said. “It was very scary.”

The blast came from a vault that houses four Pacific Gas & Electric Co. transformers fed by a 34,000-volt electrical cable, said company spokesman Paul Moreno.

Ah! Explosion in a transformer vault. Be still my throbbing heart. This is the stuff dreams are made of!

The cause could not immediately be determined because a bomb squad was investigating, but Moreno said there have been vault explosions in the past.

No sh*t, Sherlock! We don’t like ’em, but they ARE a fact of electrical life. We do all sorts of testing and predicting, and we can, with a well-engineered and properly maintained sytem, reduce the number of these explosions, but they DO happen.

No utility workers were present when the explosion buckled a sidewalk and shot a manhole cover 25 feet across the street, according to Fire Chief Joanne Hayes-White.

We generally aren’t. Silly us! If we think the d*mned thing is getting ready to blow up, we haul major butt and shut it off!

Okay! Okay! I know THIS ONE!

Electrical disasters are both my hobby and my profession. Allow me a few points here.

34,000 volt cable. That’s a decent voltage level. Above that level, insulated cables get REALLY expensive and interesting to deal with. That’s also a huge amount of power. A cable with copper as thick as your thumb can carry multiple thousands of horsepower under perfectly normal conditions. That “normal conditions” presupposes that all the insulation in every component in the system is in good shape.

But sometimes, it isn’t. Solid insulations age and deteriorate. Heat, dirt and moisture accelerate their failure. Liquid insulation, the oil inside common transformers, it deteriorates also. Somewhere along the line, the insulation gets to the point that it can’t keep the high pressure of the electricity inside it under control, and it fails. Think of the electricity as the air inside a balloon. It’s all nicely contained. You can pinch off the neck and release the air nice and slow, with no sound. Or you can poke the balloon with a needle, rupturing the skin, and instead of a nice controlled release, you get a loud pop. In case one, you cna reuse the balloon. In case two, you can’t.

In electricity, that’s an apt analogy. The insulation fails, and instead of a nice, peaceful, useful steady flow, you get a pop. Except this pop is an electrical arc, a ball of plasma, ionized air hotter than the sun’s surface. In the immediate vicinity of that arc, metal is vaporized. Copper increases explosively in volume, 40,000 times, as it is vaporized. What isn’t vaporized is blown outward by the force of the fault, molten globules which can cause fires yards away from the fault site. The heat of the arc is sufficient to start fires on its own: Huge amounts of infrared energy are released. Think of the Mother of All Heat Lamps. Second and third degree burns are caused to exposed body parts in milliseconds.

In cases where the actual fault is inside enclosures like cabinets or, like this incident, vaults, doors and panels may be blown open or apart. I have personal knowledge of a man who died when he was hit by the cover of a transformer which faulted. His error? Walking up to the transformer to investigate the unusual noise it was making. The noise was the insulating fluid breaking down inside the transformer.

I’ve seen a cast iron manhole cover four feet in diameter blown into the air like a flipped coin from a cable fault. And this was just (JUST!) 4160 volts.

That’s why when **I** hear a funny noise or smell a funny smell, I get out of the area and start talking about isolating and de-energizing equipment. My company pays me well, but not well enough to put up with a close-proximity electrical explosion.

Another mess with which I had the pleasure of association was a 230,000 instrument transformer. This little jewel was in an outdoor substation. It was nine feet tall, a foot and a half in diameter, metal base on a pedestal eight feet off the ground, another six feet of glazed porcelain insulator, then a metal cap. Inside was a little transformer which changed the 230,000 volts on the high voltage power system to 120 volts to be used by the clients meters and protective relays. Surrounding the transformer inside that insulating column was a generous amount of transformer oil, a clean, clear fluid a little heavier and a bit less flammable than diesel fuel.

Well, the manufacturer of these devices had a problem, and there was a spate of failures, including mine. This one. Mine went one fine evening in an isolated part of the facility with nobody else around. The owner of the equipment was quick to detect the failure since half of a major oil refinery immediately went dark and dead. Dead, but NOT silent, as safety valves opened to depressure critical vessels and tons of hydrocarbons rushed to flare towers where they safely burned off in flaming plumes hundreds of feet long. But THAT was not MY problem.

That little transformer didn’t gently pop. It freakin’ exploded. That glazed porcelain insulating column? We’re talking about the same stuff as your bathroom toilet is made from, except my transformer’s insulating column was over an inch thick at its thinnest, and six feet tall. The biggest piece we found after the explosion was no bigger than a dinner plate. Pices as big as a man’s hand were blown two hundred yards from the origin. Pieces which struck nearby power transformers had sufficient force to puncture radiators, adding hundreds of gallons more oil on the ground to the original disaster. And pieces of porcelain from the explosion which struck the cast concrete wall of the nearby switchgear building broke out pieces of that concrete. It was quite the mess.

Fortunately for us, these events in outdoor yards aren’t too bad to clear up. We repaired the radiators on the power transformers. We replaced the exploded instrument transformer. We cleaned the nearby insulators which were covered with oily soot from the fire that followed the explosion. An environmental contractor succked up all the spilt oil and hauled off the debris which wasn’t necessary for the investigation into the failure. And we were back online in a couple of days.

Oh, the plant? It was back online in a couple of hours as electrical loads were shifted to redundant equipment designed for just this situation.

Indoor faults can be a much bigger problem. That vaporized copper condenses on everything, along with carbon from burnt plastic and rubber insulation. That all has to be removed. The source of the vaporized copper, the current carrying components of the equipment, that has to be repaired or replaced. Bent, twisted and torn structural components must be either repaired or replaced.

This is usually a nasty, dirty job, often in sweaty conditions, and usually in a big hurry. But we do it. Sometimes we do it fast and somewhat jury-rigged (but safe!) to get a client out of a bind until we can come back and do a permanent job. Sometimes there’s not enough there to save, and we pull in our resources to get new equipment delivered to the site so we can go back online.

But one way or another, we get the job done. And the lights go back on, and the pumps start pumping, and the mixers start mixing, and various strange chmicals start mixing and splitting and changing, and somewhere down the line, out comes your plastic lawn furniture or whatever…

Aren’t you glad?