Channel-surfing this morning, on three separate occasions I happened on an NBC reporter, live from the latest big wildfire in southern California.
She was about as close to the fire as she could get, with smoke drifting through and hints of flame in the background. The report had "B-roll" shots from even closer, nightmarish images.
But what kept giving me the shivers was the immediate background for the live report: A downed high-tension power line, the pole slanting away from the viewer's lower left to center screen, with a couple of crossarms making a steeper angle from lower right to upper left, big insulators gleaming, fat cables in slack catenaries crossing behind her making a dramatic scene--
Dramatic and potentially fatal. A downed live power line does not always arc, smoke or hum. Electricity itself has no color, no smell, no sound. Not every inert-looking wire is dead. Power companies do not protect the high-voltage lines with the kinds of fuses and circuit breakers that trip once and stay off until reset. They use "reclosers:" gadgets that open on a fault, wait some set amount of time, re-energize and try again, over and over. It takes less human intervention and most faults -- a swinging branch, an incautious squirrel, a Mylar balloon -- will clear themselves. Your lights at home flicker a little, maybe go out and come right back on.
You not only can't tell if a downed power line is live or not, you can't even count on it to stay off! California electric utilities routinely shut off power in lines feeding fire zones, especially if there's an evacuation. They (somewhat reluctantly) shut them off in high-risk areas during fire season; power grids allow a certain amount of re-routing, though it takes extra effort. Re-routing can light up a previously-off downed line, too; there's nothing magical about monitoring a power grid and the central control at even the most up-to-date utilities have only a limited picture of what's going on.
The voltage gradient from a downed power line tapers off gradually with distance, in a logarithmic or inverse-square way. The current is limited by the resistance of the soil, and current across a resistor gives us a voltage differential. The reality of this rough math means if you're too close, even standing with your feet too far apart can be fatal. Holding onto a microphone connected to a wire plugged into a camera that is itself connected to a van some distance away will be fatal if the juice comes back on. Oh, maybe she's got a wireless mic; maybe the camera is plugged into a video-over-cellular backpack. Maybe -- and even then, maybe a long step to get back to the news van and make ready for her next live report will be her last.
In most TV markets, the news photographers (don't call 'em "cameramen," they're photojournalists), any tech who runs a remote truck and as many live-news reporters as can be rounded up and made to hold still for an hour are subjected to regular training sessions on the dangers of overhead* and downed power lines. The industry didn't used to do 'em, but a string of fatal and near-fatal accidents over thirty years ago caused our insurance carriers to insist. The NBC crew ought to know better. I hope they don't learn better the hard way.
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* Overhead? Way up there? Yes indeed. For a terrestrial microwave link, those trucks carry tall pneumatic masts that will easily reach power lines -- if the operator was fool enough to park under them. Filling in on an ENG shift, I was once waved into a spot at the State Fairgrounds, started the mast up, grabbed a reel of audio/video cable and stepped out of the truck to run it into the venue -- only to look up and see they'd put me right under a ridiculously low power drop. I darned near broke a wrist, flailing for the air compressor shutoff, and had a short, heated discussion with the well-meaning Fairgrounds worker.
Update
5 weeks ago
5 comments:
And "uninsulated". Including the feeder lines that are sometimes on the top of local power poles.
Ever see the videos of the crews that work on the hot lines from helicopters? I know it's safe, but man, those guys must clank when they walk.
Our city had a live truck mast accident in the late 1990's with two people from one of the other stations in town. Both survived, but were disfigured horribly.
Our two live trucks are used exactly six times a year, and I am the only one operating them. I still look up, even though I know I'm in an empty field. When we had more operators, we did the yearly training...written test followed by a checkride, and all were taught how to bunny-hop to safety if something happened.
They can turn off the auto-reset of those high power lines, and have started doing so her in Colorado if wind conditions etc. are being labeled as "dangerous". I get emails about this from the local power company warning that instead of the lights flickering and coming back on, that any outage will last for 2-3 hours as the linemen check why a line tripped it's breaker in case the line caused a fire.
Chris: inconvenient as that is, it's much better than starting a wildfire. CA and CO face similar challenges in burying electric utilities, though in places with high population density and high fire risk, it's the best option. (Also expensive and messy; years ago, the power, phone and cable companies in fast-growing Hamilton County, IN had weekly tally-ups, swapping out accidental cuts to buried service until they could work out who owed whom and settle up. Despite marking and best intentions, you could count on several every week.)
Comrade Misfit: What has always caught my attention is the amount of things a utility linesperson can do -- and prefers to do -- from the ground using a long insulated "hot stick" with various specialized attachments. I got to see a guy swap out insulators on a very tall pole -- over 30 feet! -- that way. They'd rather do that than go up in the bucket, despite excellent insulation: it's a lot easier to get out of the way when you;re working from a distance.
Grich: amen!
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