A Balloon Makes the Lights Go Out in San Francisco, and We Ask: Just How Does That Work?

More than 4,700 PG&E customers in San Francisco lost power Wednesday afternoon when a bunch of Mylar balloons hit a power line. KQED happened to be one of those customers (it's OK; essential TV and radio operations have back-up generators), so we began to selfishly wonder: How, exactly, do balloons cause power outages?

It turns out there are two ways. The first is if the balloon makes contact with two power lines. Since they're coated with a thin layer of metal, they conduct electricity between the lines and create a short.

"It's kind of like letting the lightning out of those wires," explains Joe Molica, a spokesman for PG&E. (I don't watch "Breaking Bad," but apparently this is a notable—spoiler and profanity alert—example.)

The other way is if the balloon's metal streamers come in contact with something else, creating a ground that the electricity travels down.

Either way the power lines can be damaged, circuit breakers trip and the power goes out. So there are two elements to restoring power: resetting the breakers and repairing any damage. On Wednesday two lines came down. PG&E got most customers' power back within about half an hour, but 75 were in the dark for about five hours.

Balloon vs. power line incidents have more than doubled in PG&E's territory in the past 10 years. There were nearly 300 last year, and the utility says they're seasonal.

"The busiest time of year for these type of accidents is basically Valentine's Day, right around Mothers' Day and the weeks around graduation," Molica says.

In 2008, there was a bill moving through the Legislature that would have banned metallic balloons because of the problems they cause for power companies and their customers. It was opposed by the balloon lobby—there actually is one—and eventually vetoed by then-Gov. Arnold Schwarzenegger. A 1990 state law requires that metallic balloons come with weights attached to keep them from floating away into power lines.