Ottawa·CBC Explains

What's an 'arcing flash,' and why is it ruining your commute?

Loud bangs. Flickering flames. Showering sparks. 'Arc flashing' can be scary for passengers and even cause damage to trains, but don't panic, the city says.

No danger when sparks fly on Confederation Line, city assures LRT passengers

Two LRT trains pass beneath the electrical lines that power Ottawa's Confederation Line on Jan. 21, 2020. (Adrian Wyld/Canadian Press)

Riki Philogene was on his way to work on Ottawa's Confederation Line Saturday afternoon when he was startled by what sounded like a gunshot.

He and his fellow passengers on the westbound train froze, and as they approached Tremblay Station, they heard the sound twice more. Then sparks began showering past one of the windows.

"When we saw the sparks, that's why we were like, OK, lets just leave the train. Because you don't know what's going to happen next," Philogene told CBC.

Riki Philogene was on an LRT train on Saturday when he heard several loud noises, followed by what he describes as sparks coming from somewhere on the vehicle's exterior. 0:54

Meanwhile, nine stops to the west, Melanie Grant stood on the platform at Tunney's Pasture station, waiting for a train. Suddenly, she spotted a flame flickering where the arm atop a stationary train across the tracks met the power cable above. She and the other people on the platforms edged away nervously, unsure what was about to happen next.

"I mean, we were told there would be growing pains and stuff, but I wasn't expecting to stand on the platform and think, oh, what if that explodes?" Grant said. 

Since those incidents on Saturday, city officials have said emphatically that the public was never in danger from what they and Rideau Transit Maintenance (RTM) are calling "arcing flashes."

Riki Philogene said he and other passengers fled the LRT train they were riding Saturday when they heard loud bangs and saw sparks cascade past a window. (Matthew Kupfer/CBC)

Wet weather to blame 

Arcing flashes happen when the arm that extends from the train, called the pantograph, loses contact with the power cable above, or the catenary. That loss of contact is what causes the loud bang and the sparks, and causes the trains to lose power.

The phenomenon is common in train systems with overhead electrical power, according to Troy Charter, the city's director of transit operations. But the issue has only been causing LRT delays since late December, and first came to the public's attention during a particularly long delay on New Year's Eve.

At the time, city and LRT officials blamed a buildup of dirt on the electrical components of the trains.

"This is something that with proper maintenance should not have occurred," Charter told the city's transit commission just last week. In response, RTM assured commissioners it had stepped up efforts to clean and inspect the trains, and the problem seemed to have been resolved.

In a memo Monday, OC Transpo boss John Manconi assured councillors the root cause of the arcing flashes is under investigation. (CBC)

But two days later, during Saturday's snowstorm, it happened again.

"The vehicles appear to be more prone to these failures during wet or inclement weather," the city's transit manager, John Manconi, wrote in a memo to council Monday. The root cause of the issue is still under investigation by RTM, Manconi wrote. 

Trains damaged

While Manconi said he recognizes the incidents cause inconvenient delays for passengers, arcing flashes are actually a sign the system is working properly. Like a circuit breaker in your home, the trains are shutting down as a defence mechanism against damage from irregular voltage.

The trains often do sustain damage and require repairs after arcing flashes. Such was the case on New Year's Eve, when officials described what looked like a burn mark on the train's roof. They also replaced some of the electrical components out of an "abundance of caution," Rideau Transit Group CEO Peter Lauch told the transit commission last week.

In other cases, the required repairs are more substantial, which contributed to this week's ongoing train shortage.

The city has promised to release more information about any further measures needed to fix and prevent arcing flashes once they're confirmed by RTM.

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