Above watch: Investigators believe a relay used to control street lights was to blame for an underground fire last year that plunged a large portion of the downtown core into darkness. Doug Vaessen reports.
CALGARY – Investigators believe a relay used to control street lights was to blame for an underground fire last year that plunged a large portion of the downtown core into darkness.
Thousands of people were left without power for five nights after the fire sparked under a manhole in the area of 8th Street and 5th Avenue S.W., severely damaging electrical systems.
On Friday, officials released the findings of an investigation into the October 11th fire.
Although they were able to determine it was a relay that sparked the blaze, Investigators say they haven’t been able to determine exactly what caused the relay to fail.
“The exact cause of the fire is difficult to determine due to the extent of damage caused by the fires,” said Deputy Chief Ken Uzeloc with the Calgary Fire Department.
“Investigators spent a fair amount of time sifting through the debris and reviewing the contents of the manhole,” he added. “However, they were unable to determine why the relay failed or why the failure resulted in a fire.”
What exactly is a relay?
A relay is an electronic circuit that uses a mercury sensor or a photo-electric sensor to switch street lights on and off.
There are approximately 10,000 relays around Calgary controlling approximately 90,000 street lights.
All relays in the downtown core are located in ENMAX manholes while relays outside the core are located on street light poles in weather-rated boxes.
External factors such as weather, temperature and the number and type of lights activated by a relay, impact its lifespan, but on average they last 30 years.
What is the City of Calgary doing to prevent this from happening again?
Logan says The City is taking steps to reduce the likelihood of a similar event happening again by replacing all mercury-based relays in the downtown core over the next six months. Older relays will be replaced first.
The City is also relocating all relays in the downtown core from manholes to light poles, to allow for easier access.
In 2014, approximately 60 relays underwent maintenance or were replaced as part of infrastructure projects such as the Edmonton Trail construction project and the 13 Avenue Heritage Greenway project in the southwest.
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