Manhole Fire Investigation Concluded

The investigation has concluded into the October 11, 2014, electrical fire in a downtown manhole.

Investigators believe the origin of the fire was a relay used to control street lights. Due to the extent of the damage caused by the fire and a subsequent blaze a few hours later, investigators cannot determine what caused the relay failure.

“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. “Investigators spent a fair amount of time sifting through the debris and reviewing the contents of the manhole. However, they were unable to determine why the relay failed or why the failure resulted in a fire.”

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.

Mac Logan, General Manger of Transportation, said The City of Calgary has never experienced a relay failure that has resulted in a fire.

“In the past, relay failures have resulted in street lights either not coming on or staying on in daylight hours,” said Logan.

Given the normal lifecycle of relays, external factors such as weather, temperatures and the numbers and types of lights activated by a relay, the relays last on average 30 years. 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.

The City has a contract with ENMAX’s subsidiary ENMAX Power Services Corp (EPSC) to maintain the street light system.

Logan said while the cause of the fire remains unknown, The City is taking immediate steps to reduce the likelihood of a similar event occurring 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 to street light infrastructure and reduce traffic disruptions required when accessing manholes.

The City is using opportunities provided by other projects in five locations in the downtown core where street light infrastructure is being upgraded and replaced. As that work occurs, the relays controlling those streetlights will be relocated.

“We recognize this incident had an impact on residents and businesses,” said Logan. “We want to thank Calgarians for your cooperation and understanding as first responders worked to ensure everyone’s safety and as crews work over the next several months to enhance our systems.”