The builders of the Réseau express métropolitain revealed on Wednesday that leftover explosive material from the century-old Mount Royal tunnel’s original construction detonated in July.

No workers were injured by the explosion, which along with the pandemic, has meant that construction of the Mount Royal tunnel portion of the project will be delayed by up to 18 months.

“People in general are disappointed, but no one is really very surprised (about the delay),” said Francis Millaire, a spokesperson for commuters using the Deux-Montagnes train line, which has pushed the government to improve its plan for alternative transit service during the tunnel closure. “This is why we were so concerned about mitigation measures, because everyone knew this would impact our lives for a long period of time.”

Service on the Deux-Montagnes Line from Bois-Franc to Central Station was stopped in May when the tunnel was closed to be refurbished, as two stations will be built underground — connecting to the McGill and Édouard-Montpetit métro stations.

The explosion happened in the tunnel near Town of Mount Royal on July 21 when heat from drills came into contact and ignited explosive material left over from the tunnel’s original construction in between 1912 and 1918.

Work was interrupted until recent days so that new safety measures could be put in place for workers, Jean-Marc Arbaud, the managing director of CDPQ Infra, told reporters in a briefing. REM builders worked with officials from the province’s workplace safety board, the CNESST, to put in place the additional safety measures, because there remains a risk of further explosions, CDPQ Infra officials said.

Keep reading in the Montreal Gazette