UPDATED 04/10/12 9:17 a.m.

CHICAGO (CBS) — Busy Grand Avenue was shut down for a time on the city’s West Side Tuesday morning, after an explosion in a ComEd vault blew off a manhole cover.

CBS 2’s Kris Habermehl reports just as the morning rush was beginning, the manhole cover flew off as a small fire broke out in the ComEd vault below.

Grand Avenue was closed between Armitage and Laramie avenues following the explosion. The street had reopened by 7:30 a.m.

The Fire Department caused a Level 1 Hazardous Materials response for the explosion, which happened outside a ComEd substation.

No one was injured, and the Fire Department had turned the scene over to ComEd by 7:30 a.m.

Fire Media Affairs Director Larry Langford, who said the explosion might have resulted from a power load issue.

Speaking to the the Sun-Times Media Wire, ComEd spokeswoman Tabrina Davis characterized the incident as a cable failure, which cut power for about 3,500 customers in the area around 6:50 a.m.

Power was restored for all the affected customers as of 7:35 a.m., she told the wire.