UPDATED 06/14/11 1:33 p.m.

SOUTH HOLLAND, Ill. (CBS) — A buildup of gas is being blamed for an explosion in a reservoir drop shaft, which blew debris in all directions and ripped down a utility pole.

Cars were damaged, but no one was injured.

Just after 6 a.m., the South Holland Fire Department responded to a reported explosion at 169th and State Street, a release from the department said. The explosion occurred in an existing drop shaft of the Metropolitan Water Reclamation District, a section separate from the Deep Tunnel project.

A portion of the tunnel, which directs sewer overflow into area reservoirs, runs through South Holland near that location.

According to Fire Chief Don Bettenhausen, “the cause of the explosion appears to a build-up of gas in the MWRD’s tunnel shaft.” It appears that energy from the blast traveled north from the point of origin, he said, but debris was spread in all directions.

Bettenhausen said he heard and felt the explosion from his home about a mile away, reports WBBM Newsradio 780’s Bernie Tafoya.

MWRD director of engineering Kenneth Kits says a build-up of methane gas is the suspected cause of the explosion but that, because “we can’t get down in the shaft at the present time”, it’s too early to tell what the cause might have been.

There were no reported injuries, according to the fire department and the MWRD, but some cars in the industrial area were damaged by debris. There also was no fire, MWRD spokeswoman Patricia Young said.

“We’re very grateful nobody was hurt,” she said. “Our main concern right now is to keep the public away from the area.” She noted there is a 240-foot deep drop shaft at that reservoir.

Bettenhausen says it’s fortunate the explosion happened so early in the morning when not many workers were around.

LISTEN: Newsradio 780’s Bernie Tafoya Reports

CBS 2’s Kris Habermehl reports debris was seen strewn around the concrete-line caisson where the explosion happened, and large items appeared to have blown out of the hole.

Feet away from the shaft, a utility pole had been snapped off by heavy girders that came down.

Bettenhausen says surrounding areas were checked for any build-up of gas and none was found.

“We’ve conducted precautionary air monitoring, and fortunately there is no danger to residents and businesses in the surrounding areas,” Bettenhausen said.

The vent shaft where the explosion happened is linked to a reservoir system that handles water from any flooding from nearby Thorn Creek.

The Sun-Times Media Wire contributed to this report.

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