Concrete crashed onto a Washington, D.C., train station platform during the evening rush hour Nov. 17, but no one was injured.

Investigators are checking why the chunks of concrete fell from the ceiling of the Farragut North Metro station in downtown Washington, D.C., an underground Metrorail station.

The largest chunk was the “size of a human head,” says a Washington, D.C,. fire department spokesperson.

The concrete fell approximately 25 ft to the platform, creating a debris field that was 20 ft across, he said. No one was injured.

Investigators are homing in on the possibility that construction crews doing roadwork on Connecticut Avenue, directly above the station, could have triggered the incident, says John Lisle, spokesperson for the District Dept. of Transportation.

“Our engineers believe that the work our contractor was doing on the surface dislodged a piece of concrete that fell down a shaft,” he says. “We are still investigating it.”

Fort Myer Construction of Washington is the contractor. A company representative deferred to DDOT for comment about the incident.

Crews are building a new raised center median on Connecticut Avenue. Lisle says that crews and Metro engineers met prior to construction on Nov. 15 and that crews were aware of the need to stay a “safe distance” from ventilation shafts.

“We’re trying to figure out exactly what information we were we given, was it accurate and did we follow it accurately,” he says.

Lisle estimates that crews were digging no more than 8 in. into the roadway and that the tunnel ceiling is roughly 15 ft below the surface.

Following the incident, roadwork was halted and Connecticut Avenue was closed to traffic in the section above the station. The street reopened later the night of the accident and the station reopened the next morning.