PHILADELPHIA, Pa. -

A Philadelphia City Councilman says a cigarette may have led to an explosion that took out a row home.

Councilman Mark Squilla says witnesses told him a contractor that was working on the home lit a cigarette before the explosion.

However, Mayor Michael Nutter says that's pure speculation.

Officially, inspectors say a gas leak triggered the explosion.

The contractor had been working on a water heater.

Squilla says the blast blew the contractor out of the first floor of the home.

The contractor suffered severe burns.

Seven other people suffered only minor injuries.