Dallas Fire-Rescue Chief Justin Ball provided new details Friday about the moments leading up to the deadly apartment explosion that claimed three lives Thursday. Responding to a gas leak report, the first four firefighters reached the complex within two minutes, Ball told reporters. Over the next 10 minutes, the crew followed standard safety procedures: they blocked off the street, searched for the source of the leak, put on protective equipment, and established a water supply — all while preparing to begin evacuating residents.

“Right before they were going to enter and evacuate, it exploded,” Ball said. The blast leveled part of the building in a fireball that killed three occupants and left several others injured. Search-and-rescue teams continued working into Friday to ensure no additional victims remained in the rubble, officials said.

Ball’s description paints a picture of a near-miss for the responding firefighters, whose discipline in following safety protocols kept them outside the structure at the critical moment. “Heroics” was the word the chief chose Friday to characterize their conduct in the face of a routine call that escalated without warning.

The cause of the gas leak that fueled the explosion remains under investigation, and Dallas Fire-Rescue has not released the identities of the deceased. The Associated Press first reported the blast on Thursday, and MSI carried an initial account the same day.