Here’s an update Ken Ward Jr. called in from federal court this morning.

A mine safety expert for the federal government continued testifying this morning as the criminal trial of former Massey Energy CEO Don Blankenship entered into the second day.

Longtime Kentucky state mine investigator Tracy Stumbo explained to jurors how mine companies must build various structures underground to direct clean air from mine fans and separate it from dirty air contaminated with methane or coal dust.

Stumbo described one type of structure called an overcast, which carries clean air in one tunnel over an intersection with another tunnel that contains dirty air.

“Its just a way to let the air come up over the track,” Stumbo testified. “Its an intersection just like you’d have over a road.”

Stumbo also explained the process that mine examiners, or firebosses, are supposed to use to check mines for potential hazards.

“They’re looking for anything unusual, anything hazardous,” Stumbo said. “Things can change in a minute in a coal mine. Many things can happen.”

Also this morning the front row of the courtroom was filled with a handful of family members of the miners who died in the Upper Big Branch Mine disaster.

Stumbo said that as underground mines dig further and further, expanding into many miles of tunnels, it takes more workers to check for safety hazards and fix any that are found.

“You’ve got to have several people working on ventilation, several people rock-dusting every day in these large mines,” Stumbo said.

As Assistant U.S. Attorney Steve Ruby began to ask Stumbo about a huge map of the Upper Big Branch Mine, Blankenship got up from the counsel table and walked across the courtroom so he could see the map, eventually taking a seat immediately next to the jury box.