Teams from Massey, the US Mine Safety and Health Administration and the West Virginia Office of Miners’ Health, Safety and Training went into the mine at about 7.45am local time Tuesday.

“They will continue to explore the initial entry areas of the mine,” the company said.

“Air sample readings continue to indicate that conditions in the mine are stable.”

Federal officials said at about 2pm that the crews were still underground as of that time at the mine’s North portal.

“They explored in the North Mains area and seal sets along the North Mains,” MSHA said.

“As of 1pm, teams continued to explore in North Mains. Seal sets No. 6 and No. 7 have been examined and no issues of significance have been identified at this time.”

MSHA confirmed that Monday’s re-entry lasted from 8am to 4.30pm and that teams did not find elevated levels of carbon monoxide or explosive methane gas.

“Mine rescue teams entered the North and South portals … to explore outby areas,” the agency said.

“They found no elevated gas readings and are following the prescribed plan for re-entry and exploration. The teams examined the No. 1, 2, 3, 4 and 5 sets of seals and reported no problems.”

The initial re-entry into UBB was made last Wednesday, in the first attempt since the 29 workers killed in the blast were removed from the mine in April.

While that first attempt was thwarted briefly by elevated gas issues recorded on handheld meters, investigators returned later that day and re-established portal-to-portal phone communications.

Massey had intended to attempt an entry into the mine last Friday, but the drilling of a ventilation shaft delayed the timeline. That borehole, measuring approximately 1100 feet, was completed over the weekend, the producer said.

Keep reading ILN for further updates on the investigation of the Upper Big Branch explosion.