CHARLESTON, W.Va. – CHARLESTON, W.Va. (AP) — The underground search for clues to the nation's worst coal mining disaster in 40 years started Wednesday as two teams began exploring the West Virginia mine where 29 men died in an explosion in April.
The four-member exploratory teams are trying to determine if it's safe for government investigators to begin working underground at Massey Energy Co.'s Upper Big Branch mine. The April 5 explosion is the subject of separate civil and criminal investigations.
Massey called the re-entry an important step to finding out what happened at Upper Big Branch.
Critics from organized labor to members of Congress have questioned Massey's safety record, and the Richmond, Va.-based company has consistently rebutted charges that it puts profits ahead of safety.
Federal and state regulators are eager to begin looking for clues to what caused the April 5 explosion. No one had entered the sprawling southern West Virginia mine since rescuers removed the last of the dead in April.
Wednesday's re-entry was not without problems.
The teams made it about 1,000 feet into the mine before turning back about 10:45 a.m., federal Mine Safety and Health Administration spokeswoman Amy Louviere said. The teams of government and Massey employees retreated after about an hour underground because handheld meters registered potentially elevated levels of toxic carbon monoxide and explosive methane gas.
They went underground again several hours later after analysis of samples collected during the first visit showed the mine was safe to re-enter, Massey said.
High levels of carbon monoxide can indicate the presence of a mine fire, but Louviere said the source of the gas is not known.
The aim of the initial visit is to explore the mine and collect air samples. MSHA wants a borehole drilled to improve ventilation before investigators attempt to reach the area where the men killed in the blast were working. Louviere expects the borehole to be finished by Thursday.