Following a walk-through on June 25 and June 28, the Mine Safety and Health Administration (MSHA)  federal team investigating the April 5 explosion at the Upper Big Branch Mine will begin its underground examination this week.

Investigators previously had been prevented from beginning their physical probe underground due to conditions resulting from the explosion.

On June 24, mine rescue teams wrapped up a nearly month-long effort to explore the mine and ensure that it was safe for investigators to proceed underground. During that time, MSHA, the state and the mine company engaged in a series of mine rehabilitation efforts, including drilling boreholes and repairing damaged ventilation systems. Rescue teams also discovered an active hot spot and several previous hot spots during their exploration of the mine that may have accounted for high concentrations of toxic gases.

“A critical component of this investigation has now begun,” said Joseph A. Main, assistant secretary of labor for mine safety and health, in a press statement. ”Along with the already extensive witness interviews that have been conducted, the physical examination of the mine hopefully will provide answers to the cause of a tragic explosion that has affected so many lives.”

The underground investigation will consist of several different teams with specific expertise: mapping, dust survey, electrical, photography, flames and forces, geologic and evidence gathering.

The federal agency, along with West Virginia’s Office of Miners’ Health Safety & Training, has outlined specific protocols to ensure the preservation of evidence. All team members will follow these protocols to ensure the integrity and confidence of the evidence collected in the mine:

The members of each team will remain together at all times while inside the mine. They are permitted to take notes during the investigation. One map only will be produced by each mapping team for each area of the mine and will be distributed to each party at the conclusion of each shift.

MSHA representatives will collect evidence such as mine dust samples and will take steps to ensure that evidence is not disturbed during the sampling or mapping process. Samples are to be taken out of the mine at the end of each shift. These samples will be transferred to MSHA investigators on the Evidence Gathering Team, which will store all samples in a secure location.