A team of US Federal investigators are expected to launch an underground mine examination next week at the site of the Upper Branch mine explosion in Arlington, Virginia, US.

Last week the mine was declared safe for investigators to proceed following the explosion which killed 29 miners.

During their exploration, rescue teams discovered an active hot spot and several previous hot spots that may have accounted for high concentrations of toxic gases, the Mine Safety and Health Administration (MSHA) said.

“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,” MSHA assistant secretary of labor Joseph Main said in a statement.