Sonya Rockhouse's son Daniel was on the loader when the first explosion hit.
The team reached an area known as Pit Bottom in Stone.
It was found on the walls and roof of the tunnel.
"The information that they've uncovered is of national importance."
"This shows that we can get in and we can get evidence out."
"It's another momentous day."
It's the first time they passed it since 2011.
Four people are going in.
They can go further than the 170m mark.