Search operations continue after fatal blast at Pennsylvania steel plant

Let's turn now to another breaking story our team's been following. At least one person's been killed in an explosion at a steel plant in Pennsylvania. And we've learned several others have also been injured.This happened at a US Steel facility just south of Pittsburgh. A county spokesperson tells NBC News an unknown number of people are still trapped somewhere inside that rubble. NBC's Maris Francis is following this one for us.Uh Maris, I know this is a fluid story, but what more do we know about this exp ...