The explosion is from the beginning of the 1988-1989 season, when Carter McKay first shows up and moves in to Ray's house. The main arc at the beginning of the season was the "Ewing-McKay range war" over disputed Southfork land. I don't recall the details, but the explosion itself is a big deal in the context of the arc, as Miss Ellie finally gives the go-ahead to the boys to blow up the dam on the Southfork side of the disputed land.
People say the show was shit after the dream season, but this arc (the range war) in particular was an excellent string of episodes and even brought Ray Krebbs back for a few episodes after initially exited the series.
But yeah, it's completely obvious in War of the Ewings
that he's started dying his hair; even my mom, at the time it was first broadcast was disappointed as she'd always liked his silver hair during the series.