In episode 4.04, Elongated Journey Into Night" Ralph Dibny is "discovered" as one of the metas to be transformed on the bus where Barry came out of the Speed Force. This is supposedly his first encounter with the Dark Matter.
However, back in episode 1.09, "Power Outage", Farooq aka Blackout, confronted Wells, who began naming people killed/harmed during the particle accelerator explosion, including one Ralph Dibny.