The autumn morning is sunny with heavy crowds using the several subway trains. It is a perfect day for shopping at the mall and other shopping areas around the city. As passengers are boarding a subway there's an explosion that rips the on-coming train apart.  Panic gets over most of the crowd.  Various minutes there's another explosion in the station.  More panic.
A security guard quickly dials 9-1-1: "I'm calling from the Waldorf Station. We've just had an explosion in station and one on a train." Everybody's screaming. I don't know how many are injured... People are injured and some appear to be quite serious! "

Based on the over description, what type of disaster do you believe happened at this instance?