two separate reactors. is that as frightening as it sounds? explain to me, when we talk explosion, what really happens? >> well, the explosions were a result of the accumulation of hydrogen gas in the floors of the reactor building above the containment area. the hydrogen is a product of a nuclear reactor that's in trouble. when the fuel rods are not covered completely with water, they get very hot. there's steam in the environment. a combination of steam and the metal colliding with the fuel results in a chemical reaction that produces hydrogen. that hydrogen can't burn inside the containment, but they've had to vent the containments because they're getting so pressurized. that hydrogen is getting out into other parts of this building, and oxygen plus hydrogen makes for a very explosive mixture. >> it's oxygen and hydrogen. that's why we've seen some of