On April 17, when 30 tons of fertilizer detonated in West, Texas, a shock wave traveling faster than the speed of sound crushed homes. Windows shattered seven miles away. The United States Geological Survey recorded a 2.1 magnitude tremor from the blast.
Fifteen people died, 12 of them firefighters and emergency responders, and 200 were injured.
The same chemical that blew up West — ammonium nitrate — is manufactured in Donora, Pa., 20 miles south of Pittsburgh.