Investigators work at the site of a destroyed fertilizer plant in West, Texas, Thursday, May 2, 2013. Investigators face a slew of challenges in figuring out what caused the explosion at the fertilizer plant that killed 14 people and destroyed part of the small Texas town. (AP Photo/LM Otero, Pool)

Associated Press
Investigators work at the site of a destroyed fertilizer plant in West, Texas, Thursday, May 2, 2013. Investigators face a slew of challenges in figuring out what caused the explosion at the fertilizer plant that killed 14 people and destroyed part of the small Texas town. (AP Photo/LM Otero, Pool)
Investigators work at the site of a destroyed fertilizer plant in West, Texas, Thursday, May 2, 2013. Investigators face a slew of challenges in figuring out what caused the explosion at the fertilizer plant that killed 14 people and destroyed part of the small Texas town. (AP Photo/LM Otero, Pool)