From the article:
At least 800,000 people in the United States live within a mile of 440 sites that store potentially explosive ammonium nitrate, which investigators say was the source of the explosion in West, according to a Reuters analysis of hazardous-chemical storage data maintained by 29 statesA click on the facility brings you a local view showing the potentially vulnerable population. Below is the West Fertilizer Company with six schools within the mile radius.
*West, Texas is not in West Texas - a fact that bothers me and probably not many other people.
** The geographic pattern of non responding states and those that refused is kind of curious.