NEW YORK (Reuters) - At least 800,000 people across the United States live near hundreds of sites that store large amounts of potentially explosive ammonium nitrate, which investigators are blaming as the source of last month’s deadly blast at a fertilizer plant in West, Texas, a Reuters analysis shows.

The remains of a fertilizer plant burn after an explosion at the plant in the town of West, near Waco, Texas, in this April 18, 2013 file photo. The deadly explosion injured more than 100 people, leveling dozens of homes and damaging other buildings including a school and nursing home, authorities said. REUTERS/Mike Stone/Files

Hundreds of schools, 20 hospitals and 13 churches, as well as hundreds of thousands of households, also sit near the sites. At least 12 ammonium-nitrate facilities have 10,000 or more people living within a mile.

Fourteen people were killed and about 200 injured April 17 when a fire at West Fertilizer Co. was followed by a massive explosion. Ten of the dead were first responders from area fire departments.

The explosion destroyed an apartment complex and nursing home that sat within a few hundred yards of the fertilizer plant, damaged homes within a half mile of the plant and cracked windows even farther away.

Investigators say ammonium nitrate stored at the plant was the source of the explosion, but they have not identified the cause.

Since 1990, companies have reported more than 380 incidents involving ammonium nitrate to the National Response Center, a federal agency that collects reports of spills, leaks and other discharges within the United States. Eight people were killed, 66 injured and more than 6,300 evacuated in those incidents, according to the center’s data. But reporting is voluntary, and center officials say the records cover only a fraction of all incidents.

Reuters’ analysis of hazardous chemical inventories found schools, hospitals and churches within short distances of facilities storing ammonium nitrate, such as an elementary school in Athens, Texas, that is next door to a fertilizer plant. The Hiawatha Community Hospital in Padonia, Kansas, is less than a quarter-mile from one site and three-quarters of a mile from another.

The Athens school district said it is reviewing its emergency plans now, but until a reporter called on Friday had not considered the potential danger from the fertilizer plant.

“It’s amazing how a tragedy like West makes us rethink things,” said Janie Sims, assistant superintendent. “Who would have even mentioned it or thought of it before?”

Some sites are in heavily urbanized areas. Acid Products Co. in Chicago, which reported storing between 10,000 and 99,999 pounds of ammonium nitrate in 2012, is surrounded by about 24,000 people. Company officials declined to comment.

The number of people affected nationwide, as well as the count of nearby hospitals, churches and schools, are likely higher because Reuters was unable to get information from all 50 states.

Reuters spent about four weeks obtaining copies of hazardous-chemical inventories, known as Tier II reports, collected by states under the federal Emergency Planning and Community Right to Know Act. Twenty-nine states provided information, identifying 440 sites. Not all sites in those states were included in the analysis because of incomplete location information.

Reporters used mapping software, combined with Census and other data, to identify the nearby population, schools, churches and hospitals.

Of the 21 remaining states, 10 declined to provide their data, one declined to provide it in electronic form, and the rest either provided incomplete information, did not respond, do not maintain the filings electronically or are still considering the requests. Federal law allows 45 days to provide the information.

Among those that withheld data was Missouri, which The Fertilizer Institute, an industry association, said is the No. 1 user of ammonium-nitrate fertilizer in the United States. The group said Missouri accounts for 20 percent of the nation’s use of the product.