(CNN) -- The fertilizer plant that blew up in Texas last week warned state and local officials but not federal agencies that it had 270 tons of highly volatile ammonium nitrate on site, according to regulatory records.

The April 17 fire and explosion at West Fertilizer Co. killed 14 people and devastated the small town of West, Texas. Investigators have said they're not sure how much ammonium nitrate was actually on site at the time of the explosion, however, since plant records were destroyed in the blast.

The company sold ammonium nitrate and anhydrous ammonia, both commonly used as fertilizers. It had notified state and local emergency management officials of its stock of both in its most recent declaration of hazardous chemicals, filed in February.

However, the risk management plan it filed with the federal Environmental Protection Agency in 2011 mentioned only anhydrous ammonia, which produces suffocating fumes and can cause burns if mishandled. The plan listed as a worst-case scenario "the release of the total contents of a storage tank released as a gas over 10 minutes" and did not warn of the risks of explosion.

Federal law requires any operation that holds more than a ton of fertilizer-grade ammonium nitrate to report that stock to the Department of Homeland Security. Proposed new rules would cut that to 25 pounds. But Homeland Security Secretary Janet Napolitano told a Senate subcommittee Tuesday that West Fertilizer doesn't appear to have reported its ammonium nitrate stock to federal officials, adding, "We're following up on that."

In a statement issued earlier this week, after the first lawsuit against it was filed in connection with the explosion, the company said its focus "remains on the fact finding."

"We continue to do everything we can to understand what happened to ensure nothing like this ever happens again in any community," it said. "To that end, the owners and staff of West Fertilizer Co. are working closely with investigating agencies. We have encouraged all employees to assist in the fact finding to whatever degree possible."

Among the dead was plant foreman Cody Dragoo, who was also a member of the town's volunteer fire department.

The explosion happened about 20 minutes after the first report of a fire there. It registered on seismographs as a magnitude 2.1 earthquake and could be felt 50 miles away.

Last week's explosion damaged numerous houses, a nursing home and the town's high school and middle school, all of which were built within a few hundred feet of the plant. That's raised concern about similar facilities in other towns, both in rural communities like West and major cities like Houston, the heart of the oil industry.

"I know there's hundreds of public schools on the fenceline or very close to these industrial plants," said Neil Carman, a former Texas Department of Environmental Quality inspector now working for the state Sierra Club. "I wouldn't be surprised if it's over 1,000."

Zoning restrictions are rare in the state, and Carman said there have been thousands of complaints from neighborhoods in areas like Houston, Beaumont and Corpus Christi, home to numerous oil refineries.

West Fertilizer had been twice cited by federal regulators twice since 2006.

In 2012, the Transportation Department's Pipeline and Hazardous Materials Safety Administration fined West Fertilizer $5,250 for storing anhydrous ammonia in tanks that lacked the proper warning labels. The agency originally recommended a $10,000 penalty, but it was reduced after the company took corrective action.

In 2006, the EPA fined it $2,300 owners to correct problems that included a failure to file a risk management program plan on time. The TCEQ also investigated a complaint about the lingering smell of ammonia around the plant the same year.