A correction has been made to this article.

By Bill Dedman, Investigative Reporter, NBC News

The fertilizer storage facility that exploded this week in the town of West, Texas, had informed a state agency in February that it was storing up to 270 tons of ammonium nitrate – the highly explosive chemical compound used in the domestic terror attack on the Oklahoma City federal building.

The company's risk management plan, filed with the federal Environmental Protection Agency in 2011, made no mention of ammonium nitrate. (Update: Reuters news agency reported that the EPA does not require disclosure of the ammonium nitrate, but the Department of Homeland Security does require that disclosure, which the company did not do.)

It's not clear whether the ammonium nitrate, which was not initially reported as being present at the site in the wake of Wednesday's massive blast, was responsible for the explosion, or whether volunteer firefighters battling a fire at the facility knew of its presence. Under state law, hazardous chemicals must be disclosed to the community fire department and to the county emergency planning agency, in addition to the state. News reports on Thursday focused on tanks of anhydrous ammonia –a less volatile fertilizer.

Adair Grain, doing business as West Fertilizer Co., told the Texas Department of Health Services on Feb. 26 that it was storing up to 540,000 pounds of ammonium nitrate, along with up to 110,000 pounds of the liquid ammonia, according to the disclosure report. (Read the document provided by the state.) The company's disclosure was first reported Thursday evening by The Los Angeles Times.

The facility in West served primarily as a distribution point for fertilizer to farmers, a retail outfit, not a manufacturing plant, it said in its regulatory filings.

A deadly historyAmmonium nitrate fertilizer was involved in the worst industrial accident in U.S. history, when a container ship exploded in 1947 in Texas City, Texas, killing more than 500 people. It also was combined with fuel and used by Timothy McVeigh in the bombing of the federal building in Oklahoma City on April 19, 1995.

Firefighters were trying to put out a blaze at the facility when it exploded on Wednesday evening. An official with the Texas Division of Emergency Management told reporters that he believed ammonium nitrate was one of the chemicals on site, but authorities have not said what chemical was responsible for the tremendous explosion, how much of each chemical was stored at the time or what caused the fire.

Making sure that firefighters know what chemicals are on site is a primary reason for the disclosures such as the one the company made to the state in February. Spokesman Carrie Williams of the Department of Health Services told NBC News that although the state requires registration of hazardous materials to alert emergency planners and the community, the department's role is limited to receiving the reports and making them available to the public. More than 65,000 facilities in Texas submit reports, which are available in the state's Emergency and Chemical Inventory.

West Fertilizer said in its 2011 risk management plan filed with the EPA that its anhydrous ammonia did not pose any threat of fire or explosions. "The worst-case release scenario would be the release of the total contents of a storage tank released as a gas over 10 minutes," the plan said. Ammonium nitrate isn't listed on the plan, which is described as a five-year update to the EPA. A copy of the plan was posted online by the watchdog group Center for Effective Government.

"Last night’s tragic explosion points to the need for stricter regulations of plants that store and use large quantities of hazardous chemicals," said a statement from Tom O’Connor, executive director of a union safety group, the National Council for Occupational Safety and Health. "We need a system in which facilities that are inherently dangerous are required to develop detailed disaster prevention plans before they’re allowed to operate."

West Fertilizer is owned by Adair Grain, a small company with only seven or eight employees. The company declined to comment when reached by phone by NBC News.

The company has been the subject of several disciplinary actions from state and federal regulators:

Last summer, the U.S. Pipeline and Hazardous Materials Safety Administration fined West Fertilizer $10,000 for safety violations, including planning to transport anhydrous ammonia without adequate security and failing to properly label ammonia tanks. The company paid a reduced fine of $5,250 after agreeing to take corrective action. The fine was reported by several news organizations.

In 2006, the company was fined $2,300 by the EPA for not having filed a risk management plan, according to the EPA's compliance database. The EPA said it had poor employee training records, failed to document hazards and didn't have a written maintenance program. The EPA said the company corrected the deficiencies and filed an updated plan in 2011 – making no mention of the presence of ammonium nitrate – and was then in compliance with EPA regulations.

Also in 2006, the state Department of Environmental Quality found that the company was operating without a permit for its two 12,000-gallon tanks for anhydrous ammonia, which is stored as a liquid under high pressure. The state department hadn't known about the tanks until a neighbor complained of a "very bad" smell of ammonia at night. The chemical is used on farms directly as a fertilizer, and can be combined with nitric acid to make ammonium nitrate fertilizer. No state permit for the tanks had been required when the plant was built in 1962, and it was grandfathered in until a 2004 change in state law required even those older plants to have permits.

State environmental officials received two complaints about the company. One, in 2002, said, "This place is in the northern part of town and every day during the grain harvest season there is a cloud of dust. Particles are falling like snow around town. People are afraid to complain, however this is effecting (sic) neighbors' health with scratchy throats, cough and sneezing." The other was in 2006, and led to the plant getting a permit for its anhydrous ammonia tanks: "Ammonia Smell very bad last night from fertilizer plant, lingered until after they went to bed," it said.

Location is up to zoning rulesThe spokeswoman for a trade group, The Fertilizer Institute, said the West plant was not a manufacturing facility but instead a retail distribution point for farmers to buy fertilizers. The spokeswoman, Kathy Mathers, said there are 5,000 to 6,000 such facilities in the U.S. Such facilities must register with the EPA and with state authorities, she said. But any limits on their placement near homes or schools would be limited only by local zoning ordinances, Mathers said.

The county engineer in McLennan County, Texas, in the county seat of Waco, said counties in the state don't have zoning regulations, and neither do most towns. He said he didn't know if the town of West had rules that would have affected this plant. Although some homes were close by when the fertilizer facility opened, a subdivision, schools and a nursing home were built near the plant in subsequent years.

Mathers said Thursday that the most recent fatal accident involving a fertilizer facility in the U.S. was in 1994 in Port Neal, Iowa, where four workers were killed and 18 injured. (Read the EPA investigative report.)

She said the institute's employees on Thursday were "pretty damn mad," because an incident such as this can sully a good industry's reputation. "This industry has ethics," she said. The Fertilizer Institute sponsors training sessions for the industry, in addition to performing the usual support and lobbying functions of a trade group.

The Fertilizer Institute removed from its website on Thursday morning a map of fertilizer production and mining facilities. Mathers said officials did so because people were confusing those facilities with smaller storage and mixing facilities, like West Fertilizer. "We weren't trying to do anything dirty or underhanded," she said. A copy of the map is available here.

The accident is being investigated by the U.S. Chemical Safety Board. An article this week from the Center for Public Integrity described how overworked and underfunded that agency is.

Polly DeFrank and Rich Gardella of NBC News contributed reporting.

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