(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.

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.

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