The Texas fertiliser factory in which an earthquake-like explosion killed at least five people was fined by United States regulators last year over its transport of hazardous materials.
The blast at the West Fertiliser Company on Thursday - which destroyed dozens of homes in the small town of West - came after a fire at the plant, which is believed to have held large amounts of volatile ammonia.
The company was last year fined US$10,100 ($12,000) by the US Pipelines and Hazardous Materials Safety Administration for mislabelled cargo tanks and "failing to develop and adhere to a security plan" for transporting a large quantity of anhydrous ammonia, according to a copy of the citation.
The company reached a settlement with US regulators in which it paid a US$5250 fine, official documents show.
The violations involved the transport of anhydrous (without water) ammonia, and not its storage at the factory, which exploded nearly an hour after a fire broke out on Thursday, according to officials.
In 2006, the Texas Commission on Environmental Quality carried out an "odour complaint investigation" at the plant.
It later issued a notice saying the plant was operating without authorisation.
The matter was resolved the company filed an application, the commission said.
The fertiliser company could not immediately be reached for comment.
The Dallas Morning News, meanwhile, reported that the company had told the US Environmental Protection Agency and local authorities that its factory posed no risk of fire or explosion despite holding up to 25 tonnes of ammonia.
Anhydrous ammonia, NH3, is a pungent, flammable colourless gas which is commonly used in making soil fertiliser.
It is compressed into liquid form and stored in high-pressure tanks. It becomes potentially explosive when high concentrations are ignited by a heat source greater than 651C.
Officials have not yet confirmed the cause of this week's explosion - which registered as a 2.1-magnitude seismic event and sent up a huge fireball and plume of smoke.
But they said they had not ruled out the possibility of foul play.
An alternative form of ammonia delivery is in granulated form as ammonium nitrate which derives from NH3 combined with nitric acid.
Ammonium nitrate has been used in primitive fertiliser bombs of the kind used in the 1995 bomb attack on a US federal building in Oklahoma City, and in Oslo in 2011 by Norwegian mass murderer Anders Breivik.
Accidents involving ammonium nitrate include a 2001 blast at a French plant where 300 tonnes of the chemical were stored.
Thirty-one people died in the blast, and the exact cause has never been determined.