DALLAS - The fertilizer-plant explosion that killed 15 people last year in a tiny Texas town could have been prevented, even if it is still not clear what started an initial fire that triggered the explosion, federal officials said Tuesday.

The U.S. Chemical Safety Board announced its findings after a year of investigating the blast in West, Texas, that also injured 200 and decimated parts of the town. Among those killed were 12 volunteer firefighters.

The safety board said the owners of West Fertilizer Co. failed to safely store hazardous chemicals or prepare for a potential disaster. The board also said several levels of federal, state, and local government missed opportunities to prevent the tragedy.

"It should never have occurred," said Rafael Moure-Eraso, the chairman of the safety board, which does not have any regulatory authority.

Despite investigations that have yielded information about safety deficiencies at the plant and voluntary safety steps taken by the nation's fertilizer industry, not a single state or federal law requiring change has been passed since April 17, 2013.

As many as 34 tons of ammonium nitrate detonated inside the West Fertilizer Co. It is a chemical commonly used in fertilizer and as an industrial explosive, but it is dangerous under certain conditions or in the wrong hands.

The plant in West had 40 to 60 tons of ammonium nitrate stored in wooden containers inside a wooden building with no sprinkler system, investigators said Tuesday. There was more ammonium nitrate in a railcar outside the building.

A spokesman for the owners of the plant did not immediately respond to a message. The plant's owners have denied the allegations of dozens of residents and companies suing them in civil court, saying the plant was negligent in how it handled and stored ammonium nitrate.