WEST (CBSDFW.COM) – For the first time since the West fertilizer plant exploded last April killing 15 people, the EPA is responding to questions posed by Congress.

In a letter sent to U.S. Senator Barbara Boxer, Democrat of California, an assistant administrator at the agency reveals its criminal investigators are looking to see if the plant’s operator complied with all regulations. The letter also discusses why the EPA doesn’t regulate ammonium nitrate, the chemical that exploded at the West facility.

Damage from the explosion is considered to be among the worst in the nation. Now, much of the focus is how to keep this disaster from repeating itself.

CBS 11 recently caught up with Ron Curry, the director of the EPA’s regional office in Dallas, who told us, “We are going to work with all the agencies involved, both at the federal and state level to try to prevent something like this from happening.”

With that in mind, Senator Boxer and the Committee on Environment and Public Works she chairs, will hold a hearing June 27.

After the explosion, many people, including residents, the Mayor and state leaders acknowledged they never thought the ammonium nitrate stored at the plant could explode.

The EPA doesn’t consider the chemical an extreme hazard as a dry fertilizer; as it was stored at the West plant.

In that form, it’s not considered explosive on its own — something else would have to cause it to change its composition and set it off — such as an accelerant or an intense fire reaching 450 degrees.

Senator Boxer asked the EPA why ammonium nitrate isn’t included on its list of chemicals covered by its risk management program, which requires facilities like the West plant to develop a worst case scenario in the event of an accident.

In this letter to the Senator, an assistant administrator at the EPA said, “Ammonium nitrate fertilizer does not meet criteria as it is not intended to function as an explosive and would not have been regulated.” But the U.S. Chemical Safety Board, which is also investigating the incident, is urging the EPA to include ammonium nitrate in the program, saying it would help protect the surrounding communities.

When asked if the chemical should now be considered an extreme hazard, Curry said, “To make a general statement like that, at this point, I’m not going to do that.”

CBS 11 spoke with a consultant for the chemical industry.

He said the bottom line is the government needs to figure out what gaps exist in process safety for ammonium nitrate and other materials, and determine what regulations should be in place to discover potentially catastrophic risks in communities.

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