WAXAHACHIE (CBSDFW.COM) – The CEO of a company that owns a Waxahachie chemical plant that caught fire Monday says the chemicals being mixed at the plant Monday should have not caught fire.

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Magnablend CEO Scott Pendery told members of the media Thursday employees were mixing chemicals for a wastewater product.

He called the fire “a situation where something went catastrophically wrong.”

Pendery says the company began working with the product this past August and had completed 16 batches on a pilot basis.

On Monday, Pendery says employees began mixing much larger quantities.

“What we didn’t expect, when we scaled up to doing that 2500 gallon batch, the amount of steam it was generating was significantly greater than what we had believed we would see.”

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He says workers reported seeing sparks, then flames.

Waxahachie Fire chief David Hudgins says investigators believe the mixing of chemicals produced hydrogen, which is an accelerant.

Hudgins says the hydrogen may have been rising out of the vat along with the steam, and something could have ignited it.

“If it was hydrogen at the ceiling and something ignited it, then you would have had a fire up there… They probably weren’t able to view the ceiling well because of the steam, so if the hydrogen did ignite, there’s a possibility they didn’t see it.”

Hudgins reiterated that a hydrogen fire was just one theory, not definitely what happened.  He says they may never know for certain what ignited the fire.

Firefighters were still putting out remaining hot spots Thursday, and hope to finish that by Friday.

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People who work near the plant report they can still smell a strong smoke and chemical odor in the area.   The EPA says it is still monitoring air quality, and has found elevated levels of particulates or soot northwest of the plant, but insist there is no major hazard.