CRESSON (CBSDFW.COM/AP)Hazardous materials crews and firefighters have resumed the search for a North Texas worker who is missing and presumed dead after an explosion at a chemical plant that injured two co-workers.

Texas Department of Public Safety Staff Sgt. Earl Gillum says recovery crews are using heavy equipment Friday to clear burned debris at the Tri-Chem Industries plant in Cresson, about 25 miles southwest of Fort Worth.

The search resumed Friday for the missing worker who Gillum has said is presumed dead.  According to his brother, Austin Mitchell, that missing man is Dylan Mitchell and he has worked for Tri-Chem for four years.

The Hood County Fire Marshal told CBS 11 News that rescuers did six separate searches on Thursday — in the part of the building that’s still standing. The plan today is to make sure things are safe and then go in and continue their search.

Investigators believe a worker dragging his foot along the floor while chemicals were being mixed sparked Thursday’s explosion. That worker is hospitalized with critical burns. Another worker was treated for lesser injuries.

“(They) said that he kind of kicked something out of the way and it started a spark which ignited the vapors where he was…and then the explosion,” said Austin Mitchell. “The guys working with my brother got blasted out of the back door, and then no one really saw him since.”

Mitchell said his brother mixed chemicals for a living and at the time of the blast was working on a new formula with the company. 

Sergeant Gillum says air quality experts have determined there’s no danger of another blast after toxicity concerns stalled initial firefighting efforts.

(© Copyright 2018 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)