(CNN) Twenty-two people were injured in an explosion and fire at Kuraray America Eval, a plastic fabrication company in Pasadena, Texas, according to John Krueger, emergency media spokesperson for the city of La Porte.

Jeff Suggs, the corporate emergency manager for Kuraray, said the explosion happened around 10 a.m. and was caused by an over-pressurization of piping in the building.

A valve blew and a minor fire erupted, which was put out quickly, Krueger said.

All those injured are adult men who work in the maintenance department of Kuraray, Suggs said.

Most of the injured had topical burns and a couple had injured backs and knees from running away from the explosion, Krueger said. A total of 20 were transported via ground to local hospitals, and two with more severe burns were flown via helicopter, he added.

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