ExxonMobil sent 66 of its employees and contractors for medical evaluation yesterday after an explosion and fire at one of its Texas oil refineries. News sources say an estimated 37 people sustained minor burn injuries.

The incident at the Baytown facility, which processes propane and propylene, occurred shortly after 11 a.m. Authorities issued a shelter-in-place order for approximately 5,000 area residents.

Plant manager Jason Duncan reportedly said many were who were burned were being treated at a local clinic.

The Texas Commission on Environmental Quality, which monitored air quality at the scene, did not report any concerns.

The cause of the fire is under investigation.

This was the second fire to occur at ExxonMobil’s Baytown complex this year. Harris County has sued the company for violating the federal Clean Air Act.