A voluntary evacuation order is in effect for residents of Port Neches.
A shelter-in-place order was prompted by the detection of elevated levels of butadiene in the air on Wednesday.
It was later upgraded to a voluntary evacuation, which is in effect until further notice.
After last week's explosion at the local TPC plant, butadiene burned in a fire at the site until it was put out on Tuesday evening.
Officials are continuing to monitor the air around the damaged facility and will update the situation as needed.