Roughly a week after a massive explosion tore through a petrochemical plant in Port Neches, residents of the Southeast Texas city are being asked to leave to avoid its lingering effects.

On Thursday morning officials in town and Jefferson County reaffirmed a voluntary evacuation order due to high levels of a harmful chemical in the area.

The order, initially issued Wednesday, followed an earlier shelter-in-place advisory that warned of unhealthy amounts of 1,3-Butadiene — a chemical associated with synthetic rubber and plastics processing that, when inhaled, can cause headaches, fatigue and even central nervous system damage and fainting, according to the National Library of Medicine.

"If you are experiencing any of these symptoms you are encouraged to leave your location. Any of these symptoms experienced are reversible and will not have long term effects," the local office of emergency management explained in a statement overnight, adding that expected shifts in wind direction and humidity were compounding the issue.

Classes at local schools have also been canceled for the remainder of the week.

"This will allow the current shelter in place that has been called for an area of Port Neches to come to an end, and provide the district adequate time to retest the air quality in our schools before students and staff return," the Port Neches-Groves ISD announced in a statement issued late Wednesday.

The precautionary measures come in the wake of a blast late last month at a plant owned by owned by the TPC Group, a petrochemical company based in Houston, 95 miles to the west of Port Neches. The early morning incident injured three workers as a cacophony of shattered glass rudely woke nearby residents.

Port Neches native Eddie Ramirez, who says he lives roughly a mile from the plant, captured video that revealed the immense scale of the blast.

"I never thought it would be this extreme," one resident told the Houston Chronicle. "Our friends' homes are destroyed."

As extreme as it was, such blasts are not uncommon in the region. In April alone earlier this year, the Houston area saw three fires at petrochemical plants. Just a few months later, dozens of workers had to receive treatment after a fire erupted at an ExxonMobil plant in Baytown, directly between Houston and Port Neches.

"You know, we have a lot of chemicals that are being handled," Jim Blackburn, an environmental engineering professor at Rice University, told Florian Martin of Houston Public Media back in April. "All of these chemical processes are dangerous. Inherent in that is the potential for explosion."

According to records kept by the Texas Commission on Environmental Quality, the TPC Group has had to pay more than $378,000 in penalties for more than half a dozen violations this year at its plants, including the one in Port Neches.

As NPR's Merrit Kennedy noted last week, the Trump administration recently rolled back Obama-era regulations covering how companies keep harmful chemicals. The rules, issued after 15 people died in a 2013 fertilizer plant explosion in West, Texas, mandated that companies provide public access to information about chemical storage at their plants and carry out other measures intended to prevent similar incidents.

But those rules proved to be altogether too "burdensome, costly, [and] unnecessary," the Environmental Protection Agency said in its statement announcing the rollback.

Copyright 2021 NPR. To see more, visit https://www.npr.org.