DEER PARK, Texas (AP) — A flame that towered over a southeast Houston suburb subsided Tuesday but was still burning following a pipeline explosion that happened when a vehicle drove through a fence along a parking lot and struck an above-ground valve, officials said.

“Progress has been made as first responder crews worked through the night. The fire is significantly smaller,” according to a statement from Deer Park. The city said Energy Transfer, the Dallas-based owner of the pipeline, expects the fire to burn itself out later Tuesday.

City officials said police and FBI agents found no preliminary evidence to suggest a coordinated or terrorist attack, and said it “appears to be an isolated incident,” but they haven’t offered any details on how they came to that conclusion.

Investigators were trying to learn more about the driver of the sport utility vehicle. The car was incinerated by the explosion, which scorched the ground across a wide radius, severed nearby power transmission lines, melted playground equipment and ignited nearby homes. Over 24 hours after the explosion, the driver still had not been publicly identified.

The valve, which appears to have been protected by a chain-link fence topped with barbed wire, is located within a long grassy corridor where high-voltage power lines run. Below the ground run several pipelines. On one side of the corridor is a neighborhood of homes; on the other is a Walmart. Officials say the driver went through a fence alongside the Walmart parking lot and across the grassy right-of-way before striking the valve.

Officials have not given any information on the condition of the driver. Deer Park spokesperson Kaitlyn Bluejacket said four people were injured, but provided no details about the seriousness of the injuries. Authorities said one firefighter sustained minor injuries.

The roaring fire shot orange flame and then black smoke hundreds of feet into the air, prompting authorities to evacuate nearly 1,000 homes and order people in nearby schools to shelter in place. By Tuesday, the City of La Porte said it slightly reduced the evacuation area south of the fire, but did not say how many people were affected.

Operators shut off the flow of natural gas liquids after the explosion rattled homes and businesses in Deer Park and the adjacent suburb of La Porte shortly before 10 a.m. on Monday. But Harris County Judge Lina Hidalgo said 20 miles (32 kilometers) of pipeline stretched between the two closed valves, and all the chemicals inside had to burn off before the fire would stop.

Robert Hall, a senior advisor at the nonprofit Pipeline Safety Trust, said it’s not surprising that it’s taken more than a day for the material to stop burning.

“You’re talking about 20-inch pipelines and miles between valves, so it takes a long time to burn down,” Hall said.

The fire was burning so hot that all firefighters could do is use ladder trucks to hose down nearby houses that began smoking in the radiant heat.

Houston, Texas’ largest city, is the nation’s petrochemical heartland and is home to a cluster of refineries and plants and thousands of miles of pipelines. Explosions and fires are a familiar sight, and some have been deadly, raising recurring questions about industry efforts to protect the public and the environment.

Hall, who previously oversaw pipeline and hazardous materials investigations for the National Transportation Safety Board, said there are few regulations that govern the location of pipelines near homes and businesses.

“That becomes a very local issue, community by community,” said Hall, who added that some jurisdictions require bollards — sturdy pipes filled with concrete — to prevent vehicles from crashing into sensitive infrastructure.

Energy Transfer did not immediately respond Tuesday to a question about what safety precautions were in place near their valve.

Hall said regulations that were put in place in 2022 aimed at reducing deaths and environmental damage from pipeline ruptures were geared toward gas lines, not those carrying liquids, and would not have applied to the Texas pipeline. He added that many new safety regulations that have been put in place do not apply retroactively to pipelines that have already been constructed.

Anna Lewis, who was walking into the Walmart when the explosion happened, said it sounded “like a bomb went off.” She said everyone inside was rushed to the back of the store and then taken across the street to a grocery store before being bussed to a community center.

“It scared me,” she said. “You really don’t know what to do when it’s happening.”

Geselle Melina Guerra heard the explosion as she ate breakfast with her boyfriend in their mobile home.

“All of a sudden we hear this loud bang and then I see something bright, like orange, coming from our back door that’s outside,” said Guerra, who lives within the evacuation area.

Both Energy Transfer and Harris County Pollution Control are conducting air monitoring in the area and have found no health issues, according to Deer Park officials.

The Railroad Commission of Texas, which regulates oil and gas in the state, said Tuesday its safety inspectors will enter the site when it’s safe to do so to begin their investigation.

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Murphy contributed to this report from Oklahoma City. AP writers Christopher L. Keller in Albuquerque, New Mexico, Valerie Gonzalez in McAllen, Texas, Ken Miller in Oklahoma City and Jamie Stengle in Dallas also contributed to this report.