(CNN) A mandatory evacuation order issued after a series of explosions at a Texas chemical plant has been lifted, a county official said Friday morning.
Tens of thousands of residents within a 4-mile radius of the TPC Group plant in the small city of Port Neches had been told to leave their homes Wednesday after explosions at the site, which led to fires.
The fires are not extinguished, but they are contained, said Jefferson County Judge Jeff Branick, who issued the evacuation order. He previously said the evacuation order would be lifted when the fires were contained, because that would give him confidence that more explosions would not come. The evacuation order covered the cities of Port Neches, Groves, Nederland and part of Port Arthur.
"TPC is going to continue their efforts to put the remaining fires out," Branick said Friday.
Though residents in the zone can return, not all will come back to whole homes. Wednesday's blasts damaged some houses, shattering windows and destroying roofs.
Eight people injured in the blasts were treated and released, Branick said. Three of the injured worked for TPC, a company spokesman said.
TPC has not yet said what caused the explosion. It could take several months before the cause is known, Branick said.
Officials have been monitoring the air because the fires were burning a chemical called butadiene, a colorless gas with a gasoline-like smell that is considered a health hazard, according to the US National Library of Medicine.
Butadiene is made from processing petroleum and is used to make synthetic rubber and plastics. The plant makes products for chemical and petroleum companies, TPC said.
Branick said Friday that residents should be on the lookout for pieces of asbestos that might have been expelled in the explosions.
Part of the facility were completed in the 1940s and had pipe coverings with the fibrous substance, he said. Because asbestos is linked to diseases and cancers like mesothelioma, widespread use of asbestos products stopped years ago.
Wednesday's explosions "could have blown that asbestos debris over the neighborhoods and into some yards," Branick said.
Any white, chalky substance should be reported to TPC, and should not be touched, he said.
Health effects from butadiene exposure can vary, the Occupational Safety and Health Administration says.
Lower exposures can cause irritation to the eyes, throat nose and lungs as well as cause frostbite if the skin is exposed.
Higher exposures can damage the central nervous system or cause symptoms including distorted blurred vision, vertigo, general tiredness, fainting, lowered blood pressure and pulse rate, headaches or nausea.
More chronic effects are disputed, the agency says.
"Several human epidemiological studies have shown an increase in cardiovascular diseases and cancer," OSHA says. "However, due to the small numbers of cancers and confounding factors such as smoking, and simultaneous exposure to benzene and styrene, a true causal relationship cannot be established."
Experiments on mice and rats showed there was a "strong causal relationship" between butadiene exposure and cancer, the agency said.