(Reuters) The fire initially ignited on Friday afternoon in an explosion in an olefins unit, used to make plastics and rubber.
The fire was extinguished for a few hours on Saturday morning before it reignited around 3 p.m. CDT (2000 GMT), said Shell spokesperson Curtis Smith.
No injuries were reported from the fire. Nine people were evaluated and released at local hospitals on Friday for possible chemical exposure.
Water is being sprayed onto the fire to keep it under control until the chemicals, which were being processed at the time of the explosion, burn away, Smith said.
Water may continue to be sprayed for up to 36 hours after the fire is extinguished to keep nearby equipment cool, he said.
Water runoff has exceeded the chemical plant's wastewater capacity and is being diverted into the Houston Ship Channel, Smith said. A boom has been deployed in the channel to contain any chemicals that may be carried by the water runoff.
Smith said air monitoring in neighboring communities "has not detected any harmful levels of chemicals" from the fire.
Jennifer Hadayia, executive director of Air Alliance Houston, said Shell's statements about risks to the community were self-serving.
"History has shown that these early statements are for the benefit of industry public relations and not public health," Hadayia said.
Olefins units are the central units in petrochemical complexes, producing ethylene, butadiene and propylene from hydrocarbon feedstocks.
