The district said the phone battery, despite initial reports from first responders, "did not explode."
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According to students, a classmate with an older model flip phone was patting or hitting the device after the battery became warm to the touch.
"It started smoking," said one student who was nearby, "and it smelled like chemicals."
Another said a cafeteria worker put a damp towel over the phone to contain the fumes. Students were told to exit the area.
According to the Westlake Fire Department, which responded to the call, none of the 10 students transported by ambulance were in serious condition. They were said to be coughing from the smoke and fumes.
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A possible burn injury was also reported.
"It was probably the students with the phone," said Katy ISD Police Chief Robert Jinks. "I'm sure it got hot, but we don't believe they were transported. They went home."
The school class time was scheduled to be cut short Friday to allow for a Valentine's Day party at the school. That was cancelled because of the smoking cell phone disruption.
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