Officials say a container of formaldehyde started leaking in a science classroom around 1 p.m.
There was no immediate word on what caused the leak.
The view from Chopper 6 showed a handful of emergency vehicles at the scene, as students waited in the stadium bleachers.
Emergency workers in hazmat suits could be seen entering the building.
Bensalem police say students near the spill were checked by medical personnel but did not need to be treated. However, one teacher who was affected drove to the hospital for treatment.
School district officials say students were dismissed at their regular time.
No vehicles are permitted to enter or leave via Hulmeville Road, school officials said.
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