Staffordshire Fire and Rescue Service said the chemical had been isolated, with the Conway Road building since ventilated.
A statement from the school posted on Facebook said: “Earlier today, an issue was identified with a piece of science equipment. Following our normal processes and procedures, emergency services attended.
“They have confirmed the site is safe for normal operations to continue.
“We are grateful for the swift and professional response of our staff and students and the support provided by the emergency services. The wellbeing and safety of our students and staff remain our highest priority.”
