UPDATED | November 15, 2017  4:40 PM

CH Collegiate Academy Middle School (Chopper11)

CEDAR HILL (CBSDFW.COM) – Cedar Hill police and firefighters responded to a gas odor inside CH Collegiate Academy High School on Wednesday afternoon.

A gas valve was left open in a science lab according to Atmos Energy.  The valve has been closed.

School district officials told CBS11 a gas detector used in science labs did not engage. 

Police said approximately 28 total students and staff complained of feeling affects of gas odor.

Eight people have gone to an area hospital.

The school was evacuated.

CH Collegiate Academy evacuation (Chopper11)

CH Collegiate Academy evacuation (Chopper11)

“There was an ambulance bus here most were transported by that bus. Paramedics transported some. Some parents refused transport. Others wanted to go to hospital to be checked out,” said Cedar Hill Fire Chief John Klein.

The school’s science lab has gas detection monitors but the alarms did not go off.

“That is a fairly new state of the art science lab so all of those system are in place, so we are checking right now to see if it’s working effectively,” said Kellie Spencer, Cedar Hill ISD Assistant Superintendent.