Four people are in the hospital Thursday morning after a hazmat alert at a future Apple plant in Mesa.
Firefighters said they got a call to respond to a building near Signal Butte Road and Elliot just after midnight.
More than 200 employees were evacuated after firefighters said they started complaining about a strange burning sensation.
First responders didn't find any obvious chemical spills or contaminants inside the building.
While onscene firefighters, said they treated 20 people for nausea and headaches. Four people were sick enough they decided to go to the hospital.
The hazmat situation happened in the old First Solar facility. The building is currently being converted by Apple and GT Advanced Technologies.
Once up and running the new plant will produce glass for Apple cell phones.
It's not clear what type of work was happening inside of the building at the time of the emergency.