The H-3 tunnel control center was evacuated Tuesday morning after three workers complained of headaches caused by a chemical odor, a Fire Department spokesman said.

Firefighters received the chemical odor alarm at 8:14 a.m. 

The  source of the odor was a battery backup located in a telecommunications vault in the center, said Honolulu fire inspector Ken Ige.  The unit apparently overheated.  A technician removed the  battery backup unit and firefighters ventilated the center. About a dozen workers had to be evacuated.

Paramedics checked out the three affected workers, but did not take them to the hospital.