The hydrotreater unit leaked Thursday evening at the Marathon Oil Refinery in Detroit.
The unit had to be shut down and depressed to the flare system, which caused some hydrogen flaring activities, according to a spokesman for the refinery.
The emergency alarms were activated as a precautionary measure. Detroit firefighters responded to the alarms, along with Marathon's own firefighters.
There were no injuries.
The refinery is at South Fort Street and Interstate 75.
In April, a fire broke out after an explosion at the refinery.