Seventeen people needed medical treatment Monday after they were exposed to diesel exhaust fumes from a submarine at Naval Base Kitsap’s maintenance facility, according to the U.S. Navy.

The USS Alabama was operating its backup diesel generator while moored at the Navy base when sailors and civilians assigned to the base’s Trident Refit Facility reported exposure symptoms like coughing, nausea and throat irritation. Twelve sailors were taken to medical centers and five civilians received medical treatment on base and were able to return to work.

The diesel generator was immediately secured, the Navy said, and the USS Alabama, an Ohio-class ballistic missile submarine, has resumed normal operations. The cause is under investigation.

Monday was the second known exposure incident at the base this year. In June, 64 sailors and six civilians were sickened by diesel exhaust fumes from the USS Nebraska during a routine pier shift.