A 59-year-old civilian contract worker was listed in serious condition after apparently being exposed to carbon dioxide from a fire-supression system on a Coast Guard vessel, the city Emergency Services Department said.

The incident happened on the Coast Guard Cutter Kukui about 11:30 a.m. at Coast Guard Station Sand Island.

The Kukui’s commanding officer,  Lt. Cmdr. Steven Ramassini, said the worker was in the stern thruster space, which is a below-deck compartment at the water line, and had been clearing the way for work on a generator.

That’s when the fire-suppression system was accidentally activated, audible and visual alarms were activated and carbon dioxide was released.

Other civilian and Coast Guard workers were also in the space, but the affected worker was in the lowest point of that space and did not make it out, Ramassini said.

He lost consciousness and collapsed, and the Coast Guard fire team on board brought the worker onto the deck within three minutes and he revived on his own, Ramassini said.

When Honolulu firefighters arrived, the patient was alert, fire Capt. Terry Seelig said.

Emergency Medical Services transported the man by ambulance to an area hospital.

Carbon dioxide is a common shipbard extinguishing agent, which acts by displacing oxygen in the air, Seelig said. No one else was affected by the carbon dioxide release, an Emergency Services spokeswoman said.

The Coast Guard is investigating the the timing delays between the alarms and the discharge.