Carbon monoxide poisoning is blamed for hospitalizing 29 people at a seafood business in Bellingham, Washington.

Investigators suspect fumes from forklifts. The warehouse doors were closed because of the cold.

The local fire chief says when they arrived, everyone was conscious but people were showing carbon monoxide symptoms, which can include headaches, nausea and vomiting.

A hospital spokeswoman says four of those brought in were later transferred to a Seattle medical center for treatment in a hyperbaric chamber. A hyperbaric chamber increases oxygen pressure in body tissues, and the amount of oxygen blood can transport.