Mukilteo, WA – Five people were hospitalized Wednesday after suffering from carbon monoxide poisoning, Mukilteo Fire officials said.

Medics were called to the 11000 block of Chennault Beach Road around 4 a.m. after getting a report of a medical emergency. Upon arrival, they found one person having difficulty breathing. A second person began having issues several minutes later and a second ambulance was called. Then the fire crews began experiencing symptoms.

Air monitoring identified the culprit as carbon monoxide, said Chief Chris Alexander with Mukilteo Fire.

The two at the home and three firefighters were taken to a local hospital for treatment of carbon monoxide poisoning, fire officials said. The three firefighters were treated and released but the condition of the residents was not given.

“Blocked vents and flues can cause the CO to build up to dangerous levels,” Alexander said. “Signs and symptoms may include a dull headache, weakness, dizziness, nausea or vomiting, shortness of breath, confusion, blurred vision, and loss of consciousness.”