Steven Nelson, 55, was pronounced dead at a hospital after he was found unconscious in the basement of a local seafood restaurant that he managed.
First responders had been called to help another woman who fainted from exposure to high amounts of carbon monoxide.
The Huntington Fire Marshall believes a faulty water heater pipe caused the lethal gas build-up, forcing multiple locations to evacuate and shut down temporarily.
About two dozen people were taken to the hospital for treatment and are expected to fully recover.
Town officials report that carbon monoxide detectors are not required in commercial spaces.
While the Cheesecake Factory nearby was open Sunday, it is not yet known when the Panera Bread that shared a gas line with Legal Sea Foods will open again. Legal Sea Foods employees continue to grieve the loss of their manager.