According to ABC 7, Justin Gau and Kyle Page, two volunteer EMTs, went to their Long Island Applebee's for dinner.  When they walked in, their carbon monoxide alarm went off.  

After investigating, it was found that the restaurant's hot water heater malfunctioned, sending the odorless, colorless, deadly gas into the restaurant, ABC 7 reported.

According to WCVB, a Legal Seafood manager died when a hot water heater's flue pipe malfunctioned.  Twenty-seven other people, including three responding police officers, were sent to the hospital with carbon monoxide poisoning symptoms.

The restaurant did not have a carbon monoxide detector.  New York law, according to WCVB, only requires them where people sleep.