Several people were evaluated, and four were hospitalized after a carbon monoxide alarm in an Ocean City, Maryland, hotel on Friday afternoon, according to fire officials.

Ocean City building inspectors and gas company personnel worked to determine the source of the gas. 

Carbon monoxide in Ocean City hotel 

Ocean City Fire crews responded to the alarm at the Ashore Hotel at 10100 Coastal Highway around 11 a.m., officials said. 

Additional EMS crews and resources were requested at the scene due to the number of people affected.

A total of 13 people were evaluated on the scene, and four were transported to hospitals due to elevated levels of carbon monoxide in their blood, according to officials.

What is carbon monoxide? 

Carbon monoxide is a gas that, when inhaled, can lead to illness or death, according to the Centers for Disease Control and Prevention (CDC). Symptoms of carbon monoxide poisoning include dizziness, headache, vomiting and confusion. Some of the symptoms are similar to flu symptoms. 

The odorless gas can be produced by burning furnaces, car exhaust, portable generators, charcoal grills and some other household appliances, the CDC said. 

More than 400 people die from unintentional carbon monoxide poisoning each year in the U.S., according to the CDC.  

Similar hazmat incident in Baltimore 

Ten people were treated after becoming ill during a similar incident in Baltimore last week. Though in that case, carbon dioxide was detected, the Baltimore Fire Department said. 

The elevated levels of carbon dioxide prompted nearly 100 people to be evacuated from a poultry processing plant in the 2100 block of Wicomico Street. Five people were taken to hospitals with non-life-threatening injuries, officials said. 

Carbon dioxide (CO2) is an odorless gas that occurs in the atmosphere naturally, according to the CDC. Humans create CO2 when they breathe out, but a buildup in the blood can lead to carbon dioxide poisoning. The gas is also created by burning fossil fuels

Crews checked the building for air quality and CO2 levels, though they have yet to determine the source of the elevated levels.