San Antonio, TX – Six people were hospitalized Saturday after toxic gas crept through their apartment building on the Northwest Side.

San Antonio Fire Department Battalion Chief Jonathan Jones said three people who lived in the building, in the Melia Apartments at 3431 Oakdale St., admitted themselves to an area hospital suffering from flu-like symptoms. Doctors determined that all three had been exposed to carbon monoxide and alerted the fire department.

Crews arrived at the complex around 5:40 p.m. and found high levels of carbon monoxide in the apartment building.

Three other residents, one with life-threatening injuries, also needed to be taken to the hospital. Another was treated at the scene.

Jones said the gas had been released from burning insulation on a water heater housed in a room adjacent to residential units. The gas caused 16 total units to be evacuated while crews worked to clear the air.

“Carbon monoxide is an asphyxiant that binds to red blood cells and prevents oxygen from attaching to cells,” Jones said, adding exposure to the gas can cause death by suffocation.

The gas is also flammable.

“High levels of carbon monoxide in a confined space … all it needs is an ignition source,” he said.

While the gas is odorless and colorless, it is fairly easy to detect with a carbon monoxide detector, which Jones said can be purchased at area stores and installed by SAFD, if needed.

“It is dangerous, but it is also really easy and inexpensive to prevent,” he said.