Brandywine, MD — Two brothers were killed by carbon monoxide poisoning when they attempted to use a generator placed inside their house to heat and power it during an extended outage in Brandywine, according to family members. Prince George’s County Fire & EMS authorities say a third man was hospitalized and is expected to survive.

Herrera said the Carranza brothers had gone to bed Tuesday after starting a generator inside the home when they returned from work that night to find their house had no power; the brothers had been working to remove snow for a contractor throughout the storm, Herrera said. The power had been out for at least 36 hours in the wake of Monday’s snow, according to neighbors.

Monday’s snow storm knocked out power to hundreds of thousands of people in D.C., Maryland and Virginia. According to the Southern Maryland Electric Co-Op, an outage map shows 9,000 homes still without power in their service area, which includes Brandywine, as of Wednesday morning.

The U.S. Department of Energy warns that using a portable generator inside a home can lead to dangerous situations including carbon monoxide poisoning from engine exhaust.

CO is a colorless, odorless gas that can be released by faulty gas-burning appliances, as well as from internal combustion engines that power generators and vehicles, according to the U.S. Centers for Disease Control.

“Even if you can’t smell exhaust fumes, you may still have been exposed to carbon monoxide. If you start to feel sick, dizzy, or weak while using a generator, get fresh air right away,” the Energy Department says on its website.

The department also recommends installing battery-operated carbon monoxide alarms. There was no carbon monoxide detector in the home, Herrera said.

According to the CDC, at least 430 people die annually from Carbon Monoxide poisoning incidents. At least 50,000 are treated in hospitals. January is the worst month for carbon monoxide incidents, the CDC reports.