After an unusually cold April night two years ago, Prince George’s County firefighters were called to an Oxon Hill home. There, they found five people, all dead. But there were no signs of forced entry and no visible injuries on the bodies.

Authorities later discovered that everyone in the house had died of carbon monoxide poisoning. An exhaust pipe from the furnace broke overnight, leaking gas into the home and slowly poisoning them as they slept.

“That family never work up,” County Fire Chief Marc Bashoor said. “They had no alarm. Nothing to warn them.”

Since then, four more people in Prince George’s have died of carbon monoxide poisoning. But officials hope a law that goes into effect July 1 will prevent similar tragedies.

Starting next week, all houses in the county with gas service, an attached garage or a fireplace must have a carbon monoxide detector on every level.

The gas is “colorless and odorless,” Bashoor said. “You don’t know it’s there until it’s too late.”

Prince George’s is one of the first counties in Maryland to require carbon monoxide detectors in homes, Bashoor said. The detectors cost at least $20, and the fire department recommends 10-year alarms that don’t require frequent battery changes.

Bashoor said he understands that some homeowners may be reluctant to spend the money, but the small investment could save a family. “It’s probably the cheapest insurance policy you’re going to find,” he said.

Although there is a civil penalty for violating the legislation — a $100 fine — the department will probably be generous with warnings, officials said. The fire department plans to “passively enforce” the law, fire department spokesman Mark Brady said. County officials won’t be going door-to-door to check whether alarms have been installed.

“We’ll try to help you get an alarm as opposed to giving you a ticket,” Brady said.

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