Pikesville, MD- Two people, identified by neighbors as construction workers who boarded with a family, died Sunday in a carbon monoxide incident in the 4000 block of Colby Road in Pikesville.

Baltimore County Fire Department spokeswoman Elise Armacost said 10 others, including civilians and police officers who were overcome when they entered the home, were taken to local hospitals. Armacost said five were treated and released at Maryland Shock Trauma Center, while 5 taken to the hyperbaric unit at the University of Maryland Medical Center.

A neighbor, Elias Sanchez, said the house was occupied by Navis Arevalo, who lives with her husband, David Martinez; their two children; Arevalo’s nephew and brother; plus four other men who all worked with Martinez in construction.

Sanchez said the men who died were among the four workers who resided in the house. All the men worked together each day. Sanchez said the family had lived in the house since 2008.

The house, a rental property, had no carbon monoxide detector, according to Fire Department Divisional Chief Michael Robinson. According to a county ordinance, rental properties must be equipped with the device.

Robinson said the owner of the property had not been located. He declined to release the owner’s identity. The state property records database lists the owner as Santos D. Martinez and also says the house is a principal residence.

According to Baltimore County online records of rental properties, the house was not registered as a rental as of Dec. 3, 2010.

Carbon monoxide, or CO, leaks occur most often in winter, typically when an improperly vented furnace is turned on for the season and worsening as the weather grows colder and the furnace runs more often. The lethal fumes — which, when breathed, reduce the amount of oxygen the blood can carry — are also associated with improperly vented hot water heaters, as well as with generators powered by gasoline or kerosene.

It was not known Sunday what led to the carbon monoxide leak at the Pikesville home.

Heather Meekins, another neighbor, said the family was quiet and hard-working. “Several people came out of the house then tried to go back in but were stopped by police,” Meekins, who has lived on Colby Road for two months, said. “It’s very scary. It goes to show that people should get the type of alarm [for carbon monoxide] they need in their houses.”

Meekins said the neighborhood woke to the sounds of sirens as first police, then fire units arrived.

A 911 call came in about 8:40 a.m. for an emergency involving possibly deceased people at the single-family home on Colby Road, off Reisterstown Road in the heart of Pikesville.

Fire commanders subsequently declared a mass casualty incident.

Firefighters reported dangerous carbon monoxide levels of 400 ppm in the home. A reading of about 9 ppm is considered hazardous.

Fire equipment on the scene included six medic units, two engine companies, four EMS officers, a hazmat unit and a physician. All the windows in the house were open by mid-morning as emergency vehicles were leaving. On the front lawn were three children’s bicycles and a plastic off-road-vehicle type toy. A pair of pickup trucks were parked in the driveway.

Carbon monoxide, or CO, poisoning is the leading cause of accidental poisoning in the United States, responsible for more than 2,100 deaths a year, according to the Journal of the American Medical Association.