On Sunday, March 3, 2002, mem-bers of the B-shift assigned to Fairfax County (VA) Fire Station One in McLean had finished a full day of training in unseasonably warm, spring-like weather when they received a telephone call from a nearby garden apartment complex. The caller stated she had smelled a “funny odor” and had seen “mold” leaking from the radiator in her apartment for several days. Rescue 401, one of the department’s heavy rescue/hazardous-materials companies, responded to investigate. Company members, all certified firefighter/EMTs and haz-mat technicians, weren’t sure what to expect. On arrival, we took handlights, small tools, and a four-gas atmospheric monitor incorporating oxygen (O2), carbon monoxide (CO), and hydrogen sulfide (H2S) sensors, a combustible gas indicator (CGI) calibrated to methane (CH4), and an internal sample-drawing pump. Before leaving the rig, we tested the monitor against a “bump gas” mixture containing known concentrations of the aforementioned gases.

The resident met us at the front door with her eight-year-old son. We stepped inside a typical two-bedroom apartment built in the early 1970s. She told us she had called the maintenance department the previous day because she was worried about a gas leak. Maintenance personnel told her not to worry since all of the systems and appliances were electric and heat was provided using hot water from a central boiler distributed through radiators located in each apartment.

Soot stains on the radiator/blower unit cover. (Photos by Craig Furneisen Sr.)

Within one minute, as she related this story, our atmospheric monitor went into alarm, displaying rapidly escalating CO readings and a negative reading in the CGI section. Initially, thinking that the monitor had gone haywire, we brought in another device and approached the child’s room, which the occupant identified as the source of the “leaking mold.” She had kept the door to this room closed all day with a bath towel stuffed along its base. Again, our monitor went into alarm for CO, with readings fast approaching 100 parts per million (ppm) in the hallway.

After asking the occupants to step outside and opening the sliding glass door to the balcony for ventilation, we cracked the door to the child’s room and placed the detection probe inside. CO readings in this room quickly exceeded 300 ppm. Investigating further, we entered the room and saw what appeared to be soot stains on the louvers of the radiator housing (see photo 1) and on the carpet underneath. This is what the resident identified as “mold” (see photo 2). A fan control switch, still in the “on” position, was located on the wall, but we couldn’t hear the fan running. CO readings at this point were in the 370 to 400 ppm range, so we opened the windows and special-called a ladder tower to assist with ventilation.

Removing the radiator cover, it became apparent that while hot water from a central boiler located elsewhere in the complex provided the heat, each radiator unit had an electric motor-driven fan to distribute heated air throughout the room. This electric motor, original equipment from circa 1973, had finally given up and burned out. Although it did not produce enough heat to ignite surrounding combustibles, the burning motor was the source of the soot stains around the radiator and released relatively large quantities of CO throughout the apartment. When the ladder tower arrived, members set up electric fans and performed mechanical ventilation for about 10 minutes, until CO readings throughout the apartment were reduced to 0 ppm. We called the after-hours number for building maintenance. They sent someone over. We explained the problem. He began making repairs immediately.


  • Carbon monoxide incidents are not just a cold-weather phenomenon. They can happen anytime, anywhere. Fire departments often think carbon monoxide calls are strictly a cold-weather problem or one principally involving appliances burning fossil fuels, wood stoves, fireplaces, or vehicle exhaust. But CO can be present in toxic concentrations whenever and wherever incomplete combustion occurs. Particularly in residential settings, never assume CO is not present unless confirmed by a properly calibrated and functional atmospheric monitoring device.
  • Consider installing CO detectors on every floor of every residence. This incident suggests that, just like smoke detectors, CO detectors should be installed on every floor of every residential occupancy-regardless of the climate, type of appliances used, and heating/cooling system. The apartment in this case did not have a CO detector.
  • Expect the unexpected. Our initial response was for “leaking mold,” but to rule out other possibilities, we took a four-gas atmospheric monitor inside and were glad we did. Never take any incident at face value.
  • Always wear appropriate personal protective equipment, no matter how “routine” an incident might seem. For reported incidents involving any unknown substances, however innocuous or unlikely they might seem at first, always wear protective clothing and self-contained breathing apparatus.
  • Use natural ventilation where possible at CO incidents. Since gasoline-powered blowers produce carbon monoxide during operation, natural ventilation supplemented with electric fans seems preferable for ventilating residences containing high concentrations of CO.

Carbon Monoxide

Carbon monoxide (CO) is a colorless, odorless, and toxic gas produced by the incomplete combustion of solid, liquid, and gaseous fuels.1 In general, the fires most often encountered by firefighters are characterized by incomplete combustion, so anticipate the presence of CO after every fire, however small. Do not remove self-contained breathing apparatus (SCBA) until CO concentrations are reduced to safe levels and this is confirmed by a properly calibrated atmospheric monitoring device.

The interior of the radiator/blower unit. Note visible soot stains along the top edge and on the carpet underneath the unit. This was the “leaking mold” reported initially. It resulted from the burned-out blower motor in the middle of the unit.

Several recommendations currently exist with respect to what constitutes a “safe” level of CO in a residence or workplace. The National Institute for Occupational Safety and Health (NIOSH) sets its recommended daily exposure limit for a 40-hour workweek at 35 parts per million (ppm).2 Considering a workday typically spans eight to 10 hours and, depending on the background CO concentration in the air outside, it follows that the maximum acceptable CO levels in residences occupied around-the-clock should be roughly one-third of 35 ppm, ranging from nine to 15 ppm.

Although the effects of CO on individuals depend on variables such as age, medical condition, and the dose/duration of exposure-sustained exposure to CO concentrations greater than 70 ppm may cause symptoms including headache, fatigue, and nausea; as levels exceed 150 to 200 ppm, disorientation, unconsciousness, and death become possible.3 Symptomatic patients or those exposed to CO concentrations of this magnitude should receive a thorough medical evaluation based on local emergency medical service protocols and procedures.


  1. While the toxicity of CO is usually considered its primary hazard, it can also be flammable in very high concentrations-the NIOSH Pocket Guide to Chemical Hazards cites a lower explosive limit (LEL) for carbon monoxide of 12.5 percent gas in air, which is equivalent to 12,500 ppm.
  2. NIOSH Pocket Guide to Chemical Hazards, National Institute for Occupational Safety and Health. (United States Government Printing Office, Washington, D.C., 1997), 54.
  3. “Carbon Monoxide Questions and Answers, CPSC Document #466,” accessed online 3/26/02 at (Consumer Product Safety Commission, 2002).

ADAM K. THIEL is a career lieutenant with the Fairfax County (VA) Fire and Rescue Department, currently assigned to Rescue Company 401 in McLean. A member of the Hazardous Materials Response Team and nationally registered paramedic, he also teaches for Northern Virginia Community College and is working on a doctorate in public policy at George Mason University.

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