In North America, the fall and winter months bring colder temperatures, requiring home and business owners to use heating equipment for interior climate control. Heating equipment can include traditional fossil-fuel burning fireplaces, high-efficiency gas-fired forced-air heaters, direct-vent and ventless fireplaces, and kerosene and electric space heaters. Some departments may also encounter home cooking appliances used as improvised heating appliances, such as electric and gas ovens and stovetop burners.

Each call involving home heating equipment will challenge responders differently. We may be required to use unique extinguishment methods, climb into tight crawl spaces or attics to access the equipment, or ask occupants multiple questions about an odor’s history to find the source of a problem. Responders may also have to use gas meters to check for hazards in an occupancy.


On November 21, 2005, at 1452 hours, Evesham (NJ) Fire-Rescue responded to a carbon monoxide (CO) alarm activation at a two-story, single-family dwelling. Although the initial call was for an activated CO alarm, the engine crew’s vigilance in questioning the homeowner about the history of the CO alarm’s activation led crews to pinpoint the operation of a home heating appliance as the source of the deadly gas.

One four-member engine company responded and met the homeowner outside of the structure. He stated his CO detectors activated on the first and second floors. He was not feeling ill, and he was the dwelling’s sole occupant. After the activation, he opened all of the house’s windows and had been ventilating the house for about 15 minutes prior to the company’s arrival. A ventless gas-fired fireplace in the living room had been operating all day but had been turned off prior to our arrival.

The engine officer, using a departmental carbon monoxide alarm investigation report, interviewed the homeowner on the front porch. In the first part of this three-section form, the interviewer can determine the presence of any symptoms of CO poisoning among occupants, which potential CO sources have been shut off, and whether windows or doors have been opened to ventilate the structure.

The form’s second section, used by firefighters in searching for the source of the CO, provides space for marking CO readings obtained at various places in the occupancy. It includes a checklist of possible sources of CO (e.g. chimney, fireplace, portable heater), their condition (clogged, in an enclosed area), and the CO reading obtained at each device.

The final section provides the results of the fire department’s investigation. It details dangers of CO, whether a dangerous level of CO was found, the highest CO concentration detected, and the implications of various CO levels. The homeowner receives a copy of the complete report.


One firefighter wearing SCBA entered the residence with a three-gas meter [oxygen, CO, and lower explosive limit (LEL)]. The firefighter obtained no readings at the front door, at the stove, at the hot-water heater, at the home heater, or on any of the three floors.

With no readings present, the engine officer asked the homeowner to step inside and relight the fireplace to determine if it was the source of the CO. The homeowner was asked to close the living-room windows but leave the remaining windows in the house open, and then operate the fireplace.

Standing in the living room, the engine company officer noted new replacement windows in the 35-year-old structure. On further questioning, the homeowner indicated that the windows and fireplace were installed within the past year; a qualified plumber had installed the fireplace. Prior to CO detector activation, the fireplace had been operating all day (roughly seven hours).

The engine officer, the firefighter, and the homeowner stood across the room from the fireplace and monitored for CO readings as the fireplace was operating. We all remember from basic firefighter training that the level of oxygen in the air is normally around 20.9 percent. Our department’s meters alarm when oxygen reads a low of 19.5 percent or a high of 23.5 percent. As we monitored, our readings indicated the oxygen level in the house was around 20 percent-on the low side, we thought.

The firefighter did not receive any “alarm” readings and moved closer to the fireplace until he was about three feet away. There were still no CO readings present. However, as the firefighter was in front of the fireplace, the oxygen levels began to drop rapidly. The oxygen level dropped another 0.5 percent to 19.5 percent, activating the detector’s alarm. The firefighter then moved away from the fireplace about 10 feet, and the oxygen levels dropped even more rapidly to a low of 18.4 percent. At this time, we shut off the fireplace, ceased monitoring, and reopened the windows. But what do oxygen levels have to do with CO?


The crew surmised that several factors led to the CO detectors’ activation before our arrival. The house had newer replacement windows, making the house “tight” and relatively energy-efficient. Couple this piece of information with the fact that the home-owner had the fireplace operating all day. Putting the two pieces of the puzzle together, the crew concluded that the fireplace was actually operating normally but that it had consumed much of the oxygen in the house. As the oxygen level in the house dropped, the fireplace became inefficient and began to burn incompletely, resulting in the production of CO, which built up and activated the CO detectors.

The production cycle of CO and our findings and conclusions were explained to the homeowner. We advised the resident not to use the fireplace again until it was serviced to ensure proper operation and to call 911 again if the problem returned or anyone in the house felt ill. We presented the homeowner with a copy of the CO alarm form that contained our findings, as well as information on CO and its effects. We also advised the resident to read his fireplace operation manual before using it again. Many ventless fireplace manuals instruct homeowners to crack windows during operation to ensure plenty of oxygen and complete combustion.

This call could be considered a “typical” CO alarm call. It turned out to be anything but typical. The outcome of the investigation was positive-the homeowner was not injured, and there was no property damage. However, without the crew’s diligence, the outcome could have been fatal.


Detailed history. Responders must ensure that they obtain an accurate history of the problem for which they were summoned. Just as when on EMS calls the responders must obtain the complete history of the present illness, responding fire crews must investigate every angle for the source of the problem, which includes asking homeowners and occupants extensive questions and then piecing their answers together.

Gas detectors. A single-gas detector (CO only) would not have detected the low oxygen levels; remember, no CO was present during monitoring! Departments must invest in multiple-gas detectors, preferably those that sense the three most likely hazards on the majority of our calls (CO, oxygen, and LEL).

SCBA. All crew members must remember to wear SCBA for calls involving suspected IDLH (immediately dangerous to life and health) and oxygen-deficient atmospheres-this one certainly was. If necessary, the SCBA face piece could have been quickly donned. Members should use gas detectors during all investigation phases to ensure a safe operating atmosphere.

• • •

As responders, we must do our very best to ensure that when we leave an occupancy, it is safer than when we entered it. This holds true for structure fire calls (i.e., is the fire out?) to alarm system calls (why did it activate?) to other calls for service (is there any CO in the house?). The public trusts us to provide solutions for their problems. Sometimes, we find a problem that we can mitigate; other times, the problem may not be obvious. However, in either case, we must educate homeowners so that they can make informed decisions regarding their safety even after we depart. In this case, the crew spent time listening to the homeowner, investigating his problem, and informing him of the situation found and the steps he could take to prevent further problems. The crew cleared the call, knowing that the homeowner was left safer because of the information and findings they provided him.

Author’s note: Although not available electronically, a copy of the Carbon Monoxide Investigation Report form can be obtained by sending a stamped, self-addressed envelope to Lt. Carl Bittenbender, Evesham (NJ) Fire-Rescue, Fire Station 223, 150 Merchants Way, Marlton, NJ 08053; e-mail: cbittenbender@eveshamfire.org .

CARL BITTENBENDER is a lieutenant with Evesham (NJ) Fire-Rescue. A nine-year member of the fire service, he is a National Fire Protection Association fire officer II, a New Jersey-certified fire instructor II, and a certified CPR and EMT instructor. He has a bachelor’s degree in economics from the University of Delaware and a master’s degree in public safety from Saint Joseph’s University in Philadelphia, Pennsylvania.

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