Carbon monoxide poisoning is the most common cause of injury and death due to poisoning worldwide. In many industrialized countries carbon monoxide is the cause of more than 50 percent of fatal poisonings. It has been estimated that more than 40,000 people per year seek medical attention for carbon monoxide poisoning in the U.S. alone, and there are about 4,000 fatalities from carbon monoxide poisoning each year in the U.S. Contrary to many people’s perception hearth and barbecue products are only responsible for a very, very minor portion of carbon monoxide poisoning incidents.

A discussion of mortalities and morbidities is never pleasant but it’s prudent for responsible members of the hearth and barbecue industries to have an understanding of the role their products play in carbon monoxide health impacts. After all, carbon monoxide (CO) is produced in varying amounts from the incomplete combustion of all fossil and biomass fuels and, of course, other than electric units, heaters, fireplaces, and barbecues all burn fossil or biomass fuels and they all burn them with less than a hundred percent efficiency. Importantly, the public is concerned, and rightly so, about the dangers of carbon monoxide.

Anyone who watches the nightly news or reads a newspaper knows the media focus on sensationalism. Mundane yet important information does not attract sponsors or advertisers. It’s no different with carbon monoxide incidents. Headlines are replete with captions such as “Four Found Dead in Maine Cabin, Carbon Monoxide Poisoning Eyed,” “Neighbors Mourn Family of Eight in Carbon Monoxide Tragedy,” “Twenty Suffer Carbon Monoxide Poisoning from Indoor Grill,” and “Carbon Monoxide Leak Hospitalizes eleven.” 

It’s understandable how the public might come to think that heaters, fireplaces and barbecue grills are pretty dangerous things. The mundane fact that does not get disseminated is that hearth and barbecue units, in the overall scheme of things, play a very small role as compared to other sources of carbon monoxide health impacts. Often, when they are implicated in an incident, it’s found that the product in question was in disrepair or grossly misused, such as using a charcoal grill indoors.

Nationally Hearth and Barbecue Units Are Only Minor Sources of Carbon Monoxide

The U.S. Environmental Protection Agency (EPA) compiles annual emission inventories for various air pollutants, including carbon monoxide. An emission inventory is simply a tally of the amount of pollutant produced by each category of air emissions sources. For carbon monoxide, the two key classes of sources are: (1) internal combustion (i.e., engines) versus (2) external combustion (e.g., heaters and open fires). Mobile internal combustion engines are overwhelmingly the most significant sources of carbon monoxide, not residential stationary combustion sources such as hearth and barbecue units.

Residential hearth and barbecue products are only responsible for a small portion of carbon monoxide emissions. Their portion falls within the eight percent stationary fuel category. Other sources such as commercial activities, centralized furnaces, generators, lawn mowers, leaf blowers, etc., also share that eight percent. It should be noted that non-road mobile sources include aircraft, vessels and locomotives, and that some industrial sources such as aluminum potlines, while there are not many of them, individually are big producers of carbon monoxide. Data are from U.S. EPA for 2008. Note: the image next to the “Industrial and Other Processes” slice of the pie is not just any image for any industrial source but it is specifically an aluminum potline which produces lots of CO.

Carbon Monoxide from Hearth and Barbecue Products Currently Poses Little Health Threat Outdoors

Carbon monoxide levels in most ambient air in the U.S. are below health standards. (Ambient air is defined as air external of buildings where the public has access.) The U.S. EPA identifies six pollutants as “criteria” air pollutants. They are called “criteria” air pollutants because they are regulated by developing human health-based and/or environmentally-based criteria. These criteria are promulgated as National Ambient Air Quality Standards (NAAQS). 

Carbon monoxide is one of the six criteria pollutants. Particulate matter, probably familiar to many readers due to residential wood combustion’s emission of particles, is another. If an area exceeds the NAAQS for a specific criteria pollutant it’s deemed as a “nonattainment” area. Significantly, there are currently no carbon monoxide nonattainment areas in the U.S. In contrast, there are, based on a rough count, currently 77 counties that are in total or in part nonattainment for particulate matter. 

Outdoor (ambient) levels have fallen in the United States due primarily to reduction in mobile source emissions. U.S. EPA data.

There were originally nonattainment areas for carbon monoxide but as of 2010 they have all achieved attainment and have been redesignated as “maintenance” areas. The “maintenance” has to do primarily with reduction in vehicular emissions, oxygenated vehicular fuels, and traffic controls. Hearth products play only a minor role or no role at all in the various maintenance plans. Not surprisingly, diurnal carbon monoxide levels in urban areas follow transportation cycles, and carbon monoxide has been shown to build up in urban street “canyons,” particularly in cities at higher elevations where mobile source engines are less efficient.

Bottom line is that for hearth or barbecue products to reasonably pose a threat to human health, an enclosed space is required, not the wide-open spaces of the outdoors, plus ambient levels of carbon monoxide have been on the decrease in any event due to mobile source controls.

Carbon Monoxide from Hearth and Barbecue Products Has Little Environmental Impact.

Carbon monoxide from hearth or barbecue units, or any source for that matter, has little environmental impact. This is illustrated by the lack of a national secondary standard for carbon monoxide. The Clean Air Act requires the EPA to set national ambient air quality standards (Title 40 Code of Federal Regulations) for pollutants considered harmful to public health and the environment. 

Primary standards provide public health protection, including protecting the health of “sensitive” populations such as asthmatics, children and the elderly. Secondary standards are designed to protect the environment by providing public welfare protection, including protection against decreased visibility and damage to animals, crops, vegetation and buildings. There are six criteria air pollutants. All have both a primary and a secondary standard except carbon monoxide, which only has a health-based primary standard but no secondary environment-based standard as it was deemed unnecessary.

Additionally carbon monoxide, unlike carbon dioxide, is not known as a direct contributor to climate change. Carbon monoxide does have a small and indirect radiative forcing effect by elevating concentrations of methane and tropospheric ozone, but the overall contribution of carbon monoxide to climate change is very small as compared to the major greenhouse gases. Carbon monoxide is short lived with an atmospheric lifetime of about a month. Through natural processes in the atmosphere, it is eventually oxidized to carbon dioxide. 

One might think that since the carbon monoxide directly emitted eventually turns into carbon dioxide in the atmosphere, that it would be a significant climate change contributor. But it’s not so – it’s a matter of scale. Research directly measuring carbon monoxide emitted from a natural gas log set and a LPG log set, both used in a normal fashion that would be typical of a residential setting, illustrated this point. 

Over the course of the fire a total 0.34 grams of carbon monoxide were emitted from the natural gas log set and a total of 2.6 grams of carbon monoxide were emitted from the LPG log set. In the same fires, 6,329 grams of carbon dioxide and 7,710 grams of carbon dioxide were emitted from the natural gas and LPG log sets, respectively. Now, when the carbon monoxide gets oxidized to carbon dioxide in the atmosphere a little mass is added with the addition of one more oxygen atom, so the 0.34 grams and 2.6 grams of carbon monoxide corresponds to 0.53 grams and 4.0 grams of new carbon dioxide. 

When the numbers are compared there is 11,942 times (6,329/0.53) more carbon dioxide directly emitted in the fire than carbon dioxide formed in the atmosphere from the carbon monoxide emitted from the natural gas log set and 1,926 (7,710/4.0) times more carbon dioxide directly emitted in the fire than carbon dioxide formed in the atmosphere from the carbon monoxide emitted from the LPG log set. So it’s pretty clear that the carbon dioxide formed from the carbon monoxide does not matter much.

Hearth and barbecue units appear to be implicated in only a small fraction of carbon monoxide fatalities. On average about 170 people in the United States die every year from unintentional non-fire, non-vehicular carbon monoxide accidents, which represent only four percent of the total. Further, hearth and barbecue units are only responsible for a very small fraction of that four percent. *It should be noted that the average annual fatality comparisons are approximate because different base years have been used in the averaging and there are often multiple causes of death due to fire incidents.

Guilt by Association

Three unfortunate scenarios increase the public’s angst with carbon monoxide, yet direct carbon monoxide emissions from neither hearth or barbecue units are directly implicated with them; they are (1) suicides, (2) accidental poisoning associated with motor vehicles and (3) deaths from smoke inhalation from fires.

Suicides. Sadly, the Centers for Disease Control and Prevention (CDC) reports that each year, more than 2,000 people commit suicide by intentionally poisoning themselves with carbon monoxide. Vehicular exhaust is the most common method.

Accidental Vehicular Exposure. Besides the intentional deaths, an additional 268 accidental deaths occur annually from vehicles. Data show that about 82 percent occur from stationary vehicles with the remaining 18 percent in moving vehicles. Accidental carbon monoxide poisonings can occur when a vehicle is idled in a garage or other enclosed structure. 

Another potential source of carbon monoxide exposure is when the exhaust pipe on a running vehicle is blocked, which can cause carbon monoxide to seep into the vehicle's interior through leaks or cracks in the floorboard. Incidents have occurred when a car's exhaust pipe became blocked in ice or snow from a heavy snowfall, by a passing plow, or after backing into a snowbank.

Smoke Inhalation. The U.S. Fire Administration reported 3,005 deaths from fires in 2011. Most fire deaths are not caused by burns, but by smoke inhalation. It has been estimated that 50 percent to 80 percent of fire deaths are due to smoke inhalation. Autopsies of fire victims have shown that as many as 50 percent or more have lethal levels of carboxyhemoglobin in their blood from carbon monoxide exposure.

Non-fire, Non-vehicular Accidental Fatalities from Carbon Monoxide Poisoning

As previously noted on average, about 170 people in the United States die every year from carbon monoxide produced by non-vehicular consumer products. The Consumer Product Safety Commission (CPSC) report using the most recent data specifically for 2011 shows the number as 160 deaths for 2011. Seventy-seven percent of these incidents involved a single fatality. The consumer products included (1) malfunctioning fuel-burning appliances such as furnaces, ranges, water heaters and room heaters; (2) fireplaces; (3) charcoal that is burned in homes and other enclosed areas; and importantly (4) engine driven tools (EDT’s) such as portable generators. The key findings of the CPSC report include:

• Engine-driven tools were associated with the largest percentage of non-fire carbon monoxide poisoning fatalities at 44 percent (70 deaths). Sixty-three of the 74 EDT-related deaths (including three of the five multiple product deaths that involved an EDT – see bulleted section on multiple products) involved generators. 
  In 2005 there were at least 94 generator-related carbon monoxide poisoning deaths, 47 of these deaths were known to have occurred during power outages due to severe weather, including Hurricane Katrina.
• Heating systems-related carbon monoxide fatalities were associated with 31 percent of non-fire carbon monoxide poisoning fatalities (49 deaths). Of the estimated 49 heating systems-related fatalities in 2011, 34 deaths involved gas heating equipment. Natural gas heating equipment accounted for seven deaths. LPG heating equipment accounted for 15 deaths; and an additional 12 deaths were identified as unspecified gas heating. 
  Among the other fuel types used in heating systems: oil-fueled (two deaths), kerosene-fueled (two deaths), coal-fueled (three deaths) and wood-fueled (one death). Five additional fatalities were associated with heating systems, where the fuel type could not be ascertained. 
  Of the estimated seven deaths in 2011 that were associated with natural gas heating systems, six involved installed furnaces. One additional fatality was associated with a natural gas-fueled heater of unknown type. Of the estimated 15 deaths in 2011 that were associated with LPG heating systems, 11 involved unvented portable propane heaters. These unvented portable propane heaters were fueled by a propane tank and were not a component of an installed heating system. Unvented portable propane heaters were either camping heaters that used disposable propane tanks, one-pound propane bottles, or tank top heaters that used bulk tanks larger than one pound.
• Charcoal grills or charcoal were associated with five percent of non-fire carbon monoxide poisoning fatalities (eight deaths). In most cases these deaths occurred from the burning of charcoal indoors or in a confined space.
• Gas ranges and ovens were associated with five percent of non-fire carbon monoxide poisoning fatalities (eight deaths).
• Gas water heaters were associated with five percent of non-fire carbon monoxide poisoning fatalities (eight deaths).
• A multiple products category also comprised five percent of the total (eight deaths). All of these deaths were associated with more than one EDT and/or heating system being used.

Heating systems represent 31 percent of the 160 accidental, non-vehicular fatalities in 2011. Charcoal grills and charcoal represent five percent. It should be remembered that the accidental, non-vehicular death category already represents only about four percent of the total annual fatalities and that hearth products are only a portion of the heating system category. *EDT = Engine-Driven Tools, 63 of the EDT deaths (three were in the multiple product category) were due to generators. **MPC = Multiple Product Category (more than one EDT and/or heating system being used). ***Other = lanterns, camp stoves and grills, and other products.

Some heating system carbon monoxide fatalities in 2011 were caused by each fuel type but many were not burned in traditional hearth products. For example, as shown by the asterisks, of the 15 deaths caused by LPG heating systems, 11 involved unvented portable propane heaters. Of the seven deaths caused by natural gas heating systems, six involved installed furnaces, and one was a heater of unknown type.

Detection

Carbon monoxide is an odorless and colorless gas. Because it’s impossible to see, taste or smell, carbon monoxide poisoning can occur before a potential victim is aware it’s in the home. Any fuel-burning appliance can be a source of harmful carbon monoxide levels. Fuels, such as natural gas, LPG, kerosene, oil, coal and wood can produce large amounts of carbon monoxide when there is insufficient oxygen available for combustion. 

Where and When Eighty-three percent (133 deaths) of the 160 carbon monoxide deaths from consumer products in 2011 occurred in a home location. Of these 133 estimated fatalities, 10 occurred in an external structure at a residence, such as a shed or detached garage, and six occurred in a non-fixed location domicile (e.g., camper trailer or boat) used as a permanent home, or a structure not designed for habitation used as a home (e.g., sea-land shipping container, metal shed). Additionally, an estimated 10 percent (16 deaths) occurred in tents, camper trailers, and other temporary shelters. During 2006-2010, 73 percent of municipal fire department responses to carbon monoxide incidents were at one- or two-family dwellings and 17 percent were at apartments or multi-family dwellings. More carbon monoxide fatalities occurred in the cold months of the year. In 2011, 51 percent (82 of 160 deaths) occurred during the four cold months of November, December, January, and February. This is not surprising in that more heating is required then, homes are closed up tight to conserve heat, and there are generally more storms causing power outages and requiring generators to be used. While not considered here a consumer product, vehicles also often are “warmed up” before use in an enclosed or attached garage during cold weather. Carbon monoxide calls to fire departments are more common during the early evening hours.

Consumer products that burn kerosene, oil, coal, or wood (such as wood stoves, oil boilers, and kerosene heaters) produce an irritating smoke that can alert the victim to a potentially hazardous situation. EDT powered by gasoline engines produce large amounts of carbon monoxide, even when they are run where there is sufficient oxygen available for combustion; yet EDT may not emit an irritating exhaust smoke. 

Other fuels, such as charcoal briquettes and pressed wood-chip logs produce relatively smokeless fires, even at times of inefficient combustion. In these cases, victims receive no obvious sensory warning that high carbon monoxide levels are present. Another hazard scenario is present when gas appliances are not vented properly or are malfunctioning. 

Natural gas and LPG burn more efficiently and cleanly, compared with other forms of fuel. In circumstances of poor maintenance, inadequate ventilation, or faulty exhaust pathways, natural gas and LPG appliances may be responsible for high amounts of carbon monoxide without any irritating fumes; leaving a home occupant unaware of a potential problem.

With the advent of carbon monoxide alarms and detectors the risk of accidental indoor carbon monoxide poisoning has been greatly diminished. There is some confusion about the differences between a carbon monoxide alarm, a carbon monoxide detector, and a smoke detector (alarm). A carbon monoxide alarm is a stand-alone unit that is tested to Underwriters Laboratory (UL) Standard 2034 and has its own built-in power supply and audible device. These units are typically installed in a single-family dwelling. 

A carbon monoxide detector is a unit that is tested to UL Standard 2075 and is designed to be used with a fire alarm system and receives its power from the fire alarm panel. Smoke detectors (household smoke detectors are sometimes referred to as smoke alarms) detect smoke by responding to the presence of particles formed by incomplete combustion of fuel, not carbon monoxide gas. Combination smoke detectors and carbon monoxide alarms are available for home use.

The majority of states recognize the value of a carbon monoxide alarm or detector. States with carbon monoxide legislation for various types of habitable structures (homes, schools, hotels, daycares, etc.) as of May 2014 are shown. As of August 2015, 29 states have enacted statutes regarding carbon monoxide detectors, and another 11 have promulgated regulations on CO detectors.

Morbidities from Carbon Monoxide Poisoning

During 2006-2010, municipal fire departments responded to an annual average of 72,000 carbon monoxide incidents, excluding incidents where nothing was found or fire was present. It has been estimated that more than 40,000 people per year seek medical attention for carbon monoxide poisoning in the U.S. While solid statistics on the causes of the fortunately much fewer fatalities from carbon monoxide poisoning are available and show that hearth and barbecue products are only a very minor fraction of the problem, less data are available from non-lethal illnesses caused by carbon monoxide. 

At lower levels of exposure, carbon monoxide causes mild effects that are often mistaken for the flu. These symptoms include headaches, dizziness, disorientation, nausea and fatigue. Carbon monoxide may not result in obvious symptoms of carbon monoxide poisoning at the time of exposure, yet exposure to low levels of carbon monoxide can cause long-term health damage even after the carbon monoxide source is no longer present. 

*In addition to the appliances identified in the table as potentially hearth products there were eight deaths from heating systems identified as “Unspecified Heater/System,” of which one or more could have been a hearth product. Most heater related deaths were from furnaces, boilers and portable heaters – not traditional hearth systems.

These health effects include long-term neurological damage such as learning and memory impairments, emotional and personality effects, and sensory and motor disorders. EPA’s National Ambient Air Quality Standards for carbon monoxide were not designed to protect human health from long-term or regular exposure to low levels that might occur in a residence with a malfunctioning appliance or inadequate venting, but more for episodic exposures. 

Further, people, often older adults with pre-existing conditions, such as, cardiovascular disease, anemia and diabetes, along with the developing fetus, and visitors to unfamiliar high altitudes already have compromised tissue oxygenation capabilities, which are expected to place them at greater risks from a given carbon monoxide level. Similarly, smokers have elevated levels of carboxyhemoglobin in their blood, which makes them more susceptible to carbon monoxide poisoning. (Carboxyhemoglobin is formed from hemoglobin in the blood by the inhalation of carbon monoxide and hence reduces the amount of hemoglobin available to transport oxygen throughout the body.) 

Not surprisingly, as carbon monoxide concentrations and exposure times increase so does the seriousness of health impacts. A few hours exposure at less than a 100 ppm carbon monoxide level usually has no acute effects on otherwise healthy individuals, whereas a few hours exposure with carbon monoxide levels of about 1,000 ppm can cause coma and death. The average carbon monoxide level in homes ranges from 0.5 ppm to five ppm. 

Though there are no clear data documenting the relative importance of the various sources of non-lethal carbon monoxide, logic would suggest that while residential heating and cooking may play a somewhat larger role, hearth and barbecue products are still small players as compared to vehicular sources and generators.

What Can Be Done to Further Reduce Carbon Monoxide Health Impacts from Hearth Products?

Well, a lot has already been done as witnessed by the very small role hearth products play in carbon monoxide incidents. This small role is particularly impressive when one considers that hearth products are in tens of millions of homes. Our industry has been responsible: (1) Gas appliances are tested to American National Standard Institute (ANSI) standards for low carbon monoxide concentration in their flue gas. (2) Wood heaters and their wood-burning brethren have been and will be more stringently tested in the future for low particulate emissions to comply with EPA’s New Source Performance Standards (NSPS). Low particulate emissions are, in the most part, achieved by more complete combustion, which will also tend to reduce carbon monoxide emissions. (3) Many wood-burning

fireplaces have been EPA qualified for low particulate emissions and, as with certified wood stoves, this will, in most cases, cause them to have lower carbon monoxide emissions. (4) Vent-free gas units are required to have oxygen depletion sensors that reduce carbon monoxide risks, and there are guidelines for their use to avoid possible carbon monoxide exposure.

Carbon monoxide alarms and detectors are becoming more commonplace (often mandated by regulations) and there is even an installation standard to be used when carbon monoxide detection and warning equipment is installed in buildings or structures. (National Fire Protection Association NFPA 720: Standard for the Installation of Carbon Monoxide (CO) Detection and Warning). With the increased use of properly installed carbon monoxide alarms and detectors, clearly future in-home carbon monoxide incidents would be expected to decrease.

Finally, the continued certification of professionals who install and maintain hearth products and their venting systems will unquestionably reduce future carbon monoxide incidents. Notable are: (1) The training and certification offered by the Chimney Safety Institute of America (CSIA) that importantly includes how to inspect and service chimney systems, and (2) the training and certification provided by the National Fireplace Institute (NFI) for the installation of residential hearth appliances and venting systems.

Footnote:

Data in this article from the U.S. Environmental Protection Agency (EPA), Centers for Disease Control (CDC), National Fire Protection Association (NFPA), Department of Transportation, U.S. Fire Administration, and Consumer Product Safety Commission (CPSC).

About the Author

Dr. James E. Houck has been involved in environmental research and the hearth industry for over 30 years. He currently is an independent consultant and can be reached via email.