Skip directly to content

The Dangers of CO

The Dangers of Carbon Monoxide – What You Don’t See Can Kill You

What is carbon monoxide?

What is carbon monoxide made of?

What are the most common sources of carbon monoxide?

How does carbon monoxide appear in a house?

What can cause high levels of carbon monoxide in the air?

How is carbon monoxide poisoning diagnosed?

Why is carbon monoxide so dangerous?

Are some people more sensitive to carbon monoxide than others?

How can I protect my family from carbon monoxide poisoning?

Are all carbon monoxide alarms the same? Which ones should I buy?

How reliable are biotechnology carbon monoxide alarms?

Are carbon monoxide alarms enough to protect the sensitive population?

What should I do if my CO alarm or monitor goes off?

Besides installing CO alarms, what can I do to protect my family from the dangers of carbon monoxide?

What does a licensed professional check for in appliances?

What is the risk of carbon monoxide poisoning by car exhaust?

What is the real cost of carbon monoxide poisoning to society?

 What are the charateristics of carbon monoxide gas?

Invisible, odorless and tasteless, carbon monoxide (CO) is a very poisonous gas that can kill quickly and without warning. Statistics from the Journal of American Medical Association show that over 5600 U.S. deaths per year are due to carbon monoxide poisoning. 3100 of them are accidental, including 50% from fires, 36% from engine exhaust, and 14% from home appliances (1). While we mostly hear about carbon monoxide poisoning deaths, CO poisoning can happen at non-lethal levels and often go unnoticed. Home appliances are the biggest culprits of CO emissions, causing unexplained headaches or flu-like symptoms. Since other illnesses can produce similar symptoms and doctors do not always diagnose carbon monoxide poisoning properly, it is essential to monitor CO levels in your home at all times. Since you cannot see, hear, smell or taste carbon monoxide, your best protection from CO poisoning is to: Install carbon monoxide alarms in your home! Understand carbon monoxide poisoning and how it could hurt your family.

 What is carbon monoxide made of?

Carbon monoxide (CO) is made of one molecule of carbon (C) and one molecule of oxygen (O).  It is often produced by the incomplete combustion of fossil fuels used in home appliances, fireplaces, charcoal BBQs, vehicles, etc. Carbon monoxide is sometimes confused with carbon dioxide (CO2), which is the gas used to make sodas. We exhale 3.8% of CO2 with every breath and the gas is not toxic except at extremely high concentrations. For example, in 1986 the deep Lake Nyos, West of Cameroon, Africa, suddenly released enormous quantities of CO2 overnight, killing more than 1700 people and livestock. Learn more about this strange phenomenon.

 What are the most common sources of carbon monoxide?

The illustration below features the various house appliances that can emit carbon monoxide, including:

  • All fossil fuel powered heaters, water heaters, and furnaces
  • Other heaters using wood, coal, oil or other carbon-based fuels
  • Gas stoves, gas dryers, both gas and wood fireplaces
  • Cooking equipment such as ranges, ovens and BBQs
  • Engines used in power tools, snow blowers, gas or gasoline powered grass cutting equipment, trucks, autos and generators 

For a comprehensive review of all potential sources of carbon monoxide, please visit the CPSC website. 

 How does carbon monoxide appear in a house?

Fossil fuel burning appliances use a combustion process that produces small amounts of carbon monoxide. Appliances in good working order and properly vented, along with enough fresh air in your home to allow complete combustion, will generate non-dangerous, trace amounts of CO.

 What can cause high levels of carbon monoxide in the air?

Many factors can cause CO levels to rise to dangerous levels, such as:

  • Not installing an appliance properly
  • Not inspecting and repairing appliances (e.g. a cracked furnace heat exchanger can cause CO to leak in the house instead of venting out)
  • Using a forced air furnace that is over 20 years old, or a newer one that has been exposed to corrosive materials
  • Not inspecting and cleaning up outside vents (e.g. from bird nests)
  • Placing a portable generator less than 25 feet from the house
  • Keeping a smoldering fire (not properly extinguished) in the house or garage (e.g. grill or BBQ)
  • Leaving a vehicle running for more than a couple of minutes inside a garage or just outside of the house
  • Leaving a vehicle running for a long time while staying inside of it with the windows closed
  • Allowing the wind to blow carbon monoxide directly inside the house through windows or doors

What are the hidden dangers of carbon monoxide?


Even though your pool heater is located outside your house, a slight breeze could blow dangerous levels of carbon monoxide into it. This situation turned out deadly for one family. A contractor had installed a natural gas heater for their pool. Unfortunately the heater was installed improperly and then used for lengthy periods of time. One day, steady wind blew from the heater towards the house, causing dangerous CO levels to accumulate inside it. Unfortunately, the family’s three-year-old child was killed and the parents and several others were seriously poisoned.

Generators used outside but close to an open window can allow carbon monoxide to quickly enter the house. For safety, they should never be placed closer than 25 feet from a home. This happened to a nurse in Indiana who came home to find her husband and children dead, even though the generator they had been using was outside the home.

A family of four died in NJ from carbon monoxide poisoning, and the CO source was hard to find. There was no evidence of appliance malfunction or back drafting. Eventually inspectors found a dropped cigarette caused a mattress in the basement to slowly burn. The family never noticed the fire and the smoldering created lethal levels of CO to spread around the house while that family was sleeping.

 How is carbon monoxide poisoning diagnosed?

The initial symptoms of carbon monoxide poisoning are often non-specific, making it difficult to diagnose. Several tests are available to measure the CO levels in a person’s body: CO breath detectors, which are low-cost and non-invasive compared to blood tests.

A blood test, using near-infrared light to measure the absorption of carbon monoxide in the blood is commonly used.  Unfortunately many doctors don’t recognize the signs of CO poisoning (3). Research findings advise people presenting flu-like symptoms to be tested for CO poisoning (4), since 23.6% of flu patients could be suffering from it (5). That’s because carbon monoxide poisoning symptoms can include fatigue, nausea, headaches, dizzy spells, confusion, and irritability. Many other diseases can cause similar symptoms, making CO poisoning hard to pinpoint. Patients reporting headaches in the winter should also be vigilant about their health. One study at the University of Illinois Medical Center Hospital in Chicago, IL, showed that 18.9% of patients reporting headaches in the winter actually suffered from serious CO poisoning. Their carboxyhemoglobin (COHb) blood levels were over 10%, which requires immediate medical treatment (2).

 Why is carbon monoxide so dangerous?

When you breathe in carbon monoxide, it quickly attaches to the hemoglobin in your blood and creates carboxyhemoglobin (COHb). This bonding prevents oxygen from properly getting to your brain, other organs and muscles, causing damage to these vital organs very quickly.

High levels of CO are often fatal but low levels can also be dangerous. Long term, they can lead to cardiovascular diseases (heart attacks, strokes or arrhythmias). The percentage of carboxyhemoglobin in your body indicates how poisoned you have been. COHb levels over 10% require immediate treatment, but people with health issues can be affected at lower percentages (7). 

The best treatment for carbon monoxide poisoning is to deliver hyperbaric oxygen in a hospital setting. The victim is put in a chamber where the pressure and the concentration of oxygen slowly increases. 

 Are some people more sensitive to carbon monoxide than others?

Anyone can be killed or injured by carbon monoxide. However, some people are more sensitive to carbon monoxide poisoning, even at levels below 10% COHb. For example, smokers already have COHb present in their blood because the smoke contains carbon monoxide. Even second-hand smokers can be affected over time (8). 

An unborn fetus is also at risk because its blood will accumulate carbon monoxide at a much higher rate than the mother’s blood. A mother could have normal blood test results while her fetus is affected by carbon monoxide poisoning, causing injuries. At this time Quantum does not sell CO monitors for this application but recommends their use for sensitive populations, particularly pregnant women.

Most healthy people between the ages of 12 and 50 with COHb blood levels between 10 and 20% will not experience pain symptoms for an hour or two. People with severe angina are a lot more sensitive and will show serious CO poisoning symptoms with their COHb levels are as low at 4%. Measurable effects have been observed down to 2.5% (7).

 How can I protect my family from carbon monoxide poisoning?

Carbon monoxide is a by-product of incomplete combustion. If the vent for a furnace or water heater gets blocked, large amounts of CO are produced in just seconds. In one accident, the living room chair blocked the air return to the furnace, resulting in CO accumulation in the house and the tragic death of two babies.

The best and easiest way to protect your family from CO poisoning in to use carbon monoxide alarms located all around the house, including:

One in every bedroom (especially if you sleep with the bedroom doors closed and cannot hear the alarm in the hallway)

One on every floor of the house

One in the garage

One in the basement

One in the attic

All UL and ETL carbon monoxide alarms listed to UL2034 are designed to ignore low levels of CO (30 ppm – parts per million - for 30 days or more, as well as 70 ppm for 60 minutes), even if they are UL certified (UL 2034).  A low-cost solution to this problem is to purchase a color-indicating alarm, such as the Quantum Eye® 

 Are all carbon monoxide alarms the same? Which ones should I buy?

The best carbon monoxide detectors are “false-alarm” free to common household gases and vapors, typically disinfectants, insecticides, air fresheners, cleaners, and polishing products. False alarms can cause people to ignore the CO alarm, or even turn it off, which could lead to serious injury or death.

What are the dangers from false alarms?

The New York Times has reported on the risk of ignoring CO detector alarms. In a specific case, a CO alarm had gone off, but it turned out to be a false alarm. The second time the alarm went off, the owner of the alarm, who happened to be a doctor, simply unplugged the unit and went out to dinner while his four children and their baby sitter stayed home. Tragically, when he returned home, all five had died of carbon monoxide poisoning. Only one technology, Quantum biotech sensors (also called biomimetic or BIO), has been shown to be the most reliable and false-alarm free by the Lawrence Berkeley National Laboratory (LBNL), the leading national laboratory for indoor air quality (9). Quantum CO alarms using biotech sensors are available for purchase on this website or by calling 800.432.599.  For more information on the different technologies, you can read the LBNL’s carbon monoxide technology comparison research paper (24).  

The Gas Research Institute and Unified Engineering performed additional testing to compare the three CO alarm technologies: biotechnology (BIO), electrochemical (EC), and metal oxide semiconductor (MOS) (27, 28). Only Quantum’s biotechnology sensor based alarms were found to be completely false-alarm free.  BIO sensors are included in the following products:

  • Quantum Guardian® (all models) 
  • COSTAR® (all models)
  • Universal Security Inc. (USI) Model CD9000 

If you have ever had a false alarm with your current CO alarm, it is time to switch to a false-alarm free biotechnology carbon monoxide alarm such as the COSTAR® 9RV. 

 How reliable are biotechnology carbon monoxide alarms?

Biotechnology carbon monoxide alarms are extremely reliable, false-alarm free and the best way to protect your family from carbon monoxide poisoning. 

The current Underwriters Laboratory Standard UL2034 requires multi-level CO alarms to be tested under a variety of conditions, humidity levels and temperatures  (10). 

During the tests, carbon monoxide alarms are expected to perform as such:
• 30ppm of CO for 30 days must not set off alarm or signal in any way
• 70ppm of CO must set off alarm between 60-240 minutes
• 150ppm of CO must set off alarm between 10-50 minutes
• 400ppm of CO must set off alarm between 4-15 minutes

This means the current UL standards do not protect the sensitive population such as infants, small children, pregnant women and people with heart, blood or lung disease, or other serious illnesses. These people are susceptible to much lower levels of CO exposure than CO alarms available through retail chain stores can measure. Some very accurate alarms detecting low levels of CO for the sensitive population are available for purchase. 

Temperatures ranges include minus 40°C to plus 70°C.

Some tests like the 70°C test require preconditioning for 30 days for unconditioned space alarms and RV alarms but for normal conditioned space the requirement is three days. The high-humidity test for conditioned space is 52°C for seven days at 95% Relative Humidity (RH), followed by four CO tests, while the unconditioned space requirement is 67°C and 93% RH but the preconditioning is 10 days. There are many other differences, all listed in UL2034.


The UL sequential test takes two months for residential alarms (conditioned space and 4 months for unconditioned space alarms such as the Quantum Guardian® and the COSTAR® 9RV. 


 Are carbon monoxide alarms enough to protect the sensitive population?

A home CO alarm may not offer enough protection for someone who is part of the sensitive population. A more sensitive CO meter often is a better, safer choice. Read about the differences between CO alarms and CO meters. 

To learn more about CO meters and their uses in homes and businesses, visit these government websites:

Quantum does not sell carbon monoxide monitors that can accurately measure CO levels below 30 ppm at this time. If a pregnant woman, an infant, a child, or an elderly person lives in your house, it is best to set the CO monitor to 15 ppm. The same caution applies to people on drug treatment, smokers, with cardiovascular or cardio-respiratory diseases (heart and lung disease), sickle cell anemia, other anemia, leukemia, cancer, almost any blood disease, and other ailments

See CPSC Document #466.

 What should I do if my carbon monoxide alarm or monitor goes off?


The first thing to do is take everybody out the home, including pets, and call 911 for help outside. Do NOT ignore an alarm. Remember you may not feel any symptoms of carbon monoxide poisoning even though you may be affected. Sensitive people are even more at risk since they can get injured at levels below your CO alarm’s regular settings.

Wait for the first responders to arrive outside, at a neighbor’s house or in your car. Make sure the first responders ventilate your home before you go back in. Leave some windows open at all times until you have a professional fix the problem and you test to make sure your CO alarms will not go off again.


 Besides installing CO alarms, what can I do to protect my family from the dangers of carbon monoxide?

TThe best way to keep your family safe is to have a certified or licensed HVAC contractor check your appliances annually. Your gas utility company can also check all your gas burning appliances, venting and chimney systems. For oil or solid fuel appliances, ask your supplier to check your appliances, venting and chimney systems. Unless you are a licensed appliance repairperson, use the services of a professional.

Backdrafting is a serious problem that can fool even the professionals. When the air inside the home is used by combustion appliances (e.g. water heater, fireplace, gas range, oven, furnace, gas dryer) new air needs to come inside to replace it. If the air is not sufficiently replaced, you get backdrafting. The pressure outside the home becomes greater than the pressure inside, and any exhaust, including carbon monoxide, is sucked back into the home. Exhaust fans, the wind and super tight homes can cause backdrafting.  Appliances can also play tug-of-war, sucking carbon monoxide back into the home.

Additionally reverse stacking can happen when the air available is limited and one appliance starts to process the exhaust of another appliance. This causes levels of CO to quickly increase while oxygen levels get depleted. Once oxygen levels are depleted from 20% to 18%, CO levels increase exponentially.


How dangerous is backdrafting?

In Lincoln, NE, a family of 10 was unaware their furnace was sucking carbon monoxide from their fireplace back into the house, quickly poisoning the air. This nearly killed the entire family. Fortunately they were able to get treatment in time and all of them recovered. They then decided to buy the best carbon monoxide detector technology made by Quantum to protect their family’s future.

A cracked heat exchanger in a forced air furnace can also cause carbon monoxide leaks. Unfortunately this is very difficult to test for without a CO monitor, and even a qualified technician can miss small cracks, which can occur as your furnace gets older.  Small cracks can become larger until you are suddenly exposed to dangerous CO levels. It is very important to install a CO alarm close to your furnace since you probably will not know when it starts leaking. 

The Quantum Guardian® Model QG100 and the COSTAR® 9RV carbon monoxide detectors are approved for unconditioned space such as attics, garages and basements.


 What does a licensed professional check for in appliances?

When you ask certified or licensed HVAC contractors to check all of your appliances for potential carbon monoxide risks, they will perform the following:
• Check your furnace, including all fuel connections, the flue and venting systems
• Measure the concentration of carbon monoxide in your flue gases
• Measure the CO levels in your home and locate any high sources
• Check and replace furnace filters annually
• Check the air purification system if applicable
• Check pool and spa heaters
• Check the exhaust blower and circulating blower system to ensure proper air flow
• Check the combustion chamber and heat exchanger for cracks, corrosion and any obstruction
• Check ignition systems and pilot lights
• Check fireplaces to ensure the flue is clear and functioning properly
• Check vent openings on gas dryers, as lint can block ventilation and cause CO to back up into the home
• Check all gas burners for clean blue color flames including top range burners, ovens, furnaces, heaters, water heaters, pool heaters and more

• Check the venting systems for all your appliances. Look for leaves and other signs of obstruction, damage to the vents and chimneys, and corrosion of the exhaust system 
• Check the pool heater and any other outside appliances for CO emissions
• Check your thermostat as a defective thermostat could cause the heat to stay on, waste energy and exacerbate any CO problems

 What is the risk of carbon monoxide poisoning by car exhaust?

Every year carbon monoxide from engine exhaust kills more people than CO emitted by home heating appliances (13-24). Carbon monoxide from a running vehicle in an attached garage can make its way into the house via backdrafting. Home appliances can create negative pressure and pull the car exhaust right into the house. One study funded by the Canadian Government found that 10% of all homes have a backdrafting problem (12). 


What are the source of carbon monoxide may not be inside your home?.

• Neighbors

Similar accidents have killed people in apartments, townhouses, even prisons.  There have been occurrences of one person committing suicide with their car in their townhouse, causing their close neighbors to also die of carbon monoxide poisoning. 

• Hotels

In 1980 the Las Vegas MGM Grand fire killed 85 people, mostly from smoke inhalation and carbon monoxide poisoning. While the fire originally occurred in the two-story casino building, most of the victims who were killed or injured happened to be on the top four floors of the adjacent high-rise. The casino building’s HVAC systems, stairwells and elevator shafts quickly allowed the carbon monoxide to diffuse and migrate to the top of the high-rise building next door. This hotel is now operated by Bally’s and known as Bally’s Las Vegas. A similar fire occurred at the Las Vegas Hilton hotel just 90 days after the MGM Grand fire, causing a major reform of fire safety guidelines and codes for Las Vegas hotels. However, there is still no requirement for carbon monoxide alarms in Las Vegas Hotels, so it is important to protect yourself.

To protect yourself from CO poisoning while traveling, you should use a small portable CO alarm or travel CO alarm. Color indicating badges are much smaller, lighter and cheaper but they only provide a visual warning. This means they will not wake you up and therefore are not safe when you are sleeping.  

 What is the real cost of carbon monoxide poisoning to society?

Deaths from carbon monoxide poisoning are just the tip of the iceberg. Non-lethal exposures can create significant brain damage and cardiovascular problems. A study by the Carbon Monoxide Health and Safety Association (COSHA) shows the cost per each death caused by heart attack is $44,000. Current medical cost estimates after a first heart attack are about $60,000/year. Medical costs over the 10 following years can add up to $600,000 per victim. Lost work and productivity are also important to measure, costing about $100,000 per victim per year (25). 

The estimated cost of a stroke is $65,000, but lost work can cost more than $1 million per victim over 10 years (25).  We do not know how many cardiovascular victims are linked to carbon monoxide poisoning. In comparison, CO levels emitted by a gas stove used for heating are usually greater than CO levels from passive smoking, which kills 50,000 people every year (26).  Hundreds of thousands, perhaps millions of people, are exposed to CO levels above 70 ppm from the misuse or malfunctioning of cooking equipment and other combustion processes in a single year.  COSHA has estimated the medical cost CO accidents of all kinds to our society to be $5.3 billion per year (25).  Add to it the cost of lost work and industrial accidents and you reach a staggering $88 billion over 10 years.  In contrast, equipping every home with two CO alarms would cost an estimated $6 billion over 10 years, which would save our society $82 billion.  The cost of a home CO detector is $20 to $30. CO detectors last about seven years, making their yearly cost between $3 and $5 – an easy, reasonable and safe solution to protect lives. 


(1)   N. Cobb and R. A, Etzel JAMA, August 7, 1991, Vol. 266, No.5 pages 659-663
(2)   Paul Heckerling, American Journal of Emergency Medicine Volume 5, Number 3, May 1987
(3) Michael C. Dolan, M.D. published paper in the Annals of Emergency Medicine 16.7 July 1987, pages 782-787
(4) Michael Dolan, MD, Canadian Med Assoc. Journal, Vol 133, September I, 1985
(5) Michael Dolan, MD, Annuals of Emergency Medicine, 1987, 16, 782-786
(6) T. L. Kurt et al., Chest. 74, 1, July 1978

(7) E. N. Allred et al. New England Journal of Medicine, Vol. 321 No. 11, Nov. 23, 1989 Pages 1426-1432. (8)

[Federal Register Volume 75, Number 19 (Friday, January 29, 2010)] EPA, Integrated Science Assessment for Carbon Monoxide (Final Report)The EPA 2010for CO has gathered specific data on the very low-level cumulative effects of second-hand smoke.

(9) Lara A. Gundel, Michael G. Apte and Albert R. Nematollahi, Carbon Monoxide Detector; “Technology Comparison: Report to Various Gases” Lawrence Berkeley National Laboratory Report LBNL-40556 July 1998

(10) Graph from Underwriters Laboratory Standard UL2034. This UL 2034 standard is available from UL for a fee.    

(11).  W. G. Berl and B. M. Halpin, Fire Journal, September 1978 pages 105 to 123.
(12) Sebastian Moffet, “Backdrafting Woes”, Canadian Mortgage and Housing       Corporation, Progressive Builder, November 1986.
(13) Hampson NB, Norkool DM. Carbon monoxide poisoning in children riding in the back of pickup trucks. JAMA 1992;267:538 40.
(14) CDC. Carbon monoxide poisonings associated with snow-obstructed vehicle exhaust systems -- Philadelphia and New York City, January 1996. MMWR 1996;45:1.
(15) Moolenaar RL, Etzel RA, Parrish RG. Unintentional deaths from carbon monoxide poisoning in New Mexico, 1980 to 1988: a comparison of medical examiner and national mortality data. West J Med 1995;163:431 4.
(16) Cook M, Simon PA, Hoffman RE. Unintentional carbon monoxide poisoning in Colorado, 1986 through 1991. Am J Public Health 1995;85:988 90.
(17) Baron RC, Backer RC, Sopher IM. Unintentional deaths from carbon monoxide in motor vehicle exhaust: West Virginia. Am J Public Health 1989;79:328 30.
(18) COSHA Report: The Cost of Unintentional Deaths and Injuries from Carbon Monoxide Poisonings in the USA, La Jolla, California, The Carbon Monoxide Safety and Health Association, 1997.
(19) Baker SP, O'Neill B, Ginsburg MJ, Li G. The injury factbook. 2nd ed. New York: Oxford University Press, 1992.
(20) Ilano AL, Raffin TA., Management of Carbon Monoxide Poisoning. Chest., 1990; 97:165 9.
(21) CDC. Unintentional carbon monoxide poisoning following a winter storm, Washington, January 1993. MMWR 1993;42:109 11.
(22) Ed Krenzelok, PharmD.  Krenzelok is currently the Director of the Pittsburgh Poison Center at Children's Hospital of Pittsburgh and the Director of the Schools of Pharmacy & Medicine, University of Pittsburgh (July2000 private communication).
(23) “Air Quality Criteria for Carbon Monoxide” June 2000 (EPA 600/P-99/001F).
(24) William B. Helfman, MD, Lara A. Gundel and, Michael G. Apte, “CO Detectors How Selective Are They?, Security Magazine September 1997.
(25) COSHA Report: The Cost of Unintentional Deaths and Injuries from Carbon Monoxide Poisonings in the USA, La Jolla, California, Carbon Monoxide Safety
and Health Association, 1997.
(26) “Air Quality Criteria for Carbon Monoxide” June 2000 (EPA 600/P- 99/001F).
(27) GRI (GTI) CO Alarm Reliability: Field Experiments, Laboratory Testing and Certification Standards, Presented at 2001 ASHRAE Winter Meeting, Atlanta, GA.