carbon monoxide poisoning

What is carbon monoxide poisoning

Carbon monoxide (CO) is a poisonous gas that has no odor, taste or color, also known as the “Invisible Killer”, because carbon monoxide is very dangerous. Because carbon monoxide is impossible to see, taste or smell the toxic fumes, carbon monoxide can kill you before you are aware it is in your home. The effects of carbon monoxide exposure can vary greatly from person to person depending on age, overall health and the concentration and length of exposure. Carbon monoxide can cause sudden illness and death. More than 400 people in the Unites States die every year from accidental non-fire related carbon monoxide poisoning associated with consumer products, including portable power generators used for temporary or remote electric power 1). A generator’s exhaust contains carbon monoxide. This is a poison you cannot see or smell. Never use a generator inside a home or garage, even if doors and windows are open. Only use generators outside and far away from windows, doors and vents. Other products include faulty, improperly-used or incorrectly-vented fuel-burning appliances such as furnaces, stoves, water heaters and fireplaces.

Carbon monoxide is also found in combustion fumes produced any time you burn fuel in cars or trucks, small engines, stoves, lanterns, grills, fireplaces, gas ranges, or furnaces. Carbon monoxide from these fumes can build up in places that don’t have a good flow of fresh air such as indoors and poison people and animals who breathe it.

Sources of carbon monoxide:

  • unvented kerosene and gas space heaters
  • leaking chimneys and furnaces
  • back-drafting from furnaces, gas water heaters, wood stoves and fireplaces
  • gas stoves
  • generators and other gasoline powered equipment
  • automobile exhaust from attached garages
  • tobacco smoke
  • auto, truck, or bus exhaust from attached garages, nearby roads, or parking areas
  • incomplete oxidation during combustion in gas ranges, and unvented gas or kerosene heaters
  • worn or poorly adjusted and maintained combustion devices (e.g., boilers, furnaces)
    • if the flue is improperly sized, blocked or disconnected
    • if the flue is leaking

Environmental carbon monoxide is produced by incomplete combustion of any carbon containing fuel (coal, petroleum, peat, natural gas). In Britain most accidents arise through central heating faults 2). By contrast, in the USA most deaths are caused by inhalation of exhaust fumes 3). In the United Kingdom car exhaust emissions of carbon monoxide have been reduced by catalytic convertors in all new cars. Surprisingly, when deaths occur in garages there have usually been open doors and windows 4). There are even reports of poisoning occurring from carbon monoxide inhalation in the open air 5). Methylene chloride (paint stripper) fume inhalation is a rare cause of poisoning. In the liver it is converted to carbon monoxide 6).

Why is Carbon Monoxide Dangerous?

When carbon monoxide is inhaled, it passes from the lungs into the hemoglobin molecules of red blood cells. Carbon monoxide binds to hemoglobin at the same site as and preferentially to oxygen, forming carboxyhemoglobin (COHb). Carboxyhemoglobin (COHb) interferes with the oxygen transport and gas exchange abilities of red blood cells. The result is that the body becomes oxygen-starved, which can result in tissue damage and death. Low levels of carbon monoxide poisoning cause symptoms similar to those of the flu or a cold, including shortness of breath on mild exertion, mild headaches, and nausea. Higher levels of poisoning lead to dizziness, mental confusion, severe headaches, nausea, and fainting on mild exertion.
Ultimately, carbon monoxide poisoning can result in unconsciousness, permanent brain damage, and death. Carbon monoxide detectors are set to sound an alarm before the exposure to carbon monoxide would present a hazard to a healthy adult. Babies, children, pregnant women, people with circulatory or respiratory ailments, and the elderly are more sensitive to carbon monoxide than healthy adults.

You can be poisoned by breathing in carbon monoxide. The most common symptoms of carbon monoxide poisoning are:

  • Headache
  • Dizziness
  • Weakness
  • Fatigue
  • Shortness of breath
  • Nausea
  • Vomiting
  • Chest pain
  • Confusion

Carbon monoxide symptoms are often described as “flu-like”  (but without the fever). If you breathe in a lot of carbon monoxide it can make you pass out or kill you. People who are sleeping, intoxicated or drunk can die from carbon monoxide poisoning before they have symptoms.

It is often hard to tell if someone has carbon monoxide poisoning, because the symptoms may be like those of other illnesses. A carbon monoxide detector can warn you if you have high levels of carbon monoxide in your home.

If you suspect that you are experiencing carbon monoxide poisoning, get fresh air immediately. Leave the home and call for assistance from a neighbor’s home. You could lose consciousness and die from carbon monoxide poisoning if you stay in the home. Get medical attention immediately and inform medical staff that carbon monoxide poisoning is suspected. Call the Fire Department to determine when it is safe to reenter the home.

  • Never leave a car running in a garage even with the garage door open.
  • Never run a generator in the home, garage or crawlspace. Opening doors and windows or using fans will NOT prevent carbon monoxide build-up in
    the home. When running a generator outdoors, keep it away from open windows and doors.
  • Never burn charcoal in homes, tents, vehicles, or garages.
  • Never install or service combustion appliances without proper knowledge, skills, and tools.
  • Never use a gas range, oven, or dryer for heating.
  • Never put foil on bottom of a gas oven because it interferes with combustion.
  • Never operate an unvented gas-burning appliance in a closed room or in a room in which you are sleeping.

Who is at risk from carbon monoxide poisoning?

Everyone is at risk for carbon monoxide poisoning. Infants, the elderly, people with chronic heart disease, anemia, or breathing problems are more likely to get sick from carbon monoxide. Each year, more than 400 Americans die from unintentional carbon monoxide poisoning not linked to fires, more than 20,000 visit the emergency room, and more than 4,000 are hospitalized.

A study conducted in Washington State 7) among minority populations showed that Hispanic populations had a four times greater risk and black populations had a three times greater risk than white populations for carbon monoxide poisoning. The most common source of carbon monoxide poisoning among those populations was burning charcoal briquettes. Approximately 66% of Hispanic victims and 40% of black victims became poisoned as a result of indoor burning of charcoal briquettes .

What carbon monoxide level is dangerous to my health?

The health effects of carbon monoxide depend on the carbon monoxide concentration and length of exposure, as well as each individual’s health condition. Carbon monoxide concentration is measured in parts per million (ppm). Average levels in homes without gas stoves vary from 0.5 to 5 parts per million (ppm). Levels near properly adjusted gas stoves are often 5 to 15 ppm and those near poorly adjusted stoves may be 30 ppm or higher.

Most people will not experience any symptoms from prolonged exposure to carbon monoxide levels of approximately 1 to 70 ppm but some heart patients might experience an increase in chest pain.

As carbon monoxide levels increase and remain above 70 ppm, symptoms become more noticeable and can include headache, fatigue and nausea. At sustained carbon monoxide concentrations above 150 to 200 ppm, disorientation, unconsciousness, and death are possible.

What should you do when the CO alarm sounds?

Never ignore an alarming carbon monoxide alarm! It is warning you of a potentially deadly hazard.

If the alarm signal sounds DO NOT try to find the source of the carbon monoxide:

  1. Immediately move outside to fresh air.
  2. Call your local fire department or your local emergency number.
  3. After calling your local fire department or your local emergency number, do a head count to check that all persons are accounted for. DO NOT reenter the premises until the emergency services responders have given you permission. You could lose consciousness and die if you go in the home.
  4. If the source of the carbon monoxide is determined to be a malfunctioning appliance, DO NOT operate that appliance until it has been properly serviced by trained personnel.

If authorities allow you to return to your home, and your alarm reactivates within a 24 hour period, repeat steps 1, 2 and 3 and call a qualified appliance technician to investigate for sources of carbon monoxide from all fuel burning equipment and appliances, and inspect for proper operation of this equipment. If problems are identified during this inspection, have the equipment serviced immediately. Note any combustion equipment not inspected by the technician and consult the manufacturers’ instructions, or contact the manufacturers directly, for more information about carbon monoxide safety and this equipment. Make sure that motor vehicles are not, and have not been, operating in an attached garage or adjacent to the residence.

Carbon monoxide poisoning complications

Depending on the degree and length of exposure, carbon monoxide poisoning can cause:

  • Permanent brain damage
  • Damage to your heart, possibly leading to life-threatening cardiac complications
  • Death.

Around 10-15% of people who have severe carbon monoxide poisoning develop long-term complications.

Carbon monoxide poisoning long term effects

Brain damage

Prolonged exposure to carbon monoxide can cause memory problems and difficulty concentrating. It can also cause vision loss and hearing loss.

In rare cases, severe carbon monoxide poisoning can cause Parkinsonism, which is characterised by tremors, stiffness and slow movement.

Parkinsonism isn’t the same as Parkinson’s disease, which is a degenerative neurological condition linked to ageing.

Heart disease

Coronary heart disease is another serious condition that can develop as a result of long-term carbon monoxide exposure.

Coronary heart disease is where the heart’s blood supply is blocked or interrupted by a build-up of fatty substances (atheroma) in the coronary arteries.

If the blood supply is restricted, it can cause angina (chest pains). If the coronary arteries become completely blocked, it can cause a heart attack.

Harm to unborn babies

Long-term exposure to carbon monoxide gas can also damage an unborn baby. Babies exposed to carbon monoxide during pregnancy are at risk of:

  • low birth weight
  • perinatal death (stillbirth and death that occurs within the first four weeks of birth)
  • behavioral problems

Carbon monoxide poisoning causes

Carbon monoxide poisoning is caused by inhaling combustion fumes. When too much carbon monoxide is in the air you’re breathing, your body replaces the oxygen in your red blood cells with carbon monoxide. This prevents oxygen from reaching your tissues and organs.

Various fuel-burning products and engines produce carbon monoxide. Normally the amount of carbon monoxide produced by these sources isn’t cause for concern. But if they’re used in a closed or partially closed space — such as using a charcoal grill indoors — the carbon monoxide can build to dangerous levels.

Smoke inhalation during a fire also can cause carbon monoxide poisoning.

Risk factors for carbon monoxide poisoning

Exposure to carbon monoxide may be particularly dangerous for:

  • Unborn babies. Fetal blood cells take up carbon monoxide more readily than adult blood cells do. This makes unborn babies more susceptible to harm from carbon monoxide poisoning.
  • Children. Young children take breaths more frequently than adults do, which may make them more susceptible to carbon monoxide poisoning.
  • Older adults. Older people who experience carbon monoxide poisoning may be more likely to develop brain damage.

Carbon monoxide poisoning prevention at home

  • Install a battery-operated or battery back-up carbon monoxide detector in your home and check or replace the battery when you change the time on your clocks each spring and fall. Place your detector where it will wake you up if it alarms, such as outside your bedroom. Consider buying a detector with a digital readout. This detector can tell you the highest level of carbon monoxide concentration in your home in addition to alarming. Replace your carbon monoxide detector every five years.
  • Open the garage door before starting your car. Never leave your car running in your garage. Be particularly cautious if you have an attached garage. Leaving your car running in a space attached to the rest of your house is never safe, even with the garage door open.
  • Have your heating system, water heater, and any other gas, oil, or coal burning appliances serviced by a qualified technician every year.
  • Do not use portable flameless chemical heaters indoors.
  • If you smell an odor from your gas refrigerator have an expert service it. An odor from your gas refrigerator can mean it could be leaking carbon monoxide.
  • When you buy gas equipment, buy only equipment carrying the seal of a national testing agency, such as Underwriters’ Laboratories.
  • Make sure your gas appliances are vented properly. Horizontal vent pipes for appliances, such as a water heater, should go up slightly as they go toward outdoors, as shown below. This prevents carbon monoxide from leaking if the joints or pipes aren’t fitted tightly.
  • Have your chimney checked or cleaned every year. Chimneys can be blocked by debris. This can cause carbon monoxide to build up inside your home or cabin.
  • Never patch a vent pipe with tape, gum, or something else. This kind of patch can make carbon monoxide build up in your home, cabin, or camper.
  • Never use a gas range or oven for heating. Using a gas range or oven for heating can cause a build up of carbon monoxide inside your home, cabin, or camper.
  • Never burn charcoal indoors. Burning charcoal– red, gray, black, or white – gives off carbon monoxide.
  • Never use a portable gas camp stove indoors. Using a gas camp stove indoors can cause carbon monoxide to build up inside your home, cabin, or camper.
  • Never use a generator inside your home, basement, or garage or less than 20 feet from any window, door, or vent.
  • When using a generator, use a battery-powered or battery backup carbon monoxide detector in your home.

Figure 1. Carbon monoxide poisoning prevention at home

carbon monoxide poisoning prevention at homeFigure 2. Carbon monoxide poisoning prevention at home

carbon monoxide poisoning prevention at home

Carbon monoxide poisoning prevention from your car or truck

  • Have a mechanic check the exhaust system of your car or truck every year. A small leak in the exhaust system can lead to a build up of carbon monoxide inside the car.
  • Never run your car or truck inside a garage that is attached to a house even with the garage door open. Always open the door to a detached garage to let in fresh air when you run a car or truck inside.
  • If you drive a car or SUV with a tailgate, when you open the tailgate open the vents or windows to make sure air is moving through. If only the tailgate is open carbon monoxide from the exhaust will be pulled into the car or SUV.

Carbon monoxide poisoning signs and symptoms

Health effects associated with carbon monoxide poisoning

Carbon monoxide inhibits the blood’s ability to carry oxygen to body tissues including vital organs such as the heart and brain. When carbon monoxide is inhaled, it combines with the oxygen carrying hemoglobin of the blood to form carboxyhemoglobin (COHb). Once combined with the hemoglobin, that hemoglobin is no longer available for transporting oxygen.

How quickly the carboxyhemoglobin builds up is a factor of the concentration of the gas being inhaled (measured in parts per million or PPM) and the duration of the exposure. Compounding the effects of the exposure is the long half-life of carboxyhemoglobin in the blood. Half-life is a measure of how quickly levels return to normal. The half-life of carboxyhemoglobin is approximately 5 hours. This means that for a given exposure level, it will take about 5 hours for the level of carboxyhemoglobin in the blood to drop to half its current level after the exposure is terminated.

Acute effects are due to the formation of carboxyhemoglobin in the blood, which inhibits oxygen intake.

At low concentrations, fatigue in healthy people and chest pain in people with heart disease. At higher concentrations, impaired vision and coordination; headaches; dizziness; confusion; nausea. Can cause flu-like symptoms that clear up after leaving home. Fatal at very high concentrations. Acute effects are due to the formation of carboxyhemoglobin in the blood, which inhibits oxygen intake. At moderate concentrations, angina, impaired vision, and reduced brain function may result. At higher concentrations, carbon monoxide exposure can be fatal.

Your symptoms may be less severe when you’re away from the source of the carbon monoxide. If this is the case you should investigate the possibility of a carbon monoxide leak, and ask a suitably qualified professional to check any appliances you think may be faulty and leaking gas.

The longer you inhale the gas, the worse your symptoms will be. You may lose balance, vision and memory and, eventually, you may lose consciousness. This can happen within two hours if there’s a lot of carbon monoxide in the air.

Long-term exposure to low levels of carbon monoxide can also lead to neurological symptoms, such as difficulty thinking or concentrating and frequent emotional changes – for example, becoming easily irritated, depressed or making impulsive or irrational decisions.

Breathing in high levels of carbon monoxide gas can cause more severe symptoms. These may include:

  • impaired mental state and personality changes (intoxication)
  • vertigo – the feeling that you or the environment around you is spinning
  • ataxia – loss of physical co-ordination caused by underlying damage to the brain and nervous system
  • breathlessness and tachycardia (a heart rate of more than 100 beats per minute)
  • chest pain caused by angina or a heart attack
  • seizures – an uncontrollable burst of electrical activity in the brain that causes muscle spasms
  • loss of consciousness – in cases where there are very high levels of carbon monoxide, death may occur within minutes

At low concentrations:

  • tension-type headache is the most common symptom of mild carbon monoxide poisoning.
  • fatigue in healthy people
  • chest pain in people with heart disease

At moderate concentrations:

  • angina (a type of chest pain caused by reduced blood flow to the hear)
  • impaired vision
  • reduced brain function

At higher concentrations:

  • impaired vision and coordination
  • headaches
  • dizziness
  • confusion
  • nausea
  • flu-like symptoms that clear up after leaving home
  • fatal at very high concentrations

Symptoms Associated With a Given Concentration of carboxyhemoglobin (COHb)

  • 10% carboxyhemoglobin – No symptoms. Heavy smokers can have as much as 9% carboxyhemoglobin.
  • 15% carboxyhemoglobin – A tension-type headache is the most common symptom of mild carbon monoxide poisoning.
  • 25% carboxyhemoglobin – Nausea and serious headache. Fairly quick recovery after treatment with oxygen and/or fresh air.
  • 30% carboxyhemoglobin – Symptoms intensify. Potential for long term effects especially in the case of infants, children, the elderly, victims of heart disease and pregnant women.
  • 45% carboxyhemoglobin – Unconsciousness
  • 50+% carboxyhemoglobin – Death

Since one can’t easily measure carboxyhemoglobin levels outside of a medical environment, carbon monoxide poisoning levels are usually expressed in airborne concentration levels (PPM) and duration of exposure. Expressed in this way, symptoms of exposure can be stated as in the Symptoms Associated With a Given Concentration of Carbon Monoxide Over Time (see Table 1 below).

As can be seen from the table, the symptoms vary widely based on exposure level, duration and the general health and age on an individual. Also note the one recurrent theme that is most significant in the recognition of carbon monoxide poisoning – headache, dizziness and nausea. These ‘flu like’ symptoms are often mistaken for a real case of the flu and can result in delayed or misdiagnosed treatment. When experienced in conjunction with the sounding of a carbon monoxide detector, these symptoms are the best indicator that a potentially serious buildup of carbon monoxide exists.

Table 1. Symptoms Associated With a Given Concentration of Carbon Monoxide Over Time

PPM carbon monoxide
358 hoursMaximum exposure allowed by OSHA in the workplace over an eight hour period.
2002-3 hoursMild headache, fatigue, nausea and dizziness.
4001-2 hoursSerious headache-other symptoms intensify. Life threatening after 3 hours.
80045 minutesDizziness, nausea and convulsions. Unconscious within 2 hours. Death within 2-3 hours.
160020 minutesHeadache, dizziness and nausea. Death within 1 hour.
32005-10 minutesHeadache, dizziness and nausea. Death within 1 hour.
64001-2 minutesHeadache, dizziness and nausea. Death within 25-30 minutes.
12,8001-3 minutesDeath

PPM = parts per million

OHSA = Occupational Safety and Health Administration

Being aware of the signs of carbon monoxide poisoning

It’s very important to be aware of the risk of carbon monoxide poisoning and to look out for warning signs.

You should suspect carbon monoxide poisoning if:

  • other people in your house, flat or workplace fall ill with similar symptoms
  • your symptoms disappear when you go away – for example, on holiday – and return when you come back
  • your symptoms tend to be seasonal – for example, if you get headaches more often during the winter when the central heating is used more frequently
  • your pets also become ill

Pets are often the first to show signs of carbon monoxide poisoning. The smaller an animal or a person is, the faster they’ll be affected.

Investigate the possibility of a carbon monoxide leak if your pet suddenly becomes ill or dies unexpectedly, and their death isn’t related to old age or an existing health condition.

Other possible clues of a carbon monoxide leak include:

  • black, sooty marks on the front covers of gas fires
  • sooty or yellow/brown stains on or around boilers, stoves or fires
  • smoke building up in rooms due to a faulty flue
  • yellow instead of blue flames coming from gas appliances
  • pilot lights frequently blowing out.

Carbon monoxide poisoning treatment

Get into fresh air immediately and call your local emergency number or emergency medical help if you or someone you’re with develops signs or symptoms of carbon monoxide poisoning. These include headache, dizziness, nausea, shortness of breath, weakness and confusion.

Your symptoms will often indicate whether you have carbon monoxide poisoning, but a blood test will confirm the amount of carboxyhaemoglobin in your blood. A level of 30% indicates severe exposure.

People who smoke can often have higher than normal levels of carboxyhemoglobin in their blood, which can sometimes make it difficult to interpret the results.

Mild carbon monoxide poisoning doesn’t usually need hospital treatment, but it’s still important that you seek medical advice.

Your house will also need to be checked for safety before anyone returns.

Once you’re at the hospital, treatment may involve:

  • Breathing pure oxygen (100% oxygen). In the emergency room, you may breathe pure oxygen through a mask placed over your nose and mouth. This helps oxygen reach your organs and tissues. If you can’t breathe on your own, a machine (ventilator) may do the breathing for you. Therapy will continue until your carboxyhemoglobin levels decrease to less than 10%.
  • Spending time in a pressurized oxygen chamber. In many cases, hyperbaric oxygen therapy is recommended. This therapy involves breathing pure oxygen in a chamber in which the air pressure is about two to three times higher than normal. This speeds the replacement of carbon monoxide with oxygen in your blood. Hyperbaric oxygen therapy may be used in cases of severe carbon monoxide poisoning. It helps protect heart and brain tissue, which are particularly vulnerable to injury from carbon monoxide poisoning. Hyperbaric oxygen therapy may also be recommended for pregnant women because unborn babies are more susceptible to damage from carbon monoxide poisoning.
  • There’s currently insufficient evidence regarding the long-term effectiveness of hyperbaric oxygen therapy for treating severe cases of carbon monoxide poisoning. Therefore, standard oxygen therapy is usually the recommended treatment option.Hyperbaric oxygen therapy may be recommended in certain situations – for example, if there’s been extensive exposure to carbon monoxide and nerve damage is suspected. The use of hyperbaric oxygen therapy will be decided on a case-by-case basis.


The length of time it takes to recover from carbon monoxide poisoning will depend on how much carbon monoxide you’ve been exposed to and how long you’ve been exposed to it.

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