Carbon monoxide (CO) is DANGEROUS!   Hundreds of people die each year from accidental CO poisoning.  Here's some information to help protect you and your family.


You may be exposed to CO when ---

  • you leave your lawnmower or vehicle's engine running
  • your home contains a malfunctioning or incorrectly vented gas water heater, gas or oil furnace, non-electric space heater, fireplace, or gas stove
  • you burn charcoal, alcohol, gasoline, or other fuel in an enclosed tent, camper, or room
  • you smoke a cigarette, cigar, or pipe


CO prevents oxygen from being used by your body.  It  binds to the hemoglobin molecules in your blood and forms carboxyhemoglobin (COHb), which prevents oxygen molecules from being picked up and transported throughout your body.  CO is poisonous and can harm your central nervous system and your heart.


% COHb

Symptoms & Medical Findings


No symptoms. Heavy smokers can have as much as 9% COHb.


Mild headache.


Nausea and serious headache. Fairly quick recovery after treatment with oxygen and/or fresh air.


Symptoms intensify. Potential for long term effects especially in the case of infants, children, the elderly, victims of heart disease, and pregnant women.






Everyone is at risk of being poisoned by CO.  However, those with health problems such as heart or lung disease and the elderly are especially vulnerable.  Those with greater oxygen requirements such as infants, children, senior citizens, and pregnant women are also at high risk.



CO poisoning mimics many common illnesses such as influenza and food poisoning.  Some of the common symptoms associated with CO poisoning are:

  • headaches
  • dizziness
  • weakness
  • nausea
  • rapid heartbeat
  • loss of hearing
  • blurry vision
  • vomiting
  • disorientation
  • loss of consciousness
  • seizures
  • coma
  • respiratory failure
  • cardiac arrest

This list is not meant to serve as a diagnosis of CO poisoning.  It is meant to provide information on CO poisoning symptoms.  Always check with your doctor or go the nearest emergency room for a definitive diagnosis.




Have your furnace and fireplace inspected and cleaned prior to the start of each heating season.  Use non-electrical space heaters only in well-ventilated areas.  Don't start or leave running any vehicles or gasoline powered lawnmowers, snowblowers, or other fuel burning equipment in an enclosed area.

Obtain carbon monoxide detectors for your home and place one near the sleeping areas and another in the vicinity of any major gas burning appliance like a furnace, water heater, or dryer.  Mount the detectors in a low area near the floor.  Unlike smoke, CO sinks to the lowest levels of a room first.

There are a number of different types and brands of carbon monoxide detectors on the market today.  They can be most easily characterized by whether they operate on household current or batteries.  Detectors using household current typically employ a solid-state sensor which purges itself and resamples the air for CO on a periodic basis.  This cycling of the sensor is the source of its increased power demands.  Detectors powered by batteries typically use a passive sensor technology which reacts to the prolonged exposure to carbon monoxide gas.

All detectors sold on the market today should conform to minimum sensitivity and alarm characteristics.  These characteristics have been defined and are verified by Underwriters Laboratory (UL) in their standard for carbon monoxide detectors (UL 2034).  This standard was most recently revised in June of 1995 and went into effect in October of 1995.  This revision specified additional requirements regarding identification of detector type, low-level (nuisance) alarm sensitivity and alarm silencing.  Under no circumstances should one purchase a detector that is not UL listed


Where to look for problem sources of CO in your home

An improperly installed or malfunctioning forced air furnace could be the source of CO and should be carefully inspected by a professional.

  • Measure the concentration of CO in the flue gases.
  • Check furnace connections to flue pipes, chimneys, and venting systems to outside of the home for signs of corrosion, blockages, rust, gaps, or holes.
  • Check the combustion chamber and internal heat exchanger for cracks, metal fatigue, or corrosion.  Be sure that they are clean and free of debris.
  • Check burners and ignition systems.  A flame that is mostly yellow in color in natural-gas fired furnaces is often a sign that fuel is not burning completely and higher levels of CO are being released.

Check all venting systems to the outside, including flues and chimneys, for cracks, corrosion, holes, debris, or blockages.  Animals and birds can build nests in chimneys, preventing gases from escaping.

Check all other appliances that use flammable fuels such as natural gas, oil, wood, propane, or kerosene.

  • Appliances include (but are not limited to) gas furnaces, water heaters, clothes dryers, kitchen ranges, ovens, or cooktops, wood or coal burning stoves, gas refrigerators, pressure washing machines, or generators.
  • Pilot lights can be a source of CO because the byproducts of combustion are released inside the home rather than vented to the outside.  Gas ovens and ranges should be monitored closely and kept in good working order.  Stove tops or ovens that operate on flammable fuels should never be used to heat a residence.

Be sure space heaters are vented properly.  Unvented space heaters that use flammable fuel can release CO into the home.

Barbecue grills and hibachis should never be operated indoors or in an enclosed space such as a garage, even with the door open.

Check fireplaces for closed, blocked, or bent flues, soot, and debris.  When operating a fireplace and a furnace at the same time, experts recommend opening a window a crack to equalize the pressure so the combustion gases can flow freely up and out the chimney.

Check the clothes dryer vent opening outside the house to make sure it's free of any blockage such as lint or other debris.

If initial testing does not confirm the presence of CO, there may be several reasons:

  • Testing equipment used to measure the presence of Co in the air must be calibrated to sense low levels of Co concentration.
  • Testing equipment should be capable of sensing levels as low a one part per million (ppm).  UL standards for residential CO detectors require them to alarm before 90 minutes of exposure to 100 ppm CO.
  • If initial readings don't reveal sufficient concentrations of CO to set off the alarm, digital measuring equipment that produces a printed 24-hour record can be used to help identify the source.
  • If doors or windows are left open, or appliances are turned off and outside air enters the home, CO can dissipate.  This will create a lower level than the level that triggered the alarm.  To help assure proper measurements, CO readings should be conducted as soon as possible after an alarm activation.
  • If appliances, flues, and chimneys are confirmed to be in good working order, the source of CO may be from a car left running in a garage or from downdrafting.  Downdrafting exists primarily in newer, more energy efficient airtight homes.  Flue gases normally vent to the outside through flues and chimneys.. When exhaust fans are on, air pressure inside an airtight home may become lower than that outside, causing gases to be sucked down the chimney back into the home.
  • Inadequate air supply in a room where two or more combustion driven appliances share the same air source (such as a water heater and furnace in an unvented utility closet) can create a more complicated form of downdrafting called reverse stacking.  This occurs when the furnace turns on and is unable to get enough fresh air.  It will then draw CO contaminated air from the exhaust of the water heater and spread it throughout the house.

A faulty thermostat can keep the furnace running continuously, depleting the oxygen supply inside the house.

In multifamily dwellings where living spaces share walls and pipes, CO from one unit may enter a neighboring space through floor boards or cracks, or underneath doors.

Car exhaust can enter the home when a car is left idling in an attached garage, even if the garage door is open.


If the alarm activates and you are experiencing symptoms of CO poisoning, leave the premises immediately and call 911.

If the alarm activates and you have no symptoms of CO poisoning, push the reset button.  Check the detector and replace the battery or cartridge if necessary.  Turn off any appliances or other devices that may be producing CO and ventilate the area.  Have a qualified service technician adjust or repair any appliances that may not be operating properly.  If the alarm continues to sound, call 911.

If you have a detector with a digital display, the following table shows the symptoms associated with a particular level:


Parts per million (PPM) CO

Exposure Time


35 PPM

8 hours

Usually none or slight headache.  Maximum exposure allowed by OSHA in the workplace over an eight hour period.

200 PPM

2-3 hours

Mild headache, fatigue, nausea and dizziness.

400 PPM

1-2 hours

Serious headache, other symptoms intensify.  Life threatening after 3 hours.

800 PPM

45 minutes

Severe dizziness, nausea and seizures.  Unconscious within 2 hours.  Death within 2-3 hours.

1600 PPM

20 minutes

Headache, dizziness and nausea.  Death within 1 hour.

3200 PPM

5-10 minutes

Headache, dizziness and nausea.  Death within 1 hour.

6400 PPM

1-2 minutes

Headache, dizziness and nausea.  Death within 25-30 minutes. 

12800 PPM

1-3 minutes


If you are in doubt as to whether or not there is actually a CO problem, err on the side of caution and call 911! We will be happy to respond and check the CO levels in your home or business.

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