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Carbon Monoxide
ADAIR INSPECTION offers CO evaluation services as stand alone or part of the general residential or commercial inspection. Call Barry for further information

 Carbon Monoxide CO is the Invisible Killer

Carbon monoxide (CO) concentration in Parts Per Million or as percentage of air

  Parts Per Million 

   % of CO in air 

Inhalation time and toxic symptoms developed 

0 - 1 ppm


 Normal background levels

9 ppm


 Maximum allowable concentration short term in living area (ASHRAE)

25 ppm


 Maximum exposure TWA (Time Weighted Average)  (ACGIH) in the workplace.

50 ppm


 Maximum exposure allowed (OSHA) in the workplace.

200 ppm


 Mild headache, fatigue, nausea and dizziness.

400 ppm


 Serious headache - other symptoms intensify.

Life threatening after 3 hours.

800 ppm


 Dizziness, nausea and convulsions. Unconscious within 2 hours, dead within 2 to 3 hours.

1600 ppm


 Headache, dizziness and nausea.

Death within 1 - 2 hours.

3200 ppm


 Headache, dizziness and nausea.

Death within 1 hour.

6400 ppm


 Headache, dizziness and nausea.

Death within 25 - 30 minutes.

12,800 ppm


Death within 1 - 3 minutes. 

Effects can vary significantly based on age, sex, weight and overall health.




Supplied from your inspector as general information for educational purposes for LOW Level CO detectors: Made In America By Americans or NSI 3000 Low-Level CO Monitor


Carbon Monoxide Information Center

Sponsored by First Alert - (312) 337-7773

Carbon Monoxide Detectors - UL Standard

"According to UL Standard 2034, home carbon monoxide detectors must sound a warning before carbon monoxide levels reach 100 parts per million over 90 minutes, 200 parts per million over 35 minutes or 400 parts per million over 15 minutes. The standard requires the alarm must sound before an average; healthy adult begins to experience symptoms of carbon monoxide poisoning. The warning provides time to evacuate the premises."


Note: There are three organizations ASHRAE, ACGIH, and OSHA that rate levels below 100 ppm as unsafe, this is before many home UL Standard

CO alarms/monitors/detectors would ever sound for a potential problem.

If you or anyone you know owns gas-fired appliances please have them checked for proper installation, CO emission, and proper venting and make certain CO detectors are installed to manufacture specifications at every elevation of the home. Hazardous levels of CO can also be produced on or in electric appliances from spills, overcooking, self-cleaning cycles and dirty equipment.

Carbon Monoxide Hazards from Small Gasoline Powered Engines

by Mary Maclay

Carbon monoxide is a colorless, odorless, highly-poisonous gas formed by the incomplete combustion of carbon or a carbonaceous material, such as gasoline. Some producers of carbon monoxide (CO) are industrial processes, heating equipment, accidental fire, cigarettes and the internal combustion engine. Generators, candles, and space heaters can all create CO emissions.

CO is always produced when natural gas, liquid propane, oil, coal, gasoline or wood are burned; often at dangerous levels. Exhaust gases need to be vented properly to avoid CO accumulation in any living space. If the combustion takes place with excess oxygen in a properly tuned burner, not much CO is produced but improper adjustment or any smoldering fire can produce significant CO emissions.

How much is too much?
There are many standards for CO exposure limits. The OSHA standard is 50 parts per million (PPM) in the air as a maximum exposure in the workplace. 1 PPM is defined as one CO molecule in one million molecules of air. This is about the same dilution as one shot glass of gin in a railroad tanker car full of tonic.

The majority of off-the-shelf home CO detectors are designed to alarm at 100 PPM and above, to satisfy current laws concerning home CO alarms. A few home CO meters have digital readouts to show lower levels but they will not alarm at these lower levels.

The American Society of Heating Refrigeration and Air Conditioning Engineers (ASHRAE) lists a maximum allowable short term limit of 9 PPM of CO. The EPA has set two national health protection standards for CO: a one-hour standard of 35 PPM and an eight-hour standard of 9 PPM. From the above standards and guidelines it follows that any CO reading over 9 PPM should be investigated and acted upon.

Health Effects
Low-level exposure can cause chronic health conditions from cardiovascular disease to a Parkinson's like illness. The following is an excerpt from the EPA: "The health threat from lower levels of CO is most serious for those who suffer from heart disease, like angina, clogged arteries or congestive heart failure. For a person with heart disease, a single exposure to CO at low levels may cause chest pain and reduce that person's ability to exercise; repeated exposures may contribute to other cardiovascular effects. Even healthy people can be affected by high levels of CO. People who breathe high levels of CO can develop vision problems, reduced ability to work or learn, reduced manual dexterity and difficulty performing complex tasks. At extremely high levels, CO is poisonous and can cause death. CO contributes to the formation of smog ground level ozone, which can trigger serious respiratory problems." (, August 17, 2007.)

Measuring Exposure
There are portable, digital meters that measure various gases. These dosimeters have a digital display of the current level or concentration of CO. If used over time, they can compute the total exposure (over time) in units of PPM-hours. There are guidelines for keeping workplace exposure below 200
PPM-hours for an eight-hour workday.

The variables that are typically reported in a dosimeter are the maximum exposure concentration, the time when this occurs, the total exposure and the time-weighted average (TWA). The TWA is the total exposure divided by the time over which the exposure occurs (i.e. the PPM-hours divided by the period of time in hours you collected the exposure data). If the TWA is over 35 PPM for one hour, you are in an environment that exceeds the EPA's national health protection standard. Dosimeters range in price from the low $100s on up. They sometimes include a maximum exposure reading and a total exposure reading.

If at Risk, Act
If you are in CO levels above nine PPM, you can and should attempt to change your environment by opening a window to
ventilate the area with clean air or by leaving the area. Bring in fresh air if possible. While a level of nine PPM is not an emergency, you should look for possible sources and cleaner air. Determine the sources of the CO by looking for activities like smoking, burning toast, vehicle exhaust or a campfire. If the levels are over 35 PPM, consider evacuating until the source is determined. If levels are above 125 PPM, call in a professional fire department and evacuate.

Find the source and have repairs performed. Below is a chart with CO PPM values and effects. The author has a dosimeter and measures every restaurant she goes into. To date, she has found ranges from nine-45 PPM. The most likely sources are cooking fires and smokers. If a hood is not vented properly or if an owner is trying to save money and not running the hood often enough, CO concentrations can build up. Management may point to their standard plug-in alarm and insist that it must be safe because the alarm is not going off, but such alarms are designed to go off at much higher thresholds so as to not trigger false alarms. Meanwhile, workers and customers are exposed to hours of CO at undesired levels. Think about it. Don't we need to educate ourselves about CO levels and use good tools for measurement and protection? If we don't, who will?

Value Added to Inspections
Many inspectors screen for CO as part of their service to determine whether there are any issues in the structure at the date and time of the inspection. It is important to clarify for clients that screening only pertains to the day of the test and does not guarantee that there will never be a CO issue. Educating clients about buying good quality CO detectors for their home also helps reduce their risk.

CO is Everywhere
In conclusion, CO exposure is ubiquitous and even low levels are detrimental to our health and well-being, especially the very young and the old and frail. There are affordable, wearable and/or portable digital tools such as carbon monoxide dosimeters that are available to measure low levels of CO on the spot. Most CO instruments should be recalibrated on an annual basis. Such tools can help protect your health on the job, at home or on vacation.

Small, portable instruments offer an opportunity to measure various areas for CO levels: a home, HVAC ductwork, appliances, exhaust vents, fireplaces, power boats, airplanes, a truck cab, school bus, high traffic area, indoor hockey rink, tollbooth, restaurant, parking garage, smoldering campfire, garage, cigarette smoke, warehouse, workplace, private airplane, hot water tank, furnace duct, and more.

Educate yourself about CO exposure to recognize potential sources and where and how to measure them. You can add CO testing to your inspection report to add value to your service and to protect your clients. Dosimeters can help better inform you and protect your health on the job as well as the health of others.

Carbon Monoxide Protocol Carbon Monoxide Analyst Test Equipment

  • Analysts shall have a digital CO analyzer to assist CO investigations.

Standard - CO Testing Instruments

·         Carbon Monoxide test instruments must meet the following minimum requirements.

         Digital display capable of measuring 1 - 2 ppm increments@ 5 - 10 % accuracy.

         Scale to read at least up to 500 ppm.

         Reach 90% of final reading within one minute.

         Have a probe/hose assembly for flue gas sampling capable of withstanding high temperatures and the ability to remove water vapor from the combustion by - products.

         Ability for continuous sampling.


Best Practices - CO Test Instruments

  • CO test equipment can be affected by heat, cold, humidity, battery strength and mishandling.
  • Always warm up and operate the instrument per manufacturers instructions.

Best Practices - Calibration of CO Testing Equipment

         Instrument must be calibrated per manufacturer instructions or when accuracy is in doubt.

         Field zeroing of the instrument should only be done with test gases as described in the owner's manual.

         Factory or other certified calibration must be performed at recommended intervals. Do not re-zero instruments for individual houses.

         Re-zeroing an instrument without test gases may result in readings that are not absolute or accurate.

         Zeroing of instruments should never be attempted on a job. Temperature, battery level, vehicle exhaust and other factors can affect zeroing.

         A constant need to zero indicates an instrument or operator error.

         Zeroing an instrument in the field eliminates reading the true ambient level.


Standard Inspection Protocol

         A comprehensive protocol will be adhered to.

         Protocol includes:

         Ambient CO level outside of building or unit.

         Ambient CO level inside of building or unit - Subtract outside reading from inside reading to determine the magnitude of any CO problem found within unit.

         Visual inspection of appliance

         If unit has broken parts, pilot burning wrong, warped deflectors and is not repairable unit is to be replaced.

         Customer Interview

         Inspection of building

         Detector Utilization

         Customer Education

         Range top burners and oven MUST NOT BE DIRTY to the extent that it will cause false CO readings.

         Client should be informed to clean the unit before any testing can be done.

         Test range top burners.

         Remove all pots and foil from the burner area.

         Turn all range top burners on high and allow to warm.

         Test 6" above the flame without pots or test fixtures.

         When an unvented stove/range is found in a building, stress the need for a strategy to vent pollutants to the outdoor atmosphere.

Less than 25 ppm after 2 -3 minutes of operation - OK and should be cleaned by client to prevent possible CO problems.

. 25 - 50 ppm after 2 -3 minutes - Marginal Have appliance serviced.

. Greater than 50 ppm after 2 -3 minutes - Unsafe Appliance should not be used until either repaired or replaced.

  • Test ranges and ovens after all other vented appliances have been tested:
  • For oven tests, remove any items stored in the oven before proceeding.
  • Remove foil coverings from unit.
  • Make sure that self cleaning features are not activated.
  • Test oven by inserting the instrument probe into the vent sleeve before dilution air mixes with combustion by-products.
  • Continually test oven during warm up and record peak. (10minutes)
  • Units with CO air free levels less than 800ppm after initial warm-up period are OK and should only be cleaned by client to prevent possible CO problems.
  • Units with CO air free levels greater than 800ppm and less than 1000ppm after initial warm-up period indicate a problem and should be serviced.
  • Units with CO air free levels greater than 1000ppm after initial warm-up period indicate a problem and should be replaced.
  • Continually monitor ambient space around oven during testing.
  • Retest ambient air to ensure no change in CO from initial tests.

Client Interview

  • Perform interview in an area safe from CO exposure.
  • Inquire about health problems.
  • Question occupants to see if they have experienced any specific CO poisoning symptoms including: headaches, dizziness, nausea, confusion, rapid breathing, fatigue, unconsciousness, disorientation, or flue like symptoms.
  • Ask if anyone else in the home has shown signs of experiencing these symptoms.
  • If anyone appears to be experiencing symptoms, refer them to medical evaluation (see action levels).
  • Ask about unusual moisture problems.
  • Ask about recent mechanical problems.
  • Ask if a vehicle has been in or out of the garage recently (if applicable).
  • Ask if oven or range was in use. Ask if the fireplace was in use (if applicable).
  • Ask if occupants were doing laundry or vent fans were in use.
  • Repeat customer health inquiries if a serious CO problem is found and the occupants have not acknowledged any symptoms previously.
  • Reference action levels.

CO recording Form

  • Use a standardized CO recording form when performing a CO inspection. Include:
  • Company, technician, date and time of testing.
  • Client and physical location.
  • Smokers in the structure.
  • Is this an emergency situation or routine procedure - inspection classification.
  • Listing of normal CO sources to be inspected and results from testing those sources.
  • Type of fuels in use.
  • Attached or detached garage.
  • Potential exterior sources of CO production.
  • Action taken.
  • Follow-up

I encourage you to accompany your inspector so that you may ask questions and gain a better understanding of the systems located at the property.

If you have any questions, or are interested in any other services, please contact us so we may discuss your specific needs.