Carbon Monoxide: Keeping Safe

Editor’s Note: Low-level exposure to carbon monoxide can cause chronic health conditions from cardiovascular disease to an illness similar to Parkinson’s. It’s easy and inexpensive for appraisers and inspectors to stay safe in other people’s homes (and in their own). Some inspectors also include CO testing in their reports to add value to their service.

Carbon Monoxide: Keeping Safe

by Mary Maclay, Quantum Fields LLC

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. One PPM CO is defined as one CO molecule in one million molecules in air. (A million molecules of air is a simplified way of saying about 200,000 molecules of oxygen and 800,000 molecules of nitrogen, neglecting minor constituents in 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 70 – 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 nine 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 nine PPM.

From the above standards and guidelines it follows that any CO reading over nine 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.”  (, Aug 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.

Here are two examples of CO screens that paid off: A furnace repair service went into the basement of a new home and found their CO digital dosimeter rising and falling depending on where they stood. When approaching the hot water heater the values rose even higher. The water heater installer had gone to lunch and improperly hooked up the unit. The service was called and the problem corrected. A second incident occurred when a furnace was turned on. The inspector went into the children’s bedroom and read over 200 PPM CO on his dosimeter. The furnace was shut down and repaired.

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.

Learn More
Carbon monoxide is odor free and toxic. As an appraiser or home inspector you have a higher risk of CO exposure due to faulty equipment, improper maintenance or other unknown hazards. Recently the NYC Building Department purchased 100 Pocket COs to protect their staff while they go out on inspections. It is now easy and affordable to protect yourself conveniently from carbon monoxide exposure while on the job with Pocket CO. Learn more about carbon monoxide exposure and Pocket CO at;;

About the Author
Mary Maclay is president of Quantum Fields LLC, a research and development company working in sensor and physics research. She collaborates with Dr. Joseph Stetter and others at the Transducer Technology Division of KWJ Engineering, Inc in Newark, California on new product development, distribution and marketing of portable toxic gas detection instruments.

For more information on CO see HUD CO Brief.

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