Carbon monoxide is a colorless, odorless, poisonous gas. The EPA’s suggested maximum 8-hour CO exposure is 9 ppm as measured in room air. CO at or above 9 ppm is often caused by malfunctioning combustion appliances in the home, although cigarette smoking or auto exhaust are also common CO sources. The EPA’s one-hour CO limit is 35 ppm as measured.
1.3.1 Causes of Carbon Monoxide (CO)
CO is released by unvented gas space heaters, kerosene space heaters, backdrafting vented space heaters, gas ranges, leaky wood stoves, and motor vehicles idling near the home. Central furnaces and boilers that backdraft may also lead to high levels of CO.
CO is usually caused by these conditions.
• A combustion appliance is overfired compared to its rated fuel input.
• Backdrafting combustion gases are smothering the flame.
• An object interferes with the flame (a pan over a gas burner on a range top, for example).
• Too-little combustion air.
• Rapidly moving air interferes with the flame.
• Burner misalignment causes a distorted flame.
• Flue or heat exchanger blockage interferes with the flow of flue gases.
Measure CO at the exhaust port of the heat exchanger. Identify and correct CO problems.
Testing for Carbon Monoxide (CO)
The most common CO-test instruments use electronic sensors with a digital displays showing parts per million (ppm). Read the manufacturer’s instructions on zeroing the meter — usually by calibrating the meter in outdoor air. CO test equipment must usually be re-calibrated every 6 months, using factory-specified procedures.
Air-free CO measurement includes both CO and O2 sensing with a calculation to find the CO concentration in undiluted flue gases that contain no oxygen. Air-free CO measurement avoids the perception that moving the testing probe or diluting CO are solutions to elevated levels of CO. See Carbon Monoxide (CO) Testing.
Auditors, Mechanical Technicians and Quality Control Inspectors all test for CO as part of their work progress.