Carbon Monoxide


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Carbon Monoxide


Carbon Monoxide (CO) is a colorless, tasteless, odorless gas that is found naturally in the atmosphere. Emissions of this gas are released due to the incomplete combustion of fuels. Poorly vented spaces in combination with CO can be an extreme danger to people since CO can accumulate raising the concentrations above the normal range of 0-9ppm[1]. CO is a health hazard in elevated concentrations over time.


CO a byproduct of combustion is lighter than air. The fuel burning efficiency of the device will influence the amount of CO produced. Partial combustion of fuels produces more CO, the cause can be due to a number of scenarios, but the most common is a lack of available oxygen for combustion. Cars are a major contributor to CO emissions, although they have become more fuel efficient over the years and are producing less CO, due to the introduction of catalytic converters and fuel injection systems. Other sources of CO in a home range from gas fed appliances to space heaters and the concentration of the gas depends on numerous factors including the ventilation and volume of the space and the fuel gas flow rate. Incomplete combustion in a natural gas devices has the potential of producing large amounts of CO.

CO dia

CO is a covalently bonded carbon and oxygen molecule that is stable and has a unique property, polarity. The imbalance of how the electrons are shared polarizes the molecule, which influences how it interacts with other molecules. Hemoglobin is the primary oxygen carrying molecule in red blood cells. CO has an affinity for hemoglobin that is 240 times greater than oxygen. During respiration in a CO rich environment hemoglobin will bind to CO instead of oxygen. Cells through out the body begin to atrophy which eventually die. The side effects from a prolonged but mild exposure to CO cover a wide range, but closely mimic the flu and CO poisoning is commonly mistaken in this way. In greater concentrations the respiratory system is irritated and mental functions are hindered. If an individual does not evacuate a concentrated area coma and death are imminent. One of the best ways to recognize CO exposure in individuals is if some side effects quickly dissipate after a person is removed from the exposure area. The quick recovery is attributable to the effectiveness of oxygen and time as a cure.

CO exposure table

CO over long exposure times can be just as lethal as high concentrations. The table illustrates how larger concentrations can produce severe side effects, however small concentrations over long periods of time can have severe adverse side effects as well. A highly hazardous scenario occurs when the concentration in any confined space increases over time because mild side effects are generally disregarded and individuals continue to expose themselves to the gas past a safe limit.

There are documented protocols for Carbon Monoxide Analysts that indicate how to measure, assess, and handle hazards. Action levels provide analysts with guidelines when and how to respond to unsafe concentrations levels. Part of their job is not only to accurately measure concentrations but locate the source of the gas in order to eliminate potential hazards.

 Emissions Table

There are multiple kinds of early warning devices. Each system has a different method for determining unsafe CO limits. A biometric sensor works by emitting an infrared light through a gel that changes color with prolonged exposure to CO, the color interferes with signal that breaks the connection and triggers the alarm. Metal Oxide Semiconductor devices measure the current threshold in the sensing layer, when the resistance changes the heat output the alarm sounds. Electrochemical Detectors use an electrode acid combination exposed to air that reacts with CO to create an electrical potential, the current generated has to break the unsafe limit to trigger the alarm. All devices provide a first line of safety against carbon monoxide, but the best way to prevent exposure is through proper installation of equipment, venting confined areas, and recognizing when and where CO can become a hazard.

[1] Parts per million, ppm is a way to express very small concentrations by dividing a measurable unit into a million parts,  e.g. milligrams per liter