Distinguishing Carbon Monoxide from Carbon Dioxide
There is much confusion about whether carbon dioxide and carbon monoxide are the same. While most people do know they are separate gases, they are not sure of their identity or of how one is harmful while the other is beneficial. They are not able to conclude whether this type of classification is appropriate.
Both carbon monoxide and carbon dioxide are gaseous chemicals composed of oxygen and carbon. Carbon dioxide is formed when carbon is burnt completely in the presence of plenty of oxygen. Combustion does not always mean fire, but invariably involves a substance chemically combining with oxygen.
Incomplete combustion of carbon occurs if enough air is not available to convert all of it to carbon dioxide, and in such as case carbon monoxide is formed by the addition of half the amount of oxygen as is present in carbon dioxide, to the carbon atom, namely, CO instead of CO2.
Sources of Carbon Dioxide
Most of the carbon dioxide in the air comes from natural phenomena such as the oceans, respiration by animals and plants, decaying organic matter, forest fires, and volcanic emissions. Only a lesser fraction of total carbon dioxide production is due to human activity, that is, anthropogenic, but of this 87 percent is caused by burning of fossil fuels, including natural gas, coal, and oil.
When the energy in these fuels is released by burning, it is used for transportation, power generation or heat production. Other emissions are produced by land clearing, either forest land or other, as well as industrial manufacturing processes such as the production of cement. Carbon dioxide is an inert gas and diffuses rapidly throughout the air.
Carbon dioxide is produced during some fermentation processes such as wine making.
Sources of Carbon Monoxide
Carbon monoxide is not found in the air under ordinary conditions, since it is formed by incomplete carbon combustion of coal, natural gas, oil. More of it is formed under conditions in which the oxygen levels are very low, and the temperatures are cool.
CO2 and CO Generation – Domestic and Occupational
Carbon dioxide is formed mainly in industries involved in the production of ammonia or hydrogen using fossil fuels like coal or natural gas in particular, or when plant products are fermented on a large scale, to generate ethanol. It is used to produce a number of foods and beverages, such as carbonated or fizzy drinks, and in wine conservation.
It is used to promote the growth of plants, though this is not an established practice as of now. It can be solidified to make dry ice, a commonly used refrigerant for transporting perishable foods in frozen or cooled conditions, or pharmaceutical substances.
Carbon monoxide is not normally formed by choice, but may be packaged for use in metal fabrication, chemical manufacture, ore reduction to form metal carbonyl compounds, various pharmaceutical processes, and for use in manufacturing some electronic and semiconductor applications.
Carbon monoxide may be raised to toxic levels at home or in the workplace if any appliance that burns fuel malfunctions to allow combustion under conditions of limited ventilation and air supply. This may include non-electric gas furnaces, gas stoves and dryers, gas water heaters, fireplaces, and automobiles.
In a factory, most carbon monoxide exposure is due to the running of the internal combustion engine. Many ovens and furnaces in the industrial workplace also contribute to the levels of carbon monoxide, especially if they are badly kept up.
Those most likely to be affected include drivers of trucks or operators of forklifts, or people working near heavy equipment, as well as those who work in narrow or partially closed spaces, such as loading docks and warehouses, garages, tunnels and manholes, shops for vehicle repair and splicing vehicles.
Firefighters are often called in because of carbon monoxide in the home.
Dangers of Carbon Monoxide and Carbon Dioxide
Carbon monoxide poisoning affects over 10,000 people a year severely enough to require medical aid, of which 500 fatalities occur annually within the USA, according to the National Conference of State Legislatures (NCSL) statistics. About 50 percent of those who die from accidental CO toxicity do so as a result of inhaling smoke from fires while the rest may be due in part to fumes from vehicle exhaust pipes or industrial exposure.
Carbon monoxide bonds to the oxygen-carrying molecules in the bloodstream and inhibits the release of oxygen to the body tissues. Thus, if the blood levels of CO are high the body suffers from hypoxia. OSHA (Occupational Safety and Health Administration) limits for permissible exposure (permissible exposure limits, PEL) are 50 ppm over a period of eight hours.
Above 1,500 ppm, the level of exposure is immediately toxic to health and life. Since this molecule has neither odor nor color, nor taste, and does not cause irritation of the tissues exposed, it is rightly called a silent killer, and early poisoning is typically missed due to the absence of warning signs.
Carbon dioxide is not immediately toxic unlike CO, and thus poisoning with this gas is rare. However, if it builds up in a confined space, it may cause toxicity by displacing oxygen from the air in the space, thus producing conditions under which asphyxiation may occur.
Such a situation is signaled at first by headaches and dizziness, with the concentration being below 30,000 ppm. When it crosses 80,000 ppm CO2 may endanger life and health. The OSHA guidelines call for exposure to less than 5,000 ppm of CO2 over a period of eight hours, and 30,000 ppm over 10 minutes.
Detection of Gases
Selection of a gas detector for workplace use should consider that a single gas detector will be useful only for either carbon monoxide but not carbon dioxide, or vice versa. As such, the sensors are designed to be specific for the type of gas detected. The location of the gas detector is also important.
Carbon dioxide detectors must be set near the ground as this gas is heavier than air and sinks to the floor, while CO being somewhat less dense than air rises and its detectors should be located at a higher level. Single-gas, multiple-gas, portable and area monitors for gas detection are all available, but the best way to ensure that the right instrument is used is to become familiar with the setting of use and the nature of the gas detected.
References and Further Reading
This information has been sourced, reviewed and adapted from materials provided by Industrial Scientific.
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