Carbon monoxide from fire smoke

The personal security of our citizens also benefits directly from science and technology. Our police forces are equipped with light, strong bulletproof vests made of modem synthetic materials, and fire rescue personnel wear protective clothing made from temperature-resistant polymers. The smoke detectors and carbon monoxide detectors in our homes are based on chemical processes that detect dangerous substances. Personal security is enhanced in the broadest sense by water purification and by the chemical testing procedures that assure us of clean water and food. 

It is well known that hydrogen cyanide can be liberated during combustion of nitrogen containing polymers such as wool, silk, polyacrylonitrile, or nylons (1, 2). Several investigators have reported cyanide levels in smoke from a variety of fires (3, 4, 5). The levels reported are much below the lethal levels. Thus the role of cyanide in fire deaths would seem to be quite low. However, as early as 1966 the occurence of cyanide in the blood (above normal values) of fire victims was reported (6). Since then many investigators have reported elevated cyanide levels in fire victims (7-13). However, it has been difficult to arrive at a cyanide blood level which can be considered lethal in humans. In this report the results of cyanide analysis in blood of fire victims are reported as well as the possibility that cyanide may, in some cases, be more important than carbon monoxide as the principal toxicant in fire smoke. 

Smokes from hydrocarbon fires consist of liquid or solid particles of usually less than one micron in size, suspended in the combustion gases, which are primarily nitrogen, carbon monoxide and carbon dioxide, existing at elevated temperatures. At normal temperatures carbon is characterized by a low reactivity. At high combustion temperatures, carbon reacts directly with oxygen to form carbon monoxide (CO) and carbon dioxide (CO2). 

As an example, low levels of carbon monoxide (CO), together with ingested alcohol, reduce sensitivity to guaiacol, which has a smokey or burnt odor (Engen, 1986). Smokers take up CO. If they also drink, they could be impaired in their ability to detect smoke from a fire. 

High levels of indoor air pollutants result from the use of either open fires or poorly functioning stoves to bum biomass or coal (Ezzati Kammen, 2001). Women, especially those responsible for cooking, are the ones most heavily exposed. Young children who spend their time close to their mothers also have high exposures (Bruce et al., 2000). Many of the substances in smoke from either biomass or coal burning can be hazardous to humans. The most important are suspended particulate matter, carbon monoxide, nitrous oxide, sulfur oxides (coal), formaldehyde, and PAHs (Bruce et al., 2000 Smith et al., 2000). 

The range of toxicity test methods is bound to produce different fire conditions, and hence different toxic product yields. Four test methods (NBS Smoke Chamber, NF X 70-100, Fire Propagation Apparatus [FPA], and SSTF) have been compared, primarily from published data64 66 using the carbon monoxide yields and hydrocarbon yields (not recorded in the NFX tests), which are both fairly good indicators of fire condition, for four materials (LDPE, PS, PVC, and Nylon 6.6), at two fire conditions, well-ventilated and under-ventilated. The CO and hydrocarbon yields are shown in Figures 17.9 and 17.10. 

The colorless carbon monoxide (CO) is everywhere. Wherever there is combustion there is CO it is the predominant product above 800°C. The concentration of CO might vary from 0.1 ppm in clean atmosphere to 5,000 ppm in the proximity of domestic wood fire chimneys (Fawcett et al, 1992) and is present in significant quantities in cigarette smoke (Hartridge, 1920 Hoffman et al, 2001). The atmospheric lifetime of CO is 1 to 2 months, which allows its intercontinental transport (Akimoto, 2003). 

CO has always been a part of the imiverse. However, atmospheric CO has increased over time. When volcanoes erupted, continents collided, and winds embraced the trees sparking fires millions of years ago, all this contributed to the stock of CO. However, when CO first made a significant presence in the air we breathe, humans lived in the open. A very long time must have passed by before humans inhabited caves or built enclosures for protection from the effects of the weather or the tyranny of predators. In the process, however, humankind invited the unwanted guest -carbon monoxide, the silent killer. So where there is smoke, there is not only fire but also CO in terms of human cost, the latter is more dangerous than the former. Yet it must have taken several thousands of years to tame the fire, and over those years CO has claimed many innocent victims who went to sleep after a hearty meal never to wake up. The knowledge of these mysterious events has been unraveled over time. 

Carbon monoxide (CO) poisoning remains the single most common cause of fatal poisoning in developed, Western countries and most probably in the rest of the world as well. Motor vehicle exhausts, defective heating systems and smoke from all types of fires are common sources. Some 40% of an absorbed dose of dichloro-methane is also metabolized to CO. 

Combustion processes can create pollutant emissions other than carbon monoxide and oxides of nifrogen. Unbumed hydrocarbons (UHC) is a term describing any fuel or partially oxidized hydrocarbon species that exit the stack of a furnace. The cause for these emissions is typically due to incomplete combustion of the fuel from poor mixing or low furnace temperature. A low temperature environment can be created by operating the furnace at a reduced firing rate or turndown. Particulate matter (commonly called soot) is often produced from fuel rich regions in diffusion flames. Soot becomes smoke if the rate of formation of soot exceeds the rate of oxidation of soot. Oxides of sulfur are formed when sulfur is present in the fuel. 

US fire statistics show that over half of all fire deaths are from smoke inhalation, mostly of carbon monoxide and hydrogen cyanide. For the hydrogen cyanide, usually PU (mostly from foam in construction or furniture) are held responsible [81]. 

Opportunities for fires in the processing industries abound. Fire is a chain reaction that requires a constant source of fuel, oxygen, and heat. The majority of people that die in fires are asphyxiated from breathing smoke or poisoned by toxic fumes. Carbon monoxide is the number one killer and is produced in almost all burning organic compounds. During fires, carbon monoxide is produced in large quantities and can quickly reach lethal concentrations. 

Carbon monoxide is rarely used in the laboratory, and you are more likely to encounter risk from carbon monoxide poisoning at home. Carefully examine all potential sources of carbon monoxide to ensure that you and others are not exposed. Carbon monoxide detectors are relatively inexpensive, and, along with smoke detectors, every home that uses any gas or fuel-fired appliance should have one. 

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