ABSTRACT
There has been quite a lot of discussion about the combustion of plastics in fires and the toxic effects on humans due to the production of hazardous by-products that are released when plastics bum. Much of what has been reported is misleading and is directly attributable to antiplastic concerns (funded for the most part by manufacturers in the metal industry) with the sole purpose of competing against plastic materials of construction on the basis of fear. What is presented here, in large part by the Vinyl Institute, is factual data supported by testing laboratories. Also provided are practical installation suggestions to make more fire-resistant construction and meet current fire and building code standards and references. II. DECOMPOSITION OF PLASTICS
Organic materials by definition are those that contain carbon. These include many natural products such as wood, wool, cotton, silk, rubber, and leather, and many synthetic products such as vinyl (polyvinyl chloride or PVC), nylon, rayon, acrylic, Teflon, Styrofoam, polyurethane, polyethylene, and many more. All organic materials will bum (that is, undergo combustion), although the conditions required for each material to do so may differ.When any material is involved in a fire, it releases smoke, which contains many different combustion products, mainly gases, many of which are toxic. Among these gases, two are always present in a fire, irrespective of the material that is burning because they are the end products of combustion of all organic materials [1,2]. These are carbon monoxide and carbon dioxide. Wood is a common construction material of natural origin that will bum. When it does, it can release up to 200 different fire gases. These gases include not only carbon monoxide and carbon dioxide, but also benzene, acrolein, poly-nucleated aromatics, and numerous other irritating, corrosive, and carcinogenic chemicals [3-5]. 262
The nature and concentration of toxic combustion products in a real fire will depend on many variables and not only on the material that is burning. Typically the ventilation to a fire (that is, the size and number of doors and windows) is the factor that most strongly controls the type of burning (that is, flaming, smoldering, or flashover) and thus the toxic gases present in the fire atmospheres [6,7]. Two studies have been carried out in which leading research organizations equipped firefighters with devices to obtain samples of smoke from actual fires for laboratory analysis: the Harvard University School of Public Health (with the Boston Fire Department) in 1979 [8] and the Southwest Research Institute (with the San Antonio Fire Department) in 1981 [9]. Both studies concluded that the most hazardous air contaminants in real fires were carbon monoxide and acrolein. A. Carbon Monoxide
Carbon monoxide (CO) is present in all fires and, because of its abundance, CO is universally recognized as the greatest toxic hazard in real fires [10-12].Many studies have been carried out on the effects of CO on humans and of its toxicity in and out of fires. They all show that CO is toxic due to its fast (200 times faster than oxygen) reaction with hemoglobin in blood to form car-boxy hemoglobin (COHb) [13,14]. This leads to lack of oxygen, resulting in a feeling of drowsiness (narcosis) and eventually in death. The hazard of CO is particularly enhanced by the fact that it is a colorless and odorless gas that provides no warning of its presence. Furthermore, relatively low levels of CO are encountered in all smoky atmospheres (a bar, for example) and they produce no immediate symptoms of toxicity.The amount of CO that is lethal depends on the age, general health (particularly the presence of heart disease), and the level of activity of the person involved, as well as on other factors such as the presence of alcohol or the existence of thermal injury. The lethal dose of CO in the atmosphere is estimated to be 138,000 ppm/min (that is, 4600 ppm for a 30-min exposure; the permissible exposure limit is 50 ppm) [15]. A level of COHb in the blood lower than 20% will not lead to death, but any level above this can be lethal [12]. CO is the most dangerous combustion product present in a fire atmosphere. B. Carbon Dioxide
Carbon dioxide (CO2 ) is also present in all fires [1]. It is generally considered to be nontoxic, but it will increase breathing rates so that is may allow higher concentrations of other, more toxic, gases to be breathed in than would normally be the case [15]. Furthermore, it will displace equal amounts of oxygen. Therefore, CO2 also is dangerous in a fire.
