Organic materials are those which contain carbon.  These include many natural products such as wood, wool, cotton, silk, rubber, leather and many synthetic products such as vinyl (potyvinyl chloride or PVC),
nylon, rayon, acrylic, Teflon® Styrofoam® polyurethane, polyethylene and many more. All organic materials will burn (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, virtually all of which are toxic.  Among these fire gases, two are always present in a fire, irrespective of the material which is burning because they are the end products of combustion of all organic materials.  These are carbon monoxide and carbon dioxide. Wood is a common construction
material of natural origin which will, of course, burn.  When it does, it can release up to 175 different fire gases. These gases include not only carbon monoxide and carbon dioxide, but also benzene and acrolein and numerous other irritating, corrosive and carcinogenic chemicals.

The nature and concentration of toxic combustion products in real fire will depend on many variables and not only on the material which is burning.
Typically the ventilation to a fire (that is, the size and number of doors and windows) is the factor which most strongly controls the type of burning (that is, flaming, smoldering or flashover) and thus the toxic gases present in the fire atmosphere.  Two studies have been carried out in which leading research organizations equipped fire fighters 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 and the Southwest Research Institute (with the San Antonio Fire Department) in 1981.  Both studies concluded that the most hazardous air contaminants in real fires were carbon monoxide and acrolein.

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.  Many studies have been carried out on the effects of CO on
man 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 carboxyhemoglobin (COHb).  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 which 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 which is lethal depends on the age, general health (particularly the presence of heart disease) and on 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 4,600 ppm for a 30 min exposure).  A level of COHb in blood lower than 20% will not lead to death, but any level above this can be lethal.   CO is the most dangerous combustion product present in a fire atmosphere.

Carbon Dioxide

Carbon dioxide (CO₂) is also present in all fires.  It is generally considered to be non-toxic, but it will, however, increase breathing rates so that it may allow higher concentrations of other, more toxic, gases to be breathed in than would normally be the case Furthermore, it will displace equal amounts of oxygen. Therefore, CO₂  also is dangerous in a fire.

Acrolein

Acrolein is an extremely irritating gas which results mainly from the combustion of wood, cotton or paper (cellulosics), although some other materials such as polyethylene, polystyrene and oils and fats may also
produce it.  Acrolein is frequently present in a fire and it is detectable owing to its odor (odor detection level of 0.2 ppm).  The NIOSH Registry of Toxic Effects  lists 153 ppm as the dose lethal to man in 10 min (1530 ppm min).  The original reference for this entry states "a concentration of 0.35 mg per liter is lethal on 10 minutes' exposure."   It is difficult, howe-
ver, to attach any confidence to this statement because there is no associated data or information.   Kaplan et al. have studied the effects of 5 min expo- sures of baboons to acrolein.  No deaths occurred for exposures of less than 1025 ppm.    These data show that the lethal dose for acrolein is between 2525 and 5125 ppm min. Acrolein is thus one of the most dangerous gases present in a fire.

Hydrogen Chloride

Hydrogen chloride (HCI) is an irritating gas which results from the combustion of vinyl and from that of many other flame-retarded materials. It is generally best known as "stomach acid." It dissolves readily in water and it is also eliminated from the atmosphere (air) by virtually all common construction materials (dry-wall, cement, paint, ceiling tile, wood, metal and others).   It has a sharp, pungent odor (similar to ammonia) which is detectable at very low concentra-tions (odor detection level 0.8 ppm).

Recent studies by the Federal Aviation Administration and by the Southwest Research Institute have shown that baboons are not incapacitated after exposure to levels of up to 30,000 ppm of HCI (3% in air) for 5 min.  Additional research conducted by the Vinyl Institute on baboons at the Southwest Research Institute has shown that baboons exposed to 5,000 ppm of HCI (0.5% in air) for 15 min have received no
long-term lung function effects.  Furthermore only minimal long-term effects on lung functions were observed after exposures to 10,000 ppm for 15 min.  This means that the lethal dose of HCI is above 150,000 ppm min, and that exceedingly high levels of HCI are required to cause incapacitation or death.  In the Harvard University study of over 200 real fires in Boston, the maximum level of HCI found was 280 ppm, while in the Southwest Research Institute study of real fires in San Antonio, the maximum level of HCI found was 232 ppm.  This indicates that the concentrations of HCI found in real fires are much lower than those which could generate fire deaths.

Combustion Products of Vinyl

Burning vinyl (PVC) produces numerous byproducts, many of which are exactly the same as those produced by wood or by most other common organic, natural or synthetic materials.   Carbon dioxide, carbon monoxide and hydrogen chloride account for 97% of the total volume of gases produced by burning vinyl. The remaining 3% consists of benzene and
of an assortment of other gases, the composition of which is similar to that of wood smoke."  Neither chlorine nor phosgene are combustion products of vinyl. The National Bureau of Standards investigated this problem and found that only traces of phosgene were produced from vinyl wire insulation by any of three methods: thermal decomposition in a
red-hot furnace, flaming combustion and electrical overload.   However, the application of a 10,000 volt arc to a chamber overloaded with vinyl did generate some phosgene (an average of 26 ppm). This is of no consequence in terms of hazard because, at the same time, such an arc will generate, on its own (even without any wire insulation), 15,000 to 30,000 ppm of the toxic gas nitrogen dioxide.  This level of toxic gas is 100-200 times more hazardous than the phosgene and will not permit human survival.

Thermal decomposition of vinyl can, under certain conditions, generate trace amounts of vinyl chloride monomer (VCM), but a flame environment will destroy it completely during combustion. VCM can be forrned attemperatures above 527°F, with maximum levels of 15-30 ppm (compared to 6,000 ppm required to produced dizziness) at temperatures between 617 and 842°F, and is destroyed at higher temperatures. The critical temperature for human survival in a ire environment is 150°F for 1 min.

Conclusions

In conclusion, the typical combustion products of vinyl, that is carbon dioxide, carbon monoxide and hydrogen chloride, are either common to all organic materials (CO and CO₂) or of very limited hazard in a fire (HCI). Although there have recently been claims that hydrogen chloride incapacitates people in a fire by "knocking victims down" and making escape impossible, such claims are inaccurate and are totally unsupported by laboratory testing or real fire experience. In fact, the Federal Aviation Administration has recently stated that "ultraconservative guesses" roposed for incapacitation by HCI hindered their research by forcing them to expose animals to concentrations 50-100 times lower than those which
were eventually found not to be incapacitating.  It is clear, therefore, that vinyl is at least as safe as most other materials in a fire.

• Fire Performance Properties of FlowGuard™ CPVC
• FlowGuard™ in Fire-Rated Construction
• Toxicity
• Fire Safety
• Combustion Gases of Various Busilding Materials

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