The Combustion Toxicology of Polyvinylchloride Revisited

Abstract

The combustion toxicology of polyvinylchloride (PVC) has been studied extensively against a background of increasing understanding of the relevance of the toxicity of combustion products in fires. Most materials have a similar toxic potency and demonstrate asphyxia and irritancy when thermally decomposed. Hydrogen chloride is a major toxicant produced by PVC, which accounts for the irritancy shown by PVC combustion products. Carbon monoxide is also produced which becomes the most significant toxicant if the hydrogen chloride levels are reduced, which can occur rapidly in fires. The toxic potency lies within the range of 300-3000 mg/l. mins, which is similar to the majority of polymeric materials whether natural or synthetic.The toxicity of PVC can be accounted for in hazard estimation either by an assumed toxic potency based on weight loss calculations or by predicting the concentrations of hydrogen chloride and carbon monoxide. The toxicology of hydrogen chloride has been well studied and has been overestimated in the past and codes using toxicity factors for hydrogen chloride should be revised in the light of modern data. In addition, hydrogen chloride levels have been shown to decay rapidly in fires and this factor, coupled with the good flammability per-

Update on smoke toxicity of vinyl compounds

“…Guinea pigs have been shown to develop decreased respiratory response to COz challenge up to 10 days after exposure to HC1 levels as low as 1040 ppm for 30 min (31,200 ppm min) (44). For the primates tested in this study, no evidence of changes in pulmonary function were observed after exposures to levels of HCI as high as 10.000 ppm for 15 min (150,000 ppm min) following 3 months of post-exposure observations. The X-rays and the clinical observations show that these baboons, exposed to high levels of HCl(75.000-150,000 ppm min), sufferd no pulmonary edema, but only some hypoxia via small airway constriction.…”

“…The comparative rankings of materials within a certain study can vary tremendously, however. This has led to the suggestion that a toxic potency within the range of 300-3,000 mg/(l min) represents average smoke toxicity (10). Figure 1 illustrates this point by putting smoke toxic potencies in a n overall toxicological perspective.…”

Thetford plastics fire, October 1991: the role of a preventive medical team in chemical incidents.

“…Thus decision making based on a hazards and risk assessment in such emergencies is likely to be hampered by inadequate information, even when, as in the present incident, the range of combustion and pyrolysis products are relatively well known. 4 At a temperature over 300'C PVC decomposes to HC1 and carbon monoxide together with small amounts of about 50 various hydrocarbons" ; over 50% of the polymer weight may come off as HC1 gas. Phosgene is produced only in rare circumstances and the quantity of dioxin formed is likely to be not clinically significant.…”

“…Acrylonytrile, butadiene, and styrene were also present and would be expected to emit hydrogen cyanide in the smoke.5 Various other respiratory irritants such as acrolein, ammonia, SO,, NO,, aldehydes, and particulates may be found in fire smoke. 4 Although the presence of SO, is dependent on significant amounts of sulphur compounds being present in the "fuel", nitrogen oxides formed from nitrogen and oxygen in the air are always found in fire smoke. Plastics also contain additives of complex organic molecules including heavy metal salts-for example, cadmium, lead, and titanium-for ultraviolet stabilisation, antistatic properties, and colouring.…”

“…4 The clinical impression gained from the effects on the fire fighters who were seen at the hospital suggested that the irritancy of the smoke was greater than would be accounted for by HC1 alone. Relatively few studies of exposure to HC1 have been undertaken in human volunteers, including people with asthma, but concentrations of 1-10 ppm are thought to be well tolerated by healthy adults and the life threatening concentrations are probably in the range of 1300-2000 ppm for a few minutes with death being caused by laryngeal or pulmonary oedema.78 The main respiratory irritant effect of HC1 is on the upper airways where it will be scrubbed from the inspired air because of its hygroscopicity and reactivity and it is 30 times less irritant than chlorine.…”