In case of sooth, the unit value of dioxins generation from PVC is within the range of 30~3,500 μg - TEQ/t as seen from Table 5-1. From this value and the calculated value of burnt PVC in fire accidents in USA (2,470 t/year), the quantity of dioxins generated from PVC in fire accidents will be 0.074~8.6 g - TEQ/year in sooth. On the other hand, when the dioxins concentration in ash is taken as the standard, the generation unit value of dioxins (the value in literature) will be within the range of 160~5,660 μg - TEQ/t, and the annual discharge quantity will be 0.4~14.2 g - TEQ/year. Thus, the aggregate amount with dioxins from sooth becomes 0.47~22.8 g -TEQ/year. This value is based on the assumption that all PVC is burnt in fire accidents, but in actual fire accidents, the siding (external wall material, and the major application for PVC) and bathroom (with higher PVC utilization ratio) would be less affected. W.F. Carroll et al. say that it would be reasonable to take about 1 g - TEQ/year in case of ash and about 0.3 g - TEQ/year in case of sooth²⁷⁾, in consideration of the foregoing point. Besides, when the center values of respective generation unit data are used, the abovementioned dioxins generation quantities will be 1~5 ng/g for ash and 190 ng/g for sooth. From these values, the dioxins generation quantity from fire accidents will be about 5 g/year (when converted to TEQ value, it will be about 0.06 g - TEQ/year).

From the foregoing, the quantity of dioxins generation from burnt PVC in fire accidents will be about 20 g -TEQ/year at the most. This value is equivalent to only 0.2% of 9,300 g - TEQ/year, the annual discharge quantity to atmosphere in USA worked out by US Environment Protection Agency (EPA). It is clear that the quantity of dioxins generation form PVC in accidental fire is very small.

The foregoing explanations are based on the US literature, as there is no literature available for Japan. PVC flooring is used more in USA, while PVC wall covering is  used more in Japan. Anyway, as explained at a later section herein, dioxins from accidental fire would not create major threat to human life, but more deadly are the burn incurred by quick spreading of fire and suffocation by carbon monoxide.

The discharge of dioxins into environment as abovementioned may pose problems of chronic toxicity on human health. Then, what will be the acute toxicity of inhaled dioxins? There is no report of human death by inhalation of high concentration dioxins to date. The well-known dioxins exposure incident took place by explosion of an agricultural chemicals plant at Sebeso, Italy in 1976. Normally, agricultural chemicals were synthesized below 120℃, but in that explosion accident, the reaction temperature became uncontrollable and formed dioxins. It is said that the amount of dioxins discharged into atmosphere by the explosion accident was some 600 g (announcement by Sebeso Municipality) or 130 Kg (Dr. Lee). A large number of cattle
Is said to have died. But, no human casualty due to exposure to dioxins has been reported. Some 152 people developed chlor-acne (pimple-like dermatitis) out of 30,000 exposed people. Follow-up survey has been conducted with some 20,000 exposed people for sick manifestation including cancers and causes of death thereafter, but it is reported that there is no significant deviation from the national average statistics²⁸⁾. Besides, there is a report that no significant difference has been observed with 15,291 people born within 5 years after the accident for mutagenicity and others²⁹⁾.

The fire accident at Dusseldorf International Air Port in 1996 is another major example, wherein 17 people passed away. In the earlier phase, certain environment protection organization announced that they died of dioxins generated from PVC construction materials in the building. In response, mass media reported in a sensational way, such as "Dioxins claim lives of 17 people". However, as the result of investigation by Survey Commission appointed immediately after the accident by Dusseldorf Municipality, it has become clear that those people died of carbon monoxide poisoning caused by burnt heat insulator polyethylene foam³⁰⁾.

From these examples, it is thought that dioxins from accidental fire may not claim human lives. But, the magnitude of acute toxicity by inhalation of dioxins in the atmospheric gas at the fire site will be examined in the following part of this paper, to be sure.

In the case of normal fire incidence, the dioxins concentration in the atmospheric gas is reportedly³¹⁾ at the level of 0.05~0.43 ng - TEQ/m³. Besides, the analysis results of dioxins concentration in the floating particles in indoor air have shown it to be about 5 ng - TEQ/m³, when 400 Kg of wood and 40 Kg of PVC are burnt in a closed room. It is reported that this concentration is almost equal to the level in the stack flue gas of a solid municipal waste incinerator.

The acute toxicity of dioxins at the site of accidental fire has been calculated based on the foregoing data. The lethal dose of dioxins is reported to be about 70μg - TEQ/Kg in case of monkey, and about 22μg - TEQ/Kg in case of rat. Should this 22μg - TEQ/Kg be used, the dioxins concentration in the gas that may claim human life within one hour of inhalation for a man with 50 Kg body weight may be calculated by the following equation based on the breathing rate of 625 L/hour (15 m³/day). The calculated value denotes that the man will die after inhaling dioxins containing gas with a concentration of 1,760,000 ng -TEQ/m³ for one hour. This value is more than 40 million times greater than the dioxins concentration in the aforementioned atmospheric gas at the site of fire accident. It is hard to imagine that inhalation of dioxins in the atmosphere at the fire accident might cause a serious impact on human health.

22μg x 50/0.625 = 1,760μg - TEQ/m³ = 1,760, 000 ng -TEQ/m³

It is clear from the foregoing that the contribution of dioxins generated from fire accident to environmental pollution and human health is extremely low.