| Summary: | 博士 === 國立臺灣大學 === 森林學研究所 === 89 === The main purpose of wood treated with fire retardants is to improve safety in case of fire. Therefore, in addition to considering the effectiveness of preventing the spread of fire and prolonging the time for fleeing, the evolution of smoke and the components of combustion gas can not be overlooked. In other words, ideal fire retardants should not increase combustion gas toxicity of the material. For this purpose, retardant -treated wood must be assessed on its fire combustion toxicity as well as on its retardant effect.
To this end, the combustion gas toxicity of both treated (impregnation and coating) and untreated wood is analyzed according to NES 713 and colorimetric analysis to investigate the effect of combustibility on combustion gas toxicity. The results of chemical analysis are also adopted to predict the results of animal tests. Then the accumulative exposure gas amount at incapacitation time is calculated. The experimental results are summarized as follows:
1. The toxicity index of untreated wood is between 1 and 2; the toxicity index of UF bonded plywood is between 3 and 6, while the index of treated wood is between 7 and 13, varying with the components of the fire retardants. However, the incapacitation time of mouse for treated wood is longer than that of untreated one, due to the following facts: firstly, the decrease in combustion weight loss; secondly, the decrease in per unit carbon content and finally, the decrease in combustion rate.
2. Because of the increase in thickness, unburned-through samples (over 9 mm) have less combustion loss and produce lower gas toxicity. On the other hand, the combustion loss of burned-out samples (under 7mm) is not much higher, but its gas toxicity does increase. This finding indicates that gas toxicity should not be assessed only by combustion loss. However the production rate of combustion gas is a more important factor.
3. During the initial stage when the retention of fire-retardants increases (concentration within 10 %), it has a significantly positive effect on combustion loss and the incapacitation time of mice. While the retention is higher (15 % ~ 20 %), its effect on decreasing combustion loss and prolonging the incapacitation time of mice will reduce. Therefore, it is vital to strike a balance point between the fire-retardant effect and the toxicity inhibition effect in retention.
4. For treated sample, as air-dry time increases, the fire-retardant effect of per unit chemical will reduce and the incapacitation time of mice will be significantly prolonged. This illustrates that chemical effect does reduce as time increases. As for gas toxicity, the positive impact brought forth by the reduction of chemical effect is apparently higher than the negative influence caused by the reduction of fire-retardant effect.
5. When the concentration of CO in the exposure chamber is above 1.0%, the incapacitation time of mouse is within 2 minutes; when above 1.5%, the incapacitation time is within 1 minute.
6. Combustion remains of retardant-treated wood possess relatively higher O2 concentration and lower CO and CO2 concentration than the untreated counterpart. Among identical material, those of lower combustion loss yield less CO, CO2 and NOx and retain relatively higher O2 concentration. Retardants’ inhibition effect of CO and CO2 has decisive influence on the extension of the incapacitation.
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