The Influence of Temperature and Ventilation Conditions on Combustion Products of Polymers and on Smoke Toxicity

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The engineer’s methods use different approaches to calculate fire and smoke spread in enclosures and compartments. The method of Computational Fluid dynamics CFD is being increasingly used for this. For risk assessment safety parameters like temperature development in the compartment, smoke layer height or radiant heat from the fire can be predicted with CFD. This investigation focused on the prediction of critical concentrations and visibility of fire smoke. The challenge was to find a suitable method to investigate and access the effects of smoke, toxic smoke products and heat experimentally and numerically. At first a large set of experimental investigations were performed to analyze toxic and optical properties of fire smoke on different temperature and ventilation conditions. Therefore three different polymers were investigated under thermal decomposition in the DIN-tube furnace and under flaming combustion conditions in the Cone Calorimeter. The particular interest was on how the amount of the fire effluents changes under different temperature and ventilation conditions and consequently how the smoke toxicity changes. From the experimental investigations complex combustion formulas were set up to account for different combustion conditions in the simulation. For the evaluation of smoke toxicity or the exposure to toxic products for occupants the concept of Fractional Effective Dose (FED) was used. The next step was to develop a numerical model to simulate fire smoke, calculate the smoke toxicity and visibility. The numerical simulations were done with the fluid dynamics programm ANSYS CFX. This program is used to simulate fluid flow in a variety of application. CFX has to be modified for application in fire safety engineering. According to this the concept of the Fractional Effective Dose and the calculated reaction equations were implemented in ANSYS CFX. Another aspect was to investigate the change of visibility under different combustion conditions and to predict the visibility numerically. This work is part of a Ministry-funded project that aims the development of an advanced numerical approach to model smoke production, smoke distribution and toxicity using several CFD codes.