Degradation of Polystyrene Foam under Radiant Heat Flux.

摘要

As the demand for liquefied natural gas has increased, safety concerns about the performance of transport vessels under fire conditions have been raised. Current codes for the sizing of the pressure relief systems require that the vessels are able to withstand an emmissive heat flux of 108kW/m2 and do not take into account the effects of insulation loss due to thermal decomposition of the insulation materials. To address this possible oversight in the current code models were presented to a working group organized by the Society of International Gas Tanker and Terminal Operators Ltd. focusing on the decomposition rate of the polystyrene insulation used on many of these shipping vessels under fire conditions. The working group considered a range of heat flux from liquified natural gas pool fires with fluxes up to 300kW=m 2. However, without experimental verification of the behavior of the polystyrene insulation under these conditions the working group deferred the concerns stating that, “a better understanding of the foam plastic insulation vulnerability to heating is required to adequately assess the hazards that could result from loss of insulation effectiveness with fire exposure”.;Using an experimental procedure adapted from the work of Braumen, Chen and Matzinger on the thermal response of solid polystyrene under fire conditions, a rod driven apparatus was constructed to measure the regression rates of both solid and foamed samples of polystyrene as a function of external heat flux. From a plot of this data the heat loss to the surroundings and the heat of vaporization of the samples were calculated. Comparisons of the heats of vaporization were made to the values reported here as well as to independent differential scanning calorimetry and thermogravimetric analysis data.;It was shown that the mass loss rate of the foamed polystyrene is essentially the same as the solid polystyrene when exposed to high rates of heating. The only significant difference between the two forms of polystyrene is in the linear regression rate which is higher in the foamed polystyrene by approximately the same ratio as the densities, about 40 to 1. The heat of vaporization for the solid polystyrene and the foamed polystyrene were found to be 1592J/g and 1693J/g respectively. The comparison to the differential scanning calorimetry data for the samples was within 10%. The linear regression of the foamed polystyrene was found to be 0.138cm/min for each kW/m2 of absorbed heat.