Ignition of expandable polystyrene foam by a hot particle: an experimental and numerical study.

Many serious fires have occurred in recent years due to the ignition of external building insulation materials by hot metallic particles. This work studied the ignition of expandable polystyrene foam by hot metallic particles experimentally and numerically. In each experiment, a spherical steel particle was heated to a high temperature (within 1173-1373K) and then dropped to the surface of an expandable polystyrene foam block. The particles used in experiments ranged from 3mm to 7 mm in radius. The observed results for ignition were categorized into two types: "flaming ignition" and "no ignition", and the flaming ignition limit was determined by statistical analysis. According to the experimental observations, a numerical model was proposed, taking into account the reactant consumption and volatiles convection of expandable polystyrene decomposition in air. Three regimes, no ignition, unstable ignition and stable ignition, were identified, and two critical particle temperatures for separating the three regimes were determined. Comparison with the experimental data shows that the model can predict the range of critical ignition temperatures reasonably well.

Improving the assessment of activity in samples with non-uniform distribution using the sum peak count rate.

In this work a method for the evaluation of the activity when a point source containing (60)Co is located in an unknown position within a sample is developed. The method can be applied if the count rate in the 2,505 keV sum peak has an acceptable uncertainty. It is based on the correlation between the apparent efficiency for the 1,173 keV peak and the ratio of the count rate in the sum peak of 2,505 keV and in the 1,332 keV peak. The correlation was observed in the measurements of a (60)Co point source located in various positions in a soil sample. The measurements were done with a 47% efficiency n-type HPGe detector. The correlation is also observed in the measurements and simulations done with a Compton-suppressed spectrometer having a 100% n-type HPGe detector. The results obtained with the proposed method are less affected by the uncertainty of the position of the point source than the results obtained using the standard methods of activity evaluation.