Spatiotemporal measurement of light extinction coefficients in compartment fires

In case of fire, the visibility plays a major role as it limits the occupants’ orientation capabilities and the perception of signs. These effects are determined by the light extinction due to smoke or other aerosols produced in fires. The presented method is based on the optical observation of an array of light sources during a fire in a laboratory experiment. The smoke induced into the compartment leads to a drop in intensity of each individual light source. This information is used to deduce the extinction along the line-of-sight to the camera. Once the data are captured, an automated processing is used to locate the diodes on the images and determine their intensity. Here, the optical image of the small diodes is assumed to have a known shape, so that the optimisation algorithm is capable to identify the location of the diode’s centre and quantify the luminosity in a sub-pixel range. The result is a time series for each diode, indicating the change of the relative luminosity, w.r.t. the initial values. Finally, a model for the extinction along each line-of-sight is formulated. It assumes that the light extinction coefficient is distributed in homogeneous layers. The number of layers is a free model parameter. Given this spatial distribution of the extinction coefficient and the experimental geometry, each line-of-sight is impacted by a number of layers, of yet unknown coefficient values. An inverse modelling approach is used here to find coefficient values that match the modelled line-of-sight extinction with the observed luminosity drops. The final result is a time- and height-dependent distribution of the light extinction coefficient during the full experiment