Dr. Alexander Belt

Visibility in Compartment Fires

In life safety analysis, the simulation of smoke propagation, toxicity and visibility can be used to predict the tenability criteria during evacuation. The visibility strongly affects evacuation strategies and is closely related to the smoke density, which is dependent on various parameters, i.e. soot yield, particle size, particle distribution, particle deposition, agglomeration and the transport mechanism. Increasingly, computational fluid dynamic (CFD) models, like the Fire Dynamics Simulator (FDS), are used for the prediction of the quantities mentioned above, thus safety measures can be deduced from numerical simulations.

Above: DIN EN 54 n-heptane pool fire, symmetrical 3D LED setup, vertical LED on 3 m radius (next to MIREX measurement). The intensity of the LEDs is observed by two CCD cameras.

However, real scale investigations have identified non-negligible deviations between experimental data and the results of simulations with e.g. FDS. Therefore, the models need to be improved for reliable prediction of visibility in compartment fires. But suitable experimental data is not available yet.

Research activities

• Conduction of real scale compartment fires (scaling effect tests)
• Conduction of bench scale experiments (single effect tests)
• Development of a new experimental approach to measure spatiotemporal resolved extinction coefficients (LEDEX)
• Numerical simulations with different CFD methods
• Improvement and validation of visibility models in CFD methods

Applied Measurement techniques

• Mid Infra Red EXtinctioncoefficient (MIREX)
  The MIREX emits light in the mid-infrared range. This light passes a measuring section. Behind this it is reflected by a mirror. By comparing the emitted and reflected intensity of the light, the light extinktion is determined over the length of the beam.
• Light Emitting Diode EXtinctioncoefficient (LEDEX)
  LEDEX measures the change in intensity of LEDs and determines spatially resolved extinction coefficients using complex data analysis.
• Particle Image Velocimety (PIV)
  By PIV, 2D velocity fields are determined by observing particle displacements, which are illuminated by a light sheet and observed by a CCD camera, in certain time intervals.
• Electronic Low Pressure Impactor (ELPI)
  Particles of different sizes have different electrical properties and deposition characteristics, which are measured with the ELPI and from which particle size distributions are derived.

Above: The optical image of a single LED is represented by a model function. It tracks amplitude, radius, inclination and broadening of the signal.

Above: Image intensity, model based image intensity and extinction coefficient over the height of the compartment. Blue curve: Experimental image intensity, orange curve: response of the extinction coeficient. Green: Evaluated light extinction coefficient based on the layer specific light absorption properties.

Related Publications

• Lukas Arnold, Alexander Belt, Thorsten Schulze, and Lea Sichma. Spatiotemporal Measurement of Light Extinction Coefficients in Compartment Fires. Interflam, 2019.
• Alexander Belt, Lukas Arnold, Ben Hein, Thorsten Schultze, and Lea Sichma. Visibility during Compartment Fires, Part 1: Experiments. FDS User Group Meeting, Berlin (Germany), 7 Nov 2019 - 8 Nov 2019, Nov 2019.
• Lukas Arnold, Alexander Belt, Ben Hein, Thorsten Schultze, and Lea Sichma. Visibility during Compartment Fires, Part 2: Simulations. FDS User Group Meeting, Berlin (Germany), 7 Nov 2019 - 8 Nov 2019, Nov 2019.
• Lukas Arnold, Alexander Belt, Thorsten Schultze. Experimental and Numerical Investigation of Visibility in Compartment Fires. Accepted for AUBE conference (Duisburg, Germany), Sep 2021