The size of a soot particle has an effect on smoke detector alarm activation. It is the purpose of this paper to identify changes to soot particle size and examine if those size changes effect smoke detector alarm times in the ceiling jet. Changes in particle size has been attributed to delays in detector activation, however, little evidence exists to support that particle size changes occur in the ceiling jet where detector activation occurs. This paper presents the results from laser scattering experiments and calculations conducted to support and validate the experimental findings. The laser scattering from various aerosols was collected, over time, to examine changes in particle size due to agglomeration in the smoke aging process. The laser scattering measurements were made at two linear polarizations, vertical (VV) and horizontal (HH), and scattering angles ranging from 20 to 155 degrees. A laser with a wavelength of 632.8 nm was used as a light source. The aerosol laser scattering results were then compared to the results from the Mie scattering theory. The Mie scattering theory was adjusted using a lognormal distribution to generate theoretical light scattering curves expected from a polydisperse aerosol typical of smoke. The collected data was examined using a combination of the Mie theory with various particle sizing techniques, including dissymmetry ratio and polarization ratio, to look for changes in laser scattering indicating changes in particle size.

This thesis studies the following four topics by CFD simulation. First, the detailed airflow patterns and pressure characteristics of a semiconductor fab were analyzed and verified by available experimental data. Second, both transient and steady state simulations of a fire incidence were conducted to study the influences of fire source volume, fire source altitude, and clean room filter face velocity on the temperature distribution around the vicinity of fire source. Note the temperature distribution at the altitude of fire distinguisher (close to the height of ceiling) is very related to the action mechanism of fire distinguisher. Third, the mean trajectories of various particle sizes in the very early stage of a fire occurrence were simulated to provide substantial information to properly locate the VESADs (very early smoke detect active). Fourth, the performances of three commonly adopted smoke control/exhaust systems for semiconductor fabs were evaluated. An appropriate smoke control/exhaust system is provided and discussed.